New articles on Condensed Matter

[1] 2404.11623

Eight-color chiral spin liquid in the $S=1$ bilinear-biquadratic model with Kitaev interactions

Multipolar spin systems provide a rich ground for the emergence of unexpected states of matter due to their enlarged spin degree of freedom. In this study, with a specific emphasis on $S=1$ magnets, we explore the interplay between spin nematic states and spin liquids. Based on the foundations laid in the prior work [R. Pohle et al., Phys. Rev. B 107, L140403 (2023)], we investigate the $S=1$ Kitaev model with bilinear-biquadratic interactions, which stabilizes, next to Kitaev spin liquid, spin nematic and triple-$q$ phases, also an exotic chiral spin liquid. Through a systematic reduction of the spin degree of freedom -- from $\mathbb{CP}^{2}$ to $\mathbb{CP}^{1}$ and ultimately to a discrete eight-color model -- we provide an intuitive understanding of the nature and origin of this chiral spin liquid. We find that the chiral spin liquid is characterized by an extensive ground-state degeneracy, bound by a residual entropy, extremely short-ranged correlations, a nonzero scalar spin chirality marked by $\mathbb{Z}_{2}$ flux order, and a gapped continuum of excitations. Our work contributes not only to the specific exploration of $S=1$ Kitaev magnets but also to the broader understanding of the importance of multipolar spin degree of freedom on the ground state and excitation properties in quantum magnets.

[2] 2404.11634

Bis(stearoyl) Sulfide: A Stable, Odor-free Sulfur Precursor for High-Efficiency Metal Sulfide Quantum Dot Photovoltaics

The synthesis of metal sulfide nanocrystals is a crucial step in the fabrication of quantum dot (QD) photovoltaics. Control over the quantum dot size during synthesis allows for precise tuning of their optical and electronic properties, making them an appealing choice for electronic applications. This flexibility has led to the implementation of quantum dots in both highly-efficient single junction solar cells and other optoelectronic devices including photodetectors and transistors. Most commonly, metal sulfide quantum dots are synthesized using the hot-injection method utilizing toxic, and air- and moisture sensitive sulfur source: bis(trimethylsilyl) sulfide (TMS)2S. Here, we present bis(stearoyl) sulfide (St2S) as a new type of air-stable sulfur precursor for the synthesis of sulfide-based QDs, which yields uniform, pure, and stable nanocrystals. Photovoltaic devices based on these QDs are equally efficient as those fabricated by (TMS)2S but exhibit an enhanced operational stability. These results highlight that St2S can be widely adopted for the synthesis of metal sulfide quantum dots for a range of optoelectronic applications.

[3] 2404.11635

Remarkable performance recovery in highly defective perovskite solar cells by photo-oxidation

Exposure to environmental factors is generally expected to cause degradation in perovskite films and solar cells. Herein, we show that films with certain defect profiles can display the opposite effect, healing upon exposure to oxygen under illumination. We tune the iodine content of methylammonium lead triiodide perovskite from understoichiometric to overstoichiometric and expose them to oxygen and light prior to the addition of the top layers of the device, thereby examining the defect dependence of their photooxidative response in the absence of storage-related chemical processes. The contrast between the photovoltaic properties of the cells with different defects is stark. Understoichiometric samples indeed degrade, demonstrating performance at 33% of their untreated counterparts, while stoichiometric samples maintain their performance levels. Surprisingly, overstoichiometric samples, which show low current density and strong reverse hysteresis when untreated, heal to maximum performance levels (the same as untreated, stoichiometric samples) upon the photooxidative treatment. A similar, albeit smaller-scale, effect is observed for triple cation and methylammonium-free compositions, demonstrating the general application of this treatment to state-of-the-art compositions. We examine the reasons behind this response by a suite of characterization techniques, finding that the performance changes coincide with microstructural decay at the crystal surface, reorientation of the bulk crystal structure for the understoichiometric cells, and a decrease in the iodine-to-lead ratio of all films. These results indicate that defect engineering is a powerful tool to manipulate the stability of perovskite solar cells.

[4] 2404.11636

Towards low-temperature processing of efficient $γ$-CsPbI$_3$ perovskite solar cells

Inorganic cesium lead iodide (CsPbI$_3$) perovskite solar cells (PSCs) have attracted enormous attention due to their excellent thermal stability and optical bandgap (~1.73 eV), well-suited for tandem device applications. However, achieving high-performing photovoltaic devices processed at low temperatures is still challenging. Here we reported a new method to fabricate high-efficiency and stable $\gamma$-CsPbI$_3$ PSCs at lower temperatures than was previously possible by introducing the long-chain organic cation salt ethane-1,2-diammonium iodide (EDAI2) and regulating the content of lead acetate (Pb(OAc)2) in the perovskite precursor solution. We find that EDAI2 acts as an intermediate that can promote the formation of $\gamma$-CsPbI$_3$, while excess Pb(OAc)2 can further stabilize the $\gamma$-phase of CsPbI$_3$ perovskite. Consequently, improved crystallinity and morphology and reduced carrier recombination are observed in the CsPbI$_3$ films fabricated by the new method. By optimizing the hole transport layer of CsPbI$_3$ inverted architecture solar cells, we demonstrate up to 16.6% efficiencies, surpassing previous reports examining $\gamma$-CsPbI$_3$ in inverted PSCs. Notably, the encapsulated solar cells maintain 97% of their initial efficiency at room temperature and dim light for 25 days, demonstrating the synergistic effect of EDAI2 and Pb(OAc)2 on stabilizing $\gamma$-CsPbI$_3$ PSCs.

[5] 2404.11637

Solvent-antisolvent interactions in metal halide perovskites

The fabrication of metal halide perovskite films using the solvent-engineering method is increasingly common. In this method, the crystallisation of the perovskite layer is triggered by the application of an antisolvent during the spin-coating of a perovskite precursor solution. Herein, we introduce the current state of understanding of the processes involved in the crystallisation of perovskite layers formed by solvent engineering, focusing in particular on the role of antisolvent properties and solvent-antisolvent interactions. By considering the impact of the Hansen solubility parameters, we propose guidelines for selecting the appropriate antisolvent and outline open questions and future research directions for the fabrication of perovskite films by this method.

[6] 2404.11645

Mass-Assisted Local Deconfinement in a Confined $\mathbb{Z}_2$ Lattice Gauge Theory

Confinement is a prominent phenomenon in condensed matter and high-energy physics that has recently become the focus of quantum-simulation experiments of lattice gauge theories (LGTs). As such, a theoretical understanding of the effect of confinement on LGT dynamics is not only of fundamental importance, but can lend itself to upcoming experiments. Here, we show how confinement in a $\mathbb{Z}_2$ LGT can be \textit{locally} avoided by proximity to a resonance between the fermion mass and the electric field strength. Furthermore, we show that this local deconfinement can become global for certain initial conditions, where information transport occurs over the entire chain. In addition, we show how this can lead to strong quantum many-body scarring starting in different initial states. Our findings provide deeper insights into the nature of confinement in $\mathbb{Z}_2$ LGTs and can be tested on current and near-term quantum devices.

[7] 2404.11647

Quantized Acoustoelectric Floquet Effect in Quantum Nanowires

External coherent fields can drive quantum materials into non-equilibrium states, revealing exotic properties that are unattainable under equilibrium conditions -- an approach known as ``Floquet engineering.'' While optical lasers have commonly been used as the driving fields, recent advancements have introduced nontraditional sources, such as coherent phonon drives. Building on this progress, we demonstrate that driving a metallic quantum nanowire with a coherent wave of terahertz phonons can induce an electronic steady state characterized by a persistent quantized current along the wire. The quantization of the current is achieved due to the coupling of electrons to the nanowire's vibrational modes, providing the low-temperature heat bath and energy relaxation mechanisms. Our findings underscore the potential of using non-optical drives, such as coherent phonon sources, to induce non-equilibrium phenomena in materials. Furthermore, our approach suggests a new method for the high-precision detection of coherent phonon oscillations via transport measurements.

[8] 2404.11649

Stark Many-Body Localisation Under Periodic Driving

We study stability of localisation under periodic driving in many-body Stark systems. We find that localisation is stable except near special resonant frequencies, where resonances cause delocalisation. We provide approximate analytical arguments and numerical evidence in support of these results. This shows that disorder-free broken ergodicity is stable to driving, opening up the way to studying nonequilibrium driven physics in a novel setting.

[9] 2404.11650

Interacting Crystalline Topological Insulators in 2D with Spin-Orbit Coupling

Topology is routinely used to understand the physics of electronic insulators. However, for strongly interacting electronic matter, such as Mott insulators, a comprehensive topological characterization is still lacking. When their ground state only contains short range entanglement and does not break symmetries spontaneously, they generically realize crystalline symmetry protected topological phases (cFSPTs), supporting gapless modes at the boundaries or at the lattice defects. Here, we provide an exhaustive classification of cFSPTs in two-dimensions (2D) with $\mathrm{U}(1)$ charge-conservation and spinful time-reversal symmetries, namely those generically are present in spin-orbit coupled insulators, for any of the 17 wallpaper groups. It has been shown that the classification of cFSPTs can be understood from appropriate real-space decorations of lower-dimensional subspaces, and we expose how these relate to the Wyckoff positions of the lattice. We find that all nontrivial one-dimensional decorations require electronic interactions. Furthermore, we provide model Hamiltonians for various decorations, and discuss the signatures of cFSPTs. This classification paves the way to further explore topological interacting insulators, providing the backbone information in generic model systems and ultimately in experiments.

[10] 2404.11653

A many-body perturbation approach to moiré bands in twisted bilayer graphene

We develop a many-body perturbation theory to account for the emergence of moir\'e bands in the continuum model of twisted bilayer graphene. Our framework is build upon treating the moir\'e potential as a perturbation that transfers electrons from one layer to another through the exchange of the three wave vectors that define the moir\'e Brillouin zone. By working in the two-band basis of each monolayer, we analyze the one-particle Green's function and introduce a diagrammatic representation for the scattering processes. We then identify the moir\'e-induced self-energy, relate it to the quasiparticle weight and velocity of the moir\'e bands, and show how it can be obtained by summing irreducible diagrams. We also connect the emergence of flat bands to the behavior of the static self-energy at the magic angle. In particular, we show that a vanishing Dirac velocity is a direct consequence of the relative orientation of the momentum transfer vectors, suggesting that the origin of magic angles in twisted bilayer graphene is intrinsically connected to its geometrical properties. Our approach provides a many-body diagrammatic framework that highlights the physical properties of the moir\'e bands.

[11] 2404.11654

Dirac spin liquid as an "unnecessary" quantum critical point on square lattice antiferromagnets

Quantum spin liquids are exotic phases of quantum matter especially pertinent to many modern condensed matter systems. Dirac spin liquids (DSLs) are a class of gapless quantum spin liquids that do not have a quasi-particle description and are potentially realized in a wide variety of spin $1/2$ magnetic systems on $2d$ lattices. In particular, the DSL in square lattice spin-$1/2$ magnets is described at low energies by $(2+1)d$ quantum electrodynamics with $N_f=4$ flavors of massless Dirac fermions minimally coupled to an emergent $U(1)$ gauge field. The existence of a relevant, symmetry-allowed monopole perturbation renders the DSL on the square lattice intrinsically unstable. We argue that the DSL describes a stable continuous phase transition within the familiar Neel phase (or within the Valence Bond Solid (VBS) phase). In other words, the DSL is an "unnecessary" quantum critical point within a single phase of matter. Our result offers a novel view of the square lattice DSL in that the critical spin liquid can exist within either the Neel or VBS state itself, and does not require leaving these conventional states.

[12] 2404.11657

Phase sensitive information from a planar Josephson junction

We analyze both the general symmetry-related and more microscopic considerations that govern the Josephson tunneling across a finite planar junction between a known $s$-wave superconductor and a candidate unconventional superconductor (e.g., $d_{x^2-y^2}$-wave). Due to the finite size of the probe, the Josephson current possesses an edge contribution, which is shown to be the dominant contribution under certain conditions. Thus, the dependence of the edge contribution on the geometry of the junction can serve as a direct probe of the symmetry of the order parameter in the unconventional superconductor.

[13] 2404.11701

Axial, Planar-Diagonal, Body-Diagonal Fields on the Cubic-Spin Spin Glass in d=3: A Plethora of Ordered Phases under Finite Fields

A nematic phase, previously seen in the d=3 classical Heisenberg spin-glass system, occurs in the n-component cubic-spin spin-glass system, between the low-temperature spin-glass phase and the high-temperature disordered phase, for number of spin components n>=3, in spatial dimension d=3, thus constituting a liquid-crystal phase in a dirty (quenched-disordered) magnet. Furthermore, under application of a variety of uniform magnetic fields, a veritable plethora of phases are found. Under uniform magnetic fields, 15 different phases and two spin-glass phase diagram topologies, qualitatively different from the conventional spin-glass phase diagram topology, are seen. The chaotic rescaling behaviors and their Lyapunov exponents are calculated in each of these spin-glass phase diagram topologies. These results are obtained from renormalization-group calculations that are exact on the hierarchical lattice and, equivalently, approximate on the hypercubic spatial lattice. Axial, planar-diagonal, or body-diagonal finite-strength uniform fields are applied to n=2 and 3 component cubic-spin spin-glass systems in d=3.

[14] 2404.11702

Nonequilibrium finite frequency resonances in differential quantum noise driven by Majorana interference

Nonequilibrium quantum noise $S^>(\omega,V)$ measured at finite frequencies $\omega$ and bias voltages $V$ probes Majorana bound states in a host nanostructure via fluctuation fingerprints unavailable in average currents or static shot noise. When Majorana interference is brought into play, it enriches nonequilibrium states and makes their nature even more unique. Here we demonstrate that an interference of two Majorana modes via a nonequilibrium quantum dot gives rise to a remarkable finite frequency response of the differential quantum noise $\partial S^>(\omega,V,\Delta\phi)/\partial V$ driven by the Majorana phase difference $\Delta\phi$. Specifically, at low bias voltages there develops a narrow resonance of width $\hbar\Delta\omega\sim\sin^2\Delta\phi$ at a finite frequency determined by $V$, whereas for high bias voltages there arise two antiresonances at two finite frequencies controlled by both $V$ and $\Delta\phi$. We show that the maximum and minimum of these resonance and antiresonances have universal fractional values, $3e^3/4h$ and $-e^3/4h$. Moreover, detecting the frequencies of the antiresonances provides a potential tool to measure $\Delta\phi$ in nonequilibrium experiments on Majorana finite frequency quantum noise.

[15] 2404.11729

Self-organized dynamics of a viscous drop with interfacial nematic activity

We study emergent dynamics in a viscous drop subject to interfacial nematic activity. Using hydrodynamic simulations, we show how the interplay of nematodynamics, activity-driven flows and surface deformations gives rise to a sequence of self-organized behaviors of increasing complexity, from periodic braiding motions of topological defects to chaotic defect dynamics and active turbulence, along with spontaneous shape changes and translation. Our findings recapitulate qualitative features of experiments and shed light on the mechanisms underpinning morphological dynamics in active interfaces.

[16] 2404.11750

Robust Quasi-Bound States in the continuum: Accidental and Symmetry-Protected Variants in Dielectric Metasurfaces

Recently, man-made dielectric materials composed of finite-sized dielectric constituents have emerged as a promising platform for quasi-bound states in the continuum (QBICs). These states allow for an extraordinary confinement of light within regions smaller than the wavelength scale. Known for their exceptional quality factors, they have become crucial assets across a diverse array of applications. Given the circumstances, there is a compelling drive to find meta-designs that can possess multiple QBICs. Here, we demonstrate the existence of two different types of QBICs in silicon-based metasurfaces: accidental QBIC and symmetry-protected QBIC. The accidental QBIC evinces notable resilience to variations in geometrical parameters and symmetry, underscoring its capacity to adeptly navigate manufacturing tolerances while consistently upholding a distinguished quality factor of $10^5$. Conversely, the symmetry-protected QBIC inherently correlates with the disruption of unit cell symmetry. As a result, a phase delay yields an efficient channel for substantial energy transference to the continuum, endowing this variant with an exceedingly high quality factor, approaching $10^8$. Moreover, the manifestation of these QBICs stems from the intricate interplay among out-of-plane electric and magnetic dipoles, alongside in-plane quadrupoles exhibiting odd parities.

[17] 2404.11751

Magnetic structure and component-separated transitions of HoNiSi$_{3}$

HoNiSi$_{3}$ is an intermetallic compound characterized by two successive antiferromagnetic transitions at $T_{N1} = 6.3$ K and $T_{N2} = 10.4$ K. Here, its zero-field microscopic magnetic structure is inferred from resonant x-ray magnetic diffraction experiments on a single crystalline sample that complement previous bulk magnetic susceptibility data. For $T < T_{N2}$, the primitive magnetic unit cell matches the chemical cell. The magnetic structure features ferromagnetic {\it ac} planes stacked in an antiferromagnetic $\uparrow \downarrow \uparrow \downarrow$ pattern. For $T_{N1} < T < T_{N2}$, the ordered magnetic moment points along $\vec{a}$, and for $T < T_{N1}$ a component along $\vec{c}$ also orders. A symmetry analysis indicates that the magnetic structure for $T<T_{N1}$ is not compatible with the presumed orthorhombic $Cmmm$ space group of the chemical structure, and therefore a slight lattice distortion is implied. Mean-field calculations using a simplified magnetic Hamiltonian, including a reduced set of three independent exchange coupling parameters determined by density functional theory calculations and two crystal electric field terms taken as free-fitting parameters, are able to reproduce the main experimental observations. An alternative approach using a more complete model including seven exchange coupling and nine crystal electric field terms is also explored, where the search of the ground state magnetic structure compatible with the available anisotropic magnetic susceptibility and magnetization data is carried out with the help of an unsupervised machine learning algorithm. The possible magnetic configurations are grouped into five clusters, and the cluster that yields the best comparison with the experimental macroscopic data contains the parameters previously found with the simplified model and also predicts the correct ground-state magnetic structure.

[18] 2404.11756

Microwave dependent quantum transport characteristics in GaN/AlGaN FETs

Defects in semiconductors, traditionally seen as detrimental to electronic device performance, have emerged as potential assets in quantum technologies due to their unique quantum properties. This study investigates the interaction between defects and quantum electron transport in GaN/AlGaN field-effect transistors, highlighting the observation of Fano resonances at low temperatures. We observe the resonance spectra and their dependence on gate voltage and magnetic fields. To explain the observed behavior, we construct the possible scenario as a Fano interferometer with finite width. Our findings reveal the potential of semiconductor defects to contribute to the development of quantum information processing, providing their role to key components in next-generation quantum devices.

[19] 2404.11758

Coherent optical control of quantum Hall edge states

Current carrying chiral edge states in quantum Hall systems have fascinating properties that are usually studied by electron spectroscopy and interferometry. Here we demonstrate that electron occupation, current, and electron coherence in chiral edge states can be selectively probed and controlled by low-energy electromagnetic radiation in the microwave to infrared range without affecting electron states in the bulk or destroying quantum Hall effect conditions in the bulk of the sample. Both linear and nonlinear optical control is possible due to inevitable violation of adiabaticity and inversion symmetry breaking for electron states near the edge. This opens up new pathways for frequency- and polarization-selective spectroscopy and control of individual edge states.

[20] 2404.11765

2D capsid formation within an oscillatory energy landscape: orderly self-assembly depends on the interplay between a dynamic potential and intrinsic relaxation times

Multiple dissipative self-assembly protocols designed to create novel structures or to reduce kinetic traps have recently emerged. Specifically, temporal oscillations of particle interactions have been shown effective at both aims, but investigations thus far have focused on systems of simple colloids or their binary mixtures. In this work, we expand our understanding of the effect of temporally oscillating interactions to a two-dimensional coarse-grained viral capsid-like model that undergoes a self-limited assembly. This model includes multiple intrinsic relaxation times due to the internal structure of the capsid subunits and, under certain interaction regimes, proceeds via a two-step nucleation mechanism. We find that oscillations much faster than the local intrinsic relaxation times can be described via a time averaged inter-particle potential across a wide range of interaction strengths, while oscillations much slower than these relaxation times result in structures that adapt to the attraction strength of the current half-cycle. Interestingly, oscillations periods similar to these relaxation times shift the interaction window over which orderly assembly occurs by enabling error correction during the half-cycles with weaker attractions. Our results provide fundamental insights to non-equilibrium self-assembly on temporally variant energy landscapes.

[21] 2404.11768

Tensor-Networks-based Learning of Probabilistic Cellular Automata Dynamics

Algorithms developed to solve many-body quantum problems, like tensor networks, can turn into powerful quantum-inspired tools to tackle problems in the classical domain. In this work, we focus on matrix product operators, a prominent numerical technique to study many-body quantum systems, especially in one dimension. It has been previously shown that such a tool can be used for classification, learning of deterministic sequence-to-sequence processes and of generic quantum processes. We further develop a matrix product operator algorithm to learn probabilistic sequence-to-sequence processes and apply this algorithm to probabilistic cellular automata. This new approach can accurately learn probabilistic cellular automata processes in different conditions, even when the process is a probabilistic mixture of different chaotic rules. In addition, we find that the ability to learn these dynamics is a function of the bit-wise difference between the rules and whether one is much more likely than the other.

[22] 2404.11780

Dyakonov-Perel-like Orbital and Spin Relaxations in Centrosymmetric Systems

The Dyakonov-Perel (DP) mechanism of spin relaxation has long been considered irrelevant in centrosymmetric systems since it was developed originally for non-centrosymmetric ones. We investigate whether this conventional understanding extends to the realm of orbital relaxation, which has recently attracted significant attention. Surprisingly, we find that orbital relaxation in centrosymmetric systems exhibits the DP-like behavior in the weak scattering regime. Moreover, the DP-like orbital relaxation can make the spin relaxation in centrosymmetric systems DP-like through the spin-orbit coupling. We also find that the DP-like orbital and spin relaxations are anisotropic even in materials with high crystal symmetry (such as face-centered cubic structure) and may depend on the orbital and spin nature of electron wavefunctions.

[23] 2404.11787

Inducing mechanical self-healing in glassy polymer melts

Glassy polymer melts such as the plastics used in pipes, structural materials, and medical devices are ubiquitous in daily life. They accumulate damage over time due to their use, which limits their functionalities and demands periodic replacement. The resulting economic and social burden could be mitigated by the design of self-healing mechanisms that expand the lifespan of materials. However, the characteristic low molecular mobility in glassy polymer melts intrinsically limits the design of self-healing behavior. We demonstrate through numerical simulations that controlled oscillatory deformations enhance the local molecular mobility of glassy polymers without compromising their structural or mechanical stability. We apply this principle to increase the molecular mobility around the surface of a crack, inducing fracture repair and recovering the mechanical properties of the pristine material. Our findings establish a general physical mechanism of self-healing in glasses that may inspire the design and processing of new glassy materials.

[24] 2404.11820

Applicability of Eliashberg theory for systems with electron-phonon and electron-electron interaction: a comparative analysis

We present a comparative analysis of the validity of Eliashberg theory for the cases of fermions interacting with an Einstein phonon and with soft nematic fluctuations near an Ising-nematic/Ising-ferromagnetic quantum-critical point (QCP). In both cases, Eliashberg theory is obtained by neglecting vertex corrections. For the phonon case, the reasoning to neglect vertex corrections is the Migdal ``fast electron/slow boson'' argument because the phonon velocity is much smaller than the Fermi velocity, $v_F$. The same argument allows one to compute the fermionic self-energy within Eliashberg theory perturbatively rather than self-consistently. For the nematic case, the velocity of a collective boson is comparable to $v_F$ and this argument apparently does not work. Nonetheless, we argue that while two-loop vertex corrections near a nematic QCP are not small parametrically, they are small numerically. At the same time, perturbative calculation of the fermionic self-energy can be rigorously justified when the fermion-boson coupling is small compared to the Fermi energy. Furthermore, we argue that for the electron-phonon case Eliashberg theory breaks down at some distance from where the dressed Debye frequency would vanish, while for the nematic case it holds all the way to a QCP. From this perspective, Eliashberg theory for the nematic case actually works better than for the electron-phonon case.

[25] 2404.11830

Alignment-induced depression and shear thinning of anisotropic granular media

When granular materials of shape-anisotropic grains are sheared in a split-bottom shear cell, a localized shear band is formed with a depression at its center. This effect is closely related to the alignment of the particles with aspect ratio (AR), which, in turn, influences the local packing density, the stress distribution, and the system's overall bulk rheology. Particles with large AR tend to align with the shear direction, which increases the packing density in the shear band and affects rheological properties like stress, macroscopic friction coefficient, and effective viscosity. A scaling law correlates particle AR to macroscopic friction and effective viscosity, revealing shear-thinning behavior in bulk and near the surface.

[26] 2404.11867

Automated tomographic assessment of structural defects of freeze-dried pharmaceuticals

The topology and surface characteristics of lyophilisates significantly impact the stability and reconstitutability of freeze-dried pharmaceuticals. Consequently, visual quality control of the product is imperative. However, this procedure is not only time-consuming and labor-intensive but also expensive and prone to errors. In this paper, we present an approach for fully automated, non-destructive inspection of freeze-dried pharmaceuticals, leveraging robotics, computed tomography, and machine learning.

[27] 2404.11911

Tunable magnetism in bilayer transition metal dichalcogenides

Twist between neighboring layers and variation of interlayer distance are two extra ways to control the physical properties of stacked two-dimensional van der Waals materials without alteration of chemical compositions or application of external fields, compared to their monolayer counterparts. In this work, we explored the dependence of the magnetic states of the untwisted and twisted bilayer 1T-VX$_2$ (X = S, Se) on the interlayer distance by density functional theory calculations. We find that, while a magnetic phase transition occurs from interlayer ferromagnetism to interlayer antiferromagnetism either as a function of decreasing interlayer distance for the untwisted bilayer 1T-VX$_2$ or after twist, richer magnetic phase transitions consecutively take place for the twisted bilayer 1T-VX$_2$ as interlayer distance is gradually reduced. Besides, the critical pressures for the phase transition are greatly reduced in twisted bilayer 1T-VX$_2$ compared with the untwisted case. We derived the Heisenberg model with intralayer and interlayer exchange couplings to comprehend the emergence of various magnetic states. Our results point out an easy access towards tunable two-dimensional magnets.

[28] 2404.11934

Quantum simulation of honeycomb lattice model by high-order moiré pattern

Moir\'e superlattices have become an emergent solid-state platform for simulating quantum lattice models. However, in single moir\'e device, Hamiltonians parameters like lattice constant, hopping and interaction terms can hardly be manipulated, limiting the controllability and accessibility of moire quantum simulator. Here, by combining angle-resolved photoemission spectroscopy and theoretical analysis, we demonstrate that high-order moir\'e patterns in graphene-monolayered xenon/krypton heterostructures can simulate honeycomb model in mesoscale, with in-situ tunable Hamiltonians parameters. The length scale of simulated lattice constant can be tuned by annealing processes, which in-situ adjusts intervalley interaction and hopping parameters in the simulated honeycomb lattice. The sign of the lattice constant can be switched by choosing xenon or krypton monolayer deposited on graphene, which controls sublattice degree of freedom and valley arrangment of Dirac fermions. Our work establishes a novel path for experimentally simulating the honeycomb model with tunable parameters by high-order moir\'e patterns.

[29] 2404.11950

Pair density waves in the strong-coupling two-dimensional Holstein-Hubbard model: a variational Monte Carlo study

A robust theory of the mechanism of pair density wave (PDW) superconductivity (i.e. where Cooper pairs have nonzero center of mass momentum) remains elusive. Here we explore the triangular lattice $t$-$J$-$V$ model, a low-energy effective theory derived from the strong-coupling limit of the Holstein-Hubbard model, by large-scale variational Monte Carlo simulations. When the electron density is sufficiently low, the favored ground state is an s-wave PDW, consistent with results obtained from previous studies in this limit. Additionally, a PDW ground state with nematic d-wave pairing emerges in intermediate range of electron densities and phonon frequencies. For these s-wave and d-wave PDWs arising in states with spontaneous breaking of time-reversal and inversion symmetries, PDW formation derives from valley-polarization and intra-pocket pairing.

[30] 2404.11955

Electrical control of a Kondo spin screening cloud

In metals and semiconductors, an impurity spin is quantum entangled with and thereby screened by surrounding conduction electrons at low temperatures, called the Kondo screening cloud. Quantum confinement of the Kondo screening cloud in a region, called a Kondo box, with a length smaller than the original cloud extension length strongly deforms the screening cloud and provides a way of controlling the entanglement. Here we realize such a Kondo box and develop an approach to controlling and monitoring the entanglement. It is based on a spin localized in a semiconductor quantum dot, which is screened by conduction electrons along a quasi-one-dimensional channel. The box is formed between the dot and a quantum point contact placed on a channel. As the quantum point contact is tuned to make the confinement stronger, electron conductance through the dot as a function of temperature starts to deviate from the known universal function of the single energy scale, the Kondo temperature. Nevertheless, the entanglement is monitored by the measured conductance according to our theoretical development. The dependence of the monitored entanglement on the confinement strength and temperature implies that the Kondo screening is controlled by tuning the quantum point contact. Namely, the Kondo cloud is deformed by the Kondo box in the region across the original cloud length. Our findings offer a way of manipulating and detecting spatially extended quantum many-body entanglement in solids by electrical means.

[31] 2404.11956

Scanning Tunneling Microscopy for Molecules: Manipulating Electrons and Photons by Varying Buffer Layer

In scanning tunneling microscopy of molecules, an insulating buffer layer is often introduced to reduce interaction between the molecules and the substrate. Focusing on tunneling through the molecule's electronic transport gap, we demonstrate that the buffer itself strongly influences the wave function of the tunneling electron at the molecule. This is exemplified for an adsorbed platinum phthalocyanine molecule by varying the composition and thickness of the buffer. We find that, in particular, the buffer's lattice parameter is crucial. By expanding the wave function of the tunneling electron in molecular orbitals (MOs), we illustrate how one can strongly vary the relative weights of different MOs, such as the highest occupied MO versus some low-lying MOs with few nodal surfaces. The set of MOs with significant weight are important for processes used to manipulate the state of the molecule by a tunneling electron, such as molecular luminescence. The choice of buffer therefore provides an important tool for manipulating these processes.

[32] 2404.11980

Unsupervised learning approach to quantum wavepacket dynamics from coupled temporal-spatial correlations

Understanding complex quantum dynamics in realistic materials requires insight into the underlying correlations dominating the interactions between the participating particles. Due to the wealth of information involved in these processes, applying artificial intelligence methods is compelling. Yet, unsupervised data-driven approaches typically focus on maximal variations of the individual components, rather than considering the correlations between them. Here we present an approach that recognizes correlation patterns to explore convoluted dynamical processes. Our scheme is using singular value decomposition (SVD) to extract dynamical features, unveiling the internal temporal-spatial interrelations that generate the dynamical mechanisms. We apply our approach to study light-induced wavepacket propagation in organic crystals, of interest for applications in material based quantum computing and quantum information science. We show how transformation from the input momentum and time coordinates onto a new correlation-induced coordinate space allows direct recognition of the relaxation and dephasing components dominating the dynamics and demonstrate their dependence on the initial pulse shape. Entanglement of the dynamical features is suggested as a pathway to reproduce the information required for further explainability of these mechanisms. Our method offers a route for elucidating complex dynamical processes using unsupervised AI-based analysis in multi-component systems.

[33] 2404.12004

First-principles study of phase transition in cadmium titanate by molecular dynamics incorporating nuclear quantum effects

First-principles molecular dynamics (FPMD) simulations were applied for the paraelectric-ferroelectric phase transition in the perovskite-type cadmium titanate, CdTiO3. Since the phase transition is reported to occur at the low temperature around 80 K, the quantum thermal bath (QTB) method was utilized in this study, which incorporates the nuclear quantum effects (NQEs). The structural evolutions in the QTB-FPMD simulations are in reasonable agreement with the experimental results, by contrast in the conventional FPMD simulations using the classical thermal bath (CTB-FPMD). According to our phonon calculations, volume expansion is the key in the stabilization of the ferroelectric phase at low temperatures, which was well reproduced in the QTB-FPMD with the NQEs. Thus, the NQEs are of importance in phase transitions at low temperatures, particularly below the room temperature, and the QTB is useful in that it incorporates the NQEs in MD simulations with low computational costs comparable to the conventional CTB.

[34] 2404.12017

Green and Solid State Reduction of GO Monolayers Sandwiched between Arachidic Acid LB Layers

A novel, single step and environment friendly solid state approach for reduction of graphene oxide (GO) monolayers has been demonstrated, in which, arachidic acid-GO-arachidic acid (AA-GO-AA) sandwich structure obtained by Langmuir-Blodgett (LB) technique was heat treated at moderate temperatures to obtain RGO sheets. Heat treatment of AA-GO-AA sandwich structure at 200 C results in substantial reduction of GO, with concurrent removal of AA molecules. Such developed RGO sheets possess sp2-C content of 69%, O/C ratio of 0.17 and significantly reduced I(D) and I(G) ratio of ~1.1. Ultraviolet photoelectron spectroscopy (UPS) studies on RGO sheets evidenced significant increase in density of states in immediate vicinity of Fermi level and decrease in work function after reduction. Bottom gated field effect transistors fabricated with isolated RGO sheets displayed charge neutrality point at a positive gate voltage, indicating p-type nature, consistent with UPS and electrostatic force microscopy (EFM) measurement results.The RGO sheets obtained by heat treatment of AA-GO-AA sandwich structure exhibited conductivity in the range of 2-7Scm-1 and field effect mobility of 0.03-2cm2V-1s-1, which are consistent with values reported for RGO sheets obtained by various chemical or thermal reduction procedures.The extent of GO reduction is determined primarily by proximity of AA molecules and found to be unaltered with either escalation of heat treatment temperature or increase of AA content in sandwich structure. The single-step GO reduction approach demonstrated in this work is an effective way for development of RGO monolayers with high structural quality towards graphene-based electronic device applications.

[35] 2404.12072

Transport of orbital currents in systems with strong intervalley coupling: the case of Kekulé distorted graphene

We show that orbital currents can describe the transport of orbital magnetic moments of Bloch states in models where the formalism based on valley current is not applicable. As a case study, we consider Kekul\'e distorted graphene. We begin by analyzing the band structure in detail and obtain the orbital magnetic moment operator for this model within the framework of the modern theory of magnetism. Despite the simultaneous presence of time-reversal and spatial-inversion symmetries, such operator may be defined, although its expectation value at a given energy is zero. Nevertheless, its presence can be exposed by the application of an external magnetic field. We then proceed to study the transport of these quantities. In the Kekul\'e-$O$ distorted graphene model, the strong coupling between different valleys prevents the definition of a bulk valley current. However, the formalism of the orbital Hall effect together with the non-Abelian description of the magnetic moment operator can be directly applied to describe its transport in these types of models. We show that the Kekul\'e-$O$ distorted graphene model exhibits an orbital Hall insulating plateau whose height is inversely proportional to the energy band gap produced by intervalley coupling. Our results strengthen the perspective of using the orbital Hall effect formalism as a preferable alternative to the valley Hall effect

[36] 2404.12106

Landau-Lifschitz magnets: exact thermodynamics and transport

The classical Landau--Lifshitz equation -- the simplest model of a ferromagnet -- provides an archetypal example for studying transport phenomena. In one-spatial dimension, integrability enables the classification of the spectrum of linear and nonlinear modes. An exact characterization of finite-temperature thermodynamics and transport has nonetheless remained elusive. We present an exact description of thermodynamic equilibrium states in terms of interacting modes. This is achieved by retrieving the classical Landau--Lifschitz model through the semiclassical limit of the integrable quantum spin-$S$ anisotropic Heisenberg chain at the level of the thermodynamic Bethe ansatz description. In the axial regime, the mode spectrum comprises solitons with unconventional statistics, whereas in the planar regime we additionally find two special types of modes of radiative and solitonic type. The obtained framework paves the way for analytical study of unconventional transport properties: as an example we study the finite-temperature spin Drude weight, finding excellent agreement with Monte Carlo simulations.

[37] 2404.12108

Impact of non-reciprocal interactions on colloidal self-assembly with tunable anisotropy

Non-reciprocal (NR) effective interactions violating Newton's third law occur in many biological systems, but can also be engineered in synthetic, colloidal systems. Recent research has shown that such NR interactions can have tremendous effects on the overall collective behaviour and pattern formation, but can also influence aggregation processes on the particle scale. Here we focus on the impact of non-reciprocity on the self-assembly of an (originally passive) colloidal system with anisotropic interactions whose character is tunable by external fields. In the absence of non-reciprocity, that is, under equilibrium conditions, the colloids form aggregates with extremely long life times [Kogler et al., Soft Matter 11, 7356 (2015)], indicating kinetic trapping. Here we study, based on Brownian Dynamics (BD) simulations in 2D, a NR version of this model consisting of two species with reciprocal isotropic, but NR anisotropic interactions. We find that NR induces an effective propulsion of particle pairs and small aggregates forming at initial stages of self-assembly, an indication of the NR-induced non-equilibrium. The shape and stability of these initial clusters strongly depends on the degree of anisotropy. At longer times we find, for weak NR interactions, large (even system-spanning) clusters where single particles can escape and enter at the boundaries, in stark contrast to the small rigid aggregates appearing at the same time in the passive case. In this sense, weak NR shortcuts the aggregation. Increasing the degree of NR (and thus, propulsion), we even observe large-scale phase separation if the interactions are weakly anisotropic. In contrast, system with strong NR and anisotropy remain essentially disordered. Overall, NR interactions are shown to destabilize the rigid aggregates interrupting self-assembly in the passive case, helping the system to overcome kinetic barriers.

[38] 2404.12111

Optical anisotropy of the kagome magnet FeSn: Dominant role of excitations between kagome and Sn layers

Antiferromagnetic FeSn is considered to be a close realization of the ideal two-dimensional (2D) kagome lattice, hosting Dirac cones, van Hove singularities, and flat bands, as it comprises Fe$_3$Sn kagome layers well separated by Sn buffer layers. We observe a pronounced optical anisotropy, with the low-energy optical conductivity being surprisingly higher perpendicular to the kagome planes than along the layers. This finding contradicts the prevalent picture of dominantly 2D electronic structure for FeSn. Our material-specific theory reproduces the measured conductivity spectra remarkarbly well. A site-specific decomposition of the optical response to individual excitation channels shows that the optical conductivity for polarizations both parallel and perpendicular to the kagome plane is dominated by interlayer transitions between kagome layers and adjacent Sn-based layers. Moreover, the matrix elements corresponding to these transitions are highly anisotropic, leading to larger out-of-plane conductivity. Our results evidence the crucial role of interstitial layers in charge dynamics even in seemingly 2D systems.

[39] 2404.12119

Controlling 4f antiferromagnetic dynamics via itinerant electronic susceptibility

Optical manipulation of magnetism holds promise for future ultrafast spintronics, especially with lanthanides and their huge, localized 4f magnetic moments. These moments interact indirectly via the conduction electrons (RKKY exchange), influenced by interatomic orbital overlap, and the conduction electron susceptibility. Here, we study this influence in a series of 4f antiferromagnets, GdT2Si2 (T=Co, Rh, Ir), using ultrafast resonant X-ray diffraction. We observe a twofold increase in ultrafast angular momentum transfer between the materials, originating from modifications in the conduction electron susceptibility, as confirmed by first-principles calculations.

[40] 2404.12151

Vortex motion in reconfigurable three-dimensional superconducting nanoarchitectures

When materials are patterned in three dimensions, there exist opportunities to tailor and create functionalities associated with an increase in complexity, the breaking of symmetries, and the introduction of curvature and non-trivial topologies. For superconducting nanostructures, the extension to the third dimension may trigger the emergence of new physical phenomena, as well as advances in technologies. Here, we harness three-dimensional (3D) nanopatterning to fabricate and control the emergent properties of a 3D superconducting nanostructure. Not only are we able to demonstrate the existence and motion of superconducting vortices in 3D but, with simulations, we show that the confinement leads to a well-defined bending of the vortices within the volume of the structure. Moreover, we experimentally observe a strong geometrical anisotropy of the critical field, through which we achieve the reconfigurable coexistence of superconducting and normal states in our 3D superconducting architecture, and the local definition of weak links. In this way, we uncover an intermediate regime of nanosuperconductivity, where the vortex state is truly three-dimensional and can be designed and manipulated by geometrical confinement. This insight into the influence of 3D geometries on superconducting properties offers a route to local reconfigurable control for future computing devices, sensors, and quantum technologies.

[41] 2404.12159

Localization in boundary-driven lattice models

Several systems may display an equilibrium condensation transition, where a finite fraction of a conserved quantity is spatially localized. The presence of two conservation laws may induce the emergence of such transition in an out-of-equilibrium setup, where boundaries are attached to two different and subcritical heat baths. We study this phenomenon in a class of stochastic lattice models, where the local energy is a general convex function of the local mass, mass and energy being both globally conserved in the isolated system. We obtain exact results for the nonequilibrium steady state (spatial profiles, mass and energy currents, Onsager coefficients) and we highlight important differences between equilibrium and out-of-equilibrium condensation.

[42] 2404.12180

Microwave seeding time crystal in Floquet driven Rydberg atoms

Crystal seeding enables a deeper understanding of phase behavior, leading to the development of methods for controlling and manipulating phase transitions in various applications such as materials synthesis, crystallization processes, and phase transformation engineering. How to seed a crystalline in time domain is an open question, which is of great significant and may provide an avenue to understand and control time-dependent quantum many-body physics. Here, we utilize a microwave pulse as a seed to induce the formation of a discrete time crystal in Floquet driven Rydberg atoms. In the experiment, the periodic driving on Rydberg states acts as a seeded crystalline order in subspace, which triggers the time-translation symmetry breaking across the entire ensemble. The behavior of the emergent time crystal is elaborately linked to alterations in the seed, such as the relative phase shift and the frequency difference, which result in phase dependent seeding and corresponding shift in periodicity of the time crystal, leading to embryonic synchronization. This result opens up new possibilities for studying and harnessing time-dependent quantum many-body phenomena, offering insights into the behavior of complex many-body systems under seeding.

[43] 2404.12191

TMM$-$Sim: A Versatile Tool for Optical Simulation of Thin$-$Film Solar Cells

The Transfer Matrix Method (TMM) has become a prominent tool for the optical simulation of thin$-$film solar cells, particularly among researchers specializing in organic semiconductors and perovskite materials. As the commercial viability of these solar cells continues to advance, driven by rapid developments in materials and production processes, the importance of optical simulation has grown significantly. By leveraging optical simulation, researchers can gain profound insights into photovoltaic phenomena, empowering the implementation of device optimization strategies to achieve enhanced performance. However, existing TMM$-$based packages exhibit limitations, such as requiring programming expertise, licensing fees, or lack of support for bilayer device simulation. In response to these gaps and challenges, we present the TMM Simulator (TMM$-$Sim), an intuitive and user$-$friendly tool to calculate essential photovoltaic parameters, including the optical electric field profile, exciton generation profile, fraction of light absorbed per layer, photocurrent, external quantum efficiency, internal quantum efficiency, and parasitic losses. An additional advantage of TMM$-$Sim lies in its capacity to generate outcomes suitable as input parameters for electro$-$optical device simulations. In this work, we offer a comprehensive guide, outlining a step$-$by$-$step process to use TMM$-$Sim, and provide a thorough analysis of the results. TMM$-$Sim is freely available, accessible through our web server (, or downloadable from the TMM$-$Sim repository (for \textit{Unix}, \textit{Windows}, and \textit{macOS}) on \textit{GitHub}. With its user$-$friendly interface and powerful capabilities, TMM$-$Sim aims to facilitate and accelerate research in thin$-$film solar cells, fostering advancements in renewable energy technologies.

[44] 2404.12206

Attosecond dynamics of electron scattering by an absorbing layer

Attosecond dynamics of electron reflection from a thin film is studied based on a one-dimensional jellium model. Following the Eisenbud-Wigner-Smith concept, the reflection time delay $\Delta\tau_{\rm R}$ is calculated as the energy derivative of the phase of the complex reflection amplitude $r$. For a purely elastic scattering by a jellium slab of a finite thickness $d$ the transmission probability $T$ oscillates with the momentum $K$ in the solid with a period $\pi/d$, and $\Delta\tau_{\rm R}$ closely follows these oscillations. The reflection delay averaged over an energy interval grows with $d$, but in the limit of $d\to\infty$ the amplitude $r$ becomes real, so $\Delta\tau_{\rm R}$ vanishes. This picture changes substantially with the inclusion of an absorbing potential $-iV_{\rm i}$: As expected, for a sufficiently thick slab the reflection amplitude now tends to its asymptotic value for a semi-infinite crystal. Interestingly, for $V_{\rm i} \ne 0$, around the $T(E)$ maxima, the $\Delta\tau_{\rm R}(E)$ curve strongly deviates from $T(E)$, showing a narrow dip just at the $\Delta\tau_{\rm R}(E)$ maximum for $V_{\rm i}=0$. An analytical theory of this counterintuitive behavior is developed.

[45] 2404.12207

Spin-1 Haldane chains of superconductor-semiconductor hybrids

We theoretically explore the possibility of realizing the symmetry-protected topological Haldane phase of spin-1 chains in a tunable hybrid platform of superconducting islands (SIs) and quantum dots (QDs). Inspired by recent findings suggesting that an appropriately tuned QD-SI-QD block may behave as a robust spin-1 unit, we study the behavior of many such units tunnel-coupled into linear chains. Our efficient and fully microscopic modeling of long chains with several tens of units is enabled by the use of the surrogate model solver [Phys. Rev. B 108, L220506 (2023); arXiv:2402.18357]. Our numerical findings indicate that the QD-SI-QD chains exhibit emblematic features of the Haldane phase, such as fractional spin-1/2 edge states and non-vanishing string order parameters, and that these persist over a sizeable region of parameter space. Increasing the coupling between neighboring units gradually degrades their individual spin-1 character and leads to a trivial dimerized phase.

[46] 2404.12211

Anomalous diffusion and effective shear modulus in a semi-solid membrane

From the perspective of physical properties, the cell membrane is an exotic two-dimensional material that has a dual nature: it exhibits characteristics of fluids, i.e., lipid molecules show lateral diffusion, while also demonstrating properties of solids, evidenced by a non-zero shear modulus. We construct a model for such a $\textit{semi-solid}$ $\textit{membrane}$. Our model is a fluctuating randomly triangulated mesh with two different kinds of nodes. The solid nodes never change their neighbors, while the fluid nodes do. As the area fraction occupied by the solid nodes ($\Phi$) is increased the motion of fluid nodes transition from diffusion to localization via subdiffusion. Next, the solid nodes are pinned to mimic the pinning of the plasma membrane to the cytoskeleton. For the pinned membrane, there exists a range of $\Phi$ over which the model has both a non-zero shear modulus and a non-zero lateral diffusivity. The bending modulus, measured through the spectrum of height fluctuations remains unchanged.

[47] 2404.12218

Traveling strings of active dipolar colloids

We study an intriguing new type of self-assembled active colloidal polymer system in 3D. It is obtained from a suspension of Janus particles in an electric field that induces parallel dipoles in the particles as well as self-propulsion in the plane perpendicular to the field. At low packing fractions, in experiment, the particles self-assemble into 3D columns that are self-propelled in 2D. Explicit numerical simulations combining dipolar interactions and active self-propulsion find an activity dependent transition to a string phase by increasing dipole strength. We classify the collective dynamics of strings as a function of rotational and translational diffusion. Using an anisotropic version of the Rouse model of polymers with active driving, we analytically compute the strings' collective dynamics and centre of mass motion, which matches simulations and is consistent with experimental data. We also discover long range correlations of the fluctuations along the string contour that grow with the active persistence time, a purely active effect that disappears in the thermal limit.

[48] 2404.12232

Model geometries of porous materials

We describe a method for modeling the geometry of porous materials. The approach enables the independent selection of crucial parameters, including porosity, pore size distribution, pore shape, and connectivity. Consequently, it can effectively model a wide range of porous systems. Due to the diverse and systematic variation possibilities, the method is suitable for developing and optimizing porous structures. The geometries can be exported as triangular meshes, facilitating their immediate use in numerical simulation and further digital processing. We showcase the method's capabilities by minimizing the foam structure's thermal conductivity through geometry optimization.

[49] 2404.12250

Effects of Reduced Interlayer Interactions on the K-point Excitons of MoS$_2$ Nanoscrolls

Transition metal dichalcogenide (TMD) nanoscrolls (NS) exhibit significant photoluminescence (PL) signals despite their multilayer structure, which cannot be explained by the strained multilayer description of NS. Here, we investigate the interlayer interactions in NS to address this discrepancy. The reduction of interlayer interactions in NS is attributed to two factors: (1) the symmetry-broken mixed stacking order between neighbouring layers due to misalignment, and (2) the high inhomogeneity in the strain landscape resulting from the unique Archimedean spiral-like geometry with positive eccentricity. These were confirmed through transmission electron microscopy, field emission scanning electron microscopy and atomic force microscopy. To probe the effect of reduction of interlayer interactions in multilayered MoS$_2$ nanoscrolls, low-temperature PL spectroscopy was employed investigating the behaviour of K-point excitons. The effects of reduced interlayer interactions on exciton-phonon coupling (EXPC), exciton energy, and exciton oscillator strength are discussed, providing insights into the unique properties of TMD nanoscrolls.

[50] 2404.12266

Theory of Mobility Rings in Non-Hermitian Systems

Through Avila global theorem, we analytically study the non-Hermitian mobility edge. The results show that the mobility edge in non-Hermitian systems has a ring structure, which we named as "mobility ring". Furthermore, we carry out numerical analysis of the eigenenergy spectra in several typical cases, and the consistence of the numerical results with the analytical expression proves the correctness and universality of the mobility ring theory. Further, based on the analytical expression, we discuss the properties of multiple mobility rings. Finally, we compare the results of mobility rings with that of dual transformations, and find that although the self-dual method can give the interval of real eigenvalues corresponding to the extended states, it can not fully display the mobility edge information in the complex plane. The mobility ring theory proposed in this paper is universal for all non-Hermitian systems.

[51] 2404.12271

Emergent Anti-Ferroelectric Ordering and the Coupling of Liquid Crystalline and Polar Order

Polar liquid crystals possess three dimensional orientational order coupled with unidirectional electric polarity, yielding fluid ferroelectrics. Such polar phases are generated by rod-like molecules with large electric dipole moments. 2,5-Disubstituted 1,3-dioxane is commonly employed as a polar motif in said systems, and here we show this to suffer from thermal instability as a consequence of equatorial-trans to axial-trans isomerism at elevated temperatures. We utilise isosteric building blocks as potential replacements for the 1,3- dioxane unit, and in doing so we obtain new examples of fluid ferroelectric systems. For binary mixtures of certain composition, we observe the emergence of a new fluid antiferroelectric phase - a finding not observed for either of the parent molecules. Our study also reveals a critical tipping point for the emergence of polar order in otherwise apolar systems. These results hint at the possibility for uncovering new highly ordered polar LC phases and delineate distinct transition mechanisms in orientational and polar ordering.

[52] 2404.12275

Spin-Valve-Like Magnetoresistance and Anomalous Hall Effect in Magnetic Weyl Metal Mn$_2$PdSn

Realization of noncentrosymmetric magnetic Weyl metals is expected to exhibit anomalous transport properties stemming from the interplay of unusual bulk electronic topology and magnetism. Here, we present spin-valve-like magnetoresistance at room temperature in ferrimagneticWeyl metal Mn$_2$PdSn that crystallizes in the inverse Heusler structure. Anomalous magnetoresistance display dominant asymmetric component attributed to domain wall electron scattering, indicative of spin-valve-like behavior. Ab initio calculations confirm the topologically non-trivial nature of the band structure, with three pairs of Weyl nodes proximate to the Fermi level, providing deeper insights into the observed intrinsic Berry curvature mediated substantial anomalous Hall conductivity. Our results underscore the inverse Heusler compounds as promising platform to realize magnetic Weyl metals/semimetals and leverage emergent transport properties for electronic functionalities.

[53] 2404.12297

Extended unitarity and absence of skin effect in periodically driven systems

One of the most striking features of non-Hermitian quasiperiodic systems with arbitrarily small asymmetry in the hopping amplitudes and open boundaries is the accumulation of all the bulk eigenstates at one of the edges of the system, termed in literature as the skin effect, below a critical strength of the potential. In this Letter, we uncover that a time-periodic drive in such systems can eliminate the SE up to a finite strength of this asymmetry. Remarkably, the critical value for the onset of SE is independent of the driving frequency and approaches to the static behavior in the thermodynamic limit. We find that the absence of SE is intricately linked to the emergence of extended unitarity in the delocalized phase, providing dynamical stability to the system. Interestingly, under periodic boundary condition, our non-Hermitian system can be mapped to a Hermitian analogue in the large driving frequency limit that leads to the extended unitarity irrespective of the hopping asymmetry and the strength of the quasiperiodic potential, in stark contrast to the static limit. Additionally, we numerically verify that this behavior persists Based on our findings, we propose a possible experimental realization of our driven system, which could be used as a switch to control the light funneling mechanism.

[54] 2404.12307

Investigation of Spin-Pumping and -Transport in the Ni80Fe20/Pt/Co Asymmetric Trilayer

FM1/NM/FM2 trilayers have garnered considerable attention because of their potential in spintronic applications. A thorough investigation of the spin transport properties of these trilayers is therefore important. Asymmetric trilayers, particularly those including Platinum (Pt) as a spacer are less explored. Pt mediates exchange coupling between the two FM layers and thus offers a unique platform to investigate the spin-transport properties under indirect exchange coupling conditions through the spin-pumping mechanism. Our analytical focus on the acoustic mode of the ferromagnetic resonance spectrum, facilitated by the distinct magnetizations of the Ni80Fe20 and Co layers, allows for the isolation of individual layer resonances. The derived spin-pumping induced damping of the Ni80Fe20 and Co layers reveals a direct dependence on the Pt spacer thickness. Furthermore, fitting of the weighted average of the damping parameters to the spin-pumping induced damping of acoustic mode reveals that the observed FMR spectra is indeed a result of the in-phase precession of the magnetizations in two FM layers. The extracted effective spin-mixing conductance varies with the FM/NM interface, specifically 1.72x10^19 m^(-2) at the Ni80Fe20/Pt and 4.07x10^19 m^(-2) at the Co/Pt interface, indicating a strong correlation with interfacial characteristics. Additionally, we deduce the spin diffusion length in Pt to be between 1.02 and 1.55 nm and calculate the interfacial spin transparency and spin current densities, highlighting significant disparities between the Ni80Fe20/Pt and Co/Pt interfaces. This detailed analysis enhances our understanding of spin transport in Ni80Fe20/Pt/Co trilayers. It offers insights important for advancing spintronic device design and lays the groundwork for future theoretical investigations of trilayer system.

[55] 2404.12321

Area laws and thermalization from classical entropies in a Bose-Einstein condensate

The scaling of local quantum entropies is of utmost interest for characterizing quantum fields, many-body systems, and gravity. Despite their importance, theoretically and experimentally accessing quantum entropies is challenging as they are nonlinear functionals of the underlying quantum state. Here, we show that suitably chosen classical entropies capture the very same features as their quantum analogs for an experimentally relevant setting. We describe the post-quench dynamics of a multi-well spin-1 Bose-Einstein condensate from an initial product state via measurement distributions of spin observables and estimate the corresponding entropies using the asymptotically unbiased k-nearest neighbor method. We observe the dynamical build-up of quantum correlations signaled by an area law, as well as local thermalization revealed by a transition to a volume law, both in regimes characterized by non-Gaussian distributions. We emphasize that all relevant features can be observed at small sample numbers without assuming a specific functional form of the distributions, rendering our method directly applicable to a large variety of models and experimental platforms.

[56] 2404.12323

Area laws for classical entropies in a spin-1 Bose-Einstein condensate

We investigate the information extractable from measurement distributions of two non-commuting spin observables in a multi-well spin-1 Bose-Einstein condensate. We provide a variety of analytic and numerical evidence that suitably chosen classical entropies and classical mutual informations thereof contain the typical feature of quantum entropies known in quantum field theories, that is, the area law, even in the non-Gaussian regime and for a non-zero temperature. Towards a feasible experimental implementation, we estimate entropic quantities from a finite number of samples without any additional assumptions on the underlying quantum state using k-nearest neighbor estimators.

[57] 2404.12338

Hot Carrier Organic Solar Cells

Hot-carrier solar cells use the photon excess energy, that is, the energy exceeding the absorber bandgap, to do additional work. These devices have the potential to beat the upper limit for the photovoltaic power conversion efficiency set by near-equilibrium thermodynamics. However, since their conceptual inception in 1982, making this concept work under practical conditions has proven a tremendous hurdle, mostly due to the fast thermalization of photo-generated charges in typical semiconductor materials like silicon. Here, we use noise spectroscopy in combination with numerical modelling to show that common bulk heterojunction organic solar cells actually work as hot-carrier devices. Due to static energetic disorder, thermalization of photo-generated electrons and holes in the global density of states is slow compared to the charge carrier lifetime, leading to thermal populations of localized charge carriers that have an electronic temperature exceeding the lattice temperature. Since charge extraction takes place in a high-lying, narrow energy window around the transport energy, the latter takes the role of an energy filter. For common disorder values, this leads to substantial enhancements in open circuit voltage. We expect these results to inspire new strategies to more efficiently convert solar energy into electricity.

[58] 2404.12345

High spin axion insulator

Axion insulators possess a quantized axion field $\theta=\pi$ protected by combined lattice and time-reversal symmetry, holding great potential for device applications in layertronics and quantum computing. Here, we propose a high-spin axion insulator (HSAI) defined in large spin-$s$ representation, which maintains the same inherent symmetry but possesses a notable axion field $\theta=(s+1/2)^2\pi$. Such distinct axion field is confirmed independently by the direct calculation of the axion term using hybrid Wannier functions, layer-resolved Chern numbers, as well as the topological magneto-electric effect. We show that the guaranteed gapless quasi-particle excitation is absent at the boundary of the HSAI despite its integer surface Chern number, hinting an unusual quantum anomaly violating the conventional bulk-boundary correspondence. Furthermore, we ascertain that the axion field $\theta$ can be precisely tuned through an external magnetic field, enabling the manipulation of bonded transport properties. The HSAI proposed here can be experimentally verified in ultra-cold atoms by the quantized non-reciprocal conductance or topological magnetoelectric response. Our work enriches the understanding of axion insulators in condensed matter physics, paving the way for future device applications.

[59] 2404.12367

Information theory unifies atomistic machine learning, uncertainty quantification, and materials thermodynamics

An accurate description of information is relevant for a range of problems in atomistic modeling, such as sampling methods, detecting rare events, analyzing datasets, or performing uncertainty quantification (UQ) in machine learning (ML)-driven simulations. Although individual methods have been proposed for each of these tasks, they lack a common theoretical background integrating their solutions. Here, we introduce an information theoretical framework that unifies predictions of phase transformations, kinetic events, dataset optimality, and model-free UQ from atomistic simulations, thus bridging materials modeling, ML, and statistical mechanics. We first demonstrate that, for a proposed representation, the information entropy of a distribution of atom-centered environments is a surrogate value for thermodynamic entropy. Using molecular dynamics (MD) simulations, we show that information entropy differences from trajectories can be used to build phase diagrams, identify rare events, and recover classical theories of nucleation. Building on these results, we use this general concept of entropy to quantify information in datasets for ML interatomic potentials (IPs), informing compression, explaining trends in testing errors, and evaluating the efficiency of active learning strategies. Finally, we propose a model-free UQ method for MLIPs using information entropy, showing it reliably detects extrapolation regimes, scales to millions of atoms, and goes beyond model errors. This method is made available as the package QUESTS: Quick Uncertainty and Entropy via STructural Similarity, providing a new unifying theory for data-driven atomistic modeling and combining efforts in ML, first-principles thermodynamics, and simulations.

[60] 2404.12374

Tunable Kondo physics in a van der Waals kagome antiferromagnet

The Kondo lattice physics, describing the hybridization of localized spin matrix with dispersive conduction electrons, breeds numerous discoveries in the realm of strongly correlated quantum matter. Generally observed in lanthanide and actinide compounds, increasing attention has been directed towards alternative pathways for achieving flat band structures, such as Morie superlattices and Kagome metals. However, fine control of Kondo interaction outside of heterostructures remains elusive. Here we report the discovery of a van der Waals (vdW) kagome antiferromagnet CsCr6Sb6. Angle-resolved photoemission spectra and theoretical analysis show clear flat bands, consisting of half-filled 3dxz and 3dyz orbitals of Cr, situated 50 meV below the Fermi level. Importantly, we observe the emergence of anomalous Hall effect with remarkable tunability by simple reduction the sample thickness. The effective control of kondo interaction in CsCr6Sb6 render it an ideal platform for exploring unpresented phenomena using the vast toolkit of vdW structures.

[61] 2404.12384

Decoupled sound and amplitude modes in trapped dipolar supersolids

We theoretically investigate elementary excitations of dipolar quantum gases across the superfluid to supersolid phase transition in a toroidal trap. We show how decoupled first sound, second sound, and Higgs modes emerge by following their origin from superfluid modes across the transition. The structure of these excitations reveals the interplay between crystal and superfluid oscillations. Our results unify previous notions of coupled Goldstone and Higgs modes in harmonic traps, allowing us to establish a correspondence between excitations of trapped and infinitely extended supersolids. We propose protocols for selectively probing these sound and amplitude modes, accessible to state-of-the-art experiments.

[62] 2404.11360

Open-system eigenstate thermalization in a noninteracting integrable model

We study thermalization in isolated quantum systems from an open quantum systems perspective. We argue that for a small system connected to a macroscopic bath, the system observables are thermal if the combined system-bath configuration is in an eigenstate of its Hamiltonian, even for fully integrable models (unless thermalization is suppressed by localization due to strong coupling). We illustrate our claim for a single fermionic level coupled to a noninteracting fermionic bath. We further show that upon quenching the system Hamiltonian, the system occupancy relaxes to the thermal value corresponding to the new Hamiltonian. Finally, we demonstrate that system thermalization also arises for a system coupled to a bath initialized in a typical eigenstate of its Hamiltonian. Our findings show that chaos and nonintegrability are not the sole drivers of thermalization and complementary approaches are needed to offer a more comprehensive understanding of how statistical mechanics emerges.

[63] 2404.11617

Enhanced Robustness via Loss Engineering in Detuned Non-Hermitian Scattering Systems

Non-Hermitian optics has revealed a series of counterintuitive phenomena with profound implications for sensing, lasing, and light manipulation. While the non-Hermiticity of Hamitonians is well-recognized, recent advancements in non-Hermitian physics have broadened to include scattering matrices, uncovering phenomena such as simultaneous lasing and coherent perfect absorption (CPA), reflectionless scattering modes (RSMs), and coherent chaos control. Despite these developments, the investigation has predominantly focused on static and symmetric configurations, leaving the dynamic properties of non-Hermitian scattering in detuned systems largely unexplored. Bridging this gap, we extend certain stationary non-Hermitian scattering phenomena to detuned systems. We delve into the interplay between bi-directional RSMs and RSM exceptional points (EPs), and elucidate the global existence conditions for RSMs under detuning. Moreover, we introduces a novel category of EPs, characterized by the coalescence of transmission peaks, emerging independent with the presence of Hamiltonian EPs. The transmission EPs (TEPs) exhibit flat-top lineshape and can be extended to a square-shaped spectrum when detuning is involved, accompanied by a distinctive phase transition. Significantly, we demonstrate the applications of the TEPs in a one-dimensional coupled cavity system, engineered to enhance sensing robustness against environmental instabilities such as laser frequency drifts, which can exceed 10 MHz. This capability represents a substantial improvement over traditional sensing methods and an important improvement of fragile EP sensors. Our findings not only contribute to the broader understanding of non-Hermitian scattering phenomena but also paves the way for future advancements in non-Hermitian sensing technologies.

[64] 2404.11618

Fractional-Diffraction-Optics Cauchy Problem: Resolvent-Function Solution of the Matrix Integral Equation

The fractional diffraction optics theory has been elaborated using the Green function technique. The optics-fractional equation describing the diffraction X-ray scattering by imperfect crystals has been derived as the fractional matrix integral Fredholm--Volterra equation of the second kind. In the paper, to solve the Cauchy problems, the Liouville--Neumann-type series formalism has been used to build up the matrix Resolvent-function solution. In the case when the imperfect crystal-lattice elastic displacement field is the linear function $f({\bf R}) = a x+b$, $a, b = const,$ the explicit solution of the diffraction-optics Cauchy problem has been obtained and analyzed for arbitrary fractional-order-parameter $\alpha$, $\alpha\in (0, 1].$

[65] 2404.11660

Constraints on Symmetry Preserving Gapped Phases from Coupling Constant Anomalies

In this note, we will characterize constraints on the possible IR phases of a given QFT by anomalies in the space of coupling constants. We will give conditions under which a coupling constant anomaly cannot be matched by a continuous family of symmetry preserving gapped phases, in which case the theory is either gapless, or exhibits spontaneous symmetry breaking or a phase transition. We additionally demonstrate examples of theories with coupling constant anomalies which can be matched by a family of symmetry preserving gapped phases without a phase transition and comment on the interpretation of our results for the spontaneous breaking of "$(-1)$-form global symmetries."

[66] 2404.11674

Practical applications of machine-learned flows on gauge fields

Normalizing flows are machine-learned maps between different lattice theories which can be used as components in exact sampling and inference schemes. Ongoing work yields increasingly expressive flows on gauge fields, but it remains an open question how flows can improve lattice QCD at state-of-the-art scales. We discuss and demonstrate two applications of flows in replica exchange (parallel tempering) sampling, aimed at improving topological mixing, which are viable with iterative improvements upon presently available flows.

[67] 2404.11985

On the generic increase of observational entropy in isolated systems

Observational entropy - a quantity that unifies Boltzmann's entropy, Gibbs' entropy, von Neumann's macroscopic entropy, and the diagonal entropy - has recently been argued to play a key role in a modern formulation of statistical mechanics. Here, relying on algebraic techniques taken from Petz's theory of statistical sufficiency and on a Levy-type concentration bound, we prove rigorous theorems showing how the observational entropy of a system undergoing a unitary evolution chosen at random tends to increase with overwhelming probability and to reach its maximum very quickly. More precisely, we show that for any observation that is sufficiently coarse with respect to the size of the system, regardless of the initial state of the system (be it pure or mixed), random evolution renders its state practically indistinguishable from the microcanonical distribution with a probability approaching one as the size of the system grows. The same conclusion holds not only for random evolutions sampled according to the unitarily invariant Haar distribution, but also for approximate 2-designs, which are thought to provide a more physically reasonable way to model random evolutions.

[68] 2404.12036

Exploring the Premelting Transition through Molecular Simulations Powered by Neural Network Potentials

The system has addressed the error of "Bad character(s) in field Abstract" for no reason. Please refer to manuscript for the full abstract.

[69] 2404.12100

Generic free fermions with nearest neighbour interactions

Generic free fermions are free fermions with a single particle spectrum that satisfies the $q$ no resonance condition, i.e., where equal sums of single-particle energies are unique. This property guaranties that they have no degeneracies and gives them relaxation properties more similar to those of generic systems. In this article we provide a minimal example of a generic free fermionic model with nearest neighbour interactions -- a tight-binding model with complex hopping. Using some standard results from number theory we prove that this model fulfils the $q$ no resonance condition when the number of lattice sites is prime. Whenever this is not the case one can recover the $q$ no resonance condition by adding hopping terms between sites corresponding to the divisors of the number of sites. We further discuss its many-body spectral statistics and show that local probes -- like the ratio of consecutive level spacings -- look very similar to what is expected for the Poisson statistics. We however demonstrate that free fermion models can never have Poisson statistics with an analysis of the moments of the spectral form factor.

[70] 2404.12118

Quantum thermodynamics of the spin-boson model using the principle of minimal dissipation

A recently developed approach to the thermodynamics of open quantum systems, on the basis of the principle of minimal dissipation, is applied to the spin-boson model. Employing a numerically exact quantum dynamical treatment based on the hierarchical equations of motion (HEOM) method, we investigate the influence of the environment on quantities such as work, heat and entropy production in a range of parameters which go beyond the weak-coupling limit and include both the non-adiabatic and the adiabatic regimes. The results reveal significant differences to the weak-coupling forms of work, heat and entropy production, which are analyzed in some detail.

[71] 2404.12156

The birth of StatPhys: The 1949 Florence conference at the juncture of post-WWII reconstruction of national and international physics

In spring 1949 about 70 physicists from eight countries met in Florence to discuss recent trends in statistical mechanics. This scientific gathering, co-organized by the Commission on Thermodynamics and Statistical Mechanics of the International Union of Pure and Applied Physics (IUPAP) and the Italian Physical Society (SIF), initiated a tradition of IUPAP-sponsored international conferences on statistical mechanics that lasts to this day. In 1977, when this conference series took the name of StatPhys, the foundational role of the Florence conference was recognized by retrospectively naming it StatPhys1. This paper examines the dual scientific and social significance of the conference, situating it in the broader contexts of the post-World War II reconstruction in Italian physics and of the revitalization of the international science organization. Through an analysis of IUPAP archives and Italian records, we illustrate how the event's success hinged on the aligned objectives of its organizers. Internationally, it was instrumental in defining the scientific and organizational foundations for the activities of IUPAP commissions during a critical phase of IUPAP's history, when the Union was resurging on the international stage post-interwar period inactivity. Nationally, the conference served as a cornerstone in SIF's strategy to re-establish Italian physics' international stature and to aid the domestic revitalization of physics through the internationalization of its activities, notably of its flagship journal, \textit{Il Nuovo Cimento}. This analysis not only sheds light on the conference's impact but also informs recent discussions in the history of science about the multiple roles of international scientific conferences.

[72] 2404.12175

Quasiparticle cooling algorithms for quantum many-body state preparation

Probing correlated states of many-body systems is one of the central tasks for quantum simulators and processors. A promising approach to state preparation is to realize desired correlated states as steady states of engineered dissipative evolution. A recent experiment with a Google superconducting quantum processor [X. Mi et al., Science 383, 1332 (2024)] demonstrated a cooling algorithm utilizing auxiliary degrees of freedom that are periodically reset to remove quasiparticles from the system, thereby driving it towards the ground state. We develop a kinetic theory framework to describe quasiparticle cooling dynamics, and employ it to compare the efficiency of different cooling algorithms. In particular, we introduce a protocol where coupling to auxiliaries is modulated in time to minimize heating processes, and demonstrate that it allows a high-fidelity preparation of ground states in different quantum phases. We verify the validity of the kinetic theory description by an extensive comparison with numerical simulations of a 1d transverse-field Ising model using a solvable model and tensor-network techniques. Further, the effect of noise, which limits efficiency of variational quantum algorithms in near-term quantum processors, can be naturally described within the kinetic theory. We investigate the steady state quasiparticle population as a function of noise strength, and establish maximum noise values for achieving high-fidelity ground states. This work establishes quasiparticle cooling algorithms as a practical, robust method for many-body state preparation on near-term quantum processors.

[73] 2404.12182

Abnormal solutions of Bethe--Salpeter equation with massless and massive exchanges

We summarize the main properties of the so called ''abnormal solutions'' of the Wick--Cutkosky model, i.e. two massive scalar particles interacting via massless scalar exchange ("photons"), within the Bethe--Salpeter equation. These solutions do not exist in the non-relativistic limit, in spite of having very small binding energies. They present a genuine many-body character dominated by photons, with a norm of the valence constituent wave function (two-body norm) that vanishes in the limit of zero binding energy. We present new results concerning the massive-exchange case, in particular determine under which conditions is it possible to obtain such peculiar solutions without spoiling the model by tachyonic states ($M^2<0$).

[74] 2404.12254

Omnidirectional 3D printing of PEDOT:PSS aerogels with tunable electromechanical performance for unconventional stretchable interconnects and thermoelectrics

The next generation of soft electronics will expand to the third dimension. This will require the integration of mechanically-compliant three-dimensional functional structures with stretchable materials. This study demonstrates omnidirectional direct ink writing (DIW) of Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) aerogels with tunable electrical and mechanical performance, which can be integrated with soft substrates. Several PEDOT:PSS hydrogels were formulated for DIW and freeze-dried directly on stretchable substrates to form integrated aerogels displaying high shape fidelity and minimal shrinkage. The effect of additives and processing in the PEDOT:PSS hydro and aerogels morphology, and the link with their electromechanical properties was elucidated. This technology demonstrated 3D-structured stretchable interconnects and planar thermoelectric generators (TEGs) for skin electronics, as well as vertically-printed high aspect ratio thermoelectric pillars with a high ZT value of 3.2 10^-3 and ultra-low thermal conductivity of 0.065 W/(m K). Despite their comparatively low ZT, the aerogel pillars outpowered their dense counterparts in realistic energy harvesting scenarios where contact resistances cannot be ignored, and produced up to 26 nW/cm2 (corresponding to a gravimetric power density of 0.76 mW/kg) for a difference of temperature of 15 K. This work suggests promising advancements in soft and energy-efficiency electronic systems relevant to soft robotics and wearable.

[75] 2404.12340

Symmetries and conservation of spin angular momentum, helicity, and chirality in photonic time-varying media

Polarization-dependent dynamical properties of light as the spin angular momentum (SAM), helicity, and chirality are conserved quantities in free-space. Despite their similarities on account of their relationship with a circular state of polarization, SAM, helicity, and chirality emerge from distinct symmetries, which endows them with different physical meanings, properties, and practical applications. In this work, we investigate the behavior of such quantities in time-varying media (TVM), i.e., how a temporal modulation impacts their symmetries and conservation laws. Our results demonstrate that the SAM is conserved for any time modulation, helicity is only preserved in impedance-matched time modulations, while chirality is not conserved. In addition, the continuity equations highlight the dependence of the chirality with the energy content of the fields. These results provide additional insights into the similarities and differences between SAM, helicity, and chirality, as well as their physical meaning. Furthermore, our theoretical framework provides with a new perspective to analyze polarization-dependent light-matter interactions in TVM.

[76] 2404.12346

Quantum thermophoresis

Thermophoresis is the migration of a particle due to a thermal gradient. Here, we theoretically uncover the quantum version of thermophoresis. As a proof of principle, we analytically find a thermophoretic force on a trapped quantum particle having three energy levels in $\Lambda$ configuration. We then consider a model of N sites, each coupled to its first neighbors and subjected to a local bath at a certain temperature, so as to show numerically how quantum thermophoresis behaves with increasing delocalization of the quantum particle. We discuss how negative thermophoresis and the Dufour effect appear in the quantum regime.

[77] 2404.12360

False vacuum decay and nucleation dynamics in neutral atom systems

False vacuum decay and nucleation offer the opportunity to study non-equilibrium dynamical phenomena in quantum many-body systems with confinement. Recent work has examined false vacuum decay in 1D ferromagnetic Ising spins and superfluids. In this paper, we study false vacuum nucleation dynamics in 1D antiferromagnetic neutral atom chains with Rydberg interactions, using both numerical simulations and analytic modeling. We apply a staggered local detuning field to generate the false and true vacuum states. Our efforts focus on two dynamical regimes: decay and annealing. In the first, we corroborate the phenomenological decay rate scaling and determine the associated parameter range for the decay process; in the second, we uncover and elucidate a procedure to anneal the false vacuum from the initial to the final system, with intermediate nucleation events. We further propose experimental protocols to prepare the required states and perform quenches on near-term neutral atom quantum simulators, examining the experimental feasibility of our proposed setup and parameter regime.

[78] 2404.12371

Long-lived oscillations of false and true vacuum states in neutral atom systems

Metastable false vacuum states arise in a range of quantum systems and can be observed in various dynamical scenarios, including decay, bubble nucleation, and long-lived oscillations. False vacuum phenomenology has been examined in quantum many-body systems, notably in 1D ferromagnetic Ising spin systems and superfluids. In this paper, we study long-lived oscillations of false and true vacuum states in 1D antiferromagnetic neutral atom chains with long-range Rydberg interactions. We use a staggered local detuning field to achieve confinement. Using theoretical and numerical models, we identify novel spectral signatures of quasiparticle oscillations distinct to antiferromagnetic neutral atom systems and interpret them using a classical energy model of deconfinement from Rydberg tails. Finally, we evaluate the experimental accessibility of our proposed setup on current neutral-atom platforms and discuss experimental feasibility and constraints.