New articles on Condensed Matter

[1] 2312.00064

Yang-Baxter integrable open quantum systems

This work is based on the author's PhD thesis. The main result of the thesis is the use of the boost operator to develop a systematic method to construct new integrable spin chains with nearest-neighbour interaction and characterized by an R-matrix of non-difference form. This method has the advantage of being more feasible than directly solving the Yang-Baxter equation. We applied this approach to various contexts, in particular, in the realm of open quantum systems, we achieved the first classification of integrable Lindbladians. These operators describe the dynamics of physical systems in contact with a Markovian environment. Within this classification, we discovered a novel deformation of the Hubbard model spanning three sites of the spin chain. Additionally, we applied our method to classify models with $\mathfrak{su}(2)\oplus \mathfrak{su}(2)$ symmetry and we recovered the matrix part of the S-matrix of $AdS_5 \times S^5$ derived by requiring centrally extended $\mathfrak{su}(2|2)$ symmetry. Furthermore, we focus on spin 1/2 chain on models of 8-Vertex type and we showed that the models of this class satisfy the free fermion condition. This enables us to express the transfer matrix associated to some of the models in a diagonal form, simplifying the computation of the eigenvalues and eigenvectors. The thesis is based on the works: 2003.04332, 2010.11231, 2011.08217, 2101.08279, 2207.14193, 2301.01612, 2305.01922.

[2] 2312.00142

Polymeric Liquids in Nanoporous Photonic Structures: From Precursor Film Spreading to Imbibition Dynamics at the Nanoscale

Polymers are known to wet nanopores with high surface energy through an atomically thin precursor film followed by slower capillary filling. We present here light interference spectroscopy using a nanoporous membrane-based chip that allows us to observe the dynamics of these phenomena in situ with sub-nanometer spatial and milli- to microsecond temporal resolution. The device consists of a mesoporous silicon film (average pore size 6 nm) with an integrated photonic crystal, which permits to simultaneously measure the phase shift of the thin-film interference and the resonance of the photonic crystal upon imbibition. For a styrene dimer, we find a flat fluid front without a precursor film, while the pentamer forms an expanding molecular thin film moving in front of the menisci of the capillary filling. These different behaviors are attributed to a significantly faster pore-surface diffusion compared to the imbibition dynamics for the pentamer and vice versa for the dimer. In addition, both oligomers exhibit anomalously slow imbibition dynamics, which could be explained by apparent viscosities of six and eleven times the bulk value, respectively. However, a more consistent description of the dynamics is achieved by a constriction model that emphasizes the increasing importance of local undulations in the pore radius with the molecular size and includes a sub-nanometer hydrodynamic dead, immobile zone at the pore wall, but otherwise uses bulk fluid parameters. Overall, our study illustrates that interferometric, opto-fluidic experiments with nanoporous media allow for a remarkably detailed exploration of the nano-rheology of polymeric liquids.

[3] 2312.00147

Vacancies in generic Kitaev spin liquids

The Kitaev honeycomb model supports gapless and gapped quantum spin liquid phases. Its exact solvability relies on extensively many locally conserved quantities. Any real-world manifestation of these phases would include imperfections in the form of disorder and interactions that break integrability. We show that the latter qualitatively alters the properties of vacancies in the gapless Kitaev spin liquid: (i) Isolated vacancies carry a magnetic moment, which is absent in the exactly solvable case. (ii) Pairs of vacancies on even/opposite sublattices gap each other with distinct power laws that reveal the presence of emergent gauge flux.

[4] 2312.00149

What a twist cell experiment tells about a quartic twist theory for chromonics

The elastic theory of chromonic liquid crystals is not completely established. We know, for example, that for anomalously low twist constants (needed for chromonics) the classical Oseen- Frank theory may entail paradoxical consequences when applied to describe the equilibrium shapes of droplets surrounded by an isotropic phase: contrary to experimental evidence, they are predicted to dissolve in a plethora of unstable smaller droplets. We proposed a quartic twist theory that prevents such an instability from happening. Here we apply this theory to the data of an experiment devised to measure the planar anchoring strength at the plates bounding a twist cell filled with a chromonic liquid crystal; these data had before been interpreted within the Oseen-Frank theory. We show that the quartic twist theory affords a slightly better agreement with the experimental data, while delivering a larger value for the anchoring strength.

[5] 2312.00153

Dynamic Phase Transition in 2D Ising Systems: Effect of Anisotropy and Defects

We investigate the dynamic phase transition in two-dimensional Ising models whose equilibrium characteristics are influenced by either anisotropic interactions or quenched defects. The presence of anisotropy reduces the dynamical critical temperature, leading to the expected result that the critical temperature approaches zero in the full-anisotropy limit. We show that a comprehensive understanding of the dynamic behavior of systems with quenched defects requires a generalized definition of the dynamic order parameter. By doing so, we demonstrate that the inclusion of quenched defects lowers the dynamic critical temperature as well, with a linear trend across the range of defect fractions considered. We also explore if and how it is possible to predict the dynamic behavior of specific magnetic systems with quenched randomness. Various geometric quantities, such as a quasi-electric defect potential, the defect dipole moment, and the properties of the defect Delaunay triangulation, prove useful for this purpose.

[6] 2312.00159

Photo-acoustic spectroscopy using a quantum cascade laser (QCL) for analysis of ammonia in water solutions

Ammonia (NH$_3$) toxicity, stemming from nitrification, can adversely affect aquatic life and influence the taste and odor of drinking water. This underscores the necessity for highly responsive and accurate sensors to continuously monitor NH$_3$ levels in water, especially in complex environments where reliable sensors have been lacking until this point. Herein, we detail the development of a sensor comprising a compact and selective analyzer with low gas consumption and a timely response, based on photoacoustic spectroscopy. This, combined with an automated liquid sampling system, enables the precise detection of ammonia traces in water. The sensor system incorporates a state-of-the art quantum cascade laser as the excitation source emitting at 9 \textmu m in resonance with the absorption line of NH$_3$ located at 1103.46 cm$^{-1}$. Our instrument demonstrated detection sensitivity at low ppm level for total ammonia nitrogen with response times less than 60 seconds. For the sampling system, an ammonia stripping solution was designed resulting in a prompt full measurement cycle (6.35 mins). A further evaluation of the sensor within a pilot study showed good reliability and agreement with the reference method for real water samples, confirming the potential of our NH$_3$ analyzer for water-quality monitoring applications.

[7] 2312.00161

A Pedestrian's Way to Baxter's Bethe Ansatz for the Periodic XYZ Chain

A chiral coordinate Bethe ansatz method is developed to study the periodic XYZ chain. We construct a set of chiral vectors with fixed number of kinks. All vectors are factorized and have simple structures. Under roots of unity conditions, the Hilbert space has an invariant subspace and our vectors form a basis of this subspace. We propose a Bethe ansatz solely based on the action of the Hamiltonian on the chiral vectors, avoiding the use of transfer matrix techniques. This allows to parameterize the expansion coefficients and derive the homogeneous Bethe ansatz equations whose solutions give the exact energies and eigenstates. Our analytic results agree with earlier approaches, notably by Baxter, and are supported by numerical calculations.

[8] 2312.00177

Mechanical control of quantum transport in graphene

Two-dimensional materials (2DMs) are fundamentally electro-mechanical systems. Their environment unavoidably strains them and modifies their quantum transport properties. For instance, a simple uniaxial strain could completely turn off the conductivity of ballistic graphene or switch on/off the superconducting phase of magic-angle bilayer graphene. Here we report measurements of quantum transport in strained graphene which agree quantitatively with models based on mechanically-induced gauge potentials. We mechanically induce in-situ a scalar potential, which modifies graphene's work function by up to 25 meV, and vector potentials which suppress the ballistic conductivity of graphene by up to 30 % and control its quantum interferences. To do so, we developed an experimental platform able to precisely tune both the mechanics and electrostatics of suspended graphene transistors at low-temperature over a broad range of strain (up to 2.6 %). This work opens many opportunities to experimentally explore quantitative strain effects in 2DM quantum transport and technologies.

[9] 2312.00187

Proximity effect of s-wave superconductor on inversion broken Weyl Semi-Metal

Inducing superconductivity in systems with unconventional band structures is a promising approach for realising unconventional superconductivity. Of particular interest are single interface or Josephson Junction architectures involving Weyl semimetals, which are predicted to host odd parity, potentially topological, superconducting states. These expectations rely crucially on the tunneling of electronic states at the interface between the two systems. In this study, we revisit the question of induced superconductivity in an inversion broken WSM via quantum tunneling, treating the interface as an effective potential barrier. We determine the conditions under which the gap function couples to the Weyl physics and its properties within the WSM. Our simulations show that the mismatch in the nature of the low energy electronic states leads to a rapid decay of the superconductivity within the semi-metal.

[10] 2312.00212

Modeling of Plasmonic and Polaritonic Effects in Photocurrent Nanoscopy

We present a basic framework for modeling collective mode effects in photocurrent measurements performed on two-dimensional materials using nano-optical scanned probes. We consider photothermal, photovoltaic, and bolometric contributions to the photocurrent. We show that any one of these can dominate depending on frequency, temperature, applied bias, and sample geometry. Our model is able to account for periodic spatial oscillations (fringes) of the photocurrent observed near sample edges or inhomogeneities. For the case of a non-absorbing substrate, we find a direct relation between the spectra measured by the photocurrent nanoscopy and its parental scanning technique, near-field optical microscopy.

[11] 2312.00222

Anomalous Hall effect with plateaus observed in a magnetic Weyl semimetal NdAlGe at low temperatures

In the $R$Al(Si,Ge) ($R$: lanthanides) family, both spatial inversion and time-reversal symmetries are broken. This may offer opportunities to study Weyl-fermion physics in nontrivial spin structures emerging from a noncentrosymmetric crystal structure. In this study, we investigated the anomalous Hall effect (AHE) in NdAlGe via magnetotransport, magnetization, and magnetic torque measurements down to 40 mK (0.4 K for magnetization). The single crystals grown by a laser-heated floating-zone method exhibit a single magnetic phase transition at $T_{\rm M}$ = 13.5 K, where the $T_{\rm M}$ is the transition temperature. With the magnetic field parallel to the easy $\lbrack$001$\rbrack$ axis, the AHE gradually evolves as the temperature decreases below $T_{\rm M}$. The anomalous Hall conductivity (AHC) reaches $\sim$320 $\Omega^{-1}$cm$^{-1}$ at 40 mK in the magnetically saturated state. Except in low-temperature low-field plateau phases, the AHC and magnetization are proportional, and their ratio agrees with the ratios for conventional ferromagnets, suggesting that the intrinsic AHE occurs by the Karplus-Luttinger mechanism. Below $\sim$0.6 K, the curves of Hall resistivity against the field exhibit plateaus at low fields below $\sim$0.5 T, correlating with the plateaus in the magnetization curve. For the first plateau, the magnetization is one order of magnitude smaller than the magnetically saturated state, whereas the AHE is more than half that in the saturated state. This finding under well below $T_{\rm M}$ suggests that the AHE at the first plateau is not governed by the magnetization and may be interpreted based on a multipole or spin chirality.

[12] 2312.00239

A confined rod: mean field theory for hard rod-like particles

In this paper, we model the configurations of a system of hard rods by viewing each rod in a cell formed by its neighbors. By minimizing the free energy in the model and performing molecular dynamics, where, in both cases, the shape of the cell is a free parameter, we obtain the equilibrium orientational order parameter, free energy and pressure of the system. Our model enables the calculation of anisotropic stresses exerted on the walls of the cell due to shape change of the rod in photoisomerization. These results are a key step towards understanding molecular shape change effects in photomechanical systems under illumination.

[13] 2312.00251

Memory of shear flow in soft jammed materials

Cessation of flow in simple yield stress fluids results in a complex stress relaxation process that depends on the preceding flow conditions and leads to finite residual stresses. To assess the microscopic origin of this phenomenon, we combine experiments with largescale computer simulations, exploring the behavior of jammed suspensions of soft repulsive particles. A spatio-temporal analysis of microscopic particle motion and local particle configurations reveals two contributions to stress relaxation. One is due to flow induced accumulation of elastic stresses in domains of a given size, which effectively sets the unbalanced stress configurations that trigger correlated dynamics upon flow cessation. This scenario is supported by the observation that the range of spatial correlations of quasi-ballistic displacements obtained upon flow cessation almost exactly mirrors those obtained during flow. The second contribution results from the particle packing that reorganize to minimize the resistance to flow by decreasing the number of locally stiffer configurations. Regaining rigidity upon flow cessation then effectively sets the magnitude of the residual stress. Our findings highlight that flow in yield stress fluids can be seen as a training process during which the material stores information of the flowing state through the development of domains of correlated particle displacements and the reorganization of particle packings optimized to sustain the flow. This encoded memory can then be retrieved in flow cessation experiments.

[14] 2312.00255

Restructuring a passive colloidal suspension using a rotationally driven particle

The interactions between passive and active/driven particles have been explored as a means to modify structures in solutions. Often times hydrodynamics plays a significant role in explaining emergent patterns in such mixtures. In this study, we demonstrate that strong advective flows generated by a single driven rotating particle near a surface can induce large-scale structural rearrangements in a passive suspension. The resulting emergent pattern exhibits an accumulation area in front of the driven particle and a wake along its trajectory. Notably, the center of the accumulation is found at a distance from the driven particle. Through experiments and Stokesian dynamics simulations, we show that the driven-passive interaction is solely determined by the heights of both particle types, which determines the shape and the size of the pattern. By modulating the height of the driven particle we can control the extension of the emergent pattern from 3 to 6 times its diameter ($\sim 12 \, \mu \mathrm{m}$).

[15] 2312.00270

Insulator to Metal Transition, Spin-Phonon Coupling, and Potential Magnetic Transition Observed in Quantum Spin Liquid Candidate LiYbSe$_2$ under High Pressure

Metallization of quantum spin liquid (QSL) materials has long been considered as a potential route to achieve unconventional superconductivity. Here we report our endeavor in this direction by pressurizing a three-dimensional QSL candidate, LiYbSe$_2$, with a previously unreported pyrochlore structure. High-pressure X-ray diffraction and Raman studies up to 50 GPa reveal no appreciable changes of structural symmetry or distortion in this pressure range. This compound is so insulating that its resistance decreases below 10$^5$ ${\Omega}$ only at pressures above 25 GPa in the corresponding temperature range accompanying the gradual reduction of band gap upon compression. Interestingly, an insulator-to-metal transition takes place in LiYbSe$_2$ at about 68 GPa and the metallic behavior remains up to 123.5 GPa, the highest pressure reached in the present study. A possible sign of magnetic or other phase transition was observed in LiYbSe$_2$. The insulator-to-metal transition in LiYbSe$_2$ under high pressure makes it an ideal system to study the pressure effects on QSL candidates of spin-1/2 Yb$^{3+}$ system in different lattice patterns.

[16] 2312.00274

On-Demand Single-Electron Source via Single-Cycle Acoustic Pulses

Surface acoustic waves (SAWs) are a reliable solution to transport single electrons with precision in piezoelectric semiconductor devices. Recently, highly efficient single-electron transport with a strongly compressed single-cycle acoustic pulse has been demonstrated. This approach, however, requires surface gates constituting the quantum dots, their wiring, and multiple gate movements to load and unload the electrons, which is very time-consuming. Here, on the contrary, we employ such a single-cycle acoustic pulse in a much simpler way - without any quantum dot at the entrance or exit of a transport channel - to perform single-electron transport between distant electron reservoirs. We observe the transport of a solitary electron in a single-cycle acoustic pulse via the appearance of the quantized acousto-electric current. The simplicity of our approach allows for on-demand electron emission with arbitrary delays on a ns time scale. We anticipate that enhanced synthesis of the SAWs will facilitate electron-quantum-optics experiments with multiple electron flying qubits.

[17] 2312.00325

Universal Energy Functionals for Trapped Fermi Gases in Low Dimensions

We study the system of trapped two-component Fermi gases with zero-range interaction in two dimensions (2D) and one dimension (1D). We calculate the one-particle density matrix of these systems at small displacements, from which we show that the $N$-body energies are linear functionals of the occupation probabilities of single-particle energy eigenstates. Such a universal energy functional was first derived in 2011 for trapped zero-range interacting two-component Fermi gases in three dimensions (3D). We also calculate the asymptotic behaviors of the occupation probabilities of single-particle energy eigenstates at high energies. Our method can be applied to other zero-range interacting systems.

[18] 2312.00331

Effects of domain walls and chiral supercurrent in quantum anomalous Hall Josephson junctions

The intriguing interplay between topology and superconductivity has attracted significant attention, given its potential for realizing topological superconductivity. In this study, we investigate the transport properties of the chiral Josephson effect in the quantum anomalous Hall insulators (QAHIs)-based junction. We reveal a systematic crossover from edge-state to bulk-state dominant supercurrents, with a notable $0-\pi$ transition observed under non-zero magnetic flux through chemical potential adjustments. This transition underscores the competition between bulk and chiral edge transport. Furthermore, we identify an evolution among three distinct quantum interference patterns: from a $2\Phi_0$-periodic oscillation pattern, to a $\Phi_0$-periodic oscillation pattern, and then to an asymmetric Fraunhofer pattern ($\Phi_0 = h/2e$ is the flux quantum, $h$ the Planck constant, and $e$ the electron charge). Subsequently, we examine the influence of domains on quantum interference patterns. Intriguingly, a distinctive Fraunhofer-like pattern emerges due to coexistence of chiral edge states and domain wall states, even when the chemical potential is within gap. These results not only advance the theoretical understanding but also pave the way for the experimental discovery of the chiral Josephson effect based on QAHI doped with magnetic impurities.

[19] 2312.00340

Anisotropic magnetoresistance in single cubic crystals: A theory and its verification

A theory of anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) in single cubic crystals and its experimental verifications are presented for the current in the (001) plane. In contrast to the general belief that AMR and PHE in single crystals are highly sensitive to many internal and external effects and have no universal features, the theory predicts universal angular dependencies of longitudinal and transverse resistivity and various characteristics when magnetization rotates in the (001) plane, the plane perpendicular to the current, and the plane containing the current and [001] direction. The universal angular dependencies are verified by the experiments on Fe30Co70 single cubic crystal film. The findings provide new avenues for fundamental research and applications of AMR and PHE, because single crystals offer advantages over polycrystalline materials for band structure and crystallographic orientation engineering.

[20] 2312.00354

Thermodynamic bounds on the asymmetry of cross-correlations with dynamical activity and entropy production

Entropy production and dynamical activity are two complementary aspects in nonequilibrium physics. The asymmetry of cross-correlation, serving as a distinctive feature of nonequilibrium, also finds widespread utility. In this Letter, we establish two thermodynamic bounds on the normalized asymmetry of cross-correlation in terms of dynamical activity and entropy production rate. These bounds demonstrate broad applicability, and offer experimental testability.

[21] 2312.00367

Compensated Ferrimagnets with Colossal Spin Splitting in Organic Compounds

The study of the magnetic order has recently been invigorated by the discovery of exotic collinear antiferromagnets with time-reversal symmetry breaking. Examples include altermagnetism and compensated ferrimagnets, which show spin splittings of the electronic band structures even at zero net magnetization, leading to several exotic transport phenomena, notably spin-current generation. Altermagnets demonstrate anisotropic spin splitting, such as $d$-wave, in momentum space, whereas compensated ferrimagnets exhibit isotropic spin splitting. However, methods to realize compensated ferrimagnets are limited. Here, we demonstrate a method to realize a fully compensated ferrimagnet with isotropic spin splitting utilizing the dimer structures inherent in organic compounds. Moreover, based on $ab$ $initio$ calculations, we find that this ferrimagnet can be realized in the recently discovered organic compound (EDO-TTF-I)$_2$ClO$_4$. Our findings provide an unprecedented strategy for using the dimer degrees of freedom in organic compounds to realize fully compensated ferrimagnets with colossal spin splitting.

[22] 2312.00370

Effect of interface quality on spin Hall magnetoresistance in Pt/MgFe$_{2}$O$_{4}$ bilayers

We report on spin Hall magnetoresistance (SMR) in bilayers composed of Pt and magnetic insulator MgFe$_{2}$O$_{4}$ (MFO) with spinel structure. The Pt thickness dependence of the SMR reveals that annealing of the MFO surface before depositing the Pt layer is crucial for a large SMR with better interface quality. We also found that oxygen pressure during the MFO growth hardly affects the SMR while it influences on magnetic property of the MFO film. Our findings provide important clues to further understanding the spin transport at interfaces containing magnetic insulators, facilitating development of low power consumption devices.

[23] 2312.00371

Hybrid Higher-Order Topological Skin Modes in the Two-Dimensional Su-Schrieffer-Heeger Model with Nonreciprocal Hoppings

The coexistence of edge states and skin effects provides the topologically protected localized states at the corners of two-dimensional systems. In this paper, we realize such corner states in the two-dimensional Su-Schrieffer-Heeger model with the nonreciprocal hoppings. For the characterization of the real line gap topology, we introduce the $\mathbb{Z}_4$ Berry phase protected by generalized four-fold rotational symmetry. From the physical picture of the adiabatic connection, we find that the value of the $\mathbb{Z}_4$ Berry predicts the position of edge states. Additionally, by using the winding number, we characterize the point gap topology of the edge spectra. From the results of these characterizations by the first-order topological invariants, we find that the pair of values of the $\mathbb{Z}_4$ Berry phase and the winging number yields the position of the topologically protected localized states.

[24] 2312.00378

Magneto-transport in the monolayer MoS2 material system for high-performance field-effect transistor applications

Electronic transport in monolayer MoS2 is significantly constrained by several extrinsic factors despite showing good prospects as a transistor channel material. Our paper aims to unveil the underlying mechanisms of the electrical and magneto-transport in monolayer MoS2. In order to quantitatively interpret the magneto-transport behavior of monolayer MoS2 on different substrate materials, identify the underlying bottlenecks, and provide guidelines for subsequent improvements, we present a deep analysis of the magneto-transport properties in the diffusive limit. Our calculations are performed on suspended monolayer MoS2 and MoS2 on different substrate materials taking into account remote impurity and the intrinsic and extrinsic phonon scattering mechanisms. We calculate the crucial transport parameters such as the Hall mobility, the conductivity tensor elements, the Hall factor, and the magnetoresistance over a wide range of temperatures, carrier concentrations, and magnetic fields. The Hall factor being a key quantity for calculating the carrier concentration and drift mobility, we show that for suspended monolayer MoS2 at room temperature, the Hall factor value is around 1.43 for magnetic fields ranging from 0.001 to 1 Tesla, which deviates significantly from the usual value of unity. In contrast, the Hall factor for various substrates approaches the ideal value of unity and remains stable in response to the magnetic field and temperature. We also show that the MoS2 over an Al2O3 substrate is a good choice for the Hall effect detector. Moreover, the magnetoresistance increases with an increase in magnetic field strength for smaller magnetic fields before reaching saturation at higher magnetic fields. The presented theoretical model quantitatively captures the scaling of mobility and various magnetoresistance coefficients with temperature, carrier densities and magnetic fields.

[25] 2312.00385

Super Fermi polaron and Nagaoka ferromagnetism in a two-dimesnional square lattice

We consider the Fermi polaron problem of an impurity hopping around a two-dimensional square lattice and interacting with a sea of fermions at given filling factor. When the interaction is attractive, we find standard Fermi polaron quasiparticles, categorized as attractive polarons and repulsive polarons. When the interaction becomes repulsive, interestingly, we observe an unconventional highly-excited polaron quasiparticle, sharply peaked at the corner of the first Brillouin zone with momentum \mathbf{k}=(\pm\pi,\pm\pi). This super Fermi polaron branch arises from the dressing of the impurity's motion with holes, instead of particles of fermions. We show that super Fermi polarons become increasingly well-defined with increasing impurity-fermion repulsions and might be considered as a precursor of Nagaoka ferromagnetism, which would appear at sufficiently large repulsions and at large filling factors. We also investigate the temperature-dependence of super Fermi polarons and find that they are thermally robust against the significant increase in temperature.

[26] 2312.00397

Incommensurate Spiral Spin Order in CaMn$_2$Bi$_2$ observed via High Pressure Neutron Diffraction

High pressure neutron diffraction is employed to investigate the magnetic behavior of CaMn$_2$Bi$_2$ in extreme conditions. In contrast to antiferromagnetic ordering on Mn atoms reported at ambient pressure, our results reveal that at high pressure, incommensurate spiral spin order emerges due to the interplay between magnetism on the Mn atoms and strong spin-orbit coupling on the Bi atoms: sinusoidal spin order is observed at pressures as high as 7.4 GPa. Competing antiferromagnetic order is observed at different temperatures in the partially frustrated lattice. This research provides a unique toolbox for conducting experimental magnetic and spin dynamics studies on magnetic quantum materials via high pressure neutron diffraction.

[27] 2312.00423

Unravelling spontaneous Bloch-type skyrmion in centrosymmetric two-dimensional magnets

The realization of magnetic skyrmions in two-dimensional (2D) magnets holds great promise for both fundamental research and device applications. Despite recent progress, two-dimensional skyrmion hosts are still limited, due to the fact that most 2D magnets are centrosymmetric and thus lack Dzyaloshinskii-Moriya interaction (DMI). We show here, using a general analysis based on symmetry, that Bloch-type skyrmions can, in fact, be stabilized in 2D magnets, due to the interplay between in-plane component (dx) of second nearest-neighbor DMI and magnetic anisotropy. Its validity is demonstrated in the Cr2Ge2Te6 monolayer, which is also verified by recent experiments. Our work gives a clear direction for experimental studies of 2D magnetic materials to stabilize skyrmions and should greatly enrich the research on magnetic skyrmions in 2D lattices.

[28] 2312.00440

Charge doping into spin minority states mediates doubling of $T_\mathrm{C}$ in ferromagnetic CrGeTe$_3$

The recent discovery of the persistence of long-range magnetic order when van der Waals layered magnets are thinned towards the monolayer limit has provided a tunable platform for the engineering of novel magnetic structures and devices. Here, we study the evolution of the electronic structure of CrGeTe$_3$ as a function of electron doping in the surface layer. From angle-resolved photoemission spectroscopy, we observe spectroscopic fingerprints that this electron doping drives a marked increase in $T_\mathrm{C}$, reaching values more than double that of the undoped material, in agreement with recent studies using electrostatic gating. Together with density functional theory calculations and Monte Carlo simulations, we show that, surprisingly, the increased $T_\mathrm{C}$ is mediated by the population of spin-minority Cr $t_{2g}$ states, forming a half-metallic 2D electron gas at the surface. We show how this promotes a novel variant of double exchange, and unlocks a significant influence of the Ge -- which was previously thought to be electronically inert in this system -- in mediating Cr-Cr exchange.

[29] 2312.00459

A continuous-wave and pulsed X-band electron spin resonance spectrometer operating in ultra-high vacuum for the study of low dimensional spin ensembles

We report the development of a continuous-wave and pulsed X-band electron spin resonance (ESR) spectrometer for the study of spins on ordered surfaces down to cryogenic temperatures. The spectrometer operates in ultra-high vacuum and utilizes a half-wavelength microstrip line resonator realized using epitaxially grown copper films on single crystal Al$_2$O$_3$ substrates. The one-dimensional microstrip line resonator exhibits a quality factor of more than 200 at room temperature, close to the upper limit determined by radiation losses. The surface characterizations of the copper strip of the resonator by atomic force microscope, low-energy electron diffraction, and scanning tunneling microscope show that the surface is atomically clean, flat, and single crystalline. Measuring the ESR spectrum at 15 K from a few nm thick molecular film of YPc$_2$, we find a continuous-wave ESR sensitivity of $6.5 \cdot 10^{10}~\text{spins}/\text{G} \cdot \text{Hz}^{1/2}$ indicating that a signal-to-noise ratio of $7.7~\text{G} \cdot \text{Hz}^{1/2}$ is expected from a monolayer of YPc$_2$ molecules. Advanced pulsed ESR experimental capabilities including dynamical decoupling and electron-nuclear double resonance are demonstrated using free radicals diluted in a glassy matrix.

[30] 2312.00468

Cheers: a linear-scaling KBE+GKBA code

The interaction of electrons with quantized phonons and photons underlies the ultrafast dynamics of systems ranging from molecules to solids, giving rise to a plethora of physical phenomena experimentally accessible using time-resolved techniques. Green's function methods offer an invaluable interpretation tool since scattering mechanisms of growing complexity can be selectively incorporated in the theory. cheers is a general-purpose nonequilibrium Green's function code that implements virtually all known many-body approximations and is designed for first principles studies of ultrafast processes in molecular and model solid state systems. The aims of generality, extensibility, efficiency, and user friendliness of the code are achieved through the underlying theory development and the use of modern software design practices. Here, we motivate the necessity for the creation of such a code and overview its design and capabilities.

[31] 2312.00498

Comparative Analysis of Tight-Binding models for Transition Metal Dichalcogenides

We provide a comprehensive analysis of the prominent tight-binding (TB) models for transition metal dichalcogenides (TMDs) available in the literature. We inspect the construction of these TB models, discuss their parameterization used and conduct a thorough comparison of their effectiveness in capturing important electronic properties. Based on these insights, we propose a novel TB model for TMDs designed for enhanced computational efficiency. Utilizing $MoS_2$ as a representative case, we explain why specific models offer a more accurate description. Our primary aim is to assist researchers in choosing the most appropriate TB model for their calculations on TMDs.

[32] 2312.00504

Evidence of an Off-resonant Electronic Transport Mechanism in Helicenes

Helical molecules have been identified as potential candidates for investigating electronic transport, spin filtering, or even piezoelectricity. However, the description of the transport mechanism is not straightforward in single molecular junctions. In this work, we study the electronic transport in break junctions of a series of three helical molecules: dithia[$n$]helicenes, with $n=7, 9, 11$ molecular units, and detail the synthesis of two kinds of dithia[11]helicenes, varying the location of the sulfur atoms. Our experimental study demonstrates low conductance values that remain similar across different biases and molecules. Additionally, we assess the length dependence of the conductance for each helicene, revealing an exponential decay characteristic of off-resonant transport. This behaviour is primarily attributed to the misalignment between the energy levels of the molecule-electrodes system. The length dependence trend described above is supported by \textit{ab initio} calculations, further confirming the off-resonant transport mechanism.

[33] 2312.00511

Weak Electronic Correlations Observed in Magnetic Weyl Semimetal Mn$_3$Ge

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations, we systematically studied the electronic band structure of Mn$_3$Ge in the vicinity of the Fermi level. We observe several bands crossing the Fermi level, confirming the metallic nature of the studied system. We further observe several flat bands along various high symmetry directions, consistent with the DFT calculations. The calculated partial density of states (PDOS) suggests a dominant Mn $3d$ orbital contribution to the total valence band DOS. With the help of orbital-resolved band structure calculations, we qualitatively identify the orbital information of the experimentally obtained band dispersions. Out-of-plane electronic band dispersions are explored by measuring the ARPES data at various photon energies. Importantly, our study suggests relatively weaker electronic correlations in Mn$_3$Ge compared to Mn$_3$Sn.

[34] 2312.00515

Carrier density crossover and quasiparticle mass enhancement in a doped 5$d$ Mott insulator

High-temperature superconductivity in cuprates emerges upon doping the parent Mott insulator. Robust signatures of the low-doped electronic state include a Hall carrier density that initially tracks the number of doped holes and the emergence of an anisotropic pseudogap; the latter characterised by disconnected Fermi arcs, closure at a critical doping level $p^* \approx 0.19$, and, in some cases, a strongly enhanced carrier effective mass. In Sr$_2$IrO$_4$, a spin-orbit-coupled Mott insulator often regarded as a 5$d$ analogue of the cuprates, surface probes have revealed the emergence of an anisotropic pseudogap and Fermi arcs under electron doping, though neither the corresponding $p^*$ nor bulk signatures of pseudogap closing have as yet been observed. Here, we report electrical transport and specific heat measurements on Sr$_{2-x}$La$_x$IrO$_4$ over an extended doping range 0 $\leq x \leq$ 0.20. The effective carrier density $n_{\rm H}$ at low temperatures exhibits a crossover from $n_{\rm H} \approx x$ to $n_{\rm H} \approx 1+x$ near $x$ = 0.16, accompanied by \textcolor{blue}{a five-orders-of-magnitude increase in conductivity} and a six-fold enhancement in the electronic specific heat. These striking parallels in the bulk pseudogap phenomenology, coupled with the absence of superconductivity in electron-doped Sr$_2$IrO$_4$, disfavour the pseudogap as a state of precursor pairing and thereby narrow the search for the key ingredient underpinning the formation of the superconducting condensate in doped Mott insulators.

[35] 2312.00543

Longitudinal optical conductivity of graphene in van der Waals heterostructures composed of graphene and transition metal dichalcogenides

Placing and twisting graphene on transition metal dichalcogenides (TMDC) forms a van der Waals (vdW) heterostructure. The occurrence of Zeeman splitting and Rashba spin-orbit coupling (SOC) changes graphene's linear dispersion and conductivity. Hence, this paper studies the dependence of graphene's longitudinal optical conductivity on Rashba SOC, the twist-angle and temperature. At zero temperature, a main conductivity peak exists. When Rashba SOC increases, a second peak occurs, with both extremes presenting an enhanced height and width, and the frequencies where the two peaks arise will increase because the energy gap and the possibility of electron transition increase. Altering the twist-angle from 0 to 30$^{\circ}$, the conductivity is primarily affected by chalcogen atoms. Moreover, when temperature increases to room temperature, besides a Drude peak due to the thermal excitation, a new band arises in the conductivity owing to the joint effect of the thermal transition and the photon transition.

[36] 2312.00577

Phonon-Limited Transport in 2D Materials: A Unified Approach for ab initio Mobility and Current Calculations

This paper presents an ab initio methodology to account for electron-phonon interactions in 2D materials, focusing on transition metal dichalcogenides (TMDCs). It combines density functional theory and maximally localized Wannier functions to acquire material data and relies on the linearized Boltzmann transport equation (LBTE) and the non-equilibrium Green's functions (NEGF) method to determine the transport properties of materials and devices, respectively. It is shown that for MoS$_2$, both LBTE and NEGF return very close mobility values, without the need to adjust any parameter. The excellent agreement between both approaches results from the inclusion of non-diagonal entries in the electron-phonon scattering self-energies. The NEGF solver is then used to shed light on the "current vs. voltage" characteristics of a monolayer MoS$_2$ transistor, highlighting how the interactions with phonons impact both the current magnitude and its distribution. The mobility of other TMDCs is considered as well, demonstrating the capabilities of the proposed technique to assess the potential of 2D channel materials in next-generation logic applications.

[37] 2312.00611

Wehrl Entropy and Entanglement Complexity of Quantum Spin Systems

The Wehrl entropy of a quantum state is the entropy of the coherent-state distribution function (Husimi function), and is non-zero even for pure states. We investigate the Wehrl entropy for $N$ spin-1/2 particles with respect to SU(2)$^{\otimes N}$ coherent states (i.e., the direct products of spin coherent states of each particle). We focus on: (1) The statistical interpretation of this Wehrl entropy. (2) The relationship between the Wehrl entropy and quantum entanglement. For (1), despite the coherent states not forming a group of orthonormal bases, we prove that the Wehrl entropy can still be interpreted as the entropy of a probability distribution with clear physical meaning. For (2), we numerically calculate the Wehrl entropy of various entangled pure states with particle number $2\leq N\leq 20$. Our results show that for the large-$N$ ($N\gtrsim 10$) systems the Wehrl entropy of the highly chaotic entangled states are much larger than that of the regular ones (e.g., the GHZ state). These results, together with the fact that the Wehrl entropy is invariant under local unitary transformations, indicate that the Wehrl entropy can reflect the complexity of the quantum entanglement (entanglement complexity) of many-body pure states, as A. Sugita proposed directly from the definitions of the Husimi function and Wehrl entropy (Jour. Phys. A 36, 9081 (2003)). Furthermore, the Wehrl entropy per particle can serve as a quantitative description of this complexity. We further show that the many-body pure entangled states can be classified into three types, according to the behaviors of the Wehrl entropy per particle in the limit $N\rightarrow\infty$, with the states of each type having very different entanglement complexity.

[38] 2312.00615

Phase Transitions, Spontaneous Symmetry Breaking, and Goldstone's Theorem

Some important rigorous results on phase transitions accompanied by the spontaneous breaking of symmetries in statistical mechanics and relativistic quantum field theory are reviewed. Basic ideas, mainly inspired by quantum field theory, underlying the proofs of some of these results are sketched. The Goldstone theorem is proven, and the Mermin-Wagner-Hohenberg theorem concerning the absence of continuous symmetry breaking in one and two dimensions is recalled. Comments concerning rigorous results on the Kosterlitz-Thouless transition in the two-dimensional classical XY model are made.

[39] 2312.00635

Thermal conductivity of bottle-brush polymers

Using molecular dynamics (MD) simulations of a generic model, we investigate heat propagation in bottle--brush polymers (BBP). An architecture is referred to as a BBP when a linear (backbone) polymer is grafted with the side chains of different length $N_{\rm s}$ and grafting density $\rho_{\rm g}$, which control the bending stiffness of a backbone. A BBP is of particular interest due to two competing mechanics: increased backbone stiffness, via $N_{\rm s}$ and $\rho_{\rm g}$, increases the thermal transport coefficient $\kappa$, while the presence of side chains provides additional pathways for heat leakage. We show how a delicate competition between these two effects controls $\kappa$. These results reveal that going from a weakly grafting ($\rho_{\rm g} < 1$) to a highly grafting ($\rho_{\rm g} \ge 1$) regime, $\kappa$ changes non--monotonically that is independent of $N_{\rm s}$. The effect of side chain mass on $\kappa$ and heat flow in the BBP melts are also discussed.

[40] 2312.00636

Hyperdeterminants and Composite fermion States in Fractional Chern Insulators

Fractional Chern insulators (FCI) were proposed theoretically about a decade ago. These exotic states of matter are fractional quantum Hall states realized when a nearly flat Chern band is partially filled, even in the absence of an external magnetic field. Recently, exciting experimental signatures of such states have been reported in twisted MoTe$_2$ bilayer systems. Motivated by these experimental and theoretical progresses, in this paper, we develop a projective construction for the composite fermion states (either the Jain's sequence or the composite Fermi liquid) in a partially filled Chern band with Chern number $C=\pm1$, which is capable of capturing the microscopics, e.g., symmetry fractionalization patterns and magnetoroton excitations. On the mean-field level, the ground states' and excitated states' composite fermion wavefunctions are found self-consistently in an enlarged Hilbert space. Beyond the mean-field, these wavefunctions can be projected back to the physical Hilbert space to construct the electronic wavefunctions, allowing direct comparison with FCI states from exact diagonalization on finite lattices. We find that the projected electronic wavefunction corresponds to the \emph{combinatorial hyperdeterminant} of a tensor. When applied to the traditional Galilean invariant Landau level context, the present construction exactly reproduces Jain's composite fermion wavefunctions. We apply this projective construction to the twisted bilayer MoTe$_2$ system. Experimentally relevant properties are computed, such as the magnetoroton band structures and quantum numbers.

[41] 2312.00642

Interplay between Haldane and modified Haldane models in $α$-$T_{3}$ lattice: Band structures, phase diagrams and edge states

We study the topological properties of the Haldane and modified Haldane models in $\alpha$-$T_{3}$ lattice. The band structures and phase diagrams of the system are investigated. Individually, each model undergoes a distinct phase transition: (i) The Haldane-only model experiences a topological phase transition from the Chern insulator ($\mathcal{C} = 1$) phase to the higher Chern insulator ($\mathcal{C} = 2$) phase; while (ii) the modified-Haldane-only model experiences a phase transition from the topological metal ($\mathcal{C} = 2$) phase to the higher Chern insulator ($\mathcal{C} = 2$) phase and we show that $\mathcal{C}$ is insufficient to characterize this system because $\mathcal{C}$ remains unchanged before and after the phase transition. By plotting the Chern number and $\mathcal{C}$ phase diagram, we show that in the presence of both Haldane and modified Haldane models in the $\alpha$-$T_{3}$ lattice, the interplay between the two models manifests three distinct topological phases, namely the $\mathcal{C} = 1$ Chern insulator (CI) phase, $\mathcal{C} = 2$ higher Chern insulator (HCI) phase and $\mathcal{C} = 2$ topological metal (TM) phase. These results are further supported by the $\alpha$-$T_{3}$ zigzag edge states calculations.

[42] 2312.00643

Hydrogen-induced switching of perpendicular magnetic anisotropy in amorphous ferrimagnetic thin films

Unraveling the mechanisms responsible for perpendicular magnetic anisotropy (PMA) in amorphous rare earth-transition metal alloys has proven challenging, primarily due to the intrinsic complexity of the amorphous structure. Here, we investigated the atomic origin of PMA by applying an approach of voltage-driven hydrogen insertion in interstitial sites, which serve as a perturbation and probe in local atomic structure. After hydrogen charging, PMA in amorphous TbCo thin films diminished and switched to in-plane anisotropy, accompanied by distinct magnetic domain structures. By analyzing the mechanism behind the anisotropy switching, we unveiled the decisive role of Tb-Co/Tb-Tb bonding in shaping the magnetic anisotropy using both angle-dependent X-ray magnetic dichroism and ab initio calculations. Hydrogen insertion induced a reorientation of the local anisotropy axis, initially along the Tb-Co bonding direction, due to the distortion of crystal field around Tb. Our approach not only shows the atomic origin of Tb-Co bonding in inducing PMA, but also enables the voltage-driven tailoring of magnetic anisotropy in amorphous alloys.

[43] 2312.00649

Robustness of Quantum Chaos and Anomalous Relaxation in Open Quantum Circuits

Dissipation is a ubiquitous phenomenon in nature that affects the fate of chaotic quantum dynamics. To characterize the interplay between quantum chaos and dissipation in generic quantum many-body systems, we consider a minimal dissipative Floquet many-body system. We study the dissipative form factor (DFF), an extension of the spectral form factor to open quantum systems, of the random phase model in the presence of arbitrary one-site nonunitary gates (quantum channels). In the limit of large local Hilbert space dimension, we obtain an exact expression for the DFF averaged over the random unitary gates, with simple, closed-form expressions in the limit of large times. We find that, for long enough times, the system always relaxes (i.e., the DFF decays) with two distinctive regimes characterized by the presence or absence of gap closing. While the system can sustain a robust ramp for a long (but finite) time interval in the gap-closing regime, relaxation is ``assisted'' by quantum chaos in the regime where the gap remains nonzero. In the latter regime, we find that, if the thermodynamic limit is taken first, the gap does not close even in the dissipationless limit.

[44] 2312.00652

Perspective on the Vortex Mass Determination in Superconductors using Circular Dichroism

In our previous work, we estimated the mass of an Abrikosov vortex in a nearly optimally doped YBaCuO film at 45 K using circular dichroism at terahertz (THz) frequencies. In this paper, we want to underline the relevance of our method, propose improvements of our experimental approach, provide a detailed description of the calculations leading to the evaluation of the vortex mass, and present an explanation of its variation with frequency. We also partially study the case of a slightly underdoped film deposited on a different substrate.

[45] 2312.00653

Area Selective Chemical Vapor Deposition of Gold by Electron Beam Seeding

Chemical vapour deposition (CVD) is an established method for producing high-purity thin films, but it typically necessitates the pre- and post-processing of a mask to produce structures. This paper presents a novel maskless patterning technique that enables area selective CVD of gold. A focused electron beam is used to decompose the metal-organic precursor Au(acac)Me$_2$ locally, thereby creating an autocatalytically active seed layer for subsequent CVD with the same precursor. The procedure can be included in the same CVD cycle without the need for clean room lithographic processing. Moreover, it operates at low temperatures of 80 {\deg}C, over 200 K lower than standard CVD temperatures for this precursor, reducing thermal load on the specimen. Given that electron beam seeding operates on any even moderately conductive surface, the process does not constrain device design. This is demonstrated by the example of vertical nanostructures with high aspect ratios of around 40:1 and more. Written using a focused electron beam and the same precursor, these nanopillars exhibit catalytically active nuclei on their surface. Furthermore, they allow for the first time the precise determination of the local temperature increase caused by the writing of nanostructures with an electron beam.

[46] 2312.00669

Optical chiral properties in a large resonant hybrid photonic cluster

Optical chiral properties of a resonant hybrid photonic crystal (RHPC) are computed taking into account spin-orbit effect due to light-hole excitons perfectly confined in 2D quantum wells. The trends of the optical activity, expressed as a ratio between the absorption intensities of the z and xy light-hole polaritons, are obtained by computing the optical response in a rather large N-cluster of elementary cells (N= 34) and for exciton energy, in resonance with a stationery inflection point (SIP). High values of spin-orbit interaction (0.7 eV A) produce strong distortions of the optical activity polar curves that, differently, becomes rather isotropic if the experimental value (0.14 eV A) is used.

[47] 2312.00715

Magnetic phase diagram and magneto-elastic coupling of NdB$_4$ studied by high-resolution capacitance dilatometry up to 35~T

We report high-resolution dilatometry studies on single crystals of the Shastry-Sutherland-lattice magnet NdB$_4$ supported by specific heat and magnetometry data. Our dilatometric studies evidence pronounced anomalies at the phase boundaries which imply strong magneto-elastic coupling. The evolution of the three zero-field phase transitions separating distinct antiferromagnetic phases at $TN=17.2$~K, $TIT=6.8$~K and $TLT=4.8$~K can thus be traced in applied magnetic fields which provides the magnetic phase diagrams for $B\parallel c$ up to 15~T and for $B\parallel [110]$ up to 35~T. New in-field phases are discovered for both field directions and already known phases are confirmed. In particular, phase boundaries between different phases are unambiguously shown by sign changes of observed anomalies and corresponding changes in uniaxial pressure effects. For $B||c$, we find a 1/4-magnetization plateau in addition to a previously reported plateau at 1/5 of the saturation magnetization. TN increases for $B\parallel c$ in fields up to 15~T implying that magnetic moments of the all-in/all-out structure in the high temperature AFM ordered phase are driven towards the $c$ axis in high magnetic fields. Uniaxial pressure dependencies ${\partial}T_{\mathrm{crit}}/{\partial}p_{\mathrm{c}}$ of the phase transition temperatures for magnetic fields and pressure applied along the $c$ axis are derived from the data.

[48] 2312.00726

Magnetic-field-induced critical dynamics in magnetoelectric TbPO$_4$

We report on the magnetoelectric dynamics in the linear magnetoelectric antiferromagnet TbPO$_4$ studied by broadband dielectric spectroscopy. For the phase transition into the magnetoelectric antiferromagnetic phase at $T_{N} \approx 2.3$ K, a finite magnetic field $H$ induces critical behavior in the quasi-static permittivity $\varepsilon'$. Plotting the corresponding anomaly as function of $T/T_N(H)$, we observe the scaling behavior $\Delta \varepsilon' \propto H^2$, a clear fingerprint of linear magnetoelectric antiferromagnets. Above the phase transition, we find a critical slowing down of the ferroic fluctuations in finite magnetic field. This behaviour can be understood via a magnetic-field-induced relaxational response that resembles the soft-mode behaviour in canonical ferroelectrics and multiferroics.

[49] 2312.00743

Ordering Kinetics of the two-dimensional voter model with long-range interactions

We study analytically the ordering kinetics of the two-dimensional long-range voter model on a two-dimensional lattice, where agents on each vertex take the opinion of others at distance $r$ with probability $P(r) \propto r^{-\al}$. The model is characterized by different regimes, as $\al$ is varied. For $\al > 4$ the behaviour is similar to that of the nearest-neighbor model, with the formation of ordered domains of a typical size growing as $L(t) \propto \sqrt{t}$, until consensus is reached in a time or order $N\ln N$, $N$ being the number of agents. Dynamical scaling is violated due to an excess of interfacial sites whose density decays as slow as $\rho(t) \propto 1/\ln t$. Sizable finite-time corrections are also present, which are absent in the case of nearest-neighbors interactions. For $0<\al \leq 4$ standard scaling is reinstated, and the correlation length increases algebraically as $L(t)\propto t^{1/z}$, with $1/z=2/\al$ for $3<\al<4$ and $1/z=2/3$ for $0<\al<3$. In addition, for $\al \le 3$, $L(t)$ depends on $N$ at any time $t>0$. Such coarsening, however, only leads the system to a partially ordered metastable state where correlations decay algebraically with distance, and whose lifetime diverges in the $N\to \infty$ limit. In finite systems consensus is reached in a time of order $N$ for any $\al <4$.

[50] 2312.00749

Two band atomic superfluidity in the presence of orbital Feshbach resonance

We study superfluid properties of alkali-earth-like Fermi atomic systems in the presence of orbital Feshbach resonance. Using a two-band description of the ground state and excited state and a mean-field approximation of the intra-band atomic pairing, we investigate the phase transitions and crossover between superfluid/normal phases. Defining an effective scattering length by combining both inter-band and intra-band interactions, we derive closed form gap and number density equations for both ground state and excited state atomic bands. We find that our zero-temperature analytical results and finite-temperature numerical results indicate that the system can show smooth crossover between Bardeen, Cooper, and Schreifer (BCS) and Bose-Einstein Condensate (BEC) superfluidity for atoms in each band. In addition, we find that inter-band and intra-band interactions can induce quantum phase transitions between BCS/BEC superfluid states of atoms in one band to that of the other. We anticipate that our closed form analytical results can be used as a bench mark for future experimental and theoretical investigations and will have an impact on the current understanding of two-band superconductors such as MgB$_2$.

[51] 2312.00754

Measurements of nematic susceptibility with phase sensitive nuclear magnetic resonance in pulsed strain fields

We present nuclear magnetic resonance data in BaFe$_2$As$_2$ in the presence of pulsed strain fields that are interleaved in time with the radiofrequency excitation pulses. In this approach, the precessing nuclear magnetization acquires a phase shift that is proportional to the strain and pulse time. The sensitivity in this approach is limited by the homogeneous decoherence time, $T_2$, rather than the inhomogeneous linewidth. We measure the nematic susceptibility as a function of temperature, and demonstrate three orders of magnitude improvement in sensitivity. This approach will enable studies of the strain response in a broad range of materials that previously were inaccessible due to inhomogeneous broadening.

[52] 2312.00757

Giant microwave-optical Kerr nonlinearity via Rydberg excitons in cuprous oxide

Microwave-optical conversion is key to future networks of quantum devices, such as those based on superconducting technology. Conversion at the single quantum level requires strong nonlinearity, high bandwidth, and compatibility with a millikelvin environment. A large nonlinearity is observed in Rydberg atoms, but combining atomic gases with dilution refrigerators is technically challenging. Here we demonstrate that a strong microwave-optical nonlinearity in a cryogenic, solid-state system by exploiting Rydberg states of excitons in \cuprite. We measure a microwave-optical cross-Kerr coefficient of $B_0 = 0.022 \pm 0.008 $ m V$^{-2}$ at 4~K, which is several orders of magnitude larger than other solid-state systems. Our results highlight the potential of Rydberg excitons for nonlinear optics, and form the basis for a microwave-optical frequency converter based on Cu$_2$O.

[53] 2312.00767

Molecular Dynamics Study of Electro-Osmotic Flow in a Nanochannel with Molybdenum Disulfide Walls

The electro-osmotic flow (EOF) in a neutral system consisting of an aqueous NaCl solution confined in a nanochannel with two parallel Molybdenum disulfide ($\textrm{MoS}_{\textrm{2}}$) walls and in the presence of an external electric field parallel to the channel walls, is investigated for the first time. The results indicate that the thickness of the Stern layer grows as the negative electric surface charge density on the nanochannel walls increases. The Stern layer becomes thinner as the salt concentration is increased. Moreover, the EOF occurs under the no-slip condition on the walls. In addition, by increasing the surface charge density the average of the flow velocity across the nanochannel initially grows (Debye--H$\ddot{\textrm{u}}$ckel regime) and reaches its maximum value. Then, by further increasing the surface charge density the water flow rate decreases (intermediate regime), and gets the zero value and becomes negative (reverse flow regime) at even larger values of the surface charge densities. Comparing the results of the previous work wherein the channels are composed of the black phosphorene walls with those of the present study for a channel composed of $\textrm{MoS}_{\textrm{2}}$ surfaces, show that for the latter case the reverse flow occurs at a lower surface charge density and with a greater value of the peak velocity with respect to the change in the surface charge density for the former case.

[54] 2312.00768

Exploring kinetically induced bound states in triangular lattices with ultracold atoms: spectroscopic approach

Quantum simulations with ultracold fermions in triangular optical lattices have recently emerged as a new platform for studying magnetism in frustrated systems. Experimental realizations of the Fermi Hubbard model revealed striking contrast between magnetism in bipartite and triangular lattices. In bipartite lattices magnetism peaks at half filling, and doped charge carriers tend to suppress magnetic correlations. In triangular lattices for large $U/t$, magnetism is enhanced by doping away from $n=1$ because kinetic energy of dopants can be lowered through developing magnetic correlations. This corresponds to formation of magnetic polarons, with hole and doublon doping resulting in antiferro- and ferromagnetic polarons respectively. Snapshots obtained with quantum gas microscopes revealed formation of magnetic polarons around dopants at temperatures exceeding the superexchange energy scale. In this work we discuss theoretically that additional insight into properties of magnetic polarons can be achieved using spectroscopic experiments with ultracold atoms. We consider starting from a spin polarized state with small hole doping and applying a two-photon Raman photoexcitation, which transfers atoms into a different spin state. We show that such magnon injection spectra exhibit a separate peak corresponding to formation of a bound state between a hole and a magnon. This polaron peak is separated from the simple magnon spectrum by energy proportional to single particle tunneling and can be easily resolved with currently available experimental techniques. For some momentum transfer there is an additional peak corresponding to photoexciting a bound state between two holes and a magnon. We point out that in two component Bose mixtures in triangular lattices one can also create dynamical magnetic polarons, with one hole and one magnon forming a repulsive bound state.

[55] 2312.00771

Band alignment of grafted monocrystalline Si (001)/$β$-Ga$_2$O$_3$ (010) p-n heterojunction determined by X-ray photoelectron spectroscopy

Beta-phase gallium oxide ($\beta$-Ga$_2$O$_3$) research has gained accelerated pace due to its superiorly large bandgap and commercial availability of large-diameter native substrates. However, the high acceptor activation energy obstructs the development of homojunction bipolar devices employing $\beta$-Ga$_2$O$_3$. The recently demonstrated semiconductor grafting technique provides an alternative and viable approach towards lattice-mismatched $\beta$-Ga$_2$O$_3$-based p-n heterojunctions with high quality interfaces. Understanding and quantitatively characterizing the band alignment of the grafted heterojunctions is crucial for future bipolar device development employing the grafting method. In this work, we present a systematic study of the band alignment in the grafted monocrystalline Si/$\beta$-Ga$_2$O$_3$ heterostructure by employing X-ray photoelectron spectroscopy (XPS). The core level peaks and valence band spectra of the Si, $\beta$-Ga$_2$O$_3$, and the grafted heterojunction were carefully obtained and analyzed. The band diagrams of the Si/$\beta$-Ga$_2$O$_3$ heterostructure were constructed using two individual methods, the core level peak method and the valence band spectrum method, by utilizing the different portions of the measured data. The reconstructed band alignments of the Si/$\beta$-Ga$_2$O$_3$ heterostructure using the two different methods are identical within the error range. The band alignment is also consistent with the prediction from the electron affinity values of Si and $\beta$-Ga$_2$O$_3$. The study suggests that the interface defect density in grafted Si/$\beta$-Ga$_2$O$_3$ heterostructure is at a sufficiently low level such that Fermi level pinning at the interface has been completely avoided and the universal electron affinity rule can be safely employed to construct the band diagrams of grafted monocrystalline Si/$\beta$-Ga$_2$O$_3$ heterostructures.

[56] 2312.00012

Multi-fidelity uncertainty quantification for homogenization problems in structure-property relationships from crystal plasticity finite elements

Crystal plasticity finite element method (CPFEM) has been an integrated computational materials engineering (ICME) workhorse to study materials behaviors and structure-property relationships for the last few decades. These relations are mappings from the microstructure space to the materials properties space. Due to the stochastic and random nature of microstructures, there is always some uncertainty associated with materials properties, for example, in homogenized stress-strain curves. For critical applications with strong reliability needs, it is often desirable to quantify the microstructure-induced uncertainty in the context of structure-property relationships. However, this uncertainty quantification (UQ) problem often incurs a large computational cost because many statistically equivalent representative volume elements (SERVEs) are needed. In this paper, we apply a multi-level Monte Carlo (MLMC) method to CPFEM to study the uncertainty in stress-strain curves, given an ensemble of SERVEs at multiple mesh resolutions. By using the information at coarse meshes, we show that it is possible to approximate the response at fine meshes with a much reduced computational cost. We focus on problems where the model output is multi-dimensional, which requires us to track multiple quantities of interest (QoIs) at the same time. Our numerical results show that MLMC can accelerate UQ tasks around 2.23x, compared to the classical Monte Carlo (MC) method, which is widely known as the ensemble average in the CPFEM literature.

[57] 2312.00071

Studying Hopfield models via fully lifted random duality theory

Relying on a recent progress made in studying bilinearly indexed (bli) random processes in \cite{Stojnicnflgscompyx23,Stojnicsflgscompyx23}, the main foundational principles of fully lifted random duality theory (fl RDT) were established in \cite{Stojnicflrdt23}. We here study famous Hopfield models and show that their statistical behavior can be characterized via the fl RDT. Due to a nestedly lifted nature, the resulting characterizations and, therefore, the whole analytical machinery that produces them, become fully operational only if one can successfully conduct underlying numerical evaluations. After conducting such evaluations for both positive and negative Hopfield models, we observe a remarkably fast convergence of the fl RDT mechanism. Namely, for the so-called square case, the fourth decimal precision is achieved already on the third (second non-trivial) level of lifting (3-sfl RDT) for the positive and on the fourth (third non-trivial) level of lifting (4-sfl RDT) for the corresponding negative model. In particular, we obtain the scaled ground state free energy $\approx 1.7788$ for the positive and $\approx 0.3279$ for the negative model.

[58] 2312.00073

Binary perceptrons capacity via fully lifted random duality theory

We study the statistical capacity of the classical binary perceptrons with general thresholds $\kappa$. After recognizing the connection between the capacity and the bilinearly indexed (bli) random processes, we utilize a recent progress in studying such processes to characterize the capacity. In particular, we rely on \emph{fully lifted} random duality theory (fl RDT) established in \cite{Stojnicflrdt23} to create a general framework for studying the perceptrons' capacities. Successful underlying numerical evaluations are required for the framework (and ultimately the entire fl RDT machinery) to become fully practically operational. We present results obtained in that directions and uncover that the capacity characterizations are achieved on the second (first non-trivial) level of \emph{stationarized} full lifting. The obtained results \emph{exactly} match the replica symmetry breaking predictions obtained through statistical physics replica methods in \cite{KraMez89}. Most notably, for the famous zero-threshold scenario, $\kappa=0$, we uncover the well known $\alpha\approx0.8330786$ scaled capacity.

[59] 2312.00111

Multimodal Learning for Crystalline Materials

Artificial intelligence (AI) has revolutionized the field of materials science by improving the prediction of properties and accelerating the discovery of novel materials. In recent years, publicly available material data repositories containing data for various material properties have grown rapidly. In this work, we introduce Multimodal Learning for Crystalline Materials (MLCM), a new method for training a foundation model for crystalline materials via multimodal alignment, where high-dimensional material properties (i.e. modalities) are connected in a shared latent space to produce highly useful material representations. We show the utility of MLCM on multiple axes: (i) MLCM achieves state-of-the-art performance for material property prediction on the challenging Materials Project database; (ii) MLCM enables a novel, highly accurate method for inverse design, allowing one to screen for stable material with desired properties; and (iii) MLCM allows the extraction of interpretable emergent features that may provide insight to material scientists. Further, we explore several novel methods for aligning an arbitrary number of modalities, improving upon prior art in multimodal learning that focuses on bimodal alignment. Our work brings innovations from the ongoing AI revolution into the domain of materials science and identifies materials as a testbed for the next generation of AI.

[60] 2312.00117

Symmetries of quantization of finite groupoids

This paper proves certain facts concerning the equivariance of quantization of pi-finite spaces. We argue that these facts establish an analogy between this quantization procedure and the geometric quantization of a symplectic vector space. Specifically, we observe that symmetries of a given polarization/Lagrangian always induce coherent symmetries of the quantization. On the other hand, symmetries of the entire phase space a priori only induce projective symmetries. For certain three-dimensional theories, this projectivity appears via a twice-categorified analogue of Blattner-Kostant-Sternberg kernels in geometric quantization and the associated integral transforms.

[61] 2312.00132

Dynamical Magic Transitions in Monitored Clifford+T Circuits

The classical simulation of highly-entangling quantum dynamics is conjectured to be generically hard. Thus, recently discovered measurement-induced transitions between highly entangling and low-entanglement dynamics are phase transitions in classical simulability. Here, we study simulability transitions beyond entanglement: noting that some highly-entangling dynamics (e.g., integrable systems or Clifford circuits) are easy to classically simulate, thus requiring "magic"--a subtle form of quantum resource--to achieve computational hardness, we ask how the dynamics of magic competes with measurements. We study the resulting "dynamical magic transitions" focusing on random monitored Clifford circuits doped by T gates (injecting magic). We identify dynamical "stabilizer-purification"--the collapse of a superposition of stabilizer states by measurements--as the mechanism driving this transition. We find cases where transitions in magic and entanglement coincide, but also others with a magic and simulability transition in a highly (volume-law) entangled phase. In establishing our results, we use Pauli-based computation, a scheme distilling the quantum essence of the dynamics to a magic state register subject to mutually commuting measurements. We link stabilizer-purification to "magic fragmentation" wherein these measurements separate into disjoint, O(1)-weight blocks, and relate this to the spread of magic in the original circuit becoming arrested.

[62] 2312.00605

Edge modes, extended TQFT, and measurement based quantum computation

Quantum teleportation can be used to define a notion of parallel transport which characterizes the entanglement structure of a quantum state \cite{Czech:2018kvg}. This suggests one can formulate a gauge theory of entanglement. In \cite{Wong:2022mnv}, it was explained that measurement based quantum computation in one dimension can be understood in term of such a gauge theory (MBQC). In this work, we give an alternative formulation of this "entanglement gauge theory" as an extended topological field theory. This formulation gives a alternative perspective on the relation between the circuit model and MBQC. In addition, it provides an interpretation of MBQC in terms of the extended Hilbert space construction in gauge theories, in which the entanglement edge modes play the role of the logical qubit.

[63] 2312.00665

Functional Renormalization Group Study of Thermodynamic Geometry Around the Phase Transition of Quantum Chromodynamic

We investigate the thermodynamic geometry of the quark-meson model at finite temperature, $T$, and quark number chemical potential, $\mu$. We extend previous works by the inclusion of fluctuations exploiting the functional renormalization group approach. We use recent developments to recast the flow equation into the form of an advection-diffusion equation. We adopt the local potential approximation for the effective average action. We focus on the thermodynamic curvature, $R$, in the $(\mu,T)$ plane, in proximity of the chiral crossover, up to the critical point of the phase diagram. We find that the inclusion of fluctuations results in a smoother behavior of $R$ near the chiral crossover. Moreover, for small $\mu$, $R$ remains negative, signaling the fact that bosonic fluctuations reduce the capability of the system to completely overcome the fermionic statistical repulsion of the quarks. We investigate in more detail the small $\mu$ region by analyzing a system in which we artificially lower the pion mass, thus approaching the chiral limit in which the crossover is actually a second order phase transition. On the other hand, as $\mu$ is increased and the critical point is approached, we find that $R$ is enhanced and a sign change occurs, in agreement with mean field studies. Hence, we completely support the picture that $R$ is sensitive to a crossover and a phase transition, and provides information about the effective behavior of the system at the phase transition.

[64] 2312.00748

Three-Wave Mixing Quantum-Limited Kinetic Inductance Parametric Amplifier operating at 6 Tesla and near 1 Kelvin

Parametric amplifiers play a crucial role in modern quantum technology by enabling the enhancement of weak signals with minimal added noise. Traditionally, Josephson junctions have been the primary choice for constructing parametric amplifiers. Nevertheless, high-kinetic inductance thin films have emerged as viable alternatives to engineer the necessary nonlinearity. In this work, we introduce and characterize a Kinetic Inductance Parametric Amplifier (KIPA) built using high-quality NbN superconducting thin films. The KIPA addresses some of the limitations of traditional Josephson-based parametric amplifiers, excelling in dynamic range, operational temperature, and magnetic field resilience. We demonstrate a quantum-limited amplification (> 20 dB) with a 20 MHz gain-bandwidth product, operational at fields up to 6 Tesla and temperatures as high as 850 mK. Harnessing kinetic inductance in NbN thin films, the KIPA emerges as a robust solution for quantum signal amplification, enhancing research possibilities in quantum information processing and low-temperature quantum experiments. Its magnetic field compatibility and quantum-limited performance at high temperatures make it an invaluable tool, promising new advancements in quantum research.