New articles on Condensed Matter

[1] 2303.12825

Single-parameter variational wavefunctions for quantum Hall bilayers

Bilayer quantum Hall states have been shown to be described by a BCS-paired state of composite fermions. However, finding a qualitatively accurate model state valid across all values of the bilayer separation is challenging. Here, we introduce two variational wavefunctions, each with a single variational parameter, which can be thought of as a proxy for the BCS order parameter. Studying systems of up to 9+9 electrons in a spherical geometry using Monte Carlo methods, we show that the ground state can be accurately described by these single-parameter variational states. In addition, for the first time we provide a numerically exact wavefunction for the Halperin-111 state in terms of composite fermions.

[2] 2303.12829

Classification and emergence of quantum spin liquids in chiral Rydberg models

We investigate the nature of quantum phases arising in chiral interacting Hamiltonians recently realized in Rydberg atom arrays. We classify all possible fermionic chiral spin liquids with $\mathrm{U}(1)$ global symmetry using parton construction on the honeycomb lattice. The resulting classification includes six distinct classes of gapped quantum spin liquids: the corresponding variational wave functions obtained from two of these classes accurately describe the Rydberg many-body ground state at $1/2$ and $1/4$ particle density. Complementing this analysis with tensor network simulations, we conclude that both particle filling sectors host a spin liquid with the same topological order of a $\nu=1/2$ fractional quantum Hall effect. At density $1/2$, our results clarify the phase diagram of the model, while at density $1/4$, they provide an explicit construction of the ground state wave function with almost unit overlap with the microscopic one. These findings pave the way to the use of parton wave functions to guide the discovery of quantum spin liquids in chiral Rydberg models.

[3] 2303.12831

Observation of non-Hermitian edge burst in quantum dynamics

The non-Hermitian skin effect, by which the eigenstates of Hamiltonian are predominantly localized at the boundary, has revealed a strong sensitivity of non-Hermitian systems to the boundary condition. Here we experimentally observe a striking boundary-induced dynamical phenomenon known as the non-Hermitian edge burst, which is characterized by a sharp boundary accumulation of loss in non-Hermitian time evolutions. In contrast to the eigenstate localization, the edge burst represents a generic non-Hermitian dynamical phenomenon that occurs in real time. Our experiment, based on photonic quantum walks, not only confirms the prediction of the phenomenon, but also unveils its complete space-time dynamics. Our observation of edge burst paves the way for studying the rich real-time dynamics in non-Hermitian topological systems.

[4] 2303.12833

Emergence of Chern Supermetal and Pair-Density Wave through Higher-Order Van Hove Singularities in the Haldane-Hubbard Model

While advances in electronic band theory have brought to light new topological systems, understanding the interplay of band topology and electronic interactions remains a frontier question. In this work, we predict new interacting electronic orders emerging near higher-order Van Hove singularities present in the Chern bands of the Haldane model. We classify the nature of such singularities and employ unbiased renormalization group methods that unveil a complex landscape of electronic orders, which include ferromagnetism, density-waves and superconductivity. Importantly, we show that repulsive interactions can stabilize long-sought pair-density wave state and an exotic Chern supermetal, which is a new class of non-Fermi liquid with anomalous quantum Hall response. This framework opens a new path to explore unconventional electronic phases in two-dimensional chiral bands through the interplay of band topology and higher-order Van Hove singularities.

[5] 2303.12836

Photogalvanic response in multi-Weyl semimetals

We investigate the dependence of the photogalvanic response of a multi-Weyl semimetal on its topological charge, tilt, and chemical potential. We derive analytical expressions for the shift and injection conductivities for tilted charge-$n$ Weyl points $(n=1,2,3)$ using a low energy two-band effective Hamiltonian. For double-Weyl semimetals, we also compute the response from two-band and four-band tight-binding models with broken time-reversal symmetry to study the effect of band bending and the contributions from higher bands. We find a significant deviation in the responses obtained from the effective low-energy continuum model and more realistic four-band continuum and tight-binding models. We analyze several different limits of these models. We describe the nature of the deviations and provide estimates of their dependence on the frequency and other model parameters. Our analysis provides a simple explanation for the first-principle calculation based frequency dependence of the injection current in SrSi$_2$. Additionally, we find interesting parameter regimes where the frequency dependence of the non-linear optical response can be directly used to probe the type-I/type-II nature of the Weyl cone. We obtain analytical results for the charge-4 Weyl semimetal by reducing the original problem involving a triple $k$-space integral to one with only a double integral. This simplification allows us to extract all relevant information about the nature of its second-order dc response and the precise condition for observing circular photogalvanic effect quantization. The semi-analytical approach presented here can also be extended to a systematic study of second harmonic generation and first-order optical conductivity in charge-4 Weyl semimetals.

[6] 2303.12879

Phonon and magnon jets above the critical current in nanowires with planar domain walls

We show through non-equilibrium non-adiabatic electron-spin-lattice simulations that above a critical current in magnetic atomic wires with a narrow domain wall the electron flow triggers violent stimulated emission of phonons and magnons with an almost complete conversion of the incident electron momentum flux into a phonon and magnon flux. The electronic current suffers a heavy suppression above this threshold. This poses a fundamental limit to the current densities attainable in atomic wires. At the same time it opens up an exciting way of generating the alternative quasi-particle currents above once the requisite electronic-structure properties are met.

[7] 2303.12881

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers

The spin Hall effect (SHE), in which electrical current generates transverse spin current, plays an important role in spintronics for the generation and manipulation of spin-polarized electrons. The phenomenon originates from spin-orbit coupling. In general, stronger spin-orbit coupling favors larger SHEs but shorter spin relaxation times and diffusion lengths. To achieve both large SHEs and long-range spin transport in a single material has remained a challenge. Here we demonstrate a giant intrinsic SHE in AB-stacked MoTe2/WSe2 moir\'e bilayers by direct magneto optical imaging. Under moderate electrical currents with density < 1 A/m, we observe spin accumulation on transverse sample edges that nearly saturates the spin density. We also demonstrate long-range spin Hall transport and efficient non-local spin accumulation limited only by the device size (about 10 um). The gate dependence shows that the giant SHE occurs only near the Chern insulating state, and at low temperatures, it emerges after the quantum anomalous Hall breakdown. Our results demonstrate moir\'e engineering of Berry curvature and large SHEs for potential spintronics applications.

[8] 2303.12886

Theoretical studies of enhanced anomalous Nernst effect in Fe$_3$Ga

The anomalous Nernst effect (ANE) is a member of the extensive family of topological effects in solid state physics. It converts a heat current into electric voltage and originates from the Berry curvature of electronic bands near the Fermi level. Recent results established the Fe$_3$Ga alloy as one of the most promising candidates for applications, due to its flat band structure consisting of rich web of nodal lines. In this theoretical work, we study the effect of deformation of Fe$_3$Ga on the anomalous Nernst effect, which naturally occurs in thin films. Furthermore, we demonstrate that doping, which effectively shifts the position of the Fermi level, can also significantly modify the strength of the effect. Lastly, we provide detailed analysis of the origin of ANE in the electronic structure of Fe$_3$Ga which yields a deeper insight into the generating mechanisms, understanding of which can lead to substantial enhancement of the effect in the future.

[9] 2303.12887

Detecting low-energy quasilocalized excitations in computer glasses

Soft, quasilocalized excitations (QLEs) are known to generically emerge in a broad class of disordered solids, and to govern many facets of the physics of glasses, from wave attenuation to plastic instabilities. In view of this key role of QLEs, shedding light upon several open questions in glass physics depends on the availability of computational tools that allow to study QLEs' statistical mechanics. The latter is a formidable task since harmonic analyses are typically contaminated by hybridizations of QLEs with phononic excitations at low frequencies, obscuring a clear picture of QLEs' abundance, typical frequencies and other important micromechanical properties. Here we present an efficient algorithm to detect the field of quasilocalized excitations in structural computer glasses. The algorithm introduced takes a computer-glass sample as input, and outputs a library of QLEs embedded in that sample. We demonstrate the power of the new algorithm by reporting the spectrum of glassy excitations in two-dimensional computer glasses featuring a huge range of mechanical stability, which is inaccessible using conventional harmonic analyses due to phonon-hybridizations. Future applications are finally discussed.

[10] 2303.12893

Hyperbolic polaritons in topological nodal ring semimetals

In mirror-symmetric systems, there is a possibility of the realization of extended gapless electronic states characterized as nodal lines or rings. Strain induced modifications to these states lead to emergence of different classes of nodal rings with qualitatively different physical properties. Here we study optical response and the electromagnetic wave propagation in type I nodal ring semimetals, in which the low-energy quasiparticle dispersion is parabolic in momentum $k_x$ and $k_y$ and is linear in $k_z$. This leads to a highly anisotropic dielectric permittivity tensor in which the optical response is plasmonic in one spatial direction and dielectric in the other two directions. The resulting normal modes (polaritons) in the bulk material become hyperbolic over a broad frequency range, which is furthermore tunable by the doping level. The propagation, reflection, and polarization properties of the hyperbolic polaritons not only provide valuable information about the electronic structure of these fascinating materials in the most interesting region near the nodal rings but also pave the way to tunable hyperbolic materials with applications ranging from anomalous refraction and waveguiding to perfect absorption in ultrathin subwavelength films.

[11] 2303.12924

Active Learning Sensitivity Analysis of $γ^\prime$(L1$_2$) Precipitate Morphology of Ternary Co-Based Superalloys

To better understand the equilibrium $\gamma^\prime$(L1$_2$) precipitate morphology in Co-based superalloys, a phase field modeling sensitivity analysis is conducted to examine how four phase-field parameters [initial Co concentration ($c_0$), double-well barrier height ($\omega$), gradient energy density coefficient ($\kappa$), and lattice misfit strain ($\epsilon_{\rm misfit}$)] influence the $\gamma^\prime$(L1$_2$) precipitate size and morphology. Gaussian Process Regression (GPR) models are used to fit the sample points and to generate surrogate models for both precipitate size and morphology. In an Active Learning approach, a Bayesian Optimization algorithm is coupled with the GPR models to suggest new sample points to calculate and efficiently update the models based on a reduction of uncertainty. The algorithm has a user-defined objective, which controls the balance between exploration and exploitation for new suggested points. Our methodology provides a qualitative and quantitative relationship between the $\gamma^\prime$(L1$_2$) precipitate size and morphology and the four phase-field parameters, and concludes that the most sensitive phase-field parameter for precipitate size and morphology is the initial Co concentration ($c_0$) and the double-well barrier height ($\omega$), respectively. We note that the GPR model for precipitate morphology required adding a noise tolerance in order to avoid overfitting due to irregularities in some of the simulated equilibrium $\gamma^\prime$(L1$_2$) precipitate morphology.

[12] 2303.12938

Polymer Informatics Beyond Homopolymers

Polymers are diverse and versatile materials that have met a wide range of material application demands. They come in several flavors and architectures, e.g., homopolymers, copolymers, polymer blends, and polymers with additives. Searching this enormous space for suitable materials with a specific set of property/performance targets is thus non-trivial, painstaking, and expensive. Such a search process can be made effective by the creation of rapid and accurate property predictors. In this work, we present a machine-learning framework to predict the thermal properties of homopolymers, copolymers, and polymer blends. A universal fingerprinting scheme capable of handling this entire polymer chemical class has been developed and a multi-task deep learning algorithm is trained simultaneously on a large dataset of glass transition, melting, and degradation temperatures. The developed models are accurate, fast, flexible, and scalable to other properties when suitable data become available.

[13] 2303.12953

Temperature dependence of 7Li NMR relaxation rates in Li3InCl6, Li3YCl6, Li1.48Al0.48Ge1.52(PO4)3 and LiPS5Cl

Inorganic solid-state battery electrolytes show high ionic conductivities and enable the fabrication of all solid-state batteries. In this work, we present the temperature dependence of spin-lattice relaxation time (T1), spin-spin relaxation time (T2), and resonance linewidth of the 7Li nuclear magnetic resonance (NMR) for four solid-state battery electrolytes (Li3InCl6 (LIC), Li3YCl6 (LYC), Li1.48Al0.48Ge1.52(PO4)3 (LAGP) and LiPS5Cl (LPSC)) from 173 K to 403 K at a 7Li resonance frequency of 233 MHz, and from 253 K to 353 K at a 7Li resonance frequency of 291 MHz. Additionally, we measured the spin-lattice relaxation rates at an effective 7Li resonance frequency of 133 kHz using a spin-locking pulse sequence in the temperature range of 253 K to 353 K. In LPSC, the 7Li NMR relaxation is consistent with the Bloembergen-Pound-Purcell (BPP) theory of NMR relaxation of dipolar nuclei. In LIC, LYC and LAGP, the BPP theory does not describe the NMR relaxation rates for the temperature range and frequencies of our measurements. The presented NMR relaxation data assists in providing a complete picture of Li diffusion in the four solid-state battery electrolytes.

[14] 2303.12956

Thermodynamic evidence for electron correlation-driven flattening of the quasiparticle bands in the high-Tc cuprates

A flattened electronic band is one of several possible routes for increasing the strength of the pairing interactions in a superconductor. With this in mind, we show here that thermodynamic measurements of the high-Tc cuprates reveal an appreciably stronger electron correlation-driven flattening of the quasiparticle bands than has previously been indicated. Specifically, we find that thermodynamic measurements indicate an electronic entropy in excess of that that can be accounted for by the value of the universal Fermi velocity inferred from photoemission experiments. The observed band flattening implies that the Van Hove singularity features prominently in calorimetry measurements, causing it undermine prior arguments for a divergence in the renormalization of the effective mass near a critical doping $p^\ast$ based on calorimetry measurements. The band flattening is also sufficient to drive the cuprates into a strong pairing regime where the maximum transition temperature becomes constrained by phase fluctuations.

[15] 2303.12975

Electronic-mediated nuclear stopping power in proton irradiated water ice

Traditionally, it has been assumed that the stopping of a swift ion travelling through matter can be understood in terms of two essentially independent components, i.e. electronic vs. nuclear. Performing extensive Ehrenfest MD simulations of the process of proton irradiation of water ice that accurately describe not only the non-adiabatic dynamics of the electrons but also of the nuclei, we have found a stopping mechanism involving the interplay of the electronic and nuclear subsystems. This effect, which consists in a kinetic energy transfer from the projectile to the target nuclei thanks to the perturbations of the electronic density caused by the irradiation, is fundamentally different from the atomic displacements and collision cascades characteristic of nuclear stopping. Moreover, it shows a marked isotopic effect depending on the composition of the target, being relevant mostly for light water as opposed to heavy water. This result is consistent with long-standing experimental results which remained unexplained so far.

[16] 2303.12977

Anharmonic theory of superconductivity and its applications to emerging quantum materials

The role of anharmonicity on superconductivity has often been disregarded in the past. Recently, it has been recognized that anharmonic decoherence could play a fundamental role in determining the superconducting properties (electron-phonon coupling, critical temperature, etc) of a large class of materials, including systems close to structural soft-mode instabilities, amorphous solids and metals under extreme high-pressure conditions. Here, we review recent theoretical progress on the role of anharmonic effects, and in particular certain universal properties of anharmonic damping, on superconductivity. Our focus regards the combination of microscopic-agnostic effective theories for bosonic mediators with the well-established BCS theory and Migdal-Eliashberg theory for superconductivity. We discuss in detail the theoretical frameworks, their possible implementation within first-principles methods, and the experimental probes for anharmonic decoherence. Finally, we present several concrete applications to emerging quantum materials, including hydrides, ferroelectrics and systems with charge density wave instabilities.

[17] 2303.12978

Shear banding in monodisperse polymer melt

We performed a series of molecular dynamics simulations on monodisperse polymer melts to investigate the formation of shear banding. Under high shear rates, shear banding occurs, which is accompanied by the entanglement heterogeneity intimately. Interestingly, the same linear relationship between the end-to-end distance $R_{ee}$ and entanglement density $Z$ is observed at homogeneous flow before the onset of shear banding and at stable shear banding state, where $R_{ee} \sim [ln(W_i^2)- \xi_0]Z$ is proposed as the criterion to describe the dynamic force balance of molecular chain in flow with a high rate. We establish a scaling relation between the disentanglement rate $V_d$ and Weissenberg number $W_i$ as $V_d \sim W_i^2$ for stable flow. Deviating from this relation leads to force imbalance and results in the emergence of shear banding. The formation of shear banding prevents chain from further stretching and untangling. The transition from homogeneous shear to shear banding partially dissipates the increased free energy from shear and reduces the free energy of the system.

[18] 2303.12986

Self-sustained deformable rotating liquid He cylinders: The pure normal fluid $^3$He and superfluid $^4$He cases

We have studied self-sustained, deformable, rotating liquid He cylinders of infinite length. In the normal fluid $^3$He case, we have employed a classical model where only surface tension and centrifugal forces are taken into account, as well as the Density Functional Theory (DFT) approach in conjunction with a semi-classical Thomas-Fermi approximation for the kinetic energy. In both approaches, if the angular velocity is sufficiently large, it is energetically favorable for the $^3$He cylinder to undergo a shape transition, acquiring an elliptic-like cross section which eventually becomes two-lobed. In the $^4$He case, we have employed a DFT approach that takes into account its superfluid character, limiting the description to vortex-free configurations where angular momentum is exclusively stored in capillary waves on a deformed cross section cylinder. The calculations allow us to carry out a comparison between the rotational behavior of a normal, rotational fluid ($^3$He) and a superfluid, irrotational fluid ($^4$He).

[19] 2303.13007

In-situ study of rules of nanostructure evolution, severe plastic deformations, and friction under high pressure

Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. We introduce rough diamond anvils to reach maximum friction equal to yield strength in shear and perform the first in-situ study of the evolution of the pressure-dependent yield strength and nanostructural parameters for severely pre-deformed Zr. {\omega}-Zr behaves like perfectly plastic, isotropic, and strain-path-independent. This is related to reaching steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for {\alpha}-Zr obtained with smooth and rough anvils are different, which causes major challenge in plasticity theory.

[20] 2303.13028

Neutron Reflectometry: a technique for revealing emergent phenomena at interfaces in heterostructures

Neutron reflectometry (NR) has emerged as a unique technique for the investigation of structure and magnetism of thin films of both biologically relevant and magnetic materials. The advantage of NR with respect to many other surface-sensitive techniques is its sub-nanometer resolution that enables structural characterizations at the molecular level. While in the case of bio-relevant samples, NR can be used to probe thin films at buried interfaces, non-destructively, even adopting a complex sample environment. Whereas the polarized version of NR is best suited for revealing the interface magnetism with a sub-nanometer depth resolution. In this article, I will briefly describe the basic principle of NR with some applications of NR to both bio-relevant samples and magnetic heterostructures.

[21] 2303.13038

Thermodynamic bounds on correlation times

We derive a variational expression for the correlation time of physical observables in steady-state diffusive systems. As a consequence of this variational expression, we obtain lower bounds on the correlation time, which provide speed limits on the self-averaging of observables. In equilibrium, the bound takes the form of a tradeoff relation between the long- and short-time fluctuations of an observable. Out of equilibrium, the tradeoff can be violated, leading to an acceleration of self-averaging. We relate this violation to the steady-state entropy production rate, as well as the geometric structure of the irreversible currents, giving rise to two complementary speed limits. One of these can be formulated as a lower estimate on the entropy production from the measurement of time-symmetric observables. Using an illustrating example, we show the intricate behavior of the correlation time out of equilibrium for different classes of observables and how this can be used to partially infer dissipation even if no time-reversal symmetry breaking can be observed in the trajectories of the observable.

[22] 2303.13044

Lightwave-controlled band engineering in quantum materials

Stacking and twisting atom-thin sheets create superlattice structures with unique emergent properties, while tailored light fields can manipulate coherent electron transport on ultrafast timescales. The unification of these two approaches may lead to ultrafast creation and manipulation of band structure properties, which is a crucial objective for the advancement of quantum technology. Here, we address this by demonstrating a tailored lightwave-driven analogue to twisted layer stacking. This results in sub-femtosecond control of time-reversal symmetry breaking and thereby band structure engineering in a hexagonal boron nitride monolayer. The results practically demonstrate the realization of the topological Haldane model in an insulator. Twisting the lightwave relative to the lattice orientation enables switching between band configurations, providing unprecedented control over the magnitude and location of the band gap, and curvature. A resultant asymmetric population at complementary quantum valleys lead to a measurable valley Hall current, detected via optical harmonic polarimetry. The universality and robustness of the demonstrated sub-femtosecond control opens a new way to band structure engineering on the fly paving a way towards large-scale ultrafast quantum devices for real-world applications.

[23] 2303.13048

Quantum Dot Source-Drain Transport Response at Microwave Frequencies

Quantum dots are frequently used as charge sensitive devices in low temperature experiments to probe electric charge in mesoscopic conductors where the current running through the quantum dot is modulated by the nearby charge environment. Recent experiments have been operating these detectors using reflectometry measurements up to GHz frequencies rather than probing the low frequency current through the dot. In this work, we use an on-chip coplanar waveguide resonator to measure the source-drain transport response of two quantum dots at a frequency of 6 GHz, further increasing the bandwidth limit for charge detection. Similar to the low frequency domain, the response is here predominantly dissipative. For large tunnel coupling, the response is still governed by the low frequency conductance, in line with Landauer-B\"uttiker theory. For smaller couplings, our devices showcase two regimes where the high frequency response deviates from the low frequency limit and Landauer-B\"uttiker theory: When the photon energy exceeds the quantum dot resonance linewidth, degeneracy dependent plateaus emerge. These are reproduced by sequential tunneling calculations. In the other case with large asymmetry in the tunnel couplings, the high frequency response is two orders of magnitude larger than the low frequency conductance G, favoring the high frequency readout.

[24] 2303.13049

Intrinsic supercurrent non-reciprocity coupled to the crystal structure of a van der Waals Josephson barrier

Non-reciprocal electronic transport in a spatially homogeneous system arises from the simultaneous breaking of inversion and time-reversal symmetries. Superconducting and Josephson diodes, a key ingredient for future non-dissipative quantum devices, have recently been realized. Only a few examples of a vertical superconducting diode effect have been reported and its mechanism, especially whether intrinsic or extrinsic, remains elusive. Here we demonstrate a substantial supercurrent non-reciprocity in a van der Waals vertical Josephson junction formed with a Td-WTe2 barrier and NbSe2 electrodes that clearly reflects the intrinsic crystal structure of Td-WTe2. The Josephson diode efficiency increases with the Td-WTe2 thickness up to critical thickness, and all junctions, irrespective of the barrier thickness, reveal magneto-chiral characteristics with respect to a mirror plane of Td-WTe2. Our results, together with the twist-angle-tuned magneto-chirality of a Td-WTe2 double-barrier junction, show that two-dimensional materials promise vertical Josephson diodes with high efficiency and tunability.

[25] 2303.13078

Real Hopf Insulator

Establishing the fundamental relation between the homotopy invariants and the band topology of Hamiltonians has played a critical role in the recent development of topological phase research. In this work, we establish the homotopy invariant and the related band topology of three-dimensional (3D) real-valued Hamiltonians with two occupied and two unoccupied bands. Such a real Hamiltonian generally appears in $\mathcal{PT}$ symmetric spinless fermion systems where $\mathcal{P}$ and $\mathcal{T}$ indicate the inversion and time-reversal symmetries, respectively. We show that the 3D band topology of the system is characterized by two independent Hopf invariants when the lower-dimensional band topology is trivial. Thus, the corresponding 3D band insulator with nonzero Hopf invariants can be called a real Hopf insulator (RHI). In sharp contrast to all the other topological insulators discovered up to now, the topological invariants of RHI can be defined only when both the occupied and unoccupied states are simultaneously considered. Thus, the RHI belongs to the category of delicate topological insulators proposed recently. We show that finite-size systems with slab geometry support surface states with nonzero Chern numbers in a $\mathcal{PT}$-symmetric manner, and establish the bulk-boundary correspondence. We also discuss the bulk-boundary correspondence of rotation symmetric RHIs using the returning Thouless pump.

[26] 2303.13082

Boltzmann's H-Function Extended to Orientation: Anomalous Molecular Shape Dependence of Relaxation and Time Scales of Entropy Relaxation

Boltzmann's H-function H(t) is often regarded as an analog of time-dependent entropy. It provides valuable information about the time scale of relaxation of a nonequilibrium distribution function. In this work, we generalize Boltzmann's H-function (H(t)) to study the relaxation dynamics of a gas of molecules with orientational degrees of freedom. We evaluate the time (t) evolution of joint probability distribution f (p, L, t) for linear (p) and angular (L) momenta from an initial nonequilibrium state by molecular dynamics simulations for prolate and oblate-shaped particles. Our prolate and oblate molecules interact with each other by two-body Gay-Berne potential. We calculate the relaxation of the generalized H(t) with orientation from two specially prepared initial (t=0) nonequilibrium states. In the long-time limit, the H function saturates to its exact equilibrium value, which is the sum of translational and rotational contributions. These, in turn, are related to respective kinetic entropies. We find that both translational and rotational components of H(t) decay nearly exponentially with time; the rotational component is more sensitive to the aspect ratio. A remarkable rapid decrease in relaxation time is observed as the spherical limit is approached, in a way tantalizingly reminiscent of hydrodynamic predictions with slip boundary conditions. The latter is also calculated analytically by solving the appropriate Fokker-Planck equation. We introduce a physically motivated differential term to study the magnitude of translation-rotation coupling. This function shows interesting dynamical behavior at intermediate times. Overall, this study provides insights into the relaxation dynamics of a gas of molecules with different shapes and interactions and highlights the importance of considering both translational and rotational contributions to the H-function.

[27] 2303.13094

Polymorphic phase transitions in bulk triglyceride mixtures

Triacylglycerols (TAGs) are among the most important ingredients in food, cosmetic and pharmaceutical products. Many physical properties of such products, incl. morphology, texture and rheology, are determined by the phase behaviour of the included TAGs. Triglycerides are also of special interest for the production of solid lipid nanoparticles, applied for controlled drug delivery and for encapsulation of bioactive ingredients. In this paper, we study the polymorphic behaviour of complex TAG mixtures, composed of 2 to 6 mixed TAGs, by differential scanning calorimetry and X-ray scattering techniques, aiming to reveal the general rules for their phase behaviour upon cooling and heating. The results show that two or more coexisting phases form upon solidification $(\alpha$, $\beta'$ and/or $\beta)$, the number of which depends strongly on the cooling rate and on the number of components in the mixture. No completely miscible $\alpha$- or $\beta'$-phases were observed. The structure of the most stable $\beta$ polymorphs, formed upon subsequent heating of the solidified samples, does not depend on the thermal history of the samples. For all mixtures studied, we observed one-component $\beta$ domains, coexisting with binary mixed $\beta$ domains with composition and structure which do not depend on the specific TAG ratio in the mixture. In other words, for a mixture with $k$ saturated TAGs we observed $(2k-1)$ different $\beta$ phases. These conclusions provide some predictive power when analysing the phase transition properties of TAG mixtures.

[28] 2303.13098

Microwave Excitation of Atomic Scale Superconducting Bound States

Magnetic impurities on superconductors lead to bound states within the superconducting gap, so called Yu-Shiba-Rusinov (YSR) states. They are parity protected, which enhances their lifetime, but makes it more difficult to excite them. Here, we realize the excitation of YSR states by microwaves facilitated by the tunnel coupling to another superconducting electrode in a scanning tunneling microscope (STM). We identify the excitation process through a family of anomalous microwave-assisted tunneling peaks originating from a second-order resonant Andreev process, in which the microwave excites the YSR state triggering a tunneling event transferring a total of two charges. We vary the amplitude and the frequency of the microwave to identify the energy threshold and the evolution of this excitation process. Our work sets an experimental basis and proof-of-principle for the manipulation of YSR states using microwaves with an outlook towards YSR qubits.

[29] 2303.13114

Universal radiation tolerant semiconductor

Radiation tolerance is determined as an ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Based on the magnitudes of such disorder levels, semiconductors are commonly grouped into the low- or high-radiation tolerant. Nevertheless, upon exposing to sufficiently high fluences, in all cases known by far, it ends up with either extremely high disorder levels or amorphization. Here we show that gamma/beta double polymorph Ga2O3 structures exhibit unprecedently high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O-sublattice properties in gamma-Ga2O3. In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite high mobility of O atoms in collision cascades compared to Ga. Concurrently, the characteristic structure of the Ga-sublattice is nearly insensitive to the accumulated disorder. Jointly it explains macroscopically negligible structural deformations in gamma-Ga2O3 observed in experiment. Notably, we also explained the origin of the beta-to-gamma Ga2O3 transformation, as a function of increased disorder in beta-Ga2O3 and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that gamma-beta double polymorph Ga2O3 structures, in terms of their radiation tolerance properties, benchmark a new class of universal radiation tolerant semiconductors.

[30] 2303.13116

Thermodynamic bound on the asymmetry of cross-correlations

The principle of microscopic reversibility says that in equilibrium, two-time cross-correlations are symmetric under the exchange of observables. Thus, the asymmetry of cross-correlations is a fundamental, measurable, and often-used statistical signature of deviation from equilibrium. We find a simple and universal inequality between the magnitude of asymmetry and the cycle affinity, i.e., the strength of thermodynamic driving. Our result applies to a large class of systems and all state observables, and it suggests a fundamental thermodynamic cost for various nonequilibrium functions quantified by the asymmetry. It also provides a powerful tool to infer affinity from measured cross-correlations, in a different and complementary way to the thermodynamic uncertainty relations. As an application, we prove a thermodynamic bound on the coherence of noisy oscillations, which was previously conjectured by Barato and Seifert [Phys. Rev. E 95, 062409 (2017)]. We also derive a thermodynamic bound on directed information flow in a biochemical signal transduction model.

[31] 2303.13119

Brownian yet non-Gaussian diffusion of a light particle in heavy gas: Lorentz gas based analysis

Non-Gaussian diffusion was recently observed in a gas mixture with mass and fraction contrast [F. Nakai et al, Phys. Rev. E 107, 014605 (2023)]. The mean square displacement of a minor gas particle with a small mass is linear in time, while the displacement distribution deviates from the Gaussian distribution, which is called the Brownian yet non-Gaussian diffusion. In this work, we theoretically analyze this case where the mass contrast is sufficiently large. Major heavy particles can be interpreted as immobile obstacles, and a minor light particle behaves like a Lorentz gas particle within an intermediate time scale. Despite the similarity between the gas mixture and the conventional Lorentz gas system, the Lorentz gas description cannot fully describe the Brownian yet non-Gaussian diffusion. A successful description can be achieved through an ensemble average of the statistical quantities of the Lorentz gas over the initial speed.

[32] 2303.13144

Topological classification of non-Hermitian Hamiltonians with frequency dependence

We develop a topological classification of non-Hermitian effective Hamiltonians that depend on momentum and frequency. Such effective Hamiltonians are in one-to-one correspondence to single-particle Green's functions of systems that satisfy translational invariance in space and time but may be interacting or open. We employ K-theory, which for the special case of noninteracting systems leads to the well-known tenfold-way topological classification of insulators and fully gapped superconductors. Relevant theorems for K-groups are reformulated and proven in the more transparent language of Hamiltonians instead of vector bundles. We obtain 54 symmetry classes for frequency-dependent non-Hermitian Hamiltonians satisfying anti-unitary symmetries. Employing dimensional reduction, the group structure for all these classes is calculated. This classification leads to a group structure with one component from the momentum dependence, which corresponds to the non-Hermitian generalization of topological insulators and superconductors, and two additional parts resulting from the frequency dependence. These parts describe winding of the effective Hamiltonian in the frequency direction and in combined momentum-frequency space.

[33] 2303.13156

Meson Instability of Quantum Many-body Scars in a 1D Lattice Gauge Theory

We investigate the stability of meson excitations (particle-antiparticle bound states) in quantum many-body scars of a 1D $\mathbb{Z}_2$ lattice gauge theory coupled to spinless fermions. By introducing a string representation of the physical Hilbert space, we express a scar state $ |{\Psi_{n,l}}\rangle$ as a superposition of all string bases with an identical string number $n$ and a total length $l$. The string correlation function of lattice fermions hosts an exponential decay as the distance increases for the small-$l$ scar state $|{\Psi_{n,l}}\rangle$, indicating the existence of stable mesons. However, for large $l$, the correlation function exhibits a power-law decay, signaling the emergence of a meson instability. Furthermore, we show that this mesonic-nonmesonic crossover can be detected by the quench dynamics, starting from two low-entangled initial states, respectively, which are experimentally feasible in quantum simulators. Our results expand the physics of quantum many-body scars in lattice gauge theories, and reveal that the nonmesonic state can also manifest ergodicity breaking.

[34] 2303.13163

Transiently delocalized states enhance hole mobility in organic molecular semiconductors

There is compelling evidence that charge carriers in organic semiconductors (OSs) self-localize in nano-scale space because of dynamic disorder. Yet, some OSs, in particular recently emerged high-mobility organic molecular crystals, feature reduced mobility at increasing temperature, a hallmark for delocalized band transport. Here we present the temperature-dependent mobility in two record-mobility OSs: DNTT (dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]-thiophene), and its alkylated derivative, C8-DNTT-C8. By combining terahertz photoconductivity measurements with fully atomistic non-adiabatic molecular dynamics simulations, we show that while both crystals display a power-law decrease of the mobility (\mu) with temperature (T, following: \mu \propto T^(-n)), the exponent n differs substantially. Modelling provides n values in good agreement with experiments and reveals that the differences in the falloff parameter between the two chemically closely related semiconductors can be traced to the delocalization of the different states thermally accessible by charge carriers, which in turn depends on the specific electronic band structure of the two systems. The emerging picture is that of holes surfing on a dynamic manifold of vibrationally-dressed extended states with a temperature-dependent mobility that provides a sensitive fingerprint for the underlying density of states.

[35] 2303.13167

Interfacial Oxide Modulated unique Exchange Bias in CrPS4/Fe3GeTe2 van der Waals heterostructures

Two-dimensional van der Waals heterostructures are an attractive platform for studying exchange bias due to their defect free and atomically flat interfaces. Chromium thiophosphate (CrPS4), an antiferromagnet, has uncompensated magnetic spins in a single layer that make it an excellent candidate for studying exchange bias. In this study, we examined the exchange bias in CrPS4/Fe3GeTe2 van der Waals heterostructures using anomalous Hall measurements. Our results show that the exchange bias strength is robust for clean interfaces, with a hysteresis loop shift of about 55 mT at 5 K for few-layer Fe3GeTe2, which is larger than that obtained in most van der Waals AFM/FM heterostructures. However, when exposed to air, the ferromagnetic Fe3GeTe2 layer develops a thin surface oxide layer that significantly modulates the exchange bias. Remarkably, this surface oxide layer can induce exchange bias without any field-cooling, but merely by applying a 'preset field' from 5 K up to 140K due to the presence of ferrimagnetic magnetite. We also observed exchange bias beyond the N\'eel temperature of CrPS4, with two local minima due to contributions from CrPS4 and surface oxides. These results illustrate the complex behaviour of exchange bias in van der Waals heterostructures and its potential for tailored control.

[36] 2303.13169

Theory for Fourier-limited attosecond pulse generation in solids

The generation of ultrashort light pulses is essential for the advancement of attosecond science. Here, we show that attosecond pulses approaching the Fourier limit can be generated through optimized optical driving of tunneling particles in solids. We propose an ansatz for the wave function of tunneling electron-hole pairs based on a rigorous expression for massive Dirac fermions, which enables efficient optimization of the waveform of the driving field. It is revealed that the dynamic sign change in the effective mass due to optical driving is crucial for shortening the pulse duration, which highlights a distinctive property of Bloch electrons that is not present in atomic gases, i.e., the periodic nature of crystals. These results show the potential of utilizing solid materials as a source of attosecond pulses.

[37] 2303.13224

Multiple magnetic transitions and complex magnetic structures in Fe$_2$SiSe$_4$ with the sawtooth lattice

The sawtooth lattice shares some structural similarities with the kagome lattice and may attract renewed research interest. Here, we report a comprehensive study on the physical properties of Fe$_2$SiSe$_4$, an unexplored member in the olivine chalcogenides with the sawtooth lattice of Fe. Our results show that Fe$_2$SiSe$_4$ is a magnetic semiconductor with band gap of 0.66~eV. It first undergoes an antiferromagnetic transition at T$_{m1}$=110~K, then an ferrimagnetic-like one at T$_{m2}$=50~K and finally a magnetic transition at T$_{m3}$=25~K which is likely driven by the thermal populations of spin-orbit manifold on the Fe site. Neutron diffraction analysis reveals a non-collinear antiferromagnetic structure with propagation vector $\mathbf{q_1}$=(0,0,0) at T$_{m2}$<T<T$_{m1}$. Interestingly, below T$_{m2}$, an additional antiferromagnetic structure with $\mathbf{q_2}$=(0,0.5,0) appears and Fe$_2$SiSe$_4$ exhibits a complex double-$\mathbf{q}$ magnetic structure which has never been observed in sawtooth olivines. Density functional theory calculations suggest this complex noncollinear magnetic structure may originate from the competing antiferromagnetic interactions for both intra- and inter-chain in the sawtooth lattice. Furthermore, band structural calculations show that Fe$_2$SiSe$_4$ has quasi-flat band features near the valence and conduction bands. Based on the above results, we propose Fe$_2$SiSe$_4$ as a new material platform to condensed matter researches.

[38] 2303.13261

Single device offset-free magnetic field sensing principle with tunable sensitivity and linear range based on spin-orbit-torques

We propose a novel device concept using spin-orbit-torques to realize a magnetic field sensor, where we eliminate the sensor offset using a differential measurement concept. We derive a simple analytical formulation for the sensor signal and demonstrate its validity with numerical investigations using macrospin simulations. The sensitivity and the measurable linear sensing range in the proposed concept can be tuned by either varying the effective magnetic anisotropy or by varying the magnitude of the injected currents. We show that undesired perturbation fields normal to the sensitive direction preserve the zero-offset property and only slightly modulate the sensitivity of the proposed sensor. Higher-harmonics voltage analysis on a Hall cross experimentally confirms the linearity and tunability via current strength. Additionally, the sensor exhibits a non-vanishing offset in the experiment which we attribute to the anomalous Nernst effect.

[39] 2303.13263

Vortices in dipolar Bose-Einstein condensates

Quantized vortices are the hallmark of superfluidity, and are often sought out as the first observable feature in new superfluid systems. Following the recent experimental observation of vortices in Bose-Einstein condensates comprised of atoms with inherent long-range dipole-dipole interactions [Nat. Phys. 18, 1453-1458 (2022)], we thoroughly investigate vortex properties in the three-dimensional dominantly dipolar regime, where beyond-mean-field effects are crucial for stability, and investigate the interplay between trap geometry and magnetic field tilt angle.

[40] 2303.13282

Accurate solution of the Index Tracking problem with a hybrid simulated annealing algorithm

An actively managed portfolio almost never beats the market in the long term. Thus, many investors often resort to passively managed portfolios whose aim is to follow a certain financial index. The task of building such passive portfolios aiming also to minimize the transaction costs is called Index Tracking (IT), where the goal is to track the index by holding only a small subset of assets in the index. As such, it is an NP-hard problem and becomes unfeasible to solve exactly for indices with more than 100 assets. In this work, we present a novel hybrid simulated annealing method that can efficiently solve the IT problem for large indices and is flexible enough to adapt to financially relevant constraints. By tracking the S&P-500 index between the years 2011 and 2018 we show that our algorithm is capable of finding optimal solutions in the in-sample period of past returns and can be tuned to provide optimal returns in the out-of-sample period of future returns. Finally, we focus on the task of holding an IT portfolio during one year and rebalancing the portfolio every month. Here, our hybrid simulated annealing algorithm is capable of producing financially optimal portfolios already for small subsets of assets and using reasonable computational resources, making it an appropriate tool for financial managers.

[41] 2303.13306

Lifting, loading, and buckling in conical shells

Liquid crystal elastomer films that morph into cones are strikingly capable lifters. Thus motivated, we combine theory, numerics, and experiments to reexamine the load-bearing capacity of conical shells. We show that a cone squashed between frictionless surfaces buckles at a smaller load, even in scaling, than the classical Seide/Koiter result. Such buckling begins in a region of greatly amplified azimuthal compression generated in an outer boundary layer with oscillatory bend. Experimentally and numerically, buckling then grows sub-critically over the full cone. We derive a new thin-limit formula for the critical load, $\propto t^{5/2}$, and validate it numerically. We also investigate deep post-buckling, finding further instabilities producing intricate states with multiple Pogorelov-type curved ridges arranged in concentric-circles or Archimedean spirals. Finally, we investigate the forces exerted by such states, which limit lifting performance in active cones.

[42] 2303.13308

Mechanism of electrical switching of ultra-thin CoO/Pt bilayers

We study current-induced switching of the N\'eel vector in CoO/Pt bilayers to understand the underlaying antiferromagnetic switching mechanism. Surprisingly, we find that for ultra-thin CoO/Pt bilayers electrical pulses along the same path can lead to an increase or decrease of the spin Hall magnetoresistance signal, depending on the current density of the pulse. By comparing the results of these electrical measurements to XMLD-PEEM imaging of the antiferromagnetic domain structure before and after the application of current pulses, we reveal the reorientation of the N\'eel vector in ultra-thin CoO(4 nm). This allows us to determine that even opposite resistance changes can result from a thermomagnetoelastic switching mechanism. Importantly, our spatially resolved imaging shows that regions where the current pulses are applied and regions further away exhibit different switched spin structures, which can be explained by a spin-orbit torque based switching mechanism that can dominate in very thin films.

[43] 2303.13311

Antiferromagnetic order and consequences on the transport properties of Ba$_{4}$Ru$_{3}$O$_{10}$

Barium ruthenate Ba$_{4}$Ru$_{3}$O$_{10}$, in which Ru$_{3}$O$_{12}$ trimers are connected together to form a chequered two-dimensional framework, has been synthesised and its structural, magnetic and transport properties studied between 300 K and 2 K. The paramagnetic to antiferromagnetic transition at $T_N \sim 105$ K evidenced on the susceptibility curve coincides with an increase of electron localization in transport measurements. Thermoelectric power and Hall coefficient measurements both exhibit dramatic changes at $T_N$, characteristic of a reconstruction of the bands structure near the Fermi level. No pronounced structural changes are observed at TN in this compound. The magnetic scattering signal on the neutron powder diffraction patterns below $T_N$ is weak, but can be tentatively modelled with an antiferromagnetic ordering of the spins at both ends of a trimer, the spin of the more symmetric Ru site remaining idle. Crystal field and strong spin-orbit coupling at the Ru$^{4+}$ site seem to be the key parameters to understand the magnetic state of Ba$_{4}$Ru$_{3}$O$_{10}$.

[44] 2303.13312

Dynamics of active defects on the anisotropic surface of an ellipsoidal droplet

Cells are fundamental building blocks of living organisms displaying an array of shapes, morphologies, and textures that encode specific functions and physical behaviors. Elucidating the rules of this code remains a challenge. In this work, we create biomimetic structural building blocks by coating ellipsoidal droplets of a smectic liquid crystal with a protein-based active cytoskeletal gel, thus obtaining core-shell structures. By exploiting the patterned texture and anisotropic shape of the smectic core, we were able to mold the complex nematodynamics of the interfacial active material and identify new time-dependent states where topological defects periodically oscillate between rotational and translational regimes. Our nemato-hydrodynamic simulations of active nematics demonstrate that, beyond topology and activity, the dynamics of the active material are profoundly influenced by the local curvature and smectic texture of the droplet, as well as by external hydrodynamic forces. These results illustrate how the incorporation of these constraints into active nematic shells orchestrates remarkable spatio-temporal motifs, offering critical new insights into biological processes and providing compelling prospects for designing bio-inspired micro-machines.

[45] 2303.13328

$T_{3}$Pb$_{2}Ch_{2}$ ($T$=Pd,Pt and $Ch$=S,Se) with transition metal kagome net: Dynamical properties, phonon nodal line, phonon surface states, and chiral phonons

Shandite with Ni$_{3}$Pb$_{2}$S$_{2}$ chemical formula and R$\bar{3}$m symmetry, contains the kagome sublattice formed by the transition metal atoms. Recent experimental results confirmed the possibility of successfully synthesizing Pd$_{3}$Pb$_{2}Ch_{2}$ ($Ch$=S,Se) with the same structure. In this paper, we theoretically investigate the dynamical properties of such compounds. Furthermore, we study the possibility of realizing Pt$_{3}$Pb$_{2}Ch_{2}$ with the shandite structure. We show that the Pd$_{3}$Pb$_{2}${\it Ch}$_{2}$ and Pt$_{3}$Pb$_{2}$S$_{2}$ are stable with R$\bar{3}$m symmetry. In the case of Pt$_{3}$Pb$_{2}$S$_{2}$, there is a soft mode, which is the source of the structural phase transition from R$\bar{3}$m to R$\bar{3}$c symmetry, related to the distortion within the kagome sublattice. We discuss realized phonon nodal lines in the bulk phonon dispersions in upper frequency modes. We show that the shandite structure can host the phonon surface states, with strong dependence by the surface kind. Additionally, chiral phonons with circular motion of the Pb atoms around the equilibrium position are realized.

[46] 2303.13331

A [3]-catenane non-autonomous molecular motor model: geometric phase, no-pumping theorem, and energy transduction

We study a model of synthetic molecular motor - a [3]-catenane consisting of two small macrocycles mechanically interlocked with a bigger one - subjected to a time-dependent driving using stochastic thermodynamics. The model presents nontrivial features due to the two interacting small macrocycles, but is simple enough to be treated analytically in limiting regimes. Among the results obtained, we find a mapping into an equivalent [2]-catenane that reveals the implications of the no-pumping theorem stating that to generate net motion of the small macrocycles, both energies and barriers need to change. In the adiabatic limit (slow driving), we fully characterize the motor's dynamics and show that the net motion of the small macrocycles is expressed as a surface integral in parameter space which corrects previous erroneous results. We also analyze the performance of the motor subjected to a step-wise driving protocols in absence and in presence of an applied load. Optimization strategies for generating large currents and maximizing free-energy transduction are proposed. This simple model provides interesting clues into the working principles of non-autonomous molecular motors and their optimization.

[47] 2303.13358

Tailoring potentials by simulation-aided design of gate layouts for spin qubit applications

Gate-layouts of spin qubit devices are commonly adapted from previous successful devices. As qubit numbers and the device complexity increase, modelling new device layouts and optimizing for yield and performance becomes necessary. Simulation tools from advanced semiconductor industry need to be adapted for smaller structure sizes and electron numbers. Here, we present a general approach for electrostatically modelling new spin qubit device layouts, considering gate voltages, heterostructures, reservoirs and an applied source-drain bias. Exemplified by a specific potential, we study the influence of each parameter. We verify our model by indirectly probing the potential landscape of two design implementations through transport measurements. We use the simulations to identify critical design areas and optimize for robustness with regard to influence and resolution limits of the fabrication process.

[48] 2303.13368

Active Sites of Te-hyperdoped Silicon by Hard X-ray Photoelectron Spectroscopy

Multiple dopant configurations of Te impurities in close vicinity in silicon are investigated using photoelectron spectroscopy, photoelectron diffraction, and Bloch wave calculations. The samples are prepared by ion implantation followed by pulsed laser annealing. The dopant concentration is variable and high above the solubility limit of Te in silicon. The configurations in question are distinguished from isolated Te impurities by a strong chemical core level shift. While Te clusters are found to form only in very small concentrations, multi-Te configurations of type dimer or up to four Te ions surrounding a vacancy are clearly identified. For these configurations a substitutional site location of Te is found to match the data best in all cases. For isolated Te ions this matches the expectations. For multi-Te configurations the results contribute to understanding the exceptional activation of free charge carriers in hyperdoping of chalcogens in silicon.

[49] 2303.13369

Antiferromagnetic insulatronics: spintronics in insulating 3d metal oxides with antiferromagnetic coupling

Antiferromagnetic transition metal oxides are an established and widely studied materials system in the context of spin-based electronics, commonly used as passive elements in exchange bias-based memory devices. Currently, major interest has resurged due to the recent observation of long-distance spin transport, current-induced switching, and THz emission. As a result, insulating transition metal oxides are now considered to be attractive candidates for active elements in novel spintronic devices. Here, we discuss some of the most promising materials systems and highlight recent advances in reading and writing antiferromagnetic ordering. This article aims to provide an overview of the current research and potential future directions in the field of antiferromagnetic insulatronics.

[50] 2303.13389

Wigner-Seitz truncated TDDFT approach for the calculation of exciton binding energies in solids

Time-Dependent Density Functional Theory (TDDFT) has been currently established as a computationally cheaper, yet effective, alternative to the Many-Body Perturbation Theory (MBPT) for calculating the optical properties of solids. Within the Linear Response formalism, the optical absorption spectra are in good agreement with experiments, as well as the direct determination of the exciton binding energies. However, the family of exchange-correlation kernels known as long-range corrected (LRC) kernels that correctly capture excitonic features have difficulties simultaneously producing good-looking spectra and accurate exciton binding energies. More recently, this discrepancy has been partially overcome by a hybrid-TDDFT approach. We show that the key resides in the numerical treatment of the long-range Coulomb singular term. We carefully study the effect of this term, both in the pure-TDDFT and hybrid approach using a Wigner-Seitz truncated kernel. We find that computing this term presents technical difficulties that are hard to overcome in both approaches, and that points to the need for a better description of the electron-hole interaction.

[51] 2303.13392

Size-pore-dependent methanol sequestration from water-methanol mixtures by an embedded graphene slit

The separation of liquid mixture components is relevant in many applications--going from water purification to biofuel production--and a growing concern related to the UN Sustainable Development Goals (SDGs), such as ``Clean water and Sanitation'' and ``Affordable and clean energy''. One promising technique is using graphene slit-pores as filters, or sponges, because the confinement potentially affects the properties of the mixture components in different ways, favoring their separation. However, no systematic study shows how the size of a pore changes the thermodynamics of the surrounding mixture. Here, we focus on water-methanol mixtures and explore, using Molecular Dynamics simulations, the effects of a graphene pore, with size ranging from 6.5 to 13 \AA, for three compositions: pure water, 90\%-10\%, and 75\%-25\% water-methanol. We show that tuning the pore size can change the mixture pressure, density, and composition in bulk due to the size-dependent methanol sequestration within the pore. Our results can help in optimizing the graphene pore size for filtering applications.

[52] 2303.13394

Generation and decay of Higgs mode in a strongly interacting Fermi gas

We investigate the life cycle of the large amplitude Higgs mode in strongly interacting superfluid Fermi gas. Through numerical simulations with time-dependent density-functional theory and the technique of the interaction quench, we verify the previous theoretical predictions on the mode's frequency. Next, we demonstrate that the mode is dynamically unstable against external perturbation and qualitatively examine the emerging state after the mode decays. The post-decay state is characterized by spatial fluctuations of the order parameter and density at scales comparable to the superfluid coherence length scale. We identify similarities with FFLO states, which become more prominent at higher dimensionalities and nonzero spin imbalances.

[53] 2303.13403

Boosting quantum Monte Carlo and alleviating sign problem by Gutzwiller projection

Here we develop a new scheme of projective quantum Monte-Carlo (QMC) simulation combining unbiased zero-temperature (projective) determinant QMC and variational Monte-Carlo based on Gutzwiller projection wave function, dubbed as ``Gutzwiller projection QMC''. The numerical results demonstrate that employment of Gutzwiller projection trial wave function with minimum energy strongly speed up the convergence of computational results, thus tremendously reducing computational time in the simulation. More remarkably, we present an example that sign problem is enormously alleviated in the Gutzwiller projection QMC, especially in the regime where sign problem is severe. Hence, we believe that Gutzwiller projection QMC paves a new route to improving the efficiency, and alleviating sign problem in QMC simulation on interacting fermionic systems.

[54] 2303.13417

SLD Fisher information for kinetic uncertainty relations

We investigate a symmetric logarithmic derivative (SLD) Fisher information for kinetic uncertainty relations (KURs) of open quantum systems described by the GKSL quantum master equation with and without the detailed balance condition. In a quantum kinetic uncertainty relation derived by Vu-Saito [Phys. Rev. Lett. 128, 140602 (2022)], the Fisher information of probability of quantum trajectory with a time-rescaling parameter plays an essential role. This Fisher information is upper bounded by the SLD Fisher information. For a finite time and arbitrary initial state, we give concise coupled first-order ordinary differential equations to calculate the SLD Fisher information given by a double integral concerning time. We also derive a simple lower bound of the Fisher information of quantum trajectory. The SLD Fisher information also appears in the speed limit based on the Mandelstam-Tamm relation [Hasegawa, arXiv:2203.12421v4]. When the jump operators connect eigenstates of the system Hamiltonian, we show that the Bures angle is upper bounded by the square root of the dynamical activity at short times, which contrasts with the classical counterpart.

[55] 2303.13428

Polycrystalinity enhances stress build-up around ice

Damage caused by freezing wet, porous materials is a widespread problem, but is hard to predict or control. Here, we show that polycrystallinity makes a great difference to the stress build-up process that underpins this damage. Unfrozen water in grain-boundary grooves feeds ice growth at temperatures below the freezing temperature, leading to the fast build-up of localized stresses. The process is very variable, which we ascribe to local differences in ice-grain orientation, and to the surprising mobility of many grooves -- which further accelerates stress build-up. Our work will help understand how freezing damage occurs, and in developing accurate models and effective damage-mitigation strategies.

[56] 2303.13432

Ising chain: Thermal conductivity and first-principle validation of Fourier law

The thermal conductivity of a $d=1$ lattice of ferromagnetically coupled planar rotators is studied through molecular dynamics. Two different types of anisotropies (local and in the coupling) are assumed in the inertial XY model. In the limit of extreme anisotropy, both models approach the Ising model and its thermal conductivity $\kappa$, which, at high temperatures, scales like $\kappa\sim T^{-3}$. This behavior reinforces the result obtained in various $d$-dimensional models, namely $\kappa \propto L\, e_{q}^{-B(L^{\gamma}T)^{\eta}}$ where $e_q^z \equiv[1+(1-q)z]^{\frac{1}{1-q}}\;(e_1^z=e^z)$, $L$ being the linear size of the $d$-dimensional macroscopic lattice. The scaling law $\frac{\eta \,\gamma}{q-1}=1$ guarantees the validity of Fourier's law, $\forall d$.

[57] 2303.13433

Machine learning-enabled tomographic imaging of chemical short-range atomic ordering

In solids, chemical short-range order (CSRO) refers to the self-organisation of atoms of certain species occupying specific crystal sites. CSRO is increasingly being envisaged as a lever to tailor the mechanical and functional properties of materials. Yet quantitative relationships between properties and the morphology, number density, and atomic configurations of CSRO domains remain elusive. Herein, we showcase how machine learning-enhanced atom probe tomography (APT) can mine the near-atomically resolved APT data and jointly exploit the technique's high elemental sensitivity to provide a 3D quantitative analysis of CSRO in a CoCrNi medium-entropy alloy. We reveal multiple CSRO configurations, with their formation supported by state-of-the-art Monte-Carlo simulations. Quantitative analysis of these CSROs allows us to establish relationships between processing parameters and physical properties. The unambiguous characterization of CSRO will help refine strategies for designing advanced materials by manipulating atomic-scale architectures.

[58] 2303.13435

"Ultima Ratio": Simulating wide-range X-ray scattering and diffraction

We demonstrate a strategy for simulating wide-range X-ray scattering patterns, which spans the small- and wide scattering angles as well as the scattering angles typically used for Pair Distribution Function (PDF) analysis. Such simulated patterns can be used to test holistic analysis models, and, since the diffraction intensity is on the same scale as the scattering intensity, may offer a novel pathway for determining the degree of crystallinity. The "Ultima Ratio" strategy is demonstrated on a 64-nm Metal Organic Framework (MOF) particle, calculated from Q < 0.01 1/nm up to Q < 150 1/nm, with a resolution of 0.16 Angstrom. The computations exploit a modified 3D Fast Fourier Transform (3D-FFT), whose modifications enable the transformations of matrices at least up to 8000^3 voxels in size. Multiple of these modified 3D-FFTs are combined to improve the low-Q behaviour. The resulting curve is compared to a wide-range scattering pattern measured on a polydisperse MOF powder. While computationally intensive, the approach is expected to be useful for simulating scattering from a wide range of realistic, complex structures, from (poly-)crystalline particles to hierarchical, multicomponent structures such as viruses and catalysts.

[59] 2303.13498

Sign structure in the square-lattice $t$-$t^\prime$-$J$ model and numerical consequences

Understanding the doped Mott insulator is a central challenge in condensed matter physics. This study identifies an intrinsic Berry-phase-like sign structure for the square-lattice $t$-$t'$-$J$ model with the nearest-neighbor ($t$) and next-nearest-neighbor hopping ($t'$), which could help explain the origin of the quasi-long-range superconducting and stripe phases observed through density matrix renormalization group (DMRG) calculation. We first demonstrate that the hole binding underlies both the superconducting and stripe orders, and then show that the hole pairing generically disappears once the phase-string or mutual statistics component of the sign structure is switched off in DMRG calculation. In the latter case, the superexchange interaction no longer plays a crucial role in shaping the charge dynamics, where a Fermi-liquid-like phase with small hole Fermi pockets is found. It is in sharp contrast to the large Fermi surfaces in either the stripe phase found at $t'/t<0$ or the superconducting phase at $t'/t>0$ in the original $t$-$t'$-$J$ model on the 6-leg ladder.

[60] 2303.13507

Quasi-particle propagation across semiconductor-Mott insulator interfaces

As a prototypical example for a heterostructure combining a weakly and a strongly interacting quantum many-body system, we study the interface between a semiconductor and a Mott insulator. Via the hierarchy of correlations, we derive and match the propagating or evanescent quasi-particle solutions on both sides. We find some similarities between the weakly and the strongly interacting case, but also qualitative distinctions. As one consequence, tunnelling through a Mott insulating layer behaves quite different from a semiconducting (or band insulating) layer. For example, we find a strong suppression of tunnelling for energies in the middle between the upper and lower Hubbard band of the Mott insulator.

[61] 2303.13513

Majorana-Magnon Interactions in Topological Shiba Chains

A chain of magnetic impurities deposited on the surface of a superconductor can form a topological Shiba band that supports Majorana zero modes and hold a promise for topological quantum computing. Yet, most experiments scrutinizing these zero modes rely on transport measurements, which only capture local properties. Here we propose to leverage the intrinsic dynamics of the magnetic impurities to access their non-local character. We use linear response theory to determine the dynamics of the uniform magnonic mode in the presence of external $ac$ magnetic fields and the coupling to the Shiba electrons. We demonstrate that this mode, which spreads over the entire chain of atoms, becomes imprinted with the parity of the ground state and, moreover, can discriminate between Majorana and trivial zero modes located at the end of the chain. Our approach offers a non-invasive alternative to the scanning tunnelling microscopy techniques used to probe Majorana zero modes. Conversely, the magnons could facilitate the manipulation of Majorana zero modes in topological Shiba chains.

[62] 2303.12356

Plasma kinetics: Discrete Boltzmann modelling and Richtmyer-Meshkov instability

A discrete Boltzmann model (DBM) for plasma kinetics is proposed. The DBM contains two physical functions. The first is to capture the main features aiming to investigate and the second is to present schemes for checking thermodynamic non-equilibrium (TNE) state and describing TNE effects. For the first function, mathematically, the model is composed of a discrete Boltzmann equation coupled by a magnetic induction equation. Physically, the model is equivalent to a hydrodynamic model plus a coarse-grained model for the most relevant TNE behaviors including the entropy production rate. The first function is verified by recovering hydrodynamic non-equilibrium (HNE) behaviors of a number of typical benchmark problems. Extracting and analyzing the most relevant TNE effects in Orszag-Tang problem are practical applications of the second function. As a further application, the Richtmyer-Meshkov instability with interface inverse and re-shock process is numerically studied. It is found that, in the case without magnetic field, the non-organized momentum flux shows the most pronounced effects near shock front, while the non-organized energy flux shows the most pronounced behaviors near perturbed interface. The influence of magnetic field on TNE effects shows stages: before the interface inverse, the TNE strength is enhanced by reducing the interface inverse speed; while after the interface inverse, the TNE strength is significantly reduced. Both the global averaged TNE strength and entropy production rate contributed by non-organized energy flux can be used as physical criteria to identify whether or not the magnetic field is sufficient to prevent the interface inverse.

[63] 2303.12837

Staggered bosons

A model with a half boson degree of freedom per lattice site in one dimension is developed. The boson is protected from developing a gap by translation symmetry: while the left movers are at zero quasi-momentum, the associated right movers are at the midpoint of the quasi-momentum period. The model has different properties depending on if a periodic lattice has an even or an odd number of sites and similar features are found for open boundary conditions. A special case of the non-linear half boson model where even and odd lattice sites contribute differently to the Hamiltonian gives rise to the Toda chain and a more symmetric generalization of the Toda chain is found. Upon periodic identifications of the half bosons degrees of freedom under a shift, the total Hilbert space has a finite dimension and can be encoded in finitely many qubits per unit length. This way one finds interesting critical spin chains, examples of which include the critical Ising model in a transverse magnetic field and the 3-state Potts model at criticality. Extensions to higher dimensions are considered. Models obtained this way automatically produce dynamical systems of gapless fractons.

[64] 2303.12894

Signatures of a quantum phase transition on a single-mode bosonic model

Equilibrium phase transitions usually emerge from the microscopic behavior of many-body systems and are associated to interesting phenomena such as the generation of long-range order and spontaneous symmetry breaking. They can be defined through the non-analytic behavior of thermodynamic potentials in the thermodynamic limit. This limit is obtained when the number of available configurations of the system approaches infinity, which is conventionally associated to spatially-extended systems formed by an infinite number of degrees of freedom (infinite number of particles or modes). Taking previous ideas to the extreme, we argue that such a limit can be defined even in non-extended systems, providing a specific example in the simplest form of a single-mode bosonic Hamiltonian. In contrast to previous non-extended models, the simplicity of our model allows us to find approximate analytical expressions that can be confronted with precise numerical simulations in all the parameter space, particularly as close to the thermodynamic limit as we want. We are thus able to show that the system undergoes a change displaying all the characteristics of a second-order phase transition as a function of a control parameter. We derive critical exponents and scaling laws revealing the universality class of the model, which coincide with that of more elaborate non-extended models such as the quantum Rabi or Lipkin-Meshkov-Glick models. Analyzing our model, we are also able to offer insights into the features of this type of phase transitions, by showing that the thermodynamic and classical limits coincide. In other words, quantum fluctuations must be tamed in order for the system to undergo a true phase transition.

[65] 2303.12933

Quantum Efficiency of Single Dibenzoterrylene Molecules in para-Dichlorobenzene at Cryogenic Temperatures

We measure the quantum efficiency (QE) of individual dibenzoterrylene (DBT) molecules embedded in para-dichlorobenzene at cryogenic temperatures. To achieve this, we apply two distinct methods based on the maximal photon emission and on the power required to saturate the zero-phonon line. We find that the outcome of the two approaches are in good agreement, reporting a large fraction of molecules with QE values above 50%, with some exceeding 70%. Furthermore, we observe no correlation between the observed lower bound on the QE and the lifetime of the molecule, suggesting that most of the molecules have a QE exceeding the established lower bound. This confirms the suitability of DBT for quantum optics experiments. In light of previous reports of low QE values at ambient conditions, our results hint at the possibility of a strong temperature dependence of the QE.

[66] 2303.12951

The Acousto-Thermoelectric Effect

An effect we have termed the acousto-thermoelectric effect is theorized for temperature gradients driven by acoustic modulation. The effect produces a dynamic and spatially varying voltage. Adiabatic acoustic fluctuations in a solid cause temperature variations and temperature gradients that generate quasi-static thermoelectric effects correlated with the time and spatial scales of the acoustic fluctuations. This phenomenon is distinctive from the static thermoelectric effect in that the hot spots (heat sources) and cold spots (heat sinks) change locations and vary over short time scales. Predictions are made for a semiconductor material, indium antimonide, showing that the effect is measurable under laboratory conditions. The sample is excited by a resonant acoustic mode with frequency 230 kHz, wavelength of 1.37 cm, and pressure amplitude of 2.23 MPa (rms). The predicted peak voltage between positions where maximum and minimum temperatures occur is 2.6 {\mu}V. The voltage fluctuates with the same frequency as acoustic resonance.

[67] 2303.12962

Shadow molecular dynamics and atomic cluster expansions for flexible charge models

A shadow molecular dynamics scheme for flexible charge models is presented, where the shadow Born-Oppenheimer potential is derived from a coarse-grained approximation of range-separated density functional theory. The interatomic potential, including the atomic electronegativities and the charge-independent short-range part of the potential and force terms, are modeled by the linear atomic cluster expansion (ACE), which provides a computationally efficient alternative to many machine learning methods. The shadow molecular dynamics scheme is based on extended Lagrangian (XL) Born-Oppenheimer molecular dynamics (BOMD) [Eur. Phys. J. B 94, 164 (2021)]. XL-BOMD provides a stable dynamics, while avoiding the costly computational overhead associated with solving an all-to-all system of equations, which normally is required to determine the relaxed electronic ground state prior to each force evaluation. To demonstrate the proposed shadow molecular dynamics scheme for flexible charge models using the atomic cluster expansion, we emulate the dynamics generated from self-consistent charge density functional tight-binding (SCC-DFTB) theory using a second-order charge equilibration (QEq) model. The charge-independent potentials and electronegativities of the QEq model are trained for a supercell of uranium oxide (UO2) and a molecular system of liquid water. The combined ACE + XL-QEq dynamics are stable over a wide range of temperatures both for the oxide and the molecular systems, and provide a precise sampling of the Born-Oppenheimer potential energy surfaces. Accurate ground Coulomb energies are produced by the ACE-based electronegativity model during an NVE simulation of UO2, predicted to be within 1 meV of those from SCC-DFTB on average during comparable simulations.

[68] 2303.12967

Initial-state dependent quantum speed limit for dissipative state preparation: Framework and optimization

Dissipation has traditionally been considered a hindrance to quantum information processing, but recent studies have shown that it can be harnessed to generate desired quantum states. To be useful for practical applications, the ability to speed up the dissipative evolution is crucial. In this study, we focus on a Markovian dissipative state preparation scheme where the prepared state is one of the energy eigenstates. We derive an initial-state-dependent quantum speed limit (QSL) that offers a more refined measure of the actual evolution time compared to the commonly used initial-state-independent relaxation time. This allows for a passive optimization of dissipative evolution across different initial states. By minimizing the dissipated heat during the preparation process, conditioned on the minimization of evolution time using the QSL, we find that the preferred initial state has a specific permutation of diagonal elements with respect to an ordered energy eigenbasis of increasing eigenvalues. In this configuration, the population on the prepared state is the largest, and the remaining diagonal elements are sorted in an order resembling that of a passive state in the same ordered energy eigenbasis. We demonstrate the effectiveness of our strategy in a dissipative Rydberg atom system for preparing the Bell state. Our work provides new insights into the optimization of dissipative state preparation processes and could have significant implications for practical quantum technologies.

[69] 2303.13103

Low-temperature growth of piezoceramic films on glass

Integration of thin-film oxide piezoelectrics on glass is imperative for the next generation of transparent electronics to attain sensing and actuating functions. However, their crystallization temperature (above 650 {\deg}C) is incompatible with most commercial glasses. Guided by finite element analysis, we developed a low-temperature flash lamp process for direct growth of piezoelectric lead zirconate titanate films. The process enables crystallization on various types of glasses in a few seconds only. Ferroelectric, dielectric and piezoelectric properties (e$_{33,f}$ of -5 C m$^{-2}$) of these films are comparable to the properties of films processed with standard rapid thermal annealing at 700 {\deg}C. To demonstrate applicability, a surface haptic device was fabricated with a 1 $\unicode{x00B5}$m-thick film. Its ultrasonic surface deflection reached 1.5 $\unicode{x00B5}$m at 60 V, which is sufficient for its use in surface rendering applications. This demonstrated flash lamp annealing process is compatible with large glass sheets and roll-to-roll processing and, therefore, has the potential to significantly expand the applications of piezoelectric devices on glass.

[70] 2303.13270

The effect of Collaborative-Filtering based Recommendation Algorithms on Opinion Polarization

A central role in shaping the experience of users online is played by recommendation algorithms. On the one hand they help retrieving content that best suits users taste, but on the other hand they may give rise to the so called "filter bubble" effect, favoring the rise of polarization. In the present paper we study how a user-user collaborative-filtering algorithm affects the behavior of a group of agents repeatedly exposed to it. By means of analytical and numerical techniques we show how the system stationary state depends on the strength of the similarity and popularity biases, quantifying respectively the weight given to the most similar users and to the best rated items. In particular, we derive a phase diagram of the model, where we observe three distinct phases: disorder, consensus and polarization. In the latter users spontaneously split into different groups, each focused on a single item. We identify, at the boundary between the disorder and polarization phases, a region where recommendations are nontrivially personalized without leading to filter bubbles. Finally, we show that our model can reproduce the behavior of users in the online music platform This analysis paves the way to a systematic analysis of recommendation algorithms by means of statistical physics methods and opens to the possibility of devising less polarizing recommendation algorithms.

[71] 2303.13334

Bridging closed and dissipative discrete time crystals in spin systems with infinite-range interactions

We elucidate the role of dissipation on the emergence of time crystals in a periodically driven spin system with infinite-range interactions. By mapping out the phase diagrams for varying dissipation strengths, ranging from zero to infinitely strong, we demonstrate that the area in the phase diagram, where a time crystal exists, grows with the dissipation strength, but only up to an optimal point, beyond which most of the time crystals become unstable. We find signatures of time crystalline phases in both closed-system and dissipative regimes under the right conditions. However, the dissipative time crystals are shown to be more robust against random noise in the drive, and are only weakly affected by the choice of initial state. We present the finite-size behaviour and the scaling of the lifetime of the time crystals with respect to the number of spins and the interactions strength, within a fully quantum mechanical description.

[72] 2303.13370

Interplay between charge and spin noise in the near-surface theory of decoherence and relaxation of $C_{3v}$ symmetry qutrit spin-1 centers

Decoherence and relaxation of solid-state defect qutrits near a crystal surface, where they are commonly used as quantum sensors, originates from charge and magnetic field noise. A complete theory requires a formalism for decoherence and relaxation that includes all Hamiltonian terms allowed by the defect's point-group symmetry. This formalism, presented here for the $C_{3v}$ symmetry of a spin-1 defect in a diamond, silicon cardide, or similar host, relies on a Lindblad dynamical equation and clarifies the relative contributions of charge and spin noise to relaxation and decoherence, along with their dependence on the defect spin's depth and resonant frequencies. The calculations agree with the experimental measurements of Sangtawesin $\textit{et al.}$, Phys. Rev. X $\textbf{9}$, 031052 (2019) and point to an unexpected importance of charge noise.

[73] 2303.13442

Arrested on heating: controlling the motility of active droplets by temperature

One of the challenges in tailoring the dynamics of active, self-propelling agents lies in arresting and releasing these agents at will. Here, we present an experimental system of active droplets with thermally controllable and reversible states of motion, from unsteady over meandering to persistent to arrested motion. These states depend on the P\'eclet number of the chemical reaction driving the motion, which we can tune by using a temperature sensitive mixture of surfactants as a fuel medium. We quantify the droplet dynamics by analysing flow and chemical fields for the individual states, comparing them to canonical models for autophoretic particles. In the context of these models, we are able to observe in situ the fundamental first transition between the isotropic, immotile base state and self-propelled motility.

[74] 2303.13468

Quantum rotation sensor with real-time readout based on an atom-cavity system

Using an atom-cavity platform, we propose to combine the effective gauge phase of rotated neutral atoms and the superradiant phase transition to build a highly sensitive and fast quantum rotation sensor. The atoms in a well-controlled array of Bose-Einstein condensates are coupled to a single light mode of an optical cavity. The photon emission from the cavity indicates changes in the rotation frequency in real time, which is crucial for inertial navigation. We derive an analytical expression for the phase boundaries and use a semi-classical method to map out the phase diagram numerically, which provides the dependence of the photon emission on the rotation. We further suggest to operate the sensor with a bias rotation, and to enlarge the enclosed area, to enhance the sensitivity of the sensor.

[75] 2303.13476

Calculating the many-body density of states on a digital quantum computer

Quantum statistical mechanics allows us to extract thermodynamic information from a microscopic description of a many-body system. A key step is the calculation of the density of states, from which the partition function and all finite-temperature equilibrium thermodynamic quantities can be calculated. In this work, we devise and implement a quantum algorithm to perform an estimation of the density of states on a digital quantum computer which is inspired by the kernel polynomial method. Classically, the kernel polynomial method allows to sample spectral functions via a Chebyshev polynomial expansion. Our algorithm computes moments of the expansion on quantum hardware using a combination of random state preparation for stochastic trace evaluation and a controlled unitary operator. We use our algorithm to estimate the density of states of a non-integrable Hamiltonian on the Quantinuum H1-1 trapped ion chip for a controlled register of 18 qubits. This not only represents a state-of-the-art calculation of thermal properties of a many-body system on quantum hardware, but also exploits the controlled unitary evolution of a many-qubit register on an unprecedented scale.

[76] 2303.13506

The Quantization Model of Neural Scaling

We propose the $\textit{Quantization Model}$ of neural scaling laws, explaining both the observed power law dropoff of loss with model and data size, and also the sudden emergence of new capabilities with scale. We derive this model from what we call the $\textit{Quantization Hypothesis}$, where learned network capabilities are quantized into discrete chunks ($\textit{quanta}$). We show that when quanta are learned in order of decreasing use frequency, then a power law in use frequencies explains observed power law scaling of loss. We validate this prediction on toy datasets, then study how scaling curves decompose for large language models. Using language model internals, we auto-discover diverse model capabilities (quanta) and find tentative evidence that the distribution over corresponding subproblems in the prediction of natural text is compatible with the power law predicted from the neural scaling exponent as predicted from our theory.