Materials Science · Cross-listed from cs.LG
A Unified Generative-Predictive Framework for Deterministic Inverse Design
Reza T. Batley and Sourav Saha
Inverse design of heterogeneous material microstructures is a fundamentally ill-posed and famously computationally expensive problem. This is exacerbated by the high-dimensional design spaces associated with finely resolved images,
multimodal input property streams, and a highly nonlinear forward physics. Whilst modern generative models excel at accurately modeling such complex forward behavior, most of them are not intrinsically structured to support fast, stable deterministic inversion with a physics-informed bias. This work introduces Janus, a unified generative-predictive framework to address this problem. Janus couples a deep encoder-decoder architecture with a predictive KHRONOS head, a separable neural architecture. Topologically speaking, Janus learns a latent
manifold simultaneously isometric for generative inversion and pruned for physical prediction; the joint objective inducing disentanglement of the latent space. Janus is first validated on the MNIST
dataset, demonstrating high-fidelity reconstruction, accurate classification and diverse generative inversion of all ten target classes. It is then applied to the inverse design of heterogeneous microstructures labeled with thermal conductivity. It achieves a forward prediction accuracy $R^2=0.98$ (2% relative error) and sub-5% pixelwise reconstruction error. Inverse solutions satisfy target properties to within $1\%$ relative error. Inverting a sweep through properties reveal smooth traversal of the latent
manifold, and UMAP visualization confirms the emergence of a low-dimensional, disentangled
manifold. By unifying prediction and generation within a single latent space, Janus enables real-time, physics-informed inverse microstructure generation at a lower computational cost typically associated with classical optimization-based approaches.
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Statistical Mechanics · Cross-listed from physics.soc-ph
Topological Dirac cluster synchronization on directed hypergraphs
Yupeng Guo, Ahmed A. A. Zaid, Xueming Liu et al. (+1 more)
Topological higher-order synchronization reveals collective phenomena demonstrating how
topology shapes dynamics, yet providing a general theoretical framework for designing and controlling dynamical states on higher-order networks remains a challenge of the field. Here we propose a dynamical systems framework for topological cluster synchronization on directed hypergraphs that can be used to design synchronization patterns on nodes and hyperedges of directed hypergraphs. By encoding oriented hyperedges into the hypergraph topological Dirac
Hamiltonian, we obtain a spectrum whose isolated eigenstates correspond to distinct topological synchronization cluster states defined jointly on nodes and hyperedges. By selecting any isolated eigenstate, the system can be driven toward the associated dynamical state reflecting a specific partition of the hypergraph without modifying the underlying hypergraph structure. We numerically demonstrate the ability to design different topological cluster synchronization states on directed-hypergraph block models and empirical systems-including higher-order contact networks and the ABIDE functional
brain network. Our results establish a general and interpretable route for controlling collective dynamics in directed higher-order systems.
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All authors Yupeng Guo, Ahmed A. A. Zaid, Xueming Liu, Ginestra Bianconi
Strongly Correlated Electrons
Large Anomalous Hall Effect in Topologically Trivial Double-$Q$ Magnets
Satoru Ohgata and Satoru Hayami
Multi-$Q$ magnets consist of superposed
spin density waves with distinct
magnetic modulation vectors, enabling a wide range of
magnetic orders depending on their combination. Among them, topologically nontrivial
spin textures, such as a
magnetic skyrmion, has been extensively studied owing to the emergence of topological
Hall effects induced by real-space scalar
spin chirality. Contrary to this expectation, we theoretically investigate another route to enhancing the
Hall response under a topologically trivial double-$Q$
spin textures. Despite the cancellation of the scalar
spin chirality, the double-$Q$ magnetism exhibits a pronounced
Hall response with a nonmonotonic dependence on the uniform magnetization, which is in stark contrast to a
ferromagnetic state and a single-$Q$ spiral state. Analyzing the multi-orbital Kondo
lattice model, we show that orbital hybridization induced by the double-$Q$ superstructure enhances the Berry
curvature in $\mathbf{k}$-space, leading to a large anomalous
Hall effect. This mechanism accounts for the observed
giant anomalous
Hall effect in GdRu$_2$Si$_2$ and GdRu$_2$Ge$_2$, thereby highlighting topologically trivial double-$Q$
spin textures as promising spintronic materials.
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Superconductivity
Two-dimensional helical superconductivity and gapless superconducting edge modes in the 1T$^\prime$-WS$_2$/2H-WS$_2$ heterophase bilayer
Xuance Jiang, Jennifer Cano, Yuan Ping et al. (+2 more)
We propose a material platform comprised of transition metal dichalcogenide (TMDC)
heterostructures to realize the two-dimensional (2D) helical superconductivity with an intrinsic gap. By van der Waals stacking a 2D
superconductor (1T$^\prime$-WS$_2$ with inversion
symmetry) on top of a 2D topological
insulator (2H-WS$_2$ with mirror
symmetry), the resulting TMDC
bilayer exhibits Rashba superconductivity. Under an external in-plane
magnetic field, the system can host finite-momentum Cooper pairing, evidenced by the divergence in the particle-particle susceptibility of a $k\cdot p$
Hamiltonian fitted to the ab initio theory band structure. The resulting 2D helical superconducting phase can induce superconductivity in the edge states with its spatially varying order parameter. By varying the strength of the in-plane
magnetic field, we demonstrate that the helical edge state can undergo a phase transition to a one-dimensional gapless phase with narrow
Fermi segments corresponding to zero-energy Bogoliubov quasi-particles. The controllable one-dimensional gapless phase serves as a clear experimental fingerprint of 2D helical superconductivity. The proposed 2D TMDC
heterostructure is promising for intrinsic nonreciprocal superconducting transport and the development of Majorana-based
quantum devices.
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All authors Xuance Jiang, Jennifer Cano, Yuan Ping, Yafis Barlas, Deyu Lu
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Momentum-space non-Hermitian skin effect in an exciton-polariton system
Yow-Ming Hu, Mateusz Król, Daria A. Smirnova et al. (+10 more)
Localization of a macroscopic number of eigenstates on a real-space boundary, known as the non-Hermitian skin effect, is one of the striking topological features emerging from non-Hermiticity. Realizing this effect typically requires periodic (
lattice) systems with asymmetry of intersite coupling, which is not readily available in many physical platforms. Instead, it is meticulously engineered, e.g., in photonics, which results in complex structures requiring precise fabrication steps. Here, we propose a simpler mechanism: introducing an asymmetric, purely imaginary potential in a topologically trivial system induces momentum-space localization akin to the skin effect. We experimentally demonstrate this localization using
exciton polaritons, hybrid light-matter quasi-particles in a simple engineered `round box' trap, pumped by a
laser pump offset from the trap center. The effect disappears if the pump is concentric with the trap. The localization persists and becomes stronger at higher densities of polaritons, when a non-
equilibrium Bose-Einstein condensate is formed and the system becomes nonlinear. Our approach offers a new route to realizing skin effects in continuous, non-periodic systems and exploring the interplay of non-Hermiticity,
topology, and nonlinearity in macroscopic
quantum states.
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All authors Yow-Ming Hu, Mateusz Król, Daria A. Smirnova, Lev A. Smirnov, Bianca Rae Fabricante, Karol Winkler, Martin Kamp, Christian Schneider, Sven Höfling, Timothy C. H. Liew, Andrew G. Truscott, Elena A. Ostrovskaya, Eliezer Estrecho
Mesoscale and Nanoscale Physics
Harnessing Vacuum Fluctuations to Shape Electronic and Photonic Behavior
Qing-Dong Jiang
Vacuum quantum fluctuations are an inescapable and fundamental feature of modern physics. By integrating cavity-enhanced or surface-modified
vacuum quantum fluctuations with low-dimensional materials, a new paradigm-vacuumronics-emerges, enabling unprecedented control over both material properties and photonic responses at the micro- and nanoscale. This synergy opens novel pathways for engineering
quantum light-matter interactions, advancing applications in
quantum photonics, nanoscale optoelectronics, and
quantum material design.
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Quantum Gases · Cross-listed from quant-ph
Engineer coherent oscillatory modes in Markovian open quantum systems
Chun Hei Leung, Pak-Tik Fong, Tianyi Yan et al. (+1 more)
We develop a novel framework to engineer persistent oscillatory modes in Markovian open
quantum systems governed by a time-independent Lindblad master equation. We show that oscillatory modes can be created when the
Hamiltonian and jump operator can be expressed in the same block-diagonal form. A key feature of the framework is that the dissipator of the Lindblad master equation are generally non-zero. We identify the weak and strong conditions, where the onset of the oscillatory modes is dependent and independent of the parameters of the system, respectively. Our method extends beyond the typical decoherence-free subspace approach, in which the dissipator is zero. We demonstrate the applicability of this framework using various models, showing how carefully tailored system-environment interactions can produce sustained coherent oscillations.
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All authors Chun Hei Leung, Pak-Tik Fong, Tianyi Yan, Weibin Li
Statistical Mechanics · Cross-listed from math-ph
Hydrodynamics of Multi-Species Driven Diffusive Systems with Open Boundaries: A Two-Tasep Study
Ali Zahra
In this short note, we review a recently developed method for analysing multi-component driven diffusive systems with open boundaries. The approach generalises the extremal-current principle known for single-component models and is based on solving the Riemann problem for the corresponding hydrodynamic equations. As a case study, we focus on a two-species exclusion process on a
lattice (Two-TASEP), where two types of particles move in opposite directions with two arbitrary rates and exchange positions upon encounter with a third rate. Despite its simplicity, this toy model effectively captures the key features of multi-species driven diffusive systems, including phase separation phenomena. This allows us to illustrate the critical role played by the underlying Riemann invariants in determining the system's macroscopic behavior.
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Statistical Mechanics · Cross-listed from math-ph
The von Neumann algebraic quantum group $\mathrm{SU}_q(1,1)\rtimes \mathbb{Z}_2$ and the DSSYK model
Koen Schouten and Mikhail Isachenkov
The double-scaling limit of the SYK (DSSYK) model is known to possess an underlying $\mathcal{U}_q(\mathfrak{su}(1,1))$
quantum group
symmetry. In this paper, we provide, for the first time, a von Neumann algebraic
quantum group-theoretical description of the degrees of freedom and the dynamics of the DSSYK model. In particular, we construct the operator-algebraic
quantum Gauss decomposition for the von Neumann algebraic
quantum group $\mathrm{SU}_q(1,1)\rtimes \mathbb{Z}_2$, i.e. the $q$-deformation of the normaliser of $\mathrm{SU}(1,1)$ in $\mathrm{SL}(2,\mathbb{C})$, and derive the Casimir action on its
quantum homogeneous spaces. We then show that the dynamics on
quantum AdS$_{2,q}$ space reduces to that of the DSSYK model. Furthermore, we argue that the extension of the global
symmetry group to its normaliser is not only necessary for a consistent definition of the locally compact
quantum group, but that, moreover, the reduction to the DSSYK model works exclusively at the level of the normaliser. The von Neumann algebraic description is shown to give a natural restriction on the allowed quantised coordinates, elegantly ensuring length positivity and non-negative integer chord numbers. Lastly, we make remarks on the correlation function related to the strange series representation, which is argued to interpolate between the AdS and dS regions of our $q$-homogeneous space.
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Strongly Correlated Electrons
Gutzwiller approximation for paramagnetic ionic Hubbard model: Analytic expression for band-Mott insulator transition
Marcin M. Wysokiński
The ionic Hubbard model is a paradigmatic setup for studying the competition between band and Mott insulating behavior. Within the variationally exact in infinite dimensions Gutzwiller approximation, we derive a compact analytic expression for the phase boundary between Mott and band
insulator. While the method reproduces the expected band-Mott
insulator phenomenology, it does not capture the correlated metallic state at finite staggered potential found for example in dynamical mean-field theory. This absence highlights that the metallic phase originates from incoherent Hubbard-band physics rather than
Fermi-
liquid behavior well captured by Gutzwiller approximation. Our formulation establishes a concise variational framework to ionic Hubbard model, with natural extensions to nonequilibrium setups and
spin-exchange dynamics.
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Soft Condensed Matter · Cross-listed from physics.optics
Generation of Perfectly Achromatic Optical Vortices Using a Compensated Tandem Twisted Nematic Cell
Dmytro O. Plutenko and Mikhail V. Vasnetsov
The generation of white optical
vortices is currently constrained by intrinsic trade-offs between spectral bandwidth, conversion efficiency, and temporal pulse integrity in conventional diffractive and
geometric-phase approaches. In this work, we theoretically investigate a compensated tandem crossed twisted nematic (TN)
liquid crystal architecture that overcomes these fundamental limitations. By developing a rigorous Jones
matrix model and defining specific figures of merit for chromatic fidelity, we analyze the impact of manufacturing imperfections and non-adiabatic waveguiding (deviations from the Mauguin regime) on the device performance. We propose and evaluate three distinct compensation strategies, ranging from optimized passive designs for specific manufacturing tolerances to a robust active compensation scheme utilizing a tunable retarder. Our analysis demonstrates that the active approach effectively nullifies parasitic amplitude modulation, enabling the generation of perfectly achromatic
vortices with high phase purity across an arbitrary bandwidth. This establishes the compensated tandem TN
cell as a superior and versatile platform for high-fidelity white-light singular optics.
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Mesoscale and Nanoscale Physics
Direct Epitaxial Growth and Deterministic Device Integration of high-quality Telecom O-Band InGaAs Quantum Dots on Silicon Substrate
Imad Limame, Peter Ludewig, Aris Koulas-Simos et al. (+9 more)
Semiconductor quantum dots (QDs) are key building blocks for photonic
quantum technologies, enabling practical sources of non-classical light. A central challenge for scalable integration is the direct epitaxial growth of high-quality emitters on industry-compatible silicon platforms. Furthermore, for long-distance fiber-based
quantum communication, emission in the telecom O- or C-band is essential. Here, we demonstrate the direct growth of high-quality InGaAs/GaAs QDs emitting in the telecom O-band using a strain-reducing layer approach on silicon. Deterministic integration of individual QDs into circular Bragg grating resonators is achieved via in-situ electron-beam lithography. The resulting devices exhibit strong out-coupling enhancement, with
photon extraction efficiencies up to $(40 \pm 2)\%$, in excellent agreement with numerical simulations. These results highlight the high material quality of both the epitaxial platform and the photonic nanostructure, as well as the precise lateral positioning of the emitter within 20~nm of the resonator center. At cryogenic temperature (4~K) and low excitation power ($0.027\times P_\text{sat}$), the devices show excellent single-
photon purity, exceeding 99%. Operation at elevated temperatures of 40~K and 77~K, compatible with compact Stirling cryo-coolers and
liquid-nitrogen cooling, reveals robust performance, with single-
photon purity maintained at $(88.4 \pm 0.6)\%$ at 77~K. These results demonstrate a practical and scalable route toward silicon-based
quantum light sources and provide a promising path for cost-effective fabrication and seamless integration of
quantum photonics with classical electronics, representing an important step toward large-scale, chip-based
quantum information systems.
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All authors Imad Limame, Peter Ludewig, Aris Koulas-Simos, Chirag C. Palekar, Jan Donges, Ching-Wen Shih, Kartik Gaur, Sarthak Tripathi, Sven Rodt, Wolfgang Stolz, Kerstin Volz, Stephan Reitzenstein
Strongly Correlated Electrons
The magnetic structure of polar $G$-type charge and orbital ordered Hg-quadruple manganite perovskites
Ben R. M. Tragheim, Fabio Orlandi, En-Pei Liu et al. (+2 more)
The
magnetic structure of the novel Hg$_{0.7}$Na$_{0.3}$Mn$_3$Mn$_4$O$_{12}$, a quadruple manganite perovskite that exhibits a unique $G$-type charge and orbital ordered state distinct to other $A^{2+}$Mn$_3$Mn$_4$O$_{12}$ equivalents ($A$ $=$ Ca, Sr, Cd, Pb), has been solved using powder
neutron diffraction and
symmetry-motivated analysis. A $G$-type-like
antiferromagnetic (AFM) ordering of Mn on the $A'$ sites and a `up–up–down–down' AFM moment configuration of Mn
spins on the $B$ sites is found to occur. The mechanism for the onset and stabilization of $B$ site `up–up–down–down' AFM order is explored in terms of coupling between structural and
magnetic distortions. The results presented here provide evidence of the exotic charge, orbital, electronic and
magnetic orderings that quadruple manganite perovskites demonstrate, and further highlighting the distinct chemistry that Hg$^{2+}$ plays in stabilizing novel states compared to other divalent $A$-site cation equivalents.
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All authors Ben R. M. Tragheim, Fabio Orlandi, En-Pei Liu, Wei-Tin Chen, Mark S. Senn
Materials Science
Spin-phonon interactions revisited: Far-infrared emission, Raman scattering, and high-resolution x-ray diffraction at the Néel temperature in LaFeO3
Néstor E. Massa, Javier Gainza, Aurélien Canizares et al. (+2 more)
We report on the structural
evolution,
spin phonon interactions, and magnetoelastic effects in bulk LaFeO3 perovskite across its
antiferromagnetic transition. We found that while the
lattice constants exhibit slight deviations at the Neel temperature(TN), due to
spin phonon interactions, individual interatomic bonds display distinct behavior. The octahedral B site basal plane, involving oxygen ion pairs that mediate superexchange interactions, displays bond contraction (or elongation) assimilable to the observed in x ray diffraction for negative thermal expansion. These bond deviations reach a singular point near TN, where a sharp change in bond length is observed. A similar abrupt change is also detected in the nearest neighbor La O2 basal plane distances, which we interpret as arising from ion size differences within the 3d 2p hybridized states associated with the superexchange mechanism. High-resolution SXRD measurements of the c-axis Fe3+ O1 and La3+ O1 apex distances reveal a distinct inflection at the Neel temperature. This behavior supports the role of
lattice distortions and
crystal field modifications in the emergence of non collinear weak ferromagnetism in RFeO3 (R = rare earth) perovskites. Furthermore, our SXRD patterns show an increase in diffraction line intensities peaking at TN, suggesting a straightforward indicator for
spin-
phonon interactions that also resolves into
lattice metastability deduced by nonlinear thermal expansion in the paramagnetic phase. Preliminary results across the full RFeO3 (R = rare earth) series indicate a shared structural framework among all members, potentially offering insights into previously inconclusive structural interpretations in
oxides with common octahedral sublattices.
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All authors Néstor E. Massa, Javier Gainza, Aurélien Canizares, Leire del Campo, José Antonio Alonso
Statistical Mechanics · Cross-listed from cs.LG
Detailed balance in large language model-driven agents
Zhuo-Yang Song, Qing-Hong Cao, Ming-xing Luo et al. (+1 more)
Large
language model (LLM)-driven
agents are emerging as a powerful new paradigm for solving complex problems. Despite the empirical success of these practices, a theoretical framework to understand and unify their macroscopic dynamics remains lacking. This paper proposes a method based on the least action principle to estimate the underlying generative directionality of LLMs embedded within
agents. By experimentally measuring the transition probabilities between LLM-generated states, we report evidence consistent with a tendency toward detailed balance in LLM-generated transitions, indicating that LLM generation may not be achieved by generally learning rule sets and strategies, but rather by implicitly learning a class of underlying potential functions that may transcend different LLM architectures and
prompt templates. To our knowledge, this provides an effective macroscopic description of LLM generative dynamics that does not depend on specific model details. This work is an attempt to establish a macroscopic dynamics theory of complex AI systems, aiming to elevate the study of AI
agents from a collection of engineering practices to a science built on effective measurements that are predictable and quantifiable.
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All authors Zhuo-Yang Song, Qing-Hong Cao, Ming-xing Luo, Hua Xing Zhu
Soft Condensed Matter · Cross-listed from physics.bio-ph
Corkscrew motion of Trypanosoma brucei is driven by helical beating of the flagellum and facilitated by its bent shape
Sizhe Cheng, Devadyouti Das, Mykhaylo Barchuk et al. (+4 more)
In the pathogenic parasite Trypanosoma brucei, a laterally attached flagellum drives rapid deformation of the complex
cell body, producing puzzling dynamics. High-speed defocusing imaging reveals that surface points trace flower-like patterns in transverse planes. The petals arise from clockwise flagellar beating, which generates a right-handed helical wave propagating from the anterior tip along the body, advancing the
cell like a twisted corkscrew. The central lobes result from slower counterclockwise body rotation required to balance the active torque. The bent
cell shape underneath the flagellum superimposes these two
chiral motions at different radial distances, producing the observed patterns. Three-dimensional hydrodynamic simulations using the method of regularized Stokeslets reproduce these dynamics and show that bent
cell shape enhances swimming, suggesting an adaptive advantage of T. brucei's morphology.
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All authors Sizhe Cheng, Devadyouti Das, Mykhaylo Barchuk, Raveen Armstrong, Michele M. Klingbeil, Becca Thomases, Shuang Zhou
Superconductivity
Switchable half-quantum flux states in a ring of the kagome superconductor CsV$_3$Sb$_5$
Shuo Wang, Ilaria Maccari, Xilin Feng et al. (+14 more)
Magnetic flux quantization in units of $\Phi_0 = h/2e$ is a defining feature of superconductivity, rooted in the charge-2e nature of Cooper pairs. In a ring geometry, the flux quantization leads to oscillations in the critical temperature with
magnetic flux, known as the Little-Parks effect. While the maximal critical temperature is conventionally at zero flux, departures from this rule, for instance shifts by a half-
quantum flux $\Phi_0/2$, clearly signal unconventional superconducting states and require sign-changing order parameters. Historically, such $\pi$-phase shifts in Little-Parks oscillations have been found in tricrystals or engineered ring structures that intentionally incorporate a $\pi$-phase shift. Here we report the discovery of switchable half-
quantum flux states in rings made from single
crystals of the kagome
superconductor CsV$_3$Sb$_5$. We observe Little-Parks oscillations with a $\pi$-phase shift at zero bias current, which can be reversibly tuned to conventional Little-Parks oscillations upon applying a bias current. Between the $\pi$-phase and 0-phase regimes, $h/4e$ periodic oscillations appear. Our observations suggest unconventional pairing, potentially in the form of a multicomponent order parameter in the kagome
superconductor CsV$_3$Sb$_5$, and reveal an electrically tunable landscape of competing superconducting condensates and fractional flux states.
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All authors Shuo Wang, Ilaria Maccari, Xilin Feng, Ze-Nan Wu, Jia-Peng Peng, Kam Tuen Law, Y. X. Zhao, Andras Szabo, Andreas Schnyder, Ning Kang, Xiao-Song Wu, Jingchao Liu, Xuewen Fu, Mark H. Fischer, Manfred Sigrist, Dapeng Yu, Ben-Chuan Lin
Statistical Mechanics
Universal relaxation speedup in open quantum systems through transient conditional and unconditional resetting
Parvinder Solanki, Igor Lesanovsky and Gabriele Perfetto
Speeding up the relaxation dynamics of many-body
quantum systems is important in a variety of contexts, including
quantum computation and state preparation. We demonstrate that such acceleration can be universally achieved via transient
stochastic resetting. This means that during an initial time interval of finite duration, the dynamics is interrupted by resets that take the system to a designated state at randomly selected times. We illustrate this idea for few-body open systems and also for a challenging many-body case, where a first-order phase transition leads to a divergence of relaxation time. In all scenarios, a significant and sometimes even exponential acceleration in reaching the stationary state is observed, similar to the so-called Mpemba effect. The universal nature of this speedup lies in the fact that the design of the resetting protocol only requires knowledge of a few macroscopic properties of the target state, such as the order parameter of the phase transition, while it does not necessitate any fine-tuned manipulation of the initial state.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Deep Thermalization and Measurements of Quantum Resources
Naga Dileep Varikuti, Soumik Bandyopadhyay and Philipp Hauke
Quantum resource theories provide a unified framework for characterizing useful
quantum phenomena subject to physical constraints, but are notoriously hard to assess in experimental systems. In this letter, we introduce a unified protocol for quantifying the resource-generating power of arbitrary
quantum evolutions applicable to multiple resource theories. It is based on deep thermalization, which has recently gained
attention for its role in the emergence of
quantum state designs from partial projective measurements. Central to our approach is the use of projected ensembles, recently employed to probe deep thermalization, together with new twirling identities that allow us to directly infer the resource-generating powers of the underlying dynamics. These identities further reveal how resources build up and thermalize in generic
quantum circuits. Finally, we show that
quantum resources themselves undergo deep thermalization at the subsystem level, offering a complementary and another experimentally accessible route to infer the resource-generating powers. Our work connects deep thermalization to resource quantification, offering a new perspective on the essential role of various resources in generating state designs and on efficient estimation of
quantum resources in experiment.
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Superconductivity
Mechanism for Nodal Topological Superconductivity on PtBi$_2$ Surface
Kristian Mæland, Giorgio Sangiovanni and Björn Trauzettel
Experiments show that the Weyl semimetal PtBi$_2$ hosts unconventional superconductivity in its topological surface states. Hence, the material is a candidate for intrinsic topological superconductivity. Measurements indicate nodal gaps in the center of the
Fermi arcs. We derive that anisotropic electron-
phonon coupling on Weyl semimetal surfaces, combined with statically screened Coulomb repulsion, is a microscopic mechanism for this nodal pairing. The dominant solution of the linearized gap equation shows nodal gaps when the surface state bandwidth is comparable to the maximum
phonon energy, as is the case in PtBi$_2$. We further predict that if the screening of Coulomb interaction on the surface is enhanced by Coulomb engineering, the superconducting gap becomes nodeless, and the critical temperature increases.
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Superconductivity
Low-temperature dissipative conductivity of superconductors with paramagnetic impurities
Shiang-Bin Chiu, Anton Andreev, Alexander Burin et al. (+1 more)
In s-wave
superconductors with a small concentration of
magnetic impurities, the only electronic excitations that remain available at low temperatures are the excitations of the system of localized
spins. We discuss a new mechanism of interaction between electromagnetic waves and the localized
spins in disordered
superconductors. A supercurrent induces randomly distributed
spin density of the itinerant electrons, which couples to the
impurity spins by exchange interaction. Acceleration of the Cooper pair condensate by the external AC electric field of frequency $\omega$ creates a strong, time-dependent exchange field acting on the localized
spins, which is inversely proportional to $\omega$. As a result, the low-frequency dissipative part of the conductivity saturates to a nonzero value. We use the fluctuation-dissipation
theorem to evaluate the spectrum of
equilibrium current fluctuations associated with the fluctuation in the
spin subsystem. We also predict that in the presence of a DC
magnetic field parallel to the superconducting film, the system of
spins exhibits a large positive magnetoconductance.
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All authors Shiang-Bin Chiu, Anton Andreev, Alexander Burin, Boris Z. Spivak
Mesoscale and Nanoscale Physics
Fluctuation-induced giant magnetoresistance in charge-neutral graphene
A. Levchenko, E. Kirkinis and A. V. Andreev
The Johnson-Nyquist noise associated with the intrinsic conductivity of the electron
liquid, induces fluctuations of the electron density in charge-neutral
graphene devices. In the presence of external electric and
magnetic fields, the fluctuations of charge density and electric current induce a fluctuating hydrodynamic flow. We show that the resulting advection of charge produces a fluctuation contribution to the macroscopic conductivity of the system, $\sigma_{\mathrm{fl}}$, and develop a quantitative theory of $\sigma_{\mathrm{fl}}$. At zero
magnetic field, $\sigma_{\mathrm{fl}}$ diverges logarithmically with the system size and becomes rapidly suppressed at relatively small fields. This results in
giant magnetoresistance of the system.
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Strongly Correlated Electrons
Hall viscosity of the Laughlin state on noisy quantum computers
Ammar Kirmani, Andrew A. Allocca, Jian-Xin Zhu et al. (+3 more)
Hall viscosity is a quantized nondissipative stress response of a fractional
quantum Hall (FQH) fluid to adiabatic
geometric deformations. Despite strong theoretical interest, its experimental observation in the FQH state has remained elusive, making it a demanding target for realization on current IBM
quantum hardware. In this letter, we employ a quasi-one-dimensional model of an FQH state coupled to a background metric to probe the
geometric response under a metric quench. We design and implement a
quantum-
circuit protocol that realizes a
Hilbert-space-truncated version of the model and extracts the
Hall viscosity from the
geometric response encoded in the wave-function dynamics on the IBM
quantum hardware. While the truncation prevents us from accessing the fully quantized value of
Hall viscosity, the hardware data closely track analytical and numerical predictions within this regime.
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All authors Ammar Kirmani, Andrew A. Allocca, Jian-Xin Zhu, Armin Rahmani, Sriram Ganeshan, Pouyan Ghaemi
Strongly Correlated Electrons
Planckian Bounds via Spectral Moments of Optical Conductivity
Debanjan Chowdhury
The observation of Planckian scattering, often inferred from Drude fits in strongly correlated metals, raises the question of how to extract an intrinsic timescale from measurable quantities in a model-independent way. We address this by focusing on a ratio (${\cal{B}}$) of spectral moments of the dissipative part of the optical conductivity and prove a rigorous upper bound on ${\cal{B}}$ in terms of the Planckian rate. The bound emerges from the analytic structure of thermally weighted response functions of the current operator. Crucially, the bounded quantity is directly accessible via optical spectroscopy and computable from imaginary-time correlators in
quantum Monte Carlo simulations, without any need for analytic continuation. We evaluate ${\cal{B}}$ for simplified examples of both Drude and non-Drude forms of the optical conductivity with a single scattering rate in various asymptotic regimes, and find that ${\cal{B}}$ lies far below the saturation value. These findings demonstrate that Planckian bounds can arise from fundamental constraints on
equilibrium dynamics, pointing toward a possibly universal structure governing transport in correlated
quantum matter.
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Statistical Mechanics
Statistical Field Theory of Interacting Nambu Dynamics
Tamiaki Yoneya
We develop a statistical field theory for classical Nambu dynamics by employing partially the method of
quantum field theory. One of unsolved problems in Nambu dynamics has been to extend it to interacting systems without violating a generalized canonical structure associated with the presence of multiple
Hamiltonians, which together govern the dynamics of time
evolution on an equal footing. In the present paper, we propose to include interactions from the standpoint of classical statistical dynamics by formulating it as a field theory on Nambu's generalized phase space in an operator formalism. We first construct a general framework for such a field theory and its probabilistic interpretation. Then, on the basis of this new framework, we give a simple model of self-interaction in a many-body Nambu system treated as a closed dynamical system satisfying the H-
theorem. It is shown that a generalized micro-canonical ensemble and a generalized canonical ensemble characterized by many temperatures are reached dynamically as
equilibrium states, starting with certain classes of initial non-
equilibrium states via continuous Markov processes. Compared with the usual classical statistical mechanics on the basis of standard
Hamiltonian dynamics, some important new features associated with Nambu dynamics will emerge, with respect to the
symmetries underlying dynamics of the non-
equilibrium as well as the
equilibrium states and also to some conceptual properties, such as a formulation of a generalized KMS-like condition characterizing the generalized canonical
equilibrium states and a `relative' nature of the temperatures.
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Mesoscale and Nanoscale Physics
Characterizing second-order topological insulators via entanglement topological invariant in two-dimensional systems
Yu-Long Zhang, Cheng-Ming Miao, Qing-Feng Sun et al. (+2 more)
Higher-order topological
insulators have attracted significant interest in recent years. However, identifying a universal topological invariant capable of characterizing higher-order
topology remains challenging. Here, we propose a
entanglement topological invariant designed to characterize secondorder topological systems. This
entanglement topological invariant captures the
entanglement of topological corner states under open boundary conditions by employing a bipartite
entanglement entropy method. In several representative models, the
entanglement topological invariant assumes a nonzero value exclusively in the presence of second-order
topology, with its magnitude exactly matching the number of topologically protected corner states. Consequently, the proposed
entanglement topological invariant not only provides a clear criterion for detecting higher-order
topology, but also offers a quantitative measure for the related corner states. Our study establishes a universal and precise method for characterizing higher-order topological phases, opening avenues for their fundamental understanding and future investigations.
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All authors Yu-Long Zhang, Cheng-Ming Miao, Qing-Feng Sun, Jian-Jun Liu, Ying-Tao Zhang
Quantum Gases
Connecting single-layer $t$-$J$ to Kondo lattice models: Exploration with cold atoms
Hannah Lange, Eugene Demler, Jan von Delft et al. (+2 more)
The Kondo effect, a hallmark of many-body physics, emerges from the
antiferromagnetic coupling between localized
spins and conduction
fermions, leading to a correlated many-body singlet state. Here we propose to use the mixed-dimensional (mixD)
bilayer Hubbard geometry as a platform to study Kondo
lattice physics with current ultracold atom experiments. At experimentally feasible temperatures, we predict that key features of the Kondo effect can be observed, including formation of the Kondo cloud around a single
impurity and the competition of singlet formation with Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions for multiple
impurities, summarized in the Doniach phase diagram. Moreover, we show that the mixD platform provides a natural bridge between the Doniach phase diagram of the Kondo
lattice model, relevant to heavy-
fermion materials, and the phase diagram of cuprate
superconductors as described by a single-layer Zhang-Rice type $t$-$J$ model: It is possible to continuously tune between the two regimes by changing the interlayer Kondo coupling. Our findings demonstrate that the direct connection between high-temperature superconductivity and heavy-
fermion physics can be experimentally studied using currently available
quantum simulation platforms.
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All authors Hannah Lange, Eugene Demler, Jan von Delft, Annabelle Bohrdt, Fabian Grusdt