Strongly Correlated Electrons
Mapping the non-equilibrium interacting Anderson Impurity Model to an effective Gaussian theory
Emmanuel Bogacz, Graham Kells and Andrew K. Mitchell
Quantum impurity models with strong electron correlations, such as the paradigmatic Anderson
Impurity Model (AIM), are central to our understanding of a range of physical phenomena including local moment formation, Coulomb blockade and Kondo screening. They describe
magnetic atoms and molecules on surfaces,
quantum dot
circuits, and correlated materials through dynamical mean field theory. The physics of such systems in strongly non-
equilibrium conditions is particularly complex and challenging to capture, whereas Gaussian models of free
fermions can be easily solved. Here we show that the time-evolving dynamics of the AIM after a quench can be described by a completely non-interacting version of the model, at the expense of coupling to additional static auxiliary degrees of freedom. Starting from the full solution of the quenched AIM using ED and DMRG, we study the properties of this mapping using numerical optimization, and uncover intriguing structure in the auxiliary system. The method allows us to understand interacting non-
equilibrium dynamics through the simpler lens of an effective non-interacting system of larger dimension.
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Materials Science
Direct large-area observation of subsurface plastic activity in conditioned copper electrodes
Yinon Ashkenazy, Inna Popov, Victoria M. Bjelland et al. (+2 more)
High-field conditioning is the process by which
radio-frequency structures in particle accelerators and other high-gradient devices reach their operating fields, yet the underlying physical mechanism remains an open question. Models and indirect measurements point to subsurface dislocation dynamics, but large-area structural measurements have been missing. We present electron backscatter diffraction measurements spanning millimeter-scale regions on a copper cathode conditioned at pulsed direct-current fields up to $\sim$80~MV/m in a sloped-anode geometry, which imposes a known gradient of field exposure across a single electrode. Across nine regions of interest spanning this exposure range, the mean intragrain misorientation of field-exposed regions exceeds that of unexposed references by $\sim$75%; the difference is reproduced by three independent misorientation metrics and confirmed by Kolmogorov–Smirnov tests. To our knowledge, this is the first large-area observation of structural differences between conditioned and unconditioned regions of a high-field electrode. The misorientation separates into three tiers (high-field center and edge, low-field periphery, and unexposed reference) that match the spatial profile of the conditioning-state variable $E_S$ predicted by Monte Carlo simulations. These observations point to the evolving subsurface dislocation population as a candidate physical basis of conditioning.
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All authors Yinon Ashkenazy, Inna Popov, Victoria M. Bjelland, William L. Millar, Walter Wuensch
Mesoscale and Nanoscale Physics
Constriction-induced modulation of charging energy in a quantum Hall cavity
Emily Hajigeorgiou, Arup Kumar Paul, Mario Di Luca et al. (+3 more)
Electronic Fabry-Pérot interferometers (FPIs) operating in the fractional
quantum Hall regime are a key platform for probing anyonic braiding statistics, yet interpreting their interference signals is complicated by Coulomb charging effects, which are commonly treated as parasitic, static properties governed by the cavity's geometry and electrostatics. Here, using a gate-defined
quantum Hall cavity tuned to the Coulomb-dominated regime, we demonstrate that the charging energy is in fact strongly and non-monotonically modulated by the
magnetic field, varying by up to 60% over a range of only 100 mT. The effect appears exclusively when the
quantum point contacts (QPCs) forming the cavity are weakly pinched off, i.e., in the strong cavity-to-lead coupling regime. By correlating the charging energy modulation with the QPC magneto-conductance, we attribute this behavior to field-dependent changes in local compressibility and electrostatic screening between the cavity and the leads, driven by the formation of incompressible fractional
quantum Hall states within the constrictions. This result establishes QPC constrictions of
quantum Hall cavities as active electrostatic elements rather than passive boundaries, revealing a dynamic screening mechanism, with direct consequences for the interpretation of interference measurements and the extraction of anyonic statistics.
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All authors Emily Hajigeorgiou, Arup Kumar Paul, Mario Di Luca, Vladimir Umansky, Moty Heiblum, Mitali Banerjee
Superconductivity
Cavity-enhanced superconductivity in the two-dimensional limit of NbSe2
Hanxiang Zhang, Zexin Feng, I-Te Lu et al. (+13 more)
Vacuum electromagnetic fluctuations have emerged as a means of controlling collective
quantum phases without external driving. Cavity-induced modification of superconductivity has been widely predicted. What sets the size of the effect, and which microscopic channel carries it, remain open. Here we couple few-layer NbSe2 to a terahertz complementary split-ring resonator (CSRR) and show that the enhancement grows sharply on approaching the two-dimensional limit. In
bilayer NbSe2 the superconducting transition temperature rises by 10%, from 3.02 K to 3.41 K, on a cavity resonant at 0.92 THz - roughly four times the shift measured in a ten-layer device at the same resonance. Within a single device the shift maps onto the simulated cavity field profile, falling from 0.39 K at the field maximum to zero outside the resonator, with the lower critical field following the same spatial ordering; because all regions are measured on one continuous flake in a single cooldown, sample-to-sample variation is excluded by construction. The frequency dependence is non-monotonic, with suppression below resonance and maximal enhancement near 0.96 THz.
Quantum electrodynamical density functional theory calculations show that cavity coupling redistributes spectral weight in the Eliashberg function, weakening the total electron-
phonon coupling while hardening the logarithmic average
phonon frequency; competition between the two reproduces a sign change in Tc. These results identify dimensionality, local field amplitude and detuning as the control parameters of cavity-enhanced superconductivity, and point to electron-
phonon reweighting as its microscopic origin.
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All authors Hanxiang Zhang, Zexin Feng, I-Te Lu, Zhiwei Li, Songhao Guo, Qiuyu Shang, Thomas Tan, Xiaodan Lyu, Xiangming Shen, Dening Luan, Mingcheng Panmai, Kenji Watanabe, Takashi Taniguchi, Ranjan Singh, Angel Rubio, Weibo Gao
Materials Science
AdsMind: A Physics-Grounded Multi-Agent System for Self-Correcting Discovery of Adsorption Configurations on Heterogeneous Catalyst Surfaces
Zongmin Zhang, Yuyang Lou, Bowen Zhang et al. (+6 more)
Identifying the lowest-energy surface-adsorbate configuration is critical for modeling heterogeneous catalysis, yet exhaustive exploration with ab initio calculations is computationally prohibitive. Machine-learning force fields (MLFFs) accelerate structural relaxation but leave the search over the vast configurational space a major bottleneck, and open-loop large
language model (LLM)
agents lack a physics-grounded feedback mechanism to correct erroneous initial guesses. We propose AdsMind (Adsorption configuration discovery with Machine intelligence and relaxation feedback), a closed-loop multi-
agent framework that enables autonomous error correction through MLFF relaxation feedback. Across four LLM backends, AdsMind achieves consistently high search reliability, with success rates of 100% and 98.8% on the
benchmarks AA20 and OCD-GMAE62. Relative to its single-pass (1-Shot) ablation it reduces cross-backend energy dispersion, and it uses only 4.11 and 4.67 MLFF relaxations per case, respectively – an approximately 14-fold reduction over heuristic enumeration baselines. Density functional theory (DFT) validation using VASP/PBE on six representative AA20 systems shows that the reported open-loop Adsorb-
Agent outputs exhibit qualitative adsorption-energy sign errors for molecular adsorbates, whereas AdsMind preserves the correct sign in all tested cases with closer quantitative agreement. AdsMind thus delivers reliability, self-reflection, and interpretability simultaneously, supporting more DFT-informed autonomous chemistry workflows.
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All authors Zongmin Zhang, Yuyang Lou, Bowen Zhang, Junwu Chen, Ryo Kuroki, Xuan Vu Nguyen, Edvin Fako, Lixue Cheng, Philippe Schwaller
Materials Science
Controllable Growth and Characterization of {\alpha}- and {\beta}-phase MnSe by Chemical Vapor Deposition
Jennifer E. DeMell, Elias Kallon, Michael Pedowitz et al. (+3 more)
Manganese selenide (MnSe) is a promising air-stable two-dimensional
magnetic semiconductor for which theory predicts robust ferromagnetism in monolayers with Curie temperatures approaching 250 K. However, the crystallographic phases and
magnetic properties of thin-film MnSe grown by scalable methods remain poorly understood. Here, we demonstrate the controllable growth of ${\alpha}$- and ${\beta}$-phase MnSe on C-face sapphire using a three-zone chemical vapor deposition process with elemental Se and ${MnCl_{2}}$ precursors in an $Ar/{H_{2}}$ atmosphere. Using Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, we show that our process yields phase-pure ${\alpha}$-MnSe nanorods and ${\beta}$-MnSe triangular flakes with lateral sizes up to 20 ${\mu}m$ and thicknesses of 15-30 nm. Low-temperature photoluminescence of the ${\beta}$-phase films reveals a bandgap of approximately 2.0 eV. Systematic variation of growth parameters shows that precursor vapor pressure, rather than ${H_{2}}$ partial pressure, is the dominant factor controlling lateral flake size. Vibrating-sample magnetometry measurements reveal a $N{\'e}el$ temperature of 53 K in the ${\beta}$-phase films, providing clear evidence of antiferromagnetism in the multilayer regime and establishing MnSe as a tunable platform for 2D spintronic and optoelectronic devices.
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All authors Jennifer E. DeMell, Elias Kallon, Michael Pedowitz, Jimmy C. Kostakidis, Ihteyaz Aqaeed Avash, Kevin M. Daniels
Mesoscale and Nanoscale Physics · Cross-listed from math-ph
Topology of Bloch Bands from Cauchy Data
Didier Felbacq and Emmanuel Rousseau
In a previous work, the
topology of inversion-symmetric one-dimensional periodic media was characterized through the pole-zero pattern of an impedance-like function associated with Bloch waves. This construction reproduces the Berry–Zak invariant and provides a criterion for topological interface states. In the present work, we give a
geometric interpretation of this formalism. We show that poles and zeros arise naturally from the action of inversion
symmetry on the projectivized space of Cauchy data. The corresponding Dirichlet and Neumann states are identified with the two fixed points of the induced $\mathbb Z_2$ action on the Riemann sphere. The key observation is that Bloch eigenvectors are naturally constructed on the universal covering of the Brillouin circle. The
topology of the associated Real eigenline bundle is encoded in the action of the deck transformation group on lifted eigenvectors. This action is described by a monodromy sign $\rho\in\{\pm1\}$, determined by the inversion representations carried by the band at the fixed points of the Brillouin zone. We show that this monodromy defines a natural rank-one local system over the Brillouin circle. The corresponding Real line bundle is classified by its first Stiefel–Whitney class, which coincides with the associated $\mathbb Z_2$ pole-zero invariant. This establishes a
geometric connection between the pole-zero formalism, Berry–Zak phases, Real bundles and local coefficient systems.
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Strongly Correlated Electrons · Cross-listed from math-ph
Bulk-boundary correspondence of (1+1)D symmetric gapped phases
Yizhou Ma, Gen Yue and Tian Lan
We develop an operator-algebraic framework for boundary conditions and bulk-boundary correspondence in one-dimensional gapped phases with categorical
symmetry. Working directly in the thermodynamic limit, we construct half-infinite fusion
spin chains and commuting-projector boundary
Hamiltonians from a
unitary fusion category $\mathcal{C}$, an indecomposable semisimple right $\mathcal{C}$-module category $\mathcal{M}$, a Q-system $Q\in\mathcal{C}$ specifying the bulk phase, and a right $Q$-module $K\in\mathcal{M}_{Q}$, regarded as an object of $\mathcal{M}_{Q}^{\mathrm{op}}$, specifying the boundary. We prove that these
Hamiltonians have unique ground states and that the resulting realization functor $\mathcal{M}_{Q}^{\mathrm{op}}\to\mathrm{BCond}$ is an equivalence, so simple boundary conditions are classified by simple objects of $\mathcal{M}_{Q}$ and general boundary conditions by their finite direct sums. We also give a microscopic formulation of the boundary
symmetry topological field theory using DHR bimodules of the boundary quasi-local
algebra. For a half-infinite fusion
spin chain, the boundary DHR category is monoidally equivalent to $(\mathcal{C}_{\mathcal{M}}^{\vee})^{\mathrm{rev}}$, and the canonical action of the bulk DHR category on it agrees with the categorical action of $Z_1(\mathcal{C}^{\mathrm{rev}})$. Finally, we identify the action of the boundary DHR category on boundary conditions with the categorical action of $(\mathcal{C}_{\mathcal{M}}^{\vee})^{\mathrm{rev}}$ on $\mathcal{M}_{Q}^{\mathrm{op}}$. This yields a one-dimensional bulk-boundary correspondence: the enriched monoidal category describing the bulk is the enriched center of the enriched category describing the boundary.
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Materials Science · Cross-listed from physics.optics
Equivariant Graph Neural Networks Improve Optical Spectra Prediction for Materials Screening
Kasper Helverskov Petersen, François R J Cornet, Martin Ovesen et al. (+3 more)
Scalable prediction of optical spectra is a critical component of high-throughput materials screening for optoelectronic applications such as
solar cells. Existing surrogate models are trained on spectra computed from lower levels of theory or rely on rotation-invariant scalar features, limiting their
geometric expressiveness. We explore the use of equivariant graph neural networks for optical spectra prediction, adapting GotenNet to this task and evaluating it on multiple
datasets including a recently published collection of 10,533 structures with spectra computed at the level of the random phase approximation (RPA). The proposed model outperforms the current state of the art, with the largest gains in the 0-8 eV range and on predicting the static real permittivity, both of particular relevance for thin-film optics.
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All authors Kasper Helverskov Petersen, François R J Cornet, Martin Ovesen, Mikkel Jordahn, Kristian S. Thygesen, Mikkel N. Schmidt
Materials Science
Generalized deformation potential and machine-learning approaches for electron-phonon coupling and thermoelectric transport in semiconductors
Ransell D'Souza and Ivana Savic
The ability to compute electron-
phonon coupling from first principles, using density functional perturbation theory and interpolation techniques, has enabled predictive calculations of electronic transport coefficients in crystalline materials. However, these methods are still computationally expensive. Here we present two inexpensive methods to obtain thermoelectric transport properties of
semiconductors using a small number of electron-
phonon matrix elements calculated from first principles. The first method combines models for coupling of electrons with different
phonon modes whose parameters are obtained from $\sim 10$
matrix elements per electronic band and
phonon mode calculated from first principles. Within this method, we formulate the acoustic deformation potential model for arbitrary
crystal symmetries and band extrema locations. The second method uses machine learning to interpolate $\sim 100$ electron-
phonon matrix elements per electronic band and
phonon mode on dense reciprocal space grids in the parts of the Brillouin zone relevant for transport. We apply both methods to two-dimensional MoS$_2$ and show very good agreement with the state-of-the-art method. The calculated thermoelectric properties also agree well with experiments. We find that the machine-learning method is more accurate and straightforward to implement compared to the model approach.
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Superconductivity
Evidence for Multiband Superconductivity in 2H-NbSeS
K. Yadav, M. Lamba K. Bhattacharya, M. Majumder et al. (+1 more)
The nature of superconductivity in 2H-NbSe2 has generated sustained debate in the recent past. While angle resolved photoemission spectroscopy data have been interpreted as evidence for multiband superconductivity, the data from scanning tunneling microscope experiments relate to strongly anisotropic single-band superconductivity. In the later case, the charge density wave (CDW) order mimics the multigap character. Because the CDW reconstructs the
Fermi surface and modifies the superconducting gap distribution, disentangling intrinsic multiband pairing from CDW-related effects is challenging. To address this issue, we investigate single-crystalline 2H-NbSeS, a mixed-chalcogen analogue of 2H-NbSe2 in which random Se/S substitution suppresses long-range CDW order while preserving the layered
crystal structure P63/mmc. The material becomes superconducting below 6.0 K with moderate
magnetic anisotropy. The upper critical field exhibits a pronounced upward
curvature that cannot be described within a single-band framework but is well captured by a dirty-limit two-band model with a large diffusivity ratio. This indicates strong band-dependent scattering. The in-plane upper critical field exceeds the weak-coupling Pauli limit. Measurements of the lower critical field, superfluid density, and electronic specific heat are consistent with an interpretation of a fully gapped superconducting state with two nodeless gaps of different magnitudes.
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All authors K. Yadav, M. Lamba K. Bhattacharya, M. Majumder, S. Patnaik
Soft Condensed Matter
Pore-shape and its spatial organization control intrinsic permeability of porous media
Wenqiao Jiao, Isaac Pincus, Chiara Recalcati et al. (+2 more)
The structure of a porous material, and in particular its spatial variability, is known to control the intrinsic permeability of the system. We investigate how dead-end pores influence the intrinsic permeability of a porous medium beyond their contribution to total pore volume. Dead-end pores are ubiquitous in porous media, yet they are often treated as hydraulically inactive regions whose influence is assumed to be negligible or absorbed into effective-porosity descriptions. We perform pore-scale flow simulations across different dead-end pore structures, including heterogeneous arrangements, controlled granular assemblies, and a minimal single-channel model to study their impact on the system macroscopic permeability. This strategy allows us to isolate the effects of dead-end pore density, depth, and orientation while preserving the transmitting network. We find that dead-end pores can influence intrinsic permeability: increasing the density of dead-end pores along percolating flow paths enhances permeability, whereas pore depth and junction orientation have negligible effects. The observed permeability enhancement originates from localized hydrodynamic interactions at junctions between transmitting and dead-end pores. Based on these results, we propose an effective formulation that relates the density and spatial organization of dead-end pores relative to the transmitting network to macroscopic permeability. Our findings show that dead-end pore architecture provides an additional
geometric control on intrinsic permeability beyond porosity and pore-size statistics.
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All authors Wenqiao Jiao, Isaac Pincus, Chiara Recalcati, Alberto Guadagnini, Pietro de Anna
Soft Condensed Matter
Chiral Packings in Cylinders are Ultrasensitive to Confinement Deformation
Xuebin Wang, Jiahao Guo and Yao Li
Sphere packings in circular cylinders have attracted substantial research interest, among which the discovery of
chiral helical structures is the most iconic. However, recent experimental results on zebrafish do not match the known packing structures in circular cylinders. To account for the inherent imperfections of biological tubes, we take
elliptic cylinders as the canonical deformation of circular cylinders and investigate the densest packings of hard spheres in them using simulation, theory, and experiments. Starting from the
chiral structures in circular cylinders, we demonstrate that even a weak cross-sectional deformation can trigger entirely new phases, including ones that either eliminate global chirality or significantly complicate the
chiral structures. This reveals the significant effect of cylindrical anisotropy. The new helical phases under anisotropic confinement remain
chiral and develop hierarchical periodic structures, which are difficult to obtain by simulations but are predicted by our newly developed theory for helical phases in
elliptic cylinders. The theory also predicts double oscillated-chain phases without chirality, which perfectly match the simulations. Our work offers fresh insights into understanding packings in anisotropic cylinders, which will help researchers to design new materials and to understand many living systems.
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Superconductivity
Controlling magnetic domain walls with supercurrents
Tim Kokkeler, Risto Ojajärvi, F. Sebastian Bergeret et al. (+1 more)
Establishing a versatile, fast and reliable
magnetic memory technology is a
giant bottleneck for cryogenic computing since present-day room-temperature solutions either cease to work or consume too much power. The long-term goal of superconducting spintronics has been to overcome this bottleneck by generating
magnetic memories with equal-
spin triplet supercurrent driven through them to control their magnetization direction. This path has been hampered by the short
spin relaxation length and strong anisotropy in ferromagnets. Here we show how the supercurrent driven generation of
spin accumulation in a
superconductor/
magnetic insulator bilayer, together with Gilbert damping of magnetization lead to a motion of
magnetic domain walls. This manifests as a local voltage across the wall, which allows its position to be identified. Associated with this voltage and the current, there is Joule power which is dissipated via the Gilbert damping. The power required to maintain domain wall motion is orders of magnitude smaller than in the normal state, where most of the power is wasted in producing the current.
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All authors Tim Kokkeler, Risto Ojajärvi, F. Sebastian Bergeret, Tero T. Heikkilä
Soft Condensed Matter
Enucleated incompressible red blood cells in shear flow: theoretical analysis of shape instabilities
Avraham Moriel, Howard A. Stone and Simon Mendez
Red blood
cells (RBCs) are essential for oxygen transport, and their remarkable ability to undergo significant deformations during flow is a crucial feature for their physiological function. At intermediate shear rates typical of the microcirculation, RBCs can adopt complex, multi-lobed shapes, signifying a dynamic instability. Here we adopt a perturbative theoretical framework of a quasi-spherical RBC under external shear flow to study such shape instabilities. To better capture RBC maturation and enucleation, we first extend the framework to explicitly account for different excess areas between the stress-free and current membrane shapes. We revisit the reduced equations of motion obtained for an ellipsoidally-shaped RBC, and demonstrate the effect of different excess areas and initial orientation on the dynamical trajectories. Then, we introduce additional spatial modes and show that an emerging instability critically depends on the RBC's shear and bending
moduli, the internal to external viscosity ratio, and the excess area, mainly through the RBC's membrane tension. We also study the instability-induced saturation of the membrane tension, and the resulting excess area redistribution at long times. The theoretical framework and the emerging picture of the different instabilities provide insights into the emergence of stomatocyte and trilobe shapes exhibited by RBCs under external flow.
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Statistical Mechanics
Large-deviation tails of critical order-parameter distributions
Jinhong Zhu, Yihao Xu, Abbas Ali Saberi et al. (+1 more)
Large-deviation tails of critical probability distributions provide a sensitive probe of universality beyond standard finite-size scaling. We study these tails for critical percolation and Fortuin–Kasteleyn Ising models on two-dimensional
lattices, three-dimensional
lattices, and complete graphs. We consider two rescaled order parameters: the magnetization-like variable $x_m=|M|/\langle |M|\rangle$, including a signed cluster-mass analogue for percolation, and the largest-cluster variable $x_C=C_1/\langle C_1\rangle$. For $x_m$, we test the expected stretched-exponential large-deviation tail and show that the same form applies to the percolation analogue. For $x_C$, guided by the exact complete-graph result and scaling arguments, we propose universal scaling forms for both tails of the cumulative distribution and test them by extensive Monte Carlo simulations. In the complete-graph FK-Ising model, the left tail is governed by rare configurations with percolation-like scaling rather than by the typical Ising scaling. Our results show that the tails of order-parameter distributions reveal universal features of critical fluctuations that are not captured by averaged observables alone.
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All authors Jinhong Zhu, Yihao Xu, Abbas Ali Saberi, Youjin Deng
Statistical Mechanics · Cross-listed from quant-ph
Nonequilibrium steady states induced by stochastic mid-circuit measurements and resets on a quantum computer
Jakob Murauer, Sabine Tornow and Gabriele Perfetto
Stochastic resetting has emerged as a versatile protocol to drive
quantum many-body systems to non-
equilibrium steady states by interspersing
unitary dynamics with measurements and resets at random times. In spite of this, a
quantum hardware validation of such non-
equilibrium steady states is still missing. Here, we achieve this goal by first formulating a noisy discrete-time theory where
unitary gates alternate with noisy mid-
circuit projective measurements and conditional resets. This noisy conditional resetting theory is then demonstrated on a superconducting
quantum processor for up to $N=7$
qubits. We consider, as a paradigmatic case, the
unitary dynamics of the interacting Floquet transverse-field Ising model. The stationary state of the noisy conditional resetting agrees quantitatively with the experiments, and it shows crossover behavior related to the
equilibrium quantum phase transition of the model. Our results might thus pave the way for the preparation of collective stationary states on noisy
quantum devices and for further developments of
quantum algorithms involving mid-
circuit measurements.
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Superconductivity
Room-Temperature Calcium Intercalation into Graphite Catalyzed by Sodium
Akira Iyo, Shigeyuki Ishida, Hiroshi Eisaki et al. (+2 more)
Calcium (Ca) insertion into graphite (C) has been considered to require elevated temperatures, and its occurrence at room temperature (RT) has been regarded as highly unlikely. Here, we demonstrate that sodium (Na) catalysis enables the formation of superconducting CaC$_6$ even at RT. In mixtures of Ca, Na, and graphite, the gradual development of superconducting diamagnetism and the emergence of X-ray diffraction peaks confirm the formation of CaC$_6$ during storage at RT. The superconducting transition temperature increases with storage time, and the amount of CaC$_6$ scales proportionally to the square root of storage time. These findings provide new insights into the mechanism of superconductivity and Na-catalyzed formation of CaC$_6$, and highlight the potential of this RT intercalation process for practical applications such as electrode materials in Ca-ion batteries.
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All authors Akira Iyo, Shigeyuki Ishida, Hiroshi Eisaki, Hiraku Ogino, Kenji Kawashima
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Quantum circuit decomposition of the tangent-fermion Dirac operator
C.W.J. Beenakker
The Dirac operator on a
lattice cannot be both local and free of
fermion doubling, at least not without breaking fundamental
symmetries. Non-local,
symmetry-preserving discretizations that avoid doubling have a
quantum circuit representation as a linear-combination-of-
unitaries (LCU) in which both the number of terms and their norm (the subnormalization factor) grow with the
lattice size, compromising the efficiency of a
quantum algorithm. We show that the tangent-
fermion discretization escapes this obstruction when the Dirac equation is written as a generalized
eigenvalue problem with a local operator pencil: Each member of the pencil has an exact LCU, with term count that is independent of
lattice size and with subnormalization factor of order unity, on a par with
elliptic operators. This provides an efficient block-encoding primitive for Dirac spectra and Green functions without
fermion doubling.
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Mesoscale and Nanoscale Physics
From Localized Packets to Plane Waves: A Time-Domain Approach to Transport in Mesoscopic Systems
Andrzej Biborski
Quantum transport in mesoscopic systems is conventionally formulated within the Landauer–Büttiker scattering framework, where steady-state currents emerge from the transmission of plane waves representing propagating carriers. While highly successful, this description obscures the explicit time-domain dynamics of individual fermionic excitations and their role in establishing macroscopic transport. Here, we present an exact and self-contained time-domain construction of Landauer transport based on a discrete basis of orthogonal fermionic wave packets. Starting from a second-quantized formulation, we define packet creation operators via a continuous
Fourier transform over a finite transport energy window. By encoding the Pauli exclusion principle, which enforces a fundamental temporal spacing $\Delta t = h/eV$, the current is reproduced in terms of orthogonal wave packets that are used for the rigorous construction of the many-body fermionic state. In this representation, a noiseless current emerges as a deterministic sequence of charge-carrying events, yielding the Landauer conductance $G_0 = e^2/h$ without invoking momentum-space kinematics. We further demonstrate that this construction remains exact for arbitrary energy dispersion. Additionally, the underlying Fock space decomposition into finite disjoint energy sub-bands renders the numerical approach highly scalable for high performance computing platforms. Our results establish a direct and rigorous bridge between the continuous scattering description of
quantum transport and a discrete, time-resolved picture based on fermionic wave packets.
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Quantum Gases
Observation of anyonic thermodynamics and generalized Pauli principle
Fansu Wei, Chi Zhang, Zimeng Ye et al. (+4 more)
Anyons are quasiparticles with
quantum statistics interpolating between those of
bosons and
fermions. Two distinct manifestations of anyonic behaviour have been theoretically established: fractional exchange statistics where particle exchange can produce any phase, and generalized exclusion statistics which extends the Pauli exclusion principle. While anyons exhibiting fractional exchange statistics have been observed in diverse platforms, experimental realizations of generalized exclusion statistics and direct measurements of its thermodynamic signatures have remained elusive. Here, we realize an anyonic thermodynamic ensemble obeying generalized exclusion statistics and detect its anyonic thermodynamics in a one-dimensional strongly interacting
quantum gas. To achieve this, we exploit the bijective mapping between dynamical and statistical interactions in one dimension. By tuning interaction strength and temperature over a wide range, we measure the equation of state and identify clear departures from Bose-Einstein and
Fermi-Dirac statistics. These deviations are quantitatively captured by generalized exclusion statistics, providing direct evidence for the generalized Pauli principle. Independent probes of other thermodynamic quantities including pressure and the Tan contact further validate this framework. Our results establish a versatile platform for engineering anyonic exclusion statistics and open the door to thermodynamic applications of anyons in
quantum technologies.
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All authors Fansu Wei, Chi Zhang, Zimeng Ye, Dengbo Wang, Botao Wang, Xiaoji Zhou, Hepeng Yao
Statistical Mechanics · Cross-listed from quant-ph
Probing chaos and thermalization through out-of-time-ordered correlators in random field spin chains
C Jisha, Shivam Mishra and Ravi Prakash
Out-of-time-ordered correlators (OTOCs) have emerged as a diagnostic of information scrambling and
quantum chaos in many-body systems. We investigate the imprints of chaos in the dynamics of OTOCs in the Heisenberg
spin-$1/2$ chain with random fields. The system is parameterized to exhibit a crossover from integrable to chaotic dynamics. We demonstrate numerically that the approach to saturation of the OTOC can distinguish between integrable and chaotic regimes, with a power-law $(1/t)$ relaxation for integrable systems and a higher-degree power-law decay $(1/t^\alpha; \alpha \ge 1)$ followed by an exponential relaxation for the chaotic regime. We further show that long-range spectral statistics, such as the number variance, are more effective in characterizing
quantum chaos in the regime near saturation of OTOC. We also demonstrate that the relaxation and initial scrambling regimes exhibit distinct and universal features, with the former being sensitive and the latter being robust against different realizations of random-fields. The long-time saturation of OTOC also fluctuates with different realizations, and its exact expression is derived through the Eigenstate Thermalization Hypothesis.
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Strongly Correlated Electrons
Emergence of Resonating Valence-Bond Correlations in Stretched Graphene
Sam Azadi, A. Principi, T. D. Kühne et al. (+1 more)
Electronic correlations in
graphene are generally considered weak due to the large bandwidth of its $\pi$ electrons. Here we show that tensile expansion of the honeycomb
lattice provides a direct route to enhancing correlation effects. Using variational and
diffusion quantum Monte Carlo, we compare a conventional Jastrow-Slater determinant wave function with a resonating-valence-bond (RVB) Jastrow-antisymmetrized geminal product ansatz for a series of stretched
graphene lattices. We find that the energy gain of the RVB state relative to the single-determinant description increases with bond expansion up to a critical strain $\delta_{\mathrm{cr}}$, and decreases beyond it, revealing a nonmonotonic
evolution of electronic correlations. The crossover is found to occur in the range $15\% < \delta_{\mathrm{cr}} < 20\%$, in agreement with mechanical stability limits. This behavior indicates a transition from a weakly correlated Dirac semimetal to a regime with enhanced non-dynamic correlation and short-range singlet pairing. Our results provide direct many-body evidence that
lattice expansion drives
graphene into a regime where RVB-like correlations become energetically favorable, offering a simple route to tuning correlation effects in Dirac materials.
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All authors Sam Azadi, A. Principi, T. D. Kühne, M. S. Bahramy
Materials Science
Projected altermagnetism by symmetry reduction at surfaces and in thin films
Sopheak Sorn, Charanpreet Singh, Lukasz Plucinski et al. (+3 more)
Altermagnets are a newly identified class of
magnetic materials that combine vanishing net magnetization within the unit
cell with
spin-split electronic states. Their theoretical description relies on
symmetry properties of the bulk band structure. Surfaces and thin films, however, inherently break these
symmetries. Here, we investigate the consequences of such
symmetry reduction for the electronic structure of bulk altermagnets near the surface and of thin films. When the surface coincides with a
symmetry plane of the bulk altermagnetic order, the resulting two-dimensional Brillouin zone exhibits
spin-degenerate bands, corresponding to conventional
antiferromagnetic behavior. In all other cases, the
symmetry of the altermagnetic order is reduced, leading to modified
spin splitting. Remarkably, we discover a thin-film geometry of a $g$-wave altermagnet with a particular surface orientation that enables a $d$-wave
spin splitting, which is commonly accompanied by the
spin-splitter effect, suggesting the functionalization of non-$d$-wave altermagnets by surfaces. Our findings demonstrate that
symmetry breaking at surfaces and in thin films fundamentally reshapes altermagnetic
spin textures, providing a tunable platform for controlling
spin-dependent electronic phenomena.
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All authors Sopheak Sorn, Charanpreet Singh, Lukasz Plucinski, Gustav Bihlmayer, Yuriy Mokrousov, Wulf Wulfhekel
Disordered Systems and Neural Networks
Suppression of Extrinsic Anomalous Hall Conductivity in Disordered Parity Anomalous Semimetal
Shi-Hao Bi, Bo Fu and Shun-Qing Shen
We present an analytical investigation of the extrinsic contributions to the anomalous
Hall conductivity in the context of the half-quantized
Hall effect observed in disordered parity anomalous semimetal emerged from semi-
magnetic topological
insulator thin films. The gapless Dirac cone surface state, which embodies the quintessence of the half-quantized
Hall effect, exhibits remarkable robustness against disorder scattering. Two primary extrinsic mechanisms, the side-jump and skew-scattering, are deemed irrelevant and make no contributions. These results establish the parity anomalous semimetal as a disorder-resilient
quantum phase, thereby providing insights into Dirac
fermion physics.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Thermodynamic-Kinetic Decoupling Enables Stable Excitonic Emission in Defect-Tolerant Cu-Based Quantum Dots
Haoran Chen, Zhipeng Xu, Chunjian Li et al. (+7 more)
Colloidal
quantum dots that simultaneously offer room-temperature single-
photon purity and high photoluminescence
quantum yield are sought for
quantum optics, but remain elusive in environmentally benign materials. We introduce a thermodynamic-kinetic decoupling strategy that transforms defect-tolerant CuInS2
quantum dots into bright, narrowband, and photostable single-
photon emitters. Zn2+ alloying strains the
lattice, thermodynamically suppressing native copper vacancies and narrowing the emission from a broad defect band of approximately 300 meV to an excitonic line of approximately 120 meV. Ga3+ incorporation then kinetically pins the cation sublattice against Cu+ migration, preventing defect regeneration during ZnS shell growth. The resulting Cd-free core/shell dots achieve near-unity
quantum yield of approximately 98% while retaining narrow excitonic emission. Critically, room-temperature single-dot spectroscopy reveals homogeneous linewidths as low as approximately 58 meV, strongly suppressed blinking, and high-purity single-
photon emission with g2(0) = 0.06. This stabilized excitonic emission directly reduces reabsorption losses in luminescent
solar concentrators, yielding an external optical efficiency of 12.68%. Our work establishes a generalizable framework to unlock intrinsic excitonic photophysics in ion-mobile, defect-prone
semiconductors, opening a viable path toward high-performance heavy-metal-free emitters for
quantum light sources.
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All authors Haoran Chen, Zhipeng Xu, Chunjian Li, Lei Hou, Dechao Yu, Xiaobin Xie, Yue Liu, Bohua Dong, Lixin Cao, Chenghui Xia
Superconductivity
The electric-field-driven intermediate state of three-dimensional superconductors
Ion Cojocari, Enzo Andreani, Paola Verniere et al. (+5 more)
The coexistence of superconductivity and finite electric fields may enable access to intriguing forms of electronic states. We demonstrate the emergence of an intermediate state in which electric fields penetrate the system while superconductivity still persists. Our measurements reveal a nonclassical regime characterized by the simultaneous presence of supercurrent and dissipative charge transport. This state, realized in a pristine unpatterned three-dimensional system, arises from electric-field-driven order parameter fluctuations. It provides a platform to explore dissipative states of charged
quantum fluids far from
equilibrium.
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All authors Ion Cojocari, Enzo Andreani, Paola Verniere, Florian Pallier, Marc Gabay, Miguel Monteverde, Claire Marrache-Kikuchi, Shamashis Sengupta
Materials Science
Spin-orbit coupling renormalization of the natural optical activity of Pb5Ge3O11 from first-principles
Asier Zabalo, Massimiliano Stengel and Eric Bousquet
We present a first-principles study of the natural optical activity of the gyroelectric Pb$_5$Ge$_3$O$_{11}$
crystal, explicitly accounting for
spin-orbit coupling (SOC) effects. We derive a new analytical expression for the gyration coefficients within the recent framework of long-wavelength density-functional perturbation theory [Phys. Rev. Lett. 131, 086902 (2023)], which significantly improves computational efficiency by reducing the number of required response functions and includes
spin-orbit coupling effects. We use this implementation to investigate the
evolution of Pb$_5$Ge$_3$O$_{11}$'s optical rotation across the ferroelectric double-well, from the paraelectric $P\bar{6}$ phase to the ferroelectric $P3$ phase. Our results demonstrate that, in addition to the substantial renormalization of the double-well energy,
spin-orbit coupling contributions play an equally crucial role in the natural optical activity, largely through purely electronic contributions, while SOC-induced structural relaxation effects are minor.
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Statistical Mechanics
Nonequilibrium nucleation theory for nonconserved fields: from active matter to population dynamics
Michalis Chatzittofi, Noah Ziethen, Cesare Nardini et al. (+1 more)
Classical nucleation theory (CNT) describes the formation of a stable phase from a metastable one. In
equilibrium systems, it quantifies the free-energy competition between a favorable bulk gain and an unfavorable interfacial cost. For systems without detailed balance, the corresponding nonequilibrium nucleation theory (NNT) was so far developed only for cases with a conserved order parameter, such as active fluid-fluid phase separation. Here we construct the NNT for systems with a (single, scalar) nonconserved order parameter. Unlike in the conserved case, the nucleation barrier controlling (noise-driven) droplet growth is profoundly altered by deviations in the interfacial density profile from the one arising during (deterministic) droplet relaxation. The barrier can nonetheless be analysed by carefully defining the reaction coordinate (droplet radius) to project out those deviations. We give explicit NNT predictions for models drawn from population dynamics and active matter, finding excellent agreement with numerical studies.
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All authors Michalis Chatzittofi, Noah Ziethen, Cesare Nardini, Michael E. Cates
Materials Science
Self-Aligned Metallic-Semiconducting Phosphorus Nanoarrays Driven by Facet Engineering
M. Bassotti, M. Tallarida, J. Dai et al. (+10 more)
Two-dimensional (2D) materials often require specific substrate terminations for epitaxial stabilization, yet the search for suitable templates has largely focused on low-index metal surfaces, which may not provide the optimal conditions for the growth of new phases. Here, we show that
crystal-facet engineering on curved Cu surfaces enables the stabilization, within a single preparation step, of two distinct 2D phosphorus phases with different electronic properties. Hexagonal blue phosphorene forms on Cu(111) terraces, whereas a previously unreported skewed-square phosphorus phase is stabilized on Cu(513) facets. By combining complementary microscopy and spectroscopy techniques with theoretical calculations, we determine the structural and electronic properties of this new phase, which displays semiconducting character, in contrast to the metallic behavior of blue phosphorene. The coexistence of these two competing phases gives rise to a metal-to-semiconducting transition of the 2D phosphorus layer over the substrate. Locally, the competition between the two phases gives rise to self-aligned nanoarrays of alternating metallic and semiconducting phosphorus terraces. These results establish
crystal-facet engineering as a practical route for discovering and stabilizing emergent 2D material phases on high-index substrates, while also enabling the engineering of nanostructures with tailored electronic properties through a simple and scalable growth process.
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All authors M. Bassotti, M. Tallarida, J. Dai, S. Salaverria, P. Angulo-Portugal, L. Fernandez, A. El-Sayed, J.E. Ortega, A.A. Makarova, Dimas G. de Oteyza, D.Yu. Usachov, A. Verdini, F. Schiller