Statistical Mechanics
Ergodic properties of functionals of Gaussian processes
Vicenç Méndez, Carlos Hervás and Rosa Flaquer-Galmés
We derive the first two moments of generic positive
stochastic functionals in terms of the one- and two-time probability density functions of the underlying random walk, and we prove ergodicity of observables in stationary random walks. These general results are applied to the half-occupation time and the occupation time in an interval of a Gaussian random walk, for which we obtain exact analytic expressions for the first two moments. We then extend the analysis to scaled Brownian motion and fractional Brownian motion, computing the ergodicity breaking parameter and establishing a simple scaling form for the probability densities of occupation times. Within the framework of infinite ergodic theory, we further identify universal properties of positive observables. All analytical predictions are fully confirmed by numerical simulations.
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Strongly Correlated Electrons
Extension of the iterated perturbation theory at arbitrary fillings to nonequilibrium steady states
Tommaso Maria Mazzocchi and Enrico Arrigoni
We extend the Kajueter-Kotliar [Phys. Rev. Lett. 77, 131 (1996)] iterated perturbation theory (KK-IPT) away from half filling to nonequilibrium steady states. We
benchmark the resulting nonequilibrium KK-IPT approach against the auxiliary master equation approach (AMEA), whose accuracy is controlled in and out of
equilibrium. As expected, in
equilibrium, KK-IPT reproduces the AMEA results for different fillings with high accuracy at the level of both spectral properties and electron densities. Out of
equilibrium, we study
quantum transport across a correlated
impurity and compute the differential conductance and spectral functions. We find very good agreement between nonequilibrium KK-IPT and AMEA in the parameter regime where the latter is reliable, in particular at moderate temperatures and biases. Although a controlled
benchmark is not available in the low-temperature, low-bias regime, where AMEA becomes less reliable, we show that this nonequilibrium KK-IPT
impurity solver satisfies the exact spectral sum rules for the first and second moments to high accuracy throughout the entire parameter range studied. These results support nonequilibrium KK-IPT as an approximate description of nonequilibrium steady states away from half filling. At the same time, comparing against AMEA the double occupancy obtained from the nonequilibrium Galitskii-Migdal expression for the interaction energy shows that the deviation from AMEA remains small near half filling for moderate and large values of the bias, but grows markedly away from half filling, delineating the regime in which the method can be trusted quantitatively rather than merely qualitatively.
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Strongly Correlated Electrons
Yifan Wang, Chenchao Xu, Yi Liu et al. (+18 more)
Kagome metals are prone to charge-density wave (CDW),
magnetic, and superconducting phases, with their flat electronic band conducive for correlated physics. In contrast to the weakly correlated $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) kagome metals with a $2\times2$ CDW, CsCr$_3$Sb$_5$ is a correlated metal with a flat band close to the
Fermi level, and exhibits a $4\times1$ CDW intertwined with
magnetic order. Under pressure, the intertwined orders are suppressed and give way to a dome of superconductivity that emerges from a non-
Fermi liquid normal state. Here, we solve the
crystal structure of the $4\times 1$ CDW state in CsCr$_3$Sb$_5$, and show it consists of Cr dimers separated by Cr chains. First-principles calculations show the dominant exchange interaction is
antiferromagnetic within the dimers, while the intra-chain and dimer-chain couplings are much weaker. The CDW transition of CsCr$_3$Sb$_5$ is found to be more strongly first-order than those in $A$V$_3$Sb$_5$, without significant soft
phonons or diffuse scattering above the CDW transition temperature. These findings suggest that fluctuating
antiferromagnetic dimers may play a major role in the electron pairing of superconducting CsCr$_3$Sb$_5$.
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All authors Yifan Wang, Chenchao Xu, Yi Liu, Jinke Bao, Jiayu Guo, Xiaoran Yang, Yuiga Nakamura, Hiroshi Fukui, Taishun Manjo, Daisuke Ishikawa, Alfred Q. R. Baron, Saizheng Cao, Rui Li, Zilong Li, Yanan Zhang, Ruihan Chen, Ming Shi, Huiqiu Yuan, Guanghan Cao, Chao Cao, Yu Song
Strongly Correlated Electrons
Ultrafast Current Switching from Quantum Geometry in Semimetals
Youngjae Kim, Sejoong Kim and Jun-Won Rhim
Technological progress towards next-generation electronics critically relies on achieving faster switching with reduced energy consumption. Because device operation speeds are fundamentally constrained by the intrinsic properties of constituent materials, identifying systems with inherently superior switching capabilities is essential. Here, we propose that semimetallic systems characterized by non-trivial
quantum geometry, including quadratic band-touching semimetals and singular flat bands, can serve as a promising platform for ultrafast switching at voltages compatible with modern electronics. We show that, in such
quantum geometric semimetals, an electric current is generated instantaneously upon application of a moderate external electric field, reaching its steady-state value. As a consequence, the current exhibits rapid and stable on-off switching behaviour under periodic optical pulse trains, demonstrating robustness under experimentally feasible conditions. In terms of switching speed, this
quantum geometric semimetal outperforms conventional metals,
semiconductors, and
graphene. We identify the microscopic origin of this behaviour as interband coupling governed by the
Hilbert-Schmidt
quantum distance, together with a finite density of states at the band-touching point. This mechanism further leads to a universal classification of conductivity for both gapless and gapped
quantum geometric semimetals. Finally, first-principles calculations suggest realistic material platforms, including
bilayer graphene, cyclic
graphene, monolayer bismuth and V3F8-in which the predicted instantaneous current switching can be directly realized, further supported by time-dependent density functional theory simulations performed for representative systems.
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Statistical Mechanics
Using the slowest observable in one-dimensional Markov processes to construct quasi-exactly-solvable generators with two explicit levels
Cecile Monthus
The construction of Quasi-Exactly-Solvable
quantum Hamiltonians where only the first two eigenstates $\Phi_0(x)$ and $\Phi_1(x)$ of energies $E_0$ and $E_1$ are explicit is revisited from the point of view of one-dimensional Markov processes satisfying detailed-balance, whose generators are related to
quantum Hamiltonians via similarity transformations. Here, the lowest energy vanishes $E_0=0$ and is associated with the conservation of probability and with the steady state $P_*(x)$, while $E_1>0$ is the rate that governs the exponential relaxation towards the steady-state, and is associated with the slowest observable $L_1(x)$ that corresponds to the ratio $ \frac{\Phi_1(x) }{\Phi_0(x)}$ of the two
quantum eigenstates. Our main conclusion is that the Markov perspective leads to interesting re-interpretations and that the construction of quasi-exactly-solvable models with $N=2$ explicit levels is more intuitive and technically simpler when one takes the slowest observable $L_1(x)$ as the central object from which all the other properties can be reconstructed. This general approach is then applied to Fokker-Planck generators in continuous space and to Markov jump generators on the
lattice.
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Strongly Correlated Electrons
Experimental quantification of electronic symmetry breaking through orbital hybridization phase
Shungo Aoyagi, Shunsuke Kitou, Yuiga Nakamura et al. (+2 more)
Symmetry classification of
crystal structures has been central to predicting physical properties of materials. While such structural classification identifies which physical responses are
symmetry-allowed, the magnitudes of these responses are governed by the degree of
symmetry breaking in the electronic state. However, a well-defined quantitative descriptor for the electronic
symmetry breaking has been established only in limited cases such as electric polarization and magnetization. No analogous descriptor exists for most other types, including chirality. Here, we propose an experimental framework for quantifying electronic
symmetry breaking from the anisotropy of valence electron density distribution. We show that the orbital hybridization phases governing this anisotropy can be uniquely determined under site
symmetry constraints. Applying this framework to structurally
chiral transition-metal silicides, we determine hybridization phases from their valence electron densities observed by synchrotron X-ray diffraction. From the obtained complex hybridization, we quantify an electronic chirality $\chi$ and theoretically demonstrate that it is directly proportional to circular dichroism, establishing $\chi$ as a predictive descriptor of
chiral responses. This approach is systematically applicable to various point groups, offering a general route to quantifying electronic
symmetry breaking and predicting associated physical properties.
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All authors Shungo Aoyagi, Shunsuke Kitou, Yuiga Nakamura, Taka-hisa Arima, Naoya Kanazawa
Materials Science
Experimentally-validated multi-slice simulation of electron diffraction patterns
Xinke Xiao, Tianle Ma, Lingxuan Shao et al. (+4 more)
High-Resolution Electron Backscatter Diffraction (HR-EBSD) has advanced rapidly in recent years, significantly improving elastic strain measurements and dislocation density evaluation with submicron spatial resolution. To achieve better accuracy in the measurements, high-quality dynamical simulation patterns are required to be matched with experimental ones. Currently, the most widely used pattern simulation method, the Bloch Wave method (BW), can accurately predict the positions and brightness of Kikuchi poles and bands, but is intrinsically limited to perfect
crystal structures. Another simulation scheme, the multi-slice method (MS), follows the
evolution of electron waves as they travel through the sample. MS is advantageous in simulating various defect structures with more diffraction details. Yet, it is mainly considered for theoretical developments and has not been compared to experimental data. This paper optimizes the MS method by abandoning the high-energy hypothesis and utilizing higher-order Taylor expansions to approach the forward-only Schrodinger equation. Experimental EBSD patterns of polycrystal Al-Mg
alloys are used to challenge MS simulations as a reference for indexation. It is demonstrated that the 5th-order expansion of MS, referred to as MS5, achieves a good balance between computational cost and pattern precision. A tailored isotropic distortion correction model and standard stereographic triangle reconstruction enhance the precision of MS5 to be comparable with BW. To the best of our knowledge, this study provides the first comparison of MS EBSD simulations with experimental data. It opens new possibilities for EBSD characterization, such as reproducing diffraction patterns of
crystals with various defects.
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All authors Xinke Xiao, Tianle Ma, Lingxuan Shao, Jun Liu, Qiwei Shi, Canying Cai, Stéphane Roux
Superconductivity · Cross-listed from quant-ph
Digital Predistortion for Flux Control of Tunable Superconducting Qubits
Dharun Venkateswaran, Felice Francesco Tafuri, Yuanzheng Paul Tan et al. (+8 more)
Flux-tunable superconducting
qubits rely on fast flux control pulses to implement two-
qubit entangling
quantum gates, a key building block for
quantum algorithms. However, distortion effects introduced by non-ideal control electronics, parasitic components, and the cryogenic
quantum chip response can all degrade the gate fidelity. We present a digital predistortion (DPD) framework for characterizing and then compensating for these distortions using a combination of infinite impulse response (IIR) and finite impulse response (FIR) filters. Experiments on a flux-tunable
quantum processing unit (QPU) demonstrate a successful correction of step-response distortions on the flux-control line, with a compensated control signal showing only sub-percent deviations from the ideal target linear behavior. The demonstrated method enables automated rapid calibration of flux control channels for superconducting QPUs.
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All authors Dharun Venkateswaran, Felice Francesco Tafuri, Yuanzheng Paul Tan, Bruno Aznar Martinez, Alisa Danilenko, Likai Yang, Arnaud Carignan-Dugas, Christoph Hufnagel, Rainer Dumke, Philip Krantz, Eric T. Holland
Materials Science · Cross-listed from physics.chem-ph
Host-guest co-amorphous structure revealed by the suppression of the first sharp diffraction peak in isotactic poly(4-methyl-1-pentene)
Tomoki Ogihara, Yusuke Hiejima and Ayano Chiba
While host-guest co-
crystals are well established, and co-amorphous solids are recognized in materials science, the concept of a host-guest co-amorphous structure remains largely unexplored. A potential analogue is seen in SiO2 glass under high pressure with helium as a pressure medium; the drop in compressibility in this system is ascribed to helium atoms occupying internal voids. In this study, we investigated a semicrystalline
polymer, isotactic poly(4-methyl-pentene-1) (P4MP1), which shares key characteristics with SiO2 glass, particularly regarding the first sharp diffraction peak (FSDP). The FSDP in P4MP1 is attributed to internal voids, as evidenced by its suppression under pressure and recovery upon decompression for molten P4MP1. Notably, the response to helium as a pressure medium is also known to parallel the behavior observed in SiO2 glass. Here, we analyzed two-dimensional X-ray diffraction (2D-XRD) patterns of stretched P4MP1 and found a suppression of FSDP when P4MP1 is immersed in decane. The use of stretched samples enabled the clear isolation of the amorphous FSDP from overlapping crystalline diffractions. Our findings reveal the existence of a host-guest co-amorphous system at room temperature and atmospheric pressure, in which decane molecules occupy the amorphous host
matrix of P4MP1. Unlike conventional co-amorphous mixtures, this structure is defined by the specific accommodation of guests within the host's inherent voids. Intriguingly, the signature of this structure in diffraction measurements, manifested as changes in the FSDP intensity ratio, may be regarded to parallel the variations in Bragg peak intensity ratios in host-guest co-
crystals. Since selective sorption and guest exchange are well-known in co-
crystals, hosts capable of forming co-amorphous structures will be promising materials for molecular sieves, or more generally,
liquid-phase molecular sieves.
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Strongly Correlated Electrons
Enhancing Neural-Network Variational Monte Carlo through Basis Transformation
Zhixuan Liu, Dongheng Qian and Jing Wang
Neural-network variational Monte Carlo (NNVMC) has emerged as a powerful tool for solving
quantum many-body problems, yet systematic pathways for improving its accuracy remain largely heuristic. Here, we introduce a physically motivated basis transformation for NNVMC that enhances variational expressivity without increasing the complexity of the neural-network ansatz itself. By formulating the many-body wave function in a Gaussian basis, we introduce a single learnable locality parameter, $\alpha$, that reshapes the target ground state into a more learnable representation. This approach introduces minimal computational overhead and can be readily combined with existing neural-network architectures. Using the three-dimensional homogeneous electron gas as a
benchmark, we show that the optimized basis transformation consistently lowers the variational energy for both FermiNet and message-passing neural-network architectures. Notably, for the latter, it enables a more precise determination of the
Fermi liquid to Wigner
crystal phase transition. More broadly, our results highlight basis transformation as a new route to improving NNVMC in continuous space, showing that accuracy can be enhanced not only by refining the ansatz but also by making the target ground state easier to represent.
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Soft Condensed Matter
Phase behavior of thermoresponsive colloids drives re-entrant plasmon coupling
Angela Capocefalo, Francesco Brasili, Javier Pérez et al. (+8 more)
Plasmonic nanoparticles (NPs) integrated within thermoresponsive polymeric microgels provide a versatile platform for the realization of stimuli-responsive optical materials, where the microgel volume phase transition enables dynamic control of plasmon coupling. This study uncovers a counter-intuitive re-entrant behavior with increasing NP loading in which plasmon coupling initially strengthens and subsequently weakens beyond a critical NP-to-microgel number ratio. By combining light and X-ray scattering techniques with optical spectroscopy and electrophoretic mobility measurements, it is demonstrated that plasmon coupling is governed not only by the interparticle distance between NPs confined within individual microgels, but also by the colloidal stability of the hybrid complexes. At intermediate NP loadings, surface charge inhomogeneities induced by NP adsorption promote aggregation of microgel-NPs complexes, resulting in enhanced plasmon coupling. In contrast, when the complexes remain colloidally stable, coupling is dictated solely by NP organization within the corona of individual microgels. A quantitative relationship between plasmon coupling and interparticle distance reveals two distinct coupling regimes. This behavior is rationalized through a phase diagram linking colloidal stability to optical response. These findings identify colloidal stability as a key parameter for designing soft plasmonic systems with programmable optical properties.
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All authors Angela Capocefalo, Francesco Brasili, Javier Pérez, Edouard Chauveau, Stefano Casciardi, Andrea Militello, Francesco Sciortino, Emanuela Zaccarelli, Federico Bordi, Domenico Truzzolillo, Simona Sennato
Soft Condensed Matter
Voids in liquids: peculiarities of molecular dynamics simulation of fluid systems
Yu. D. Fomin
Molecular dynamics is a powerful tool to investigate the properties of fluid systems. However, a correct interpretation of the results of simulations is required. In particular, some simulations show appearance of large voids in
liquids, which contradicts our common sense on what is
liquid. In the present paper we discuss the origin of large cavities
liquids in molecular dynamics simulations. We demonstrate that the cavities appear either if the temperature of the system is above the critical temperature of
liquid-gas transition or if the system is in two-phase
liquid-gas region. These conclusions are illustrated by several examples from literature and our own simulations.
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Statistical Mechanics
General perturbative framework for kinetics of rare transitions in 1-dimensional active particle systems
Vito Seinen, Peter G. Bolhuis, Daan Crommelin et al. (+2 more)
We present a theoretical framework that enables investigating rare transitions in a general model of an active particle in an external potential, with the thermal Active Ornstein-Uhlenbeck Particle (AOUP) appearing as a special case. Using a projection-operator formalism, we compute transition rates perturbatively in two distinct asymptotic regimes. In the regime of small persistence times-where the activity evolves much faster than the particle's position-integrating out the activity reproduces the rates previously reported in the literature. In the opposite regime of large persistence times, we instead integrate out the position and obtain the corresponding rates analytically. Together, these asymptotic expansions uniquely specify a rational approximation that remains accurate across intermediate persistence times. As a result, we obtain an analytic expression for the rate valid across all persistence times and activity strengths in the rare-event limit, which are in excellent agreement with numerical simulations. The presented framework applies to rare transitions in a broad class of driven systems.
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All authors Vito Seinen, Peter G. Bolhuis, Daan Crommelin, Sara Jabbari Farouji, Michel Mandjes
Statistical Mechanics · Cross-listed from hep-lat
Hilbert Space Fragmentation and Gauge Symmetry
Thea Budde, Marina Kristć Marinković and Joao C. Pinto Barros
The
Hamiltonian formulation of
lattice gauge theories plays a central role in
quantum simulations of gauge theories, and understanding their spectrum and other properties is expected to become crucial in the upcoming years. The relevant
Hamiltonians in this framework possess local
symmetry at each
lattice site and may exhibit higher-form
symmetries. There are then an exponentially large number of dynamically disconnected
symmetry sectors, most of which are not translation-invariant. An exponential number of dynamically disconnected sectors, i.e.,
Hilbert space fragmentation, can also occur in systems in which no such
symmetries have been identified. In this contribution, we describe an emergent gauge
symmetry that is valid only in a subset of sectors of the fragmented $S=1$ dipole-conserving
spin chain. These non-invertible
symmetries can label exponentially many of the model's sectors. Simulating this
Hamiltonian, which is not gauge-invariant, yields an exact
quantum simulation of a gauge theory.
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Quantum Gases
Coupled-channels method for the scattering hypervolume in ultracold atomic three-body collisions
P.J.P. Kersbergen, J. van de Kraats, D.J.M. Ahmed-Braun et al. (+1 more)
We introduce a novel coupled-channels method for elastic three-body scattering in systems of identical bosonic alkali-metal atoms. The approach relies on the numerically exact two-body off-the-energy-shell transition
matrix, constructed from realistic multichannel molecular interaction potentials that support many bound states. By rigorously accounting for this off-shell structure, the method captures both the short-range physics as well as multichannel couplings characteristic of alkali-metal potentials without resorting to model pseudopotentials. The central output is the complex three-body scattering hypervolume – the three-body analogue of the two-body scattering length – which we obtain with controlled and verifiable numerical accuracy. As a realistic
benchmark, we apply our framework to
spin-polarized potassium-39, performing full coupled-channels three-body scattering calculations and extracting the hypervolume over experimentally relevant conditions. The method is general and transferable to other atomic species and interaction models featuring deep molecular potentials with an arbitrarily large number of bound states.
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All authors P.J.P. Kersbergen, J. van de Kraats, D.J.M. Ahmed-Braun, S.J.J.M.F. Kokkelmans
Materials Science
Direct Orientation Contrast Imaging of Anti-Phase Domains on III-V Materials Using Scanning Electron Microscopy
Brieg Le Corre, Clothilde Grenèche, Rozenn Bernard et al. (+16 more)
Direct orientation contrast imaging of zinc-blende III-V materials is studied using scanning electron microscopy. A quantitative approach is taken using a 3 {\mu}m thick orientation-patterned GaP grown on GaAs sample, studying the anti-phase domain contrast with respect to the electron beam energy and the tilt angle. A qualitative approach is taken for III-V grown on non-polar materials with and without chemical mechanical polishing. Finally, a processing of the acquired image for GaP on Si reveals in plane preferential anti-phase boundaries.
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All authors Brieg Le Corre, Clothilde Grenèche, Rozenn Bernard, Tony Rohel, Antoine Létoublon, Wijden Khelifi, Julie Le Pouliquen, Arnaud Grisard, Sylvain Combrié, Bruno Gérard, Abdelmounaim Harouri, Luc Le Gratiet, Grégoire Beaudoin, Konstantinos Pantzas, Isabelle Sagnes, Oliver Skibitzki, Gilles Patriarche, Charles Cornet, Yoan Léger
Mesoscale and Nanoscale Physics
Persistence of large and gate-tunable anisotropic magnetoresistance in an atomically thin antiferromagnet
Cheol-Yeon Cheon, Kenji Watanabe, Takashi Taniguchi et al. (+2 more)
Anisotropic magnetoresistance (AMR) offers a robust electrical readout of
antiferromagnetic (AFM) states, playing a central role in the rapidly advancing field of AFM spintronics. Despite its great versatility, electrical probing of the Néel vector via AMR remains challenging in the ultrathin limit due to interface disorder and reduced dimensionality. Here, we demonstrate electrical readout of the Néel vector down to 1.3 nm (two layers) in the two-dimensional van der Waals (vdW) AFM
semiconductor NiPS3. Leveraging
spin-flop-mediated rotation of the Néel vector and using both transistor and tunnel-junction device geometries, we identify two distinct AMR contributions in NiPS3, that dominate at low and high charge densities, respectively. We achieve full gate control over these contributions, enabling tunability of both the magnitude and sign of magnetoresistance. Our results establish semiconducting vdW antiferromagnets as a rich platform for studying AMR in the ultrathin limit, opening new avenues for multifunctional AFM spintronic devices.
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All authors Cheol-Yeon Cheon, Kenji Watanabe, Takashi Taniguchi, Alberto F. Morpurgo, Dmitry Lebedev
Quantum Gases · Cross-listed from hep-th
Holographic Stirling engines and the route to Carnot efficiency
Nikesh Lilani and Manus R. Visser
We compute the efficiency of the reversible Stirling engine, with and without regeneration, for a broad class of working substances including Van der Waals fluids,
quantum ideal gases (Bose and
Fermi), Bose-Einstein condensates, thermal conformal field theories (CFTs), and
holographic CFTs. Regeneration acts as an internal heat recycling mechanism that enhances efficiency by reducing the net heat exchange with external reservoirs. For regenerative Stirling cycles, we identify a general sufficient condition for attaining Carnot efficiency: at fixed conserved charges, the fixed-volume heat capacity is independent of volume. This ensures that, at each temperature along the isochores, the heat released during cooling equals the heat absorbed during heating. An ideal regenerator can therefore store and return this heat reversibly, returning to its initial thermodynamic state with no net change in energy or
entropy. While this condition is satisfied for classical ideal gases and Van der Waals fluids, it is violated for
quantum ideal gases and CFT working substances. For thermal CFT states dual to AdS-Schwarzschild and AdS-Reissner-Nordstrom black holes, we obtain exact expressions for the Stirling efficiency. In the fixed-potential ensemble, both the regenerative and non-regenerative efficiencies approach the Carnot value in the large-potential limit. Regeneration reduces the leading deviation from the Carnot value, although both efficiencies have corrections of the same asymptotic order.
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Statistical Mechanics
Phase Transitions as the Breakdown of Statistical Indistinguishability
Taiyo Narita and Hideyuki Miyahara
We introduce a novel characterization of phase transitions based on hypothesis testing. In our formulation, a phase transition is defined as the breakdown of statistical indistinguishability under vanishing parameter perturbations in the thermodynamic limit. This perspective provides a general, order-parameter-free framework that does not rely on model-specific insights or learning procedures. We show that conventional approaches, such as those based on the Binder parameter, can be reinterpreted as special cases within this framework. As a concrete realization, we employ a distribution-free two-sample run test and demonstrate that the critical point of the two-dimensional Ising model is accurately identified without prior knowledge of the order parameter.
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Statistical Mechanics
Extracting conformal data from finite-size tensor-network flow in critical two-dimensional classical models
Sing-Hong Chan and Pochung Chen
We present a general framework for extracting conformal data from critical two-dimensional classical
lattice models using finite-size tensor-network flow. The central idea is to identify, from transfer-
matrix spectra, a self-consistent finite-size window together with a crossover scale that separates the finite-size-scaling regime from the finite-
entanglement-scaling regime induced by bond-dimension truncation. Within this window, the central charge, scaling dimensions, and conformal
spins can be estimated without requiring a unique critical fixed-point tensor or detailed prior knowledge of the underlying conformal field theory. We
benchmark the framework using three tensor-network renormalization schemes for the critical two-dimensional Ising and three-state clock models. Across schemes, we find robust universal behavior below the crossover scale, enabling accurate extraction of conformal data up to relatively high conformal levels. The analysis also yields a natural operational definition of
entanglement scaling for classical tensor-network calculations and, in turn, a complementary
estimator of the central charge.
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Mesoscale and Nanoscale Physics
Amplitudes of Hall field-induced resistance oscillations with a two-harmonic density of states
Miguel Tierz
We derive explicit strong-field asymptotics for the normalized differential resistance in
Hall field-induced resistance oscillations (HIRO) within the Vavilov-Aleiner-Glazman kinetic framework. For a single-harmonic density of states, the leading oscillation amplitude is set by the full backscattering rate $1/\tau(\pi)$. Extending the theory to a two-harmonic density of states, we show that the off-diagonal mixed kernel $\gamma_{12}$ admits an exact single-integral representation, from which the strong-field asymptotics follow directly. The resulting odd harmonics, notably $m=1$ and $m=3$, have coefficients determined by combinations of $1/\tau(0)$ and $1/\tau(\pi)$, while the leading $m=2$ amplitude remains unchanged. On exact-kernel mock data generated and fit within the same model, with $\tau_{\rm tr}$ and $\tau_{\rm in}$ held fixed, the resulting extraction protocol recovers $\tau_q$, $\tau(\pi)$, and – when the $m=1,3$ harmonics are resolved – $\tau(0)$ to sub-percent accuracy, with $\tau(0)$ providing a consistency check on the disorder description.
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Mesoscale and Nanoscale Physics
Current-Induced Dynamics and Instability Pathways of Skyrmioniums in Chiral Magnets
Kaito Nakamura, Yuka Kotorii and Andrey O. Leonov
We present a comprehensive study of current-driven dynamics, transformations, and instabilities of skyrmioniums in
chiral magnetic films, considering both isolated objects and collective states forming skyrmionium-based meta-matter. Using micromagnetic simulations combined with an analytical description based on the generalized Thiele equation, we clarify how the internal structure of skyrmioniums governs their nonequilibrium response to electric currents. Despite having zero total topological charge, skyrmioniums exhibit a finite transverse velocity under applied currents. We show that this skyrmionium
Hall effect originates from an imbalance between positive and negative topological contributions of the inner skyrmion and surrounding ring, which typically occupy different areas. Current-induced deformations further enhance this imbalance, yielding
Hall angles comparable to those of skyrmions. At higher current densities, skyrmioniums undergo distinct instabilities depending on
magnetic field and uniaxial anisotropy, including elongation, collapse into a skyrmion, transformation into a topologically trivial droplet, and expansion into stripe textures. We map these regimes in current–field and current–anisotropy phase diagrams and resolve their microscopic pathways via the
evolution of topological charge and local rotational measures. Beyond isolated textures, mixed skyrmion–skyrmionium
lattices display rich collective dynamics, including elastic transport, polymorphic transitions,
soliton exchange, and stripe formation. Pulsed currents provide additional control, enabling access to regimes beyond continuous driving. Our results establish skyrmioniums and their meta-matter as tunable nonequilibrium systems probing the topological energy landscape far from
equilibrium.
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Materials Science
Flat-band energy filtering in interacting systems: conditions for improving thermoelectric performances
F. Cosco, R. Tuovinen, F. Plastina et al. (+1 more)
Motivated by recent theoretical and experimental studies on the role of flatbands in the thermoelectric properties of Ni$_3$In$_{1-x}$Sn$_x$ compounds, we investigate electron transport in two minimal one-dimensional flatband models, the sawtooth and diamond chains, which differ in a crucial aspect: the flatband is separated from the dispersive band by a finite gap in the former, while the two bands touch in the latter. Using a non-
equilibrium Green function framework with interactions treated at the Hartree-Fock and GW levels, we compute the full set of thermoelectric coefficients and the figure of merit $zT$ as functions of gate voltage and temperature. We show that, contrary to naive expectation, a perfectly isolated flat-band is a physically ill-founded thermoelectric: the electrical conductivity vanishes as the chemical potential enters the flat-band, rendering the large Seebeck coefficient and the apparent violation of the Wiedemann-Franz law physically meaningless. Optimal thermoelectric performance is instead achieved just below the flat-band edge, where the transmission function varies most rapidly with energy, consistent with the Mahan-Sofo picture, and requires a finite broadening of the flat-band through hybridization with dispersive states. We further show that electron-electron interactions renormalize the flat-band structure itself, inducing an interaction-driven narrowing of the bandwidth and, in the diamond chain, a correlation-induced opening of a gap between the flat-band and the dispersive band near half-filling. Mean-field treatments are found to systematically overestimate \(zT\), highlighting the importance of beyond-mean-field correlations for quantitatively reliable predictions in flat-band thermoelectrics.
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All authors F. Cosco, R. Tuovinen, F. Plastina, N. Lo Gullo
Mesoscale and Nanoscale Physics
Growth of quantum dots by droplet etching epitaxy in molecular beam epitaxy: theory, practice, and review
Declan Gossink, Undurti S. Sainadh and Glenn S. Solomon
GaAs
quantum dots grown by droplet etching epitaxy are high-quality solid-state sources of
quantum light. Despite implementation in devices that exploit
quantum phenomenon, a comprehensive review on the
crystal growth of
quantum dots grown by droplet etching epitaxy is absent, unlike for other
quantum dot growth techniques such as the related droplet epitaxy method or Stranski-Krastanov growth of InAs
quantum dots. This review presents a detailed overview of the droplet etching epitaxy growth technique in the molecular beam epitaxy environment, with emphasis on the growth parameters necessary to realize high-quality
quantum dots. We systematically cover the three main phases of droplet etching epitaxy - droplet deposition, droplet etching, and nanohole regrowth - and relate experimental results to theories on
crystal growth. The review concludes with an introduction to GaAs
quantum dot photoluminescence and the extension of droplet etching epitaxy beyond the AlGaAs/GaAs material system.
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Materials Science
Fully compensated and uncompensated ferrimagnetic ferrovalley semiconductors
Weifeng Xie, Libo Wang, Yunliang Yue et al. (+3 more)
Altermagnets (AMs) and fully compensated ferrimagnets (FC-FIMs) are emerging classes of
magnetic materials that combine the advantages of antiferromagnets and ferromagnets. Here, we elucidate the mechanism behind the uniaxial strain-driven transformation from AM to FC-FIM and find that the accompanying non-relativistic valley polarization is positively correlated with the net
magnetic moment between
magnetic atoms in opposite
spin sublattices. We then propose an uncompensated ferrimagnetic monolayer VCrSeTeO to achieve large intrinsic valley polarization.
Spin-orbit coupling (SOC) is shown to further increase the valley polarization to over 400 meV under uniaxial strains and the reason is explained in terms of SOC perturbation
theorem. Furthermore, we reveal a distinctive anomalous valley
Hall effect in which the valley
Hall voltage is reversed within the same valley in ferrimagnet VCrSeTeO. This work proposes a strategy for realizing
giant valley polarization and provides theoretical guidance for the application of ferrimagnetic ferrovalley
semiconductors derived from altermagnets in valleytronics.
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All authors Weifeng Xie, Libo Wang, Yunliang Yue, Xiong Xu, Huayan Xia, Hui Wang
Materials Science
Facet-dependent Chemical Kinetics Governed Growth of Twisted Graphene Layers with Pre-designed Angles
Chaowu Xue, Mengzhao Sun, Zixuan Zhou et al. (+8 more)
Twisted
graphene layers (TGLs) provide a powerful platform for investigating multiple
quantum phenomena, yet their scalable deployment is hindered by the lack of reliable synthesis with precise angle. Here, benefited from a deeper understanding of the interplay between grain index and
graphene growth kinetics, we report a scalable strategy to grow TGLs with pre-designed twist angles on platinum (Pt) via chemical vapor deposition (CVD), Through a combination of complementary in situ methods, we identified the activity sequence of different Pt grains and attributed it to the area ratio of exposed (110) facets during
graphene-induced surface reconstruction. Moreover, we revealed that CVD-grown
graphene orientation is determined by the grain-orientation-dependent surface morphology. By leveraging the so-established correlations between grain index with both
graphene growth priority and its orientation, we achieve controlled folding and tearing of
graphene overlayer using a pair of adjacent grains with dramatically different catalytical activity and kink-free atomic steps. We reveal that overlayer-induced step bunching and terrace reconfiguration critically govern the domain morphology and folding direction. Building on this mechanistic insight, we demonstrate a substrate-engineering framework where specific platinum grains are rationally selected to yield TGLs with pre-designed twist angles, including magic angle with flat band dispersion. This work not only highlights fundamental kinetics of Pt catalyzed
graphene CVD growth, but also offers a generalizable methodology for manipulating foldable two-dimensional materials via dynamic substrate reconstruction, exampled by programmable growth of high-quality TGLs on open surfaces.
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All authors Chaowu Xue, Mengzhao Sun, Zixuan Zhou, Zhuoran Yao, Li-Qun Shen, Xiao Kong, Honglong Zhao, Feng Ding, Marc Willinger, Zhongkai Liu, Zhu-Jun Wang
Strongly Correlated Electrons
Inductance Meets Memory in the Quantum Magnet Mn3Si2Te6
Tristan R. Cao, Gabriel Schebel, Arabella Quane et al. (+5 more)
Orbital degrees of freedom offer a largely untapped route to emergent dynamical phenomena in correlated
quantum materials. However, it remains unclear whether collective orbital states can intrinsically generate both reactive and
memory functionalities in a bulk system. Here we show that in the ferrimagnet Mn3Si2Te6, nonequilibrium reconfiguration of
chiral orbital currents produces both emergent inductance and nonvolatile memristance as intrinsic properties of a single
crystal. At low frequency and under a
magnetic field along the c axis, coherent orbital-current domains generate robust clockwise inductive I-V loops. At higher frequency and low field, current-driven first-order reconfiguration leads to incomplete reversal and metastable trapping, producing an intrinsic electromotive force and a finite remanent voltage at zero current. These results establish orbital currents as a class of
quantum state variables that encode both reactive and
memory functionalities, opening routes toward intrinsically reconfigurable and energy-efficient electronic systems.
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All authors Tristan R. Cao, Gabriel Schebel, Arabella Quane, Hengdi Zhao, Yu Zhang, Feng Ye, Longji Cui, Gang Cao
Quantum Gases · Cross-listed from nlin.PS
Dark solitons in nonlinear Su-Schrieffer-Heeger lattices
Rujiang Li, Muhammad Imran, Wencai Wang et al. (+2 more)
The introduction of nonlinearities into
lattices with topological band structures has led to the discovery of various types of
solitons. The Su-Schrieffer-Heeger (SSH)
lattice, as the most fundamental topological model, has been extended into the nonlinear regime. In particular, nonlinear edge states and bulk
solitons exhibiting intensity humps against a zero background have been extensively studied in nonlinear SSH
lattices. In this paper, we systematically investigate dark
solitons in nonlinear SSH
lattices. These dark
solitons maintain a nonzero and constant background, featuring intensity dips either in the bulk of the
lattice or at its edges, and residing spectrally in the semi-infinite gap or the middle finite gap. Regardless of the specific type of dark
soliton, the intensity dip remains wellpreserved and is not affected by the band structure of the original linear
lattice. Although the dark
solitons we have identified are generally dynamically unstable across a broad range of parameters, several types exhibit linear stability when the intracell coupling is much larger than the intercell coupling. Our findings may provide valuable insights for the exploration of novel types of
solitons in nonlinear topological
lattices.
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All authors Rujiang Li, Muhammad Imran, Wencai Wang, Yongtao Jia, Ying Liu
Strongly Correlated Electrons
Inelastic neutron scattering study on the AFM uniform spin-1/2 chain compound CuSb2O6
Masashi Hasea, Minoru Soda, Takatsugu Masuda et al. (+2 more)
We carried out inelastic
neutron scattering experiments on a powdered sample of the
antiferromagnetic (AFM) uniform
spin-1/2 chain compound CuSb2O6.The
magnetic excitations appear in the energy range of 1.8 to 13 meV at 2.5 K below the AFM transition temperature (TN = 8.7 K).The gap value (1.8 meV) is close to that evaluated from the specific heat (1.51 meV). The excitations at 12.5 K (> TN) appear gapless. Thus, the 1.8 meV gap is caused by some anisotropy in
spin-wave excitations. The gap excitations are strongest at 0.48 corresponding to a length of 0.66 nm. This result is consistent with the theoretical one that the interaction in a Cu pair with a length of 0.65562 nm (Jab) is strongest. The
magnetic excitations can be explained by the AFM uniform XXZ chain with Jab = 6.437 meV and DJab = 0.063 meV. The 1.8 meV gap is caused by the small Ising anisotropy (DJab/Jab = 0.0098).
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All authors Masashi Hasea, Minoru Soda, Takatsugu Masuda, Shinichi Itoh, Tetsuya Yokoo
Quantum Gases · Cross-listed from quant-ph
Deterministic multiphoton bundle emission via interference-interaction control
Jing Tang and Yuangang Deng
The controlled generation of nonclassical light beyond single
photons remains a central challenge in
quantum optics, due to the difficulty of enhancing multiphoton processes while suppressing lower-order excitations. Here we propose an interference-interaction-engineered scheme for programmable few-
photon emission in a cavity-QED system of three atoms coupled to orthogonal cavity modes. By adiabatically eliminating an auxiliary Fabry-Pérot cavity, we generate a tunable cavity-mediated
spin-exchange interaction $\chi$, which, combined with a controllable
geometric phase $\phi$, reshapes the many-body dressed-state spectrum. This interplay enables selective addressing of excitation
manifolds ($N=1,2,3$), establishing a direct mapping between excitation structure and
photon-emission channels. For $\phi=0$, constructive interference enhances the spectral anharmonicity of low-excitation
manifolds, yielding tunable single- and two-
photon emission associated with the $N=1$ and $N=2$
manifolds. In contrast, for $\phi=2\pi/3$, destructive interference suppresses lower-order excitation pathways and activates a resonant three-
photon channel originating from the $N=3$
manifold. Importantly, the cavity-mediated interaction $\chi$ further enhances spectral separation between
manifolds, enabling a substantial improvement in multiphoton purity while maintaining a sizable
photon population. We demonstrate a three-order-of-magnitude enhancement in two-
photon purity and more than two orders of magnitude improvement in three-
photon emission. Our results establish a unified interference-interaction framework in which effective optical nonlinearities can be programmably engineered through phase and interaction, providing a scalable route toward high-purity multiphoton sources and programmable
quantum photonic devices.
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