Quantum Gases
Josephson effects in an interaction-asymmetric junction across the BCS-BEC crossover
Tingyu Zhang and Hiroyuki Tajima
We theoretically study the Josephson effect in ultracold
Fermi gases, where the two sides of the Josephson junction are independently tuned to different regions of the Bardeen-Cooper-Schrieffer (BCS)-Bose-Einstein condensation (BEC) crossover. Using the nonequilibrium Green's function approach combined with the tunnel
Hamiltonian formalism and a mean-field approach, we evaluate the DC and AC Josephson currents throughout the entire crossover region. We calculate the DC Josephson current as a function of interaction strength by tuning both sides of the junction synchronously from the BCS to the BEC regimes, and give the asymptotic expression of the current in the deep BCS and BEC limits. We also study the AC Josephson junction through the interaction-asymmetric junction by fixing the interaction in one reservoir and tuning that of the other one. A peak of the tunneling current is found when one side is fixed in the BCS limit and the other side is tuned into the BEC regime, which corresponds to the interaction-biased Riedel peak. Our results indicate the competition between contributions of increasing pair spectral weight and decreasing chemical potential to Josephson tunneling throughout the BCS-BEC crossover, and demonstrate the realization of the Riedel peak in strong-coupling
quantum gases.
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Superconductivity
Many-body Josephson diode effect in superconducting quantum interferometers
Zelei Zhang, Jianxiong Zhai, Yi Zhang et al. (+1 more)
We propose a many-body mechanism for a strong Josephson diode effect (JDE) in an interacting nanoscale SQUID formed by two parallel
quantum dots coupled to superconducting leads. Unlike conventional diode behavior, where nonreciprocity originates from a skewed current-phase relation within a single, continuously evolving ground state, the JDE reported here is branch selected: the positive and negative critical currents are optimized on different many-body branches across the $0$-$\pi$ phase boundary, yielding a substantial enhancement of the diode efficiency. We further show that a nonlocal Cooper-pair tunneling channel, which binds the two electrons on different arms, is essential: it reshapes the $0$-$\pi$ boundary and produces a pronounced “diode band” in parameter space, in sharp contrast to the fragile hotspot obtained when only local Cooper-pair transfer is available. While the key physics is captured by an effective model in the superconducting atomic limit, our conclusions remain robust for realistic finite-gap devices, as demonstrated within a generalized atomic-limit framework.
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All authors Zelei Zhang, Jianxiong Zhai, Yi Zhang, Jiawei Yan
Strongly Correlated Electrons
Neural networks as low-cost surrogates for impurity solvers in quantum embedding methods
Rohan Nain, Philip M. Dee, Kipton Barros et al. (+2 more)
A promising application of machine learning is the creation of low-cost surrogate models to mitigate computational bottlenecks in
quantum many-body simulations. Here, we explore whether a neural network (NN) can be trained in the low-data regime, with one to two orders of magnitude fewer training examples than previous works, as an efficient substitute for the
impurity solver in dynamical mean-field theory simulations of correlated electron models. We show that the NN solver achieves accuracy comparable to popular continuous-time
quantum Monte Carlo (CT-QMC)
impurity solvers when interpolating between samples within the training set. While the NN's performance decreases notably when extrapolating to lower temperatures outside the training distribution, its output still provides an excellent initial guess for input to more accurate CT-QMC
impurity solvers, thus accelerating the time to solution up to a factor of five. We discuss our results in the context of rapid phase-space exploration.
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All authors Rohan Nain, Philip M. Dee, Kipton Barros, Steven Johnston, Thomas A. Maier
Materials Science
Revealing the Atomic-Scale Structure of the Copper Sulfuric Acid Interface
Lalith Kumar Bhaskar, Sung-Gyu Kang, Oliver R. Waszkiewicz et al. (+7 more)
Corrosion originates from atomistic reactions occurring at dynamic solid
liquid interfaces however, direct experimental observation of these reactions has remained elusive due to the inability to preserve transient interfacial states during characterization. To refine corrosion models, advanced techniques capable of analyzing corrosion interfaces at the atomic scale are essential. Recent advancements in cryogenic atom probe
tomography (cryoAPT) enabled 3D nanoscale analysis of frozen
liquid metal interfaces. However, challenges remain in sample preparation for cryoAPT on metals undergoing corrosion. This study introduces a microcorrosion
cell fabricated using localized electrodeposition in
liquid (LEL), enabling atomic scale capture of
liquid metal reactions by integrating picoliterscale electrolytes encapsulated within sealed metallic microvessels, subsequently analyzed using cryoAPT.This approach enables 3D, nanoscale mapping of corrosion reactions with simultaneous spatial, chemical, and temporal resolution. As a model system, copper exposed to aerated dilute sulphuric acid reveals temperature and time dependent interfacial
evolution, including nanoscale clustering of copper sulphate species, enhanced ion pairing at elevated temperature, and the emergence of transient carbon based interfacial complexes inaccessible to conventional characterization methods.Beyond copper corrosion, the presented microcorrosion
cell architecture establishes a strategy for interrogating confined electrochemical and degradation processes across a wide range of material
liquid systems, using a combination of microfabrication and cryoAPT.
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All authors Lalith Kumar Bhaskar, Sung-Gyu Kang, Oliver R. Waszkiewicz, Finn Giuliani, Baptiste Gault, Mary P. Ryan, Roger C. Newman, Gerhard Dehm, Rajaprakash Ramachandramoorthy, Ayman A. El-Zoka
Soft Condensed Matter
Entropic phase separation in polymer–vitrimer melts
A. A. Rispo Constantinou, B. Magyari, G. Ianniruberto et al. (+2 more)
Traditional plastics demand a choice between durability (thermosets) and reprocessability (thermoplastics). Vitrimers are a recent class of
polymer network combining both these qualities. Their increased cost of production can be offset by mixing them with a traditional thermoplastic; however, phase separation in such blends can lead to inhomogenous materials. In this paper, we adapt an existing model for the free energy of dissociative
polymer networks to their associative, vitrimeric counterpart. We test the accuracy of the model's predictions by comparing them with the results of novel molecular-dynamics simulations. We demonstrate that such melts can undergo phase separation even in the absence of energetic interactions between the components, with a phase diagram qualitatively similar to that of dissociative systems. We furthermore find that — for equal-length chains in the limit of highly functionalised vitrimers — entropic phase separation sets in as soon as two function sites per chain are cross-linked to other chains, such that only loosely cross-linked networks are stable.
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All authors A. A. Rispo Constantinou, B. Magyari, G. Ianniruberto, E. van Ruymbeke, D. J. Read
Materials Science
Anisotropic light-electron-phonon coupling and ultrafast carrier separation in ferroelectric BaTiO$_3$
Atal Bihari Swain, Somnath Kale, Rohit Soni et al. (+1 more)
Ferroelectric materials with built-in electric fields are useful for ultrafast electronics and conversion of light into electrical energy, yet the interaction of carrier motion with ultrafast relaxation processes remains nontrivial. Combining ultrafast electron diffraction with electron microscopy of electromagnetic fields, we capture ultrafast
lattice dynamics and nanometer-scale carrier transport in ferroelectric BaTiO$_3$. We discover that BaTiO$_3$ reacts to light with an anisotropic electron-
phonon coupling that depends on the optical polarization of the excitation light. Excited electrons relax two times faster into
phonons when the optical electric field aligns to the ferroelectric
symmetry break. Furthermore, ultrafast electron electrometry captures the motion and separation of photo-excited electron-hole pairs in the presence of the ferroelectric field. These combined results provide insight into the tangled and anisotropic interaction of
photons with
phonons and the ferroelectric field, producing
phonons and voltages in a stepwise reaction path.
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All authors Atal Bihari Swain, Somnath Kale, Rohit Soni, Peter Baum
Materials Science
Charge and spin photogalvanic effects in the p-wave magnet NiI2
Giuseppe Cuono, Srdjan Stavric, Javier Sivianes Castano et al. (+4 more)
NiI2 is an exotic van der Waals material in which a noncollinear
spin spiral breaks spatial inversion
symmetry without sizeable structural distortion, generating improper ferroelectric polarization, and stabilizing p-wave
magnetic states with electron-volt-scale odd-parity
spin splitting. Using first-principles calculations, here we establish that nonlinear optical transport can directly probe and separate these effects. Magnetically-induced inversion breaking associated with the
spin spiral produces a photogalvanic shift current under linearly polarized light, with conductivities exceeding those of conventional ferroelectrics. In contrast, a large photogalvanic injection current under circularly polarized light originates from helicity-selective transitions between
spin-split states at opposite
crystal momenta, directly exposing the nonrelativistic p-wave
spin texture. We further predict pure
spin photocurrents whose flow direction exchanges with that of the charge current under linear and circular excitation. The ability to generate and control pure
spin currents without accompanying charge currents makes NiI2 a promising material platform for all-optical
spin injection in van der Waals
heterostructures.
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All authors Giuseppe Cuono, Srdjan Stavric, Javier Sivianes Castano, Julen Ibanez-Azpiroz, Paolo Barone, Andrea Droghetti, Silvia Picozzi
Materials Science
Interfacial charge-transfer in 3d/5d complex oxide heterostructures
Arun Kumar Jaiswal, Di Wang, Ji Soo Lim et al. (+6 more)
Interfacial charge transfer (ICT) provides a powerful route to engineer electronic phases in correlated
oxide heterostructures, yet predictive design principles remain elusive. Here, we systematically investigate superlattices composed of the 5d
spin-orbit coupled semimetal SrIrO3 and a series of correlated 3d perovskites (LaMnO3, LaFeO3, LaCoO3, and NdNiO3), thereby establishing a quantitative framework for ICT across 3d/5d interfaces. Combining element-specific x-ray absorption spectroscopy with spatially resolved electron energy loss spectroscopy, a homogeneous electron transfer from the 5d to the 3d layers is directly quantified, reaching up to 0.35 e per unit
cell in the cobaltate superlattice. We show that the magnitude of ICT scales linearly with the difference in electronegativity between the transition-metal
oxide layers, identifying electronegativity-driven band
alignment as the dominant mechanism for ICT. Beyond interfacial doping, we find that strong 3d-5d hybridization induces a complete low-
spin to high-
spin conversion in the cobaltate layers, demonstrating interface-controlled
spin-state engineering without chemical substitution. These results establish electronegativity mismatch as a predictive design parameter for correlated
oxide interfaces and provide a materials platform for tailoring band filling, orbital hierarchy, and
spin configurations in
quantum oxide heterostructures, paving the way towards advanced
oxide electronics and next-generation information technologies.
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All authors Arun Kumar Jaiswal, Di Wang, Ji Soo Lim, Shruti Roy, Fabrice Wilhelm, Vanessa Wollersen, Andrei Rogalev, Matthieu Le Tacon, Dirk Fuchs
Strongly Correlated Electrons · Cross-listed from hep-th
What happens to wavepackets of fermions when scattered by the Maldacena-Ludwig wall?
Yuji Tachikawa, Keita Tsuji and Masataka Watanabe
We study wavepackets of exotic excitations after two-dimensional
fermions are scattered by the boundary condition constructed by Maldacena and Ludwig, which turns elementary excitations into exotic fractionally-charged objects. They are of interest in the s-wave approximation of the
fermion-monopole scattering in four-dimensional QED and of the multi-channel Kondo effect. We in particular give an explicit expression of the outgoing state of a pair of such particles; we then examine its properties, such as the charge density $\langle J(x)\rangle$ and the expectation value $\langle N\rangle$ of the number of
fermions and anti-
fermions in the state. The charge density $\langle J(x)\rangle$ is found to be localized with its integral finite and fractional, while the expectation value $\langle N\rangle$ diverges when the wavepacket is localized to a point.
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Soft Condensed Matter
Identifying the Threshold Chain Length for Stress Overshoot in Ring-Linear Polymer Blends under Uniaxial Elongation: The Role of Multiple Threading
Takahiro Murashima, Katsumi Hagita and Toshihiro Kawakatsu
The rheological behavior of ring-linear
polymer blends under uniaxial elongational flow has remained a subject of intense debate, particularly regarding the emergence of stress overshoot. Herein, we employ coarse-grained molecular dynamics simulations to investigate the chain-length dependence of elongational viscosity in 1:1 ring-linear blends of flexible chains with the equal molecular weight. Our results reveal a distinct threshold in the degree of threading, quantified by the number of entanglements Z = N /Ne (where N is the number of beads per chain and Ne is the
entanglement chain length), for the appearance of stress overshoot: while blends with shorter chains (Z $\le$ 2) exhibit monotonic stress growth, a clear stress overshoot emerges when the chain length reaches a threshold value (Z $\approx$ 4). Consistent with previous reports, this overshoot originates from a thread-to-unthread transition. At the threshold chain length, multiple linear chains penetrate a single ring, providing sufficient topological constraints to significantly stretch the ring under elongational flow. We predict that this transition can be experimentally validated via 2D small-angle
neutron scattering patterns in the plane of the stretching and perpendicular directions, offering a direct structural signature of the ring
recoil process for future experimental verification.
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Materials Science
Berry curvature induced giant anomalous and spin texture driven Hall responses in the layered kagome antiferromagnet GdTi3Bi4
Shobha Singh, Shivam Rathod, Rong chen et al. (+5 more)
In recent years, layered kagome magnets have emerged as promising platforms for Berry-
curvature engineering and unconventional transport phenomena. Here, we present the single-
crystal growth, magnetization, and electrical transport characterizations of the van der Waals-like layered antiferromagnet GdTi3Bi4. The system exhibits pronounced field-induced first-order phase transitions. Comprehensive frequency, temperature, and field-dependent ac susceptibility measurements, and
Hall analysis, reveals the formation of a
spin-cluster-like glassy
magnetic phase attributed to noncollinear
spin textures. Additionally, the system demonstrates a colossal anomalous
Hall conductivity {\sigma}_xy^{A}~ 8.6(7)10^{3} Ohm-1 cm-1 at 2 K). Detailed scaling analyses reveal the coexistence of skew scattering and intrinsic Berry-
curvature contributions to the anomalous
Hall effect. First-principles calculations highlight flat-band near the
Fermi level, with f-electrons of the Gd ion contributing large intrinsic
Hall response. Thus, GdTi3Bi4 emerges as a rare layered kagome magnet, exhibiting Berry
curvature-induced
giant anomalous and
spin texture-driven
Hall responses, providing a versatile platform for exploring
spin-texture physics and advancing low-dimensional spintronic functionalities.
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All authors Shobha Singh, Shivam Rathod, Rong chen, Lipika, Sneh, Rie Y. Umetsu, Yan Sun, Kaustuv Manna
Mesoscale and Nanoscale Physics
Topology of honeycomb nanoribbons revisited
Zebedeus F. Osseweijer, Lumen Eek, Harold J.W. Zandvliet et al. (+2 more)
We present an in-depth study of end states in honeycomb nanoribbons, focusing on the interplay between nanoribbon termination,
chiral symmetry, and complex next-nearest-neighbor hopping in the framework of the Haldane model. Although previous work has identified zero-dimensional end states in such systems, this analysis is incomplete. Here, we systematically investigate zigzag and armchair nanoribbons of various widths, using the multiband Zak phase to characterize the topological properties of the occupied bands. We show that the Zak phase is quantized only for certain ribbon terminations, and we elucidate how this termination dependence governs the existence and robustness of end states. Furthermore, we explore the effect of varying the complex next-nearest-neighbor hopping phase, demonstrating the breakdown of
chiral symmetry, the
evolution of the bulk gap, and the resulting depinning of end-state energies. Finally, we place our findings in the context of previous studies and discuss connections to the Kane-Mele model, including the role of Rashba
spin-orbit coupling. Our work provides a more detailed analysis of topological end states in nanoribbons described by the Haldane and Kane-Mele models and offers a framework for their characterization in related systems.
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All authors Zebedeus F. Osseweijer, Lumen Eek, Harold J.W. Zandvliet, Pantelis Bampoulis, Cristiane Morais Smith
Statistical Mechanics
Lattice and PT symmetries in tensor-network renormalization group: Case study of a hard-square lattice gas model
Xinliang Lyu
The tensor-network renormalization group (TNRG) is an accurate numerical real-space renormalization group method for studying phase transitions in both
quantum and classical systems. Continuous phase transitions, as an important class of phase transitions, are usually accompanied by spontaneous breaking of various
symmetries. However, the understanding of
symmetries in the TNRG is well-established mainly for global on-site
symmetries like U(1) and SU(2). In this paper, we demonstrate how to incorporate
lattice symmetries (including reflection and rotation) and the PT
symmetry in the TNRG in two dimensions (2D) through a case study of the hard-square
lattice gas with nearest-neighbor exclusion. This model is chosen because it is well-understood and has two continuous phase transitions whose spontaneously-broken
symmetries are
lattice and PT
symmetries. Specifically, we write down proper definitions of these
symmetries in a coarse-grained tensor network and propose a TNRG scheme that incorporates these
symmetries. We demonstrate the validity of the proposed method by estimating the critical parameters and the scaling dimensions of the two phase transitions of the model. The technical development in this paper has made the 2D TNRG a more well-rounded numerical method.
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Strongly Correlated Electrons
Stabilization of zigzag order in NiPS$_3$ via positive biquadratic interaction
Qiang Luo, Shuhang Yang, Xiaoying Wang et al. (+4 more)
Despite extensive research, the precise
spin Hamiltonian of the van der Waals antiferromagnet NiPS$_3$ – which hosts a zigzag-ordered ground state – remains debated. While consensus has emerged on
ferromagnetic nearest-neighbor ($J_1$) and
antiferromagnetic third-nearest-neighbor ($J_3$) Heisenberg interactions, recent studies suggest a biquadratic ($B$) exchange term may also play a role, though its estimated magnitude varies widely. To address this controversy, we perform density functional theory calculations and extract a positive biquadratic interaction with $B/J_3 \approx 0.44$. Within the minimal $J_1$-$J_3$-$B$ model, we show that these parameters naturally stabilize zigzag ordering using minimally augmented
spin-wave theory. Density-
matrix renormalization group calculations further validate our extracted parameters as a reasonable description of the ground state. Although fully resolving the
spin Hamiltonian of NiPS$_3$ requires further investigation, our findings provide new insights into its biquadratic interaction.
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All authors Qiang Luo, Shuhang Yang, Xiaoying Wang, Mengdong Li, Zhengyu Jiang, Chunlan Ma, Yan Zhu
Soft Condensed Matter · Cross-listed from physics.bio-ph
Interfacial Permeability, Reflectivity and Preferential Internal Mixing of Phase-Separated Condensates
Oihan Joyot, Zoé Ferrand, Fernando Muzzopappa et al. (+2 more)
Biomolecular condensates organize biochemical processes by spatially concentrating molecules while allowing for dynamic exchange with their surroundings. However, transport across their interface can be strongly attenuated, leading to enhanced retention and preferential internal mixing. Two key mechanisms have been proposed to describe this behavior: biased interfacial reflectivity, which compares how strongly particles are reflected at the interface when attempting to enter or leave the condensate, and interfacial resistance, which sets the kinetic rate at which particles can cross the interface. Quantifying these parameters experimentally has remained challenging. Here, we present a theoretical and experimental framework to address this issue, extending our previously developed half-FRAP approach. We solve the spherical
diffusion problem with a semipermeable interface by spectral decomposition. By evaluating the information content of the integrated recovery curves, we show that they encode sufficient information to recover interfacial parameters over extended regions of parameter space. Applying our framework to tunable coacervates composed of poly-lysine and hyaluronic acid, we find that their interfaces exhibit strongly biased reflectivity and substantial resistance, both driving preferential internal mixing. These parameters depend on salt concentration, linking interfacial transport to intermolecular interaction strength and position in the phase diagram. Our results establish a quantitative connection between interfacial properties and condensate dynamics, revealing how their interplay gives rise to distinct transport regimes.
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All authors Oihan Joyot, Zoé Ferrand, Fernando Muzzopappa, Pierre Weiss, Fabian Erdel
Materials Science
Martensitic-like transition between liquid crystalline and crystalline phases of prototypical discotic organic semiconductor
Nurjahan Khatun, Joe F. Khoury, Agnes C. Nkele et al. (+7 more)
Phase transitions between crystalline solids occur either through the nucleation and growth mechanism, a process that is slow and destructive or through the
diffusion-less and order preserving Martensitic route. In both organic and inorganic materials, Martensitic transformations are known to occur only between phases with crystalline
symmetry. We demonstrate here that for canonical discotic organic
semiconductor HAT6, the transition between the
liquid crystalline columnar hexagonal phase (ColH) and the crystalline solid can occur through a mechanism that exhibits the hallmarks of Martensitic transformations: orientational correlations between parent and daughter phases, structural reversibility, and ultrafast kinetics. To access Martensitic-like solidification, the ColH phase of HAT6 is biaxially aligned in lithographically defined microchannels and crystallization is induced on deep supercooling. The transition mechanism is studied using a combination of polarized optical microscopy and X-ray scattering. At the largest accessible supercooling, the ColH -
Crystal phase transition occurs at speeds of ~100 micrometer/s, a value that is seven orders of magnitude greater than the theoretical prediction for growth from isotropic melts. Our work suggests that Martensitic-like transformations can occur even between
liquid crystals and
crystals and are therefore more general than previously believed. Further, our work demonstrates that Martensitic-like transformations of anchored
liquid crystals can be used to grow biaxially aligned
crystals of organic molecules over arbitrarily long distances. As
lattice alignment over large areas is desirable for devices like field-effect transistors and as several high-performance molecular
semiconductors exhibit a ColH phase, our results hold general significance for organic electronics.
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All authors Nurjahan Khatun, Joe F. Khoury, Agnes C. Nkele, Lingyu Wang, Tieqiong Zhang, Partha P. Paul, Paul Chibuike Okoli, Nabila Shamim, Matteo Pasquali, Kushal Bagchi
Disordered Systems and Neural Networks
The Symmetric Perceptron: a Teacher-Student Scenario
Giovanni Catania, Aurélien Decelle and Suhanee Korpe
We introduce and solve a teacher-student formulation of the symmetric binary Perceptron, turning a traditionally storage-oriented model into a planted inference problem with a guaranteed solution at any sample density. We adapt the formulation of the symmetric Perceptron which traditionally considers either the u-shaped potential or the rectangular one, by including labels in both regions. With this formulation, we analyze both the Bayes-optimal regime at for noise-less examples and the effect of thermal noise under two different potential/classification rules. Using annealed and quenched free-
entropy calculations in the high-dimensional limit, we map the phase diagram in the three control parameters, namely the sample density $\alpha$, the distance between the origin and one of the symmetric hyperplanes $\kappa$ and temperature $T$, and identify a robust scenario where learning is organized by a second-order instability that creates teacher-correlated suboptimal states, followed by a first-order transition to full
alignment. We show how this structure depends on the choice of potential, the interplay between metastability of the suboptimal solution and its melting towards the planted configuration, which is relevant for Monte Carlo-based optimization
algorithms.
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Mesoscale and Nanoscale Physics
Tensor network methods for bound electron-hole complexes beyond strong and weak confinement in nanoplatelets
Bruno Hausmann and Marten Richter
In
semiconductor nanostructures, optical excitation typically creates bound electron-hole states, such as
excitons, trions, and larger complexes. Their relative motion is described by the Wannier equation, which is valid only for spatially extended motion in the Coulomb-dominated, weak-confinement limit. Other small nanostructures, such as
quantum dots, are in the confinement-dominated strong confinement regime, where the wavefunction factorizes into independent electron and hole parts. Nanoplatelets are in between the two regimes and require solving an unfactorized higher-dimensional Schrödinger equation, which is computationally expensive. This work demonstrates how tensor networks can partially overcome this problem, using CdSe nanoplatelets as an example. The method is also applicable to related two-dimensional systems. As a demonstration, we calculate the excitonic and trionic ground states, as well as several excited states, for nanoplatelets of varying sizes, including their energies and oscillator strengths. More importantly, overall strategies for using tensor networks in real space for systems under intermediate confinement have been developed.
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Materials Science
Self-thermometry measurements of the adiabatic temperature change in first-order phase transition magnetocaloric materials
Daniela O. Bastos, André M. R. Soares, Leonor Andrade et al. (+8 more)
Accurately measuring the magnetocaloric effect is necessary to foster the development of
magnetic refrigeration devices. However, current methods are inconvenient, requiring different instruments to measure each individual property or a custom-made setup. By measuring the time-varying magnetization in a commercially available VersaLab\textsuperscript{\textregistered} PPMS\textsuperscript{\textregistered} from
Quantum Design, we have determined the adiabatic temperature change ($\Delta$T$_{\textrm{ad}}$) of the first-order phase transition material Gd$_5$Si$_2$Ge$_2$, for a
magnetic field change of 0 to 1 T, under high
vacuum ($<$ 0.1 mTorr). For each temperature and
magnetic field, the
equilibrium magnetization is used as the magnetization-to-temperature conversion curve, allowing us to extend the validity of a previously proposed technique to the first-order phase transition material Gd$_5$Si$_2$Ge$_2$, which exhibits significant hysteresis. Our method thus enables full characterization (
magnetic entropy change, adiabatic temperature change, and heat capacity) of any magnetocaloric material, whether it has a first-order or a second-order phase transition, using a single instrument. Comparing to a directly measured $\Delta$T$_{\textrm{ad}}$, our method resulted in a peak $\Delta$T$_{\textrm{ad}}$ value of 4.47 K, within 1% of the directly measured value for a sample of the same composition.
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All authors Daniela O. Bastos, André M. R. Soares, Leonor Andrade, Randy K. Dumas, João S. Amaral, Kyle Dixon-Anderson, Yaroslav Mudryk, Victorino Franco, João P. Araújo, Rafael Almeida, João H. Belo
Mesoscale and Nanoscale Physics
Correlation-Driven Orbital Order Realizes 2D Metallic Altermagnetism
Nirmalya Jana, Atasi Chakraborty, Anamitra Mukherjee et al. (+1 more)
Two-dimensional metallic altermagnets are rare, and no correlated 2D material has been established to host large nonrelativistic
spin splitting. Here we show that spontaneous orbital order, driven by electronic correlations and
Fermi surface nesting, provides a general microscopic route to two-dimensional metallic altermagnetism. Antiferro-orbital ordering between the d$_{xz}$ and d$_{yz}$ orbitals breaks the equivalence of
magnetic sublattices with opposite
spins and generates a
symmetry-enforced altermagnetic
spin texture. As a concrete realization, we identify monolayer YbMn$_2$Ge$_2$ as a stable correlated metallic altermagnet exhibiting
giant nonrelativistic
spin splitting of order 1 eV. The resulting phase supports an exceptionally large and gate-tunable transverse
spin conductivity. These results establish correlation-driven orbital order as a robust and general mechanism for designing correlated altermagnets with large
spin splitting.
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All authors Nirmalya Jana, Atasi Chakraborty, Anamitra Mukherjee, Amit Agarwal
Statistical Mechanics · Cross-listed from math-ph
On the integrability structure of the deformed rule-54 reversible cellular automaton
Chiara Paletta and Tomaž Prosen
We study
quantum and
stochastic deformations of the rule-54 reversible cellular automaton (RCA54) on a 1+1-dimensional spatiotemporal
lattice, focusing on their integrability structures in two distinct settings. First, for the
quantum deformation, which turns the model into an interaction-round-a-face brickwork
quantum circuit (either on an infinite
lattice or with periodic boundary conditions), we show that the shortest-range nontrivial conserved charge commuting with the discrete-time
evolution operator has a density supported on six consecutive sites. By constructing the corresponding range-6 Lax operator, we prove that this charge belongs to an infinite tower of mutually commuting conserved charges generated by higher-order logarithmic derivatives of the transfer
matrix. With the aid of an intertwining operator, we further prove that the transfer
matrix commutes with the discrete-time
evolution operator. Second, for the
stochastic deformation, which renders the model into a Markov-chain
circuit, we investigate open boundary conditions that couple the system at its edges to
stochastic reservoirs. In this setting, we explicitly construct the non-
equilibrium steady state (NESS) by means of a staggered patch
matrix ansatz, a hybrid construction combining the previously used commutative patch-state ansatz for the undeformed RCA54 with the
matrix-product ansatz. Finally, we propose a simple empirical criterion for detecting integrability or exact solvability in a given model setup, introducing the notion of digit complexity.
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Other Condensed Matter · Cross-listed from quant-ph
A derivation of the late-time volume law for local operator entanglement
Guilherme Ilário Correr, John Goold and Marco Cattaneo
Local Operator
Entanglement (LOE) has emerged an indicator of
quantum chaos in many-body systems. Numerical studies have shown that, in chaotic systems, LOE grows linearly in time and displays a volume-law behavior at late times, scaling proportionally with the number of local degrees of freedom. Despite extensive numerical evidence, complemented by analytical studies in integrable systems, a fully analytical understanding of the emergence of the volume law remains incomplete. In this paper, we contribute toward this goal by deriving a late-time expression for LOE in chaotic systems that exhibits volume-law scaling. Our derivation proceeds by expressing the late-time LOE in the Liouville eigenstate basis and relies on three main assumptions: a higher-order non-resonance condition for the
Hamiltonian eigenenergies, the Eigenstate Thermalization Hypothesis (ETH) ansatz for the
matrix elements of the initial local operator, and the replacement of
Hamiltonian eigenstates with random states in the final expression for LOE. Under these assumptions, we obtain an explicit formula displaying volume-law scaling. Finally, we complement our analytical derivation with numerical simulations of the 1D mixed-field Ising model, testing the resulting formula and exploring the regime of validity of our assumptions.
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Mesoscale and Nanoscale Physics
Micromotion area as proxy for anomalous Floquet topological systems
Luca Asteria, Klaus Sengstock, André Eckardt et al. (+1 more)
Driven Floquet systems can realize topological phases with no static counterparts. These so-called anomalous Floquet
topology breaks the bulk-boundary correspondence based on the Chern number. The number of edge modes in each band gap is instead determined by another integer index, a winding number, which is calculated from the time
evolution operator of the bulk states within one driving period. While in the non-driven system, Chern markers provide a useful local proxy for the Chern number in the bulk, so far no such local bulk indicator is known for the winding number in Floquet systems. Here we consider two-band models and show that the area enclosed during a Floquet period by an initially localized particle signals the presence of an anomalous phase when it approaches half the unit
cell area. In general, we show that at the fine-tuned point of dispersionless dynamics during the micromotion, the enclosed area is quantized and an exact proportionality relation exists between the area and the winding number. Direct detection of anomalous
topology in real space could be realized in several
quantum simulation platforms, and could be useful for systems with disorder or interactions. Building on the connection between area and winding number, we also show a way to realize arbitrarily high winding numbers.
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All authors Luca Asteria, Klaus Sengstock, André Eckardt, Christof Weitenberg
Statistical Mechanics
Optimal threshold resetting in collective diffusive search
Arup Biswas, Satya N Majumdar and Arnab Pal
Stochastic resetting has attracted significant
attention in recent years due to its wide-ranging applications across physics, biology, and search processes. In most existing studies, however, resetting events are governed by an external timer and remain decoupled from the system's intrinsic dynamics. In a recent Letter by Biswas et al, we introduced threshold resetting (TR) as an alternative, event-driven optimization strategy for target search problems. Under TR, the entire process is reset whenever any searcher reaches a prescribed threshold, thereby coupling the resetting mechanism directly to the internal dynamics. In this work, we study TR-enabled search by $N$ non-interacting diffusive searchers in a one-dimensional box $[0,L]$, with the target at the origin and the threshold at $L$. By optimally tuning the scaled threshold distance $u = x_0/L$, the mean first-passage time can be significantly reduced for $N \geq 2$. We identify a critical population size $N_c(u)$ below which TR outperforms reset-free dynamics. Furthermore, for fixed $u$, the mean first-passage time depends non-monotonically on $N$, attaining a minimum at $N_{\mathrm{opt}}(u)$. We also quantify the achievable speed-up and analyze the operational cost of TR, revealing a nontrivial optimization landscape. These findings highlight threshold resetting as an efficient and realistic optimization mechanism for complex
stochastic search processes.
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Materials Science
Machine-Learned Interatomic Potentials for Predicting Physicochemical Properties of Molten Metal-Salt Systems for Calcium Electrolysis
M. Polovinkin, N. Rybin, D. Maksimov et al. (+5 more)
The design of efficient electrolysis devices for pure metal production requires accurate data on the properties of the melts used in the process. This work focuses on two key systems for calcium production: the molten Ca-Cu
alloy and the CaCl$_2$-KCl electrolyte. High-temperature experiments are often expensive and time-consuming; however, we demonstrate that molecular dynamics (MD) simulations driven by machine-learned Moment Tensor Potentials (MTPs), trained on highly accurate density functional theory data, offer an effective and accurate alternative. Our MTP-driven MD simulations accurately reproduce the structural, thermodynamic, and transport properties across a range of temperatures and compositions relevant to electrolysis systems. We report calculated densities, radial distribution functions, heat capacities, thermal conductivities, ionic conductivities (for the electrolyte), viscosities, and
diffusion coefficients, with deviations from experimental data within 20%. The strong agreement between calculations and experiments validates the proposed approach, establishing a robust framework for the computational exploration and optimization of
liquid systems in metallurgical applications.
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All authors M. Polovinkin, N. Rybin, D. Maksimov, F. Valiev, A. Khudorozhkova, M. Laptev, A. Rudenko, A. Shapeev
Mesoscale and Nanoscale Physics
Topological phases of polyacenes
Rakesh Kumar Malakar and Asim Kumar Ghosh
The introduction of Su-Schrieffer-Heeger model has led to a major breakthrough in the area of one-dimensional topological
insulators, even though this model was primarily formulated on an organic
polymer called $trans$-polyacetylene in order to explain its anomalous conductivity. In this study, a group of seven tight-binding models has been introduced which are formulated on another organic
polymer called polyacene, where a variety of topological phases have been observed in six models. Topological properties of the most common
geometric isomers known as $cis$-polyacene, and $trans$-polyacene have been investigated along with five additional modified polyacene structures. Although their
geometric structures differ by several
symmetries, tight-binding band structures of $cis$-polyacene and $trans$-polyacene are found the same, and again their topological characters are found totally opposite. The $trans$-polyacene is nontrivial as it exhibits topological phase with nonzero winding number, while the $cis$-polyacene is topologically trivial, although both the structures adhere to the same set of
symmetries required for the topological character of BDI class. However, $cis$-polyacene possesses additional mirror
symmetry in the real space but lacks inversion
symmetry. Additional two modified structures of $trans$-polyacene and three modified structures of $cis$-polyacene have been considered in order to induce the nontrivial
topology. Pair of flat bands is found both in modified $trans$-polyacene and $cis$-polyacene structures such that they are topologically nontrivial for $trans$-polyacene while trivial for $cis$-polyacene. Topological character of all the models is different.
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Strongly Correlated Electrons
Flat band driven competing charge and spin instabilities in the altermagnet CrSb
A. Korshunov, M. Alkorta, C.-Y. Lim et al. (+8 more)
The confinement of electronic wavefunctions in momentum space can give rise to flat electronic bands, where the quenching of kinetic energy enhances the density of states and amplifies interaction effects. Such conditions are fertile ground for emergent
quantum phases, as
spin, charge and
lattice degrees of freedom become strongly entangled. In these regimes, subtle competitions between intertwined order parameters often dictate the macroscopic ground state, producing complex and sometimes unexpected collective behavior. Here we show that the altermagnet CrSb provides a realization of this scenario, and uncover short-range charge-order fluctuations at the M point of the Brillouin zone, q*=(1/2 0), persisting above the Neel temperature (TN). Remarkably, these fluctuations collapse upon entering the magnetically ordered phase, revealing a direct and robust competition between charge and
spin order. At TN, the
phonon dispersion at q* develops a pronounced Kohn-like anomaly, signaling strong electron-
phonon coupling in the vicinity of the
magnetic transition. Below TN, exchange striction dramatically renormalizes the associated soft
phonon mode by approximately ~6 meV, the largest
spin-
phonon coupling ever reported. First-principles calculations attribute this behavior to a strong coupling between nearly dispersionless electronic states and a
phonon branch that appears unstable at the harmonic level only when no
magnetic order is considered, revealing the large sensitivity of the
lattice to
magnetic symmetry breaking. The competition between charge and
spin order parameters, amplified by flat-band physics, drives the observed
phonon anomaly and its abrupt reconstruction at TN. With its chemically simple structure and
symmetry-protected altermagnetic state, CrSb emerges as a model platform to explore how flat electronic bands mediate
giant spin-
phonon coupling and competing broken
symmetries.
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All authors A. Korshunov, M. Alkorta, C.-Y. Lim, F. Ballester, Cong Li, Zhilin Li, D. Chernyshov, A. Bosak, M. G. Vergniory, Ion Errea, S. Blanco-Canosa
Superconductivity
Thermal stability of pair density wave in a $d$-wave altermagnetic superconductor
Amrutha N Madhusuthanan and Madhuparna Karmakar
We study finite-momentum superconductivity in a two-dimensional $d$-wave altermagnetic
superconductor using a non-perturbative Monte Carlo approach beyond mean-field theory. We show that altermagnetism stabilizes a pair density wave (PDW) state without external
magnetic fields and enables its survival at finite temperatures with robust phase coherence. Our results establish altermagnetism as a promising route to realizing thermally stable PDW superconductivity and identify clear thermodynamic and spectroscopic signatures.
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Quantum Gases
A High-Flux Source of Cold Strontium with a Loading Rate of $4 \times 10^{10}$ atoms/s for Open Release
Thomas Walker, Anna L. Marchant, Elliot Bentine et al. (+17 more)
We present a high-flux source of cold strontium atoms based on a two-dimensional magneto-optical trap (2D MOT) and a Zeeman slower. We use the source to load a 3D MOT in a separate science chamber, observing a loading rate of $4 \times 10^{10}$ atoms/s – to our knowledge, the highest reported loading flux for strontium. To characterise the
vacuum pressure in the science chamber, we load the atoms into a
magnetic trap and measure a lifetime of between 8 and 24 seconds, depending on oven temperature. Finally, we characterise the atom flux and velocity distributions from the oven and from the 2D MOT source, finding reasonable agreement with models in the free molecular flow regime. Our results show it is possible to readily produce a cold strontium flux at comparable levels to alkali species, at oven temperatures compatible with long-term operation, and at
vacuum pressures suitable for state-of-the-art
quantum experiments. We make our design available at no cost, to benefit researchers in the
quantum community.
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All authors Thomas Walker, Anna L. Marchant, Elliot Bentine, Oliver Buchmueller, Katherine Clarke, Christopher Foot, Leonie Hawkins, Kenneth M. Hughes, Kamran Hussain, Ludovico Iannizzotto-Venezze, Alice Josset, Hamza Labiad, Dillen Lee, Timothy C. Thornton-Sparkes, Tristan Valenzuela, Maurits van der Grinten, Andrew Vick, Mark G. Bason, Charles F. A. Baynham, Richard Hobson
Quantum Gases · Cross-listed from math.NA
An efficient compact splitting Fourier spectral methods for computing the dynamics of rotating spin-orbit coupled spin-2 Bose-Einstein condenstates
Xin Liu, Ziqing Xie, Yongjun Yuan et al. (+2 more)
This paper investigates the dynamics of
spin-2 Bose-Einstein condensates (BECs) with rotation and
spin-orbit coupling (SOC). In order to better simulate the dynamics, we present an efficient high-order compact splitting
Fourier spectral method. This method splits the
Hamiltonian into a linear part, which consists of the Laplace, rotation and SOC terms, and a nonlinear part that includes all the remaining terms. The wave function is well approximated by the
Fourier spectral method and is numerically accessed with discrete Fast
Fourier transform (FFT). For linear subproblem, the handling of rotation term and SOC term poses a major challenge. Using a function mapping based on rotation, we can integrate the linear subproblem exactly and explicitly. This mapping we propose not only helps eliminate the rotation term, but also prevents the SOC term from evolving into a time-dependent form. The nonlinear subproblem is integrated analytically in physical space. Such "compact" splitting involves only two operators and facilitates the design of high-order splitting schemes. Our method is spectrally accurate in space and high order in time. It is efficient, explicit, unconditionally stable and simple to implement. In addition, we derive some dynamical properties and carry out a systematic study, including accuracy and efficiency tests, dynamical property verification, the SOC effects and dynamics of
vortex lattice.
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All authors Xin Liu, Ziqing Xie, Yongjun Yuan, Yong Zhang, Xinyi Zhao