Statistical Mechanics
On Sak's criterion for statistical models with long-range interaction
Tianning Xiao, Ziyu Liu, Zhijie Fan et al. (+1 more)
Determining the threshold value $\sigma_*$ that separates the short-range (SR) and long-range (LR) universality classes in phase transitions remains a controversial issue. While Sak's criterion, $\sigma_* = 2 - \eta_{\mathrm{SR}}$, has been widely accepted, recent studies of two-dimensional (2D) models with long-range interactions have challenged it. In this work, we focus on the crossover between LR and SR criticality in several classical 2D statistical models, including the XY, Heisenberg, percolation, and Ising models, whose interactions decay as $1/r^{2+\sigma}$. Our previous simulations for the XY, Heisenberg, and percolation models consistently indicate a universal boundary at $\sigma_* = 2$. Here, we complete the picture by performing large-scale Monte Carlo simulations of the 2D LR-Ising model, reaching
lattice sizes up to $L = 8192$. By analyzing the Fortuin-Kasteleyn critical
polynomial $R_p$, the Binder ratio $Q_m$, and the anomalous dimension $\eta$, we obtain convergent and self-consistent evidence that the universality class already changes sharply at $\sigma = 2$. Taken together, these results establish a unified scenario for LR interacting systems: across all studied models, the crossover from LR to SR universality occurs at $\sigma_* = 2$.
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All authors Tianning Xiao, Ziyu Liu, Zhijie Fan, Youjin Deng
Mesoscale and Nanoscale Physics
Edge spin galvanic effect in altermagnets
L. E. Golub
The edge
spin galvanic effect (ESGE) in $d$-wave altermagnets is proposed. ESGE is a creation of an electrical current flowing along the edge of the sample, which is driven by the
spin orientation of charge carriers. The ESGE current is formed owing to the altermagnetic
spin splitting and the scattering of carriers by the edge of the sample. The current is sensitive to the orientation of the edge in respect to the main axes of the altermagnet. The edge
spin galvanic current reverses its direction upon a reversal of the non-
equilibrium spin direction or the Néel vector. We also propose the pure
spin edge photocurrent excited by polarized radiation and formed at the edges of a sample. Its dependence on the radiation polarization and frequency is analyzed. The application of an external
magnetic field converts this pure
spin photocurrent into an electric current along the edge.
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Materials Science · Cross-listed from physics.chem-ph
Teaching a Transformer to Think Like a Chemist: Predicting Nanocluster Stability
João Marcos T. Palheta, Octavio Rodrigues Filho, Mohammad Soleymanibrojeni et al. (+6 more)
Atomically precise metal nanoclusters bridge the molecular and bulk regimes, but designing bimetallic motifs with targeted stability and reactivity remains challenging. Here we combine density functional theory (DFT) and physics-grounded predictive artificial intelligence to map the configurational landscape of 13-atom icosahedral nanoclusters X$_{12}$TM, with hosts X = (Ti, Zr, Hf), and Fe and a single transition–metal dopant spanning the 3$d$-5$d$ series.
Spin-polarized DFT calculations on 240 bimetallic clusters reveal systematic trends in binding and formation energies, distortion penalties, effective coordination number, d-band centre, and HOMO-LUMO gap that govern the competition between core-shell (in) and surface-segregated (out) arrangements. We then pretrain a
transformer architecture on a curated set of 2968 unary clusters from the
Quantum Cluster Database and fine-tune it on bimetallic data to predict formation energies and in/out preference, achieving mean absolute errors of about $0.6-0.7$eV and calibrated uncertainty intervals. The resulting model rapidly adapts to an unseen Fe-host domain with only a handful of labelled examples. At the same time,
attention patterns and Shapley attributions highlight size mismatch, $d$-electron count, and coordination environment as key descriptors. All data, code, and workflows follow FAIR/TRUE principles, enabling reproducible, interpretable screening of unexplored nanocluster chemistries for catalysis and energy conversion.
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All authors João Marcos T. Palheta, Octavio Rodrigues Filho, Mohammad Soleymanibrojeni, Alexandre Cavalheiro Dias, Diego Guedes-Sobrinho, Wolfgang Wenzel, Roland Aydin, Celso R. C. Rêgo, Maurício Jeomar Piotrowski
Strongly Correlated Electrons
Anomalous impurity-induced charge modulations in black phosphorus
Byeongin Lee, Junho Bang, Sayan Banerjee et al. (+6 more)
We observe anomalous charge modulations induced by ionized indium
impurities on the surface of the
semiconductor black phosphorus by scanning tunneling microscopy (STM). When the
impurities are switched into a negatively charged state by the STM tip, periodic charge modulations emerge around the
impurity center, but strictly confined by the nanoscale
impurity potential. These modulations form a distorted triangular pattern, whose periodicity remains unchanged in a wide range of positive bias. Furthermore, these local charge orders exhibit an anisotropy opposite to that expected based on the anisotropy of the
Fermi surface, challenging a simple band-structure interpretation. Our experiment demonstrates the possibility of creating and manipulating macroscopic charge orders through
impurity engineering.
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All authors Byeongin Lee, Junho Bang, Sayan Banerjee, João Augusto Sobral, Young Woo Choi, Claudia Felser, Mathias S. Scheurer, Jian-Feng Ge, Doohee Cho
Materials Science
Bulk photovoltaic effect in MoSe$_2$ and Janus MoSSe sliding ferroelectrics
Roumita Roy, Giuseppe Cuono and Silvia Picozzi
We present a first-principles study of the nonlinear optical properties of sliding ferroelectric
bilayers based on MoSe$_2$ and Janus MoSSe. Two Janus configurations are considered: i) one
bilayer where the two intralayer polarizations caused by Janus chemical asymmetry cancel each other out, yielding photocurrent spectra comparable to pristine MoSe$_2$
bilayers; ii) another
bilayer where the intralayer polarizations add up, for which the photoresponses are strongly enhanced. Our results show that photocurrent generation in the polar Janus structures is predominantly governed by vertical chemical asymmetry, with limited dependence on the sliding direction. These findings highlight complementary design strategies: interlayer sliding enables sensitivity to external tuning, while the Janus intralayer polarization enhances photoresponses in the visible range. The interplay between composition and stacking therefore provides a versatile platform for tailoring light-matter interactions in 2D ferroelectric materials.
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Superconductivity
Evolution of Correlated Electrons in ${\rm La_3Ni_2O_7}$ at Ambient Pressure: a Study of Double-Counting Effect
Zhong-Yi Xie, Zhihui Luo, Wéi Wú et al. (+1 more)
We employ cluster extension of dynamical mean-field theory (CDMFT) to systematically investigate the impact of double counting corrections on the correlated electronic structure of ${\rm La_3Ni_2O_7}$ under ambient pressure. By adjusting double-counting parameters, while maintaining a fixed
Fermi surface, we observe a pronounced orbital-selective density of states change: the $d_{z^2}$ orbital undergoes significant variation near the
Fermi level with increasing $E_{dc}^z$, while the $d_{x^2-y^2}$ orbital remains essentially unchanged throughout the entire range. Analysis of renormalization factor show the monotonic dependence with double counting in both $d_{z^2}$ and $d_{x^2-y^2}$ orbital, and it also identifies an optimal double counting window in $d_{z^2}$ orbital aligns with experimental values. We also find the interlayer Matsubara self energy exhibits non-monotonic dependence on $E_{dc}^z$, deviating from theoretical predictions. This anomaly is attributed to the metallization of oxygen-bridged pathways, which disrupts the prerequisite for charge transfer via apical oxygen. Our results establish $E_{dc}$ as a critical control parameter for correlated electronic structure in ${\rm La_3Ni_2O_7}$ and provide a computational framework for resolving orbital-dependent correlation effects in layered materials.
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All authors Zhong-Yi Xie, Zhihui Luo, Wéi Wú, Dao-Xin Yao
Statistical Mechanics
Smeared phase transition in the dissipative random quantum Ashkin-Teller model
Pedro S. Farinas, Rajesh Narayanan and José A. Hoyos
We study the effects of dissipation in the phase diagram of the random
quantum Ashkin-Teller model by means of a generalization of the strong-disorder renormalization group combined with adiabatic renormalization. This model has three phases and three
quantum phase transitions. We demonstrate that the combined effect of Ohmic dissipation and quenched disorder smears two out of the three
quantum phase transitions. Our analytical theory allows us to understand why one of the phase transitions remains sharp. This is due to a cancellation of the dissipation effects on the nontrivial nature of the intertwined order parameter of one of the phases.
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Mesoscale and Nanoscale Physics
Exact and mean-field analysis of the role of Hubbard interactions on flux driven circular current in a quantum ring
Rahul Samanta, Santanu K. Maiti and Shreekantha Sil
We investigate circular current in both ordered and disordered Hubbard
quantum rings threaded by
magnetic flux, employing exact diagonalization and the Hartree-Fock mean-field approach within the tight-binding framework. The influence of on-site and extended Hubbard interactions, disorder, and electron filling on the persistent current is systematically analyzed. To construct the full many-body
Hamiltonian, we introduce a linear table formalism, which, to our knowledge, has been rarely used in this context. In ordered rings, the current decreases monotonically with increasing on-site repulsion, while the impact of the extended interaction depends strongly on the filling factor. At low filling, stronger extended interaction suppresses the current, whereas near half-filling, it enhances the current up to a critical ratio, half of the on-site strength, before reducing it. Disorder significantly modifies these behaviors, notably enhancing the current at less than quarter-filling with increasing extended interaction. The localization properties of eigenstates, examined via the inverse participation ratio, further support the crucial roles of filling and the interplay between on-site and extended interactions in governing persistent current.
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Soft Condensed Matter
Why life is hot
Tanja Schilling, Patrick B. Warren and Wilson Poon
The process of
evolution by natural selection leads to phenotypes of increasing fitness. For cellular chemical reaction networks, this means optimising a variety of fitness functions such as robustness, precision, or sensitivity to external stimuli. We argue that these diverse goals can be achieved by a versatile, generic mechanism: coupling chemical reaction networks to reservoirs that are strongly out of
equilibrium. Using theory and numerics we show that this mechanism of optimisation comes at the price of significant heat dissipation. We compute the heat flux caused by kinetic proofreading in Escherichia coli and show that it constitutes a significant fraction of the total heat flux experimentally measured in this model organism. We then demonstrate that the degree of optimality achievable saturates, and that Nature appears to operate near saturation despite high energetic costs. We argue that `life is hot' largely because of the need for a versatile mechanism to optimise a variety of fitness functions.
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Materials Science
Heat transport in superionic materials via machine-learned molecular dynamics
Wenjiang Zhou, Benrui Tang, Zheyong Fan et al. (+3 more)
Precise modeling and understanding of heat transport in the superionic phase are of great interest. Although simulations combining Green-Kubo (GK) molecular dynamics with machine-learned potentials (MLPs) stand as a promising approach, substantial challenges remain due to the crucial impact of atomic
diffusion. Here, we first show that the thermal conductivity (${\kappa}$) of superionic materials calculated via conventional GK integral of the energy flux varies notably with the MLP model. Subsequently, we highlight that reliable, model-independent $\kappa$ values can be obtained by applying Onsager's reciprocal relations to correctly capture the coupled heat and mass transport. Remarkably, an anomalously invariant $\kappa$ can be observed over a wide temperature range, distinct from the characteristic trends in traditional
crystals and glasses. In addition, we illustrate that conventional $\kappa$ decompositions into kinetic, potential, and cross terms suffer from ambiguities in the physical interpretation, despite their mathematical rigor. Finally, we propose a criterion for the necessity of the Onsager correction and reveal the underlying mechanism as a competition between thermally and chemically driven ion fluxes.
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All authors Wenjiang Zhou, Benrui Tang, Zheyong Fan, Federico Grasselli, Stefano Baroni, Bai Song
Materials Science
Accelerating discovery of infrared nonlinear optical materials with large shift current via high-throughput screening
Aiqin Yang, Dian Jin, Mingkang Liu et al. (+4 more)
Discovering nonlinear optical (NLO) materials with strong shift current response, particularly in the infrared (IR) regime, is essential for next-generation optoelectronics yet remains highly challenging in both experiments and theory, which still largely relies on case by case studies. Here, we employ a high-throughput screening strategy, applying a multi-step filter to the Materials Project database (>154,000 materials), which yielded 2,519 candidate materials for detailed first-principle evaluation. From these calculations, we identify 32 NLO materials with strong shift current response ($\sigma$ > 100 $\mu A/V^2$). Our work reveals that layered structures with $C_{3v}$
symmetry and heavy $p$-block elements (e.g. Te, Sb) exhibit apparent superiority in enhancing shift current. More importantly, 9 of these compounds show shift current response peaks in the IR region, with the strongest reaching 616 $\mu A/V^2$, holding significant application potential in fields such as IR photodetection, sensing, and energy harvesting. Beyond identifying promising candidates, this work establishes a comprehensive and high-quality first-principles
dataset for NLO response, providing a solid foundation for future AI-driven screening and accelerated discovery of high-performance NLO materials, as demonstrated by a prototype machine-learning application.
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All authors Aiqin Yang, Dian Jin, Mingkang Liu, Daye Zheng, Qi Wang, Qiangqiang Gu, Jian-Hua Jiang
Superconductivity
Demonstration of surface-engineered oxidation-resistant Nb-Nb thermocompression bonding toward scalable superconducting quantum computing architectures
Harsh Mishra, Yusuke Kozuka, Sathish Bonam et al. (+4 more)
Scalable
quantum computing currently requires a large array of
qubit integration, but present two-dimensional interconnects face challenges such as wiring congestion, electromagnetic interference, and limited cryogenic space. To overcome this challenge, implementing three-dimensional (3D) vertical architectures becomes crucial. Niobium (Nb), due to its excellent superconducting characteristics and strong fabrication process compatibility, stands out as a
prime material choice. The main challenge in Nb-Nb bonding is the presence of an
oxide layer at the interface, even after post-bonding annealing across various bonding methods. The native Nb
oxide forms rapidly in air, creating a resistive barrier to supercurrent flow and introducing two-level system losses that degrade
qubit coherence while increasing the overall thermal budget. These issues show the need for effective surface engineering to suppress oxidation during bonding. This study introduces an ultrathin gold (Au) capping layer as a passivation strategy to prevent oxygen incorporation at the Nb surface. This approach enables low-temperature Nb-Nb thermocompression bonding at 350 {\deg}C under a reduced bonding pressure of 0.495 MPa. Detailed microstructural and interfacial analyses confirm that Au passivation effectively suppresses
oxide formation and hence enhances bonding uniformity and strength with keeping the superconductivity, establishing a robust route toward low-temperature, low-pressure Nb-Nb bonding for scalable 3D superconducting
quantum computing architectures.
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All authors Harsh Mishra, Yusuke Kozuka, Sathish Bonam, Jun Uzuhashi, Praveenkumar Suggisetti, Tadakatsu Ohkubo, Shiv Govind Singh
Superconductivity
Superconductivity onset above 60 K in ambient-pressure nickelate films
Guangdi Zhou, Heng Wang, Haoliang Huang et al. (+7 more)
Ambient-pressure superconductivity in nickelates has been capped at an onset transition temperature ($T_{c}^{onset}$) of ~50 K, a value that remains lower than the cuprate (~133 K) and iron-based (~55 K) counterparts, despite the promise shown under high pressure. Here, we report ambient-pressure superconductivity onset at ~63 K in epitaxial (La,Pr)3Ni2O7 thin films grown under compressive strain on SrLaAlO4 substrates. This $T_{c}$ leap is enabled by pushing our gigantic-oxidative atomic-layer-by-layer epitaxy (GAE) method into an extreme non-
equilibrium growth regime. It simultaneously enhances kinetics via higher temperatures and achieves full oxygenation in situ without post-annealing. Synchrotron X-ray diffraction and scanning transmission electron microscopy confirm that this approach yields films of large-scale crystalline purity, overcoming the inherent metastability of the strained superconducting phase. Transport measurements reveal a zero-resistance temperature ($T_{c}^{zero}$) reaching ~37 K, while mutual inductance measurements demonstrate a robust diamagnetic transition starting at ~23 K. These films exhibit a systematic
evolution in their normal-state resistivity-temperature curve: the power-law exponent $\alpha$ evolves from
Fermi-
liquid-like ($\alpha$ ~2) at lower $T_{c}^{onset}$ to strange-metal-like ($\alpha$ ~1) in higher $T_{c}^{onset}$ samples, directly linking the enhanced superconductivity to non-
Fermi liquid behavior. Mapping the
vortex melting phase diagram by the mutual inductance technique further reveals 2D melting limit suppressed to near zero, which demonstrates significantly stronger interlayer coupling than that of cuprates. These results identify the nickelates as an ambient-pressure strange-metal high-temperature
superconductors with strong interlayer coupling.
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All authors Guangdi Zhou, Heng Wang, Haoliang Huang, Yaqi Chen, Fei Peng, Wei Lv, Zihao Nie, Wei Wang, Qi-Kun Xue, Zhuoyu Chen
Materials Science
Boosting the Memory Window of Memristive Stacks via Engineered Interfaces with High Ionic Mobility
José Diogo Costa, Daniel Veira-Canle, Noa Varela-Domínguez et al. (+8 more)
Realizing the potential of
oxide-based memristive devices for high-density data storage and energy-efficient computing still relies on overcoming key technical challenges, including the need for a larger number of stable resistance states, faster switching speeds, lower SET/RESET voltages, improved endurance, and reduced variability. Addressing these limitations requires innovative material design strategies. Here, we demonstrate that introducing a thin layer of
oxide-ion conductor SrCoO3-x between the metal and the SrTiO3-based memristive elements expands the number of distinguishable resistance states from about 8 to about 22. This modification also reduced the SET/RESET voltage by 50% and markedly improved device endurance, albeit with a trade-off of reduced state retention. To assess the performance of this architecture, we trained a two-layer fully connected neural network using the experimental SrTiO3/SrCoO3-x memristor characteristics on the MNIST handwritten digit
dataset. Networks with hidden-layer sizes between 64 and 256
neurons achieved classification errors below 7%. Finally, we confirmed the transferability of this interface-engineering approach by applying it to HfOx-based devices, achieving a consistent enhancement in the resistive state window.
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All authors José Diogo Costa, Daniel Veira-Canle, Noa Varela-Domínguez, Nicholas Davey, Victor Leborán, Rafael Ramos, Fèlix Casanova, Luis E. Hueso, Victor M. Brea, P. López, Francisco Rivadulla
Disordered Systems and Neural Networks
Diffusive geodesics wandering in networks of rigid chains
Ulysse Marquis
We introduce an ensemble of spatial networks built from the junctions of hindered-rotation chains, incorporating directional correlations between bonds, an aspect ignored in the standard network modeling paradigm. The emergent random networks support geodesics with a wandering exponent $\xi = 1/2$, and a travel-time fluctuation exponent $\chi = 0$, consistent with the KPZ relation, yet violating the bound~$\chi\geq1/8$ predicted in the Poissonian framework. Transverse deviations follow the Kolmogorov distribution, indicating similarities between Brownian bridge excursions and geodesics in a random medium with correlated edges orientations. These results reveal a new universality class of Euclidean first-passage percolation, where local orientational
memory reshapes transport properties and challenges existing bounds for random spatial networks.
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Quantum Gases
Robust, fast, and efficient formation of stable tetratomic molecules from ultracold atoms via generalized stimulated Raman exact passage
Jia-Hui Zhang, Wen-Yuan Wang and Fu-Quan Dou
The study of the conversion of ultracold atoms into molecules has long remained a hot topic in atomic, molecular, and optical physics. However, most prior research has focused on diatomic molecules, with relatively scarce exploration of polyatomic molecules. Here we propose a two-step strategy for the formation of stable ultracold tetratomic molecules. We first suggest a generalized nonlinear stimulated Raman exact passage (STIREP) technique for the coherent conversion of ultracold atoms to tetratomic molecules, which is subsequently followed by a chainwise-STIREP technique to transfer the resulting molecules into a sufficiently stable ground state. Through systematic numerical analysis, we demonstrate that the proposed two-step strategy holds great potential for the robust, fast, and efficient formation of stable ultracold tetratomic molecules.
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Other Condensed Matter
Crossover from Universal Depinning to Free Domain-Wall Dynamics in Ultrathin Iron Garnet Films
V. Jeudy, D. Gouéré, N. Beaulieu et al. (+7 more)
Magnetic domain walls display universal, disorder-controlled elastic dynamics at low drive, and texture-governed free motion at high drive. Here, we establish the crossover mechanism between these two regimes. Using experiments in ultrathin epitaxial iron garnet films and Landau-Lifshitz-Gilbert simulations, including disorder, thermal, and internal texture effects, we uncover a disorder- and temperature-dependent precessional flow that bridges pinned and free dynamics. We further demonstrate that the exceptionally low pinning in garnets arises from the weak coupling between domain walls and disorder, together with a correlation length that exceeds the wall width.
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All authors V. Jeudy, D. Gouéré, N. Beaulieu, S. Husain, R. D{\i}az Pardo, A. Thiaville, J. Sampaio, J-M George, A. Anane, J. Ben Youssef
Strongly Correlated Electrons · Cross-listed from quant-ph
Fermionic neural Gibbs states
Jannes Nys and Juan Carrasquilla
We introduce fermionic neural Gibbs states (fNGS), a variational framework for modeling finite-temperature properties of strongly interacting
fermions. fNGS starts from a reference mean-field thermofield-double state and uses neural-network transformations together with imaginary-time
evolution to systematically build strong correlations. Applied to the doped
Fermi-Hubbard model, a minimal
lattice model capturing essential features of strong electronic correlations, fNGS accurately reproduces thermal energies over a broad range of temperatures, interaction strengths, even at large dopings, for system sizes beyond the reach of exact methods. These results demonstrate a scalable route to studying finite-temperature properties of strongly correlated fermionic systems beyond one dimension with neural-network representations of
quantum states.
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Statistical Mechanics · Cross-listed from hep-th
Modular Hamiltonian of the massive scalar field on the half line: A numerical approach
Christoph Minz and Erik Tonni
We study the modular
Hamiltonian of an interval for the ground state of a massive free scalar field on the half line with Robin boundary conditions, by employing a numerical method. When the interval is adjacent to the boundary, we find numerical evidence that the modular
Hamiltonian is non-local, except for the limiting cases of the massless scalar satisfying either Dirichlet or Neumann boundary conditions. When the interval is separated from the boundary, the numerical analysis indicates that the modular
Hamiltonian is non-local for all these boundary conditions and any value of the mass.
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Quantum Gases
Collective cluster nucleation dynamics in quantum magnets
Philip Osterholz, Fabio Bensch, Shuanghong Tang et al. (+4 more)
Strongly interacting many-body systems exhibit collective properties that emerge from complex correlations among microscopic degrees of freedom. These cooperative phenomena govern the non-
equilibrium response of
quantum systems, with relevance ranging from condensed matter physics to
quantum field theories describing fundamental aspects of our universe. Understanding such emergent dynamics from first principles remains one of the central challenges in
quantum many-body physics. Here we report on the observation of collective cluster nucleation dynamics following quenches in 2D
ferromagnetic quantum Ising systems implemented in an atomic Rydberg array. Our experiments reveal two distinct regimes: In the confined regime, we observe an energy-dependent cluster size, revealing large collective clusters exceeding ten
spins. In contrast, the deconfined regime is characterized by kinetically constrained, avalanche-like nucleation dynamics involving the entire system. Our findings establish a new frontier for
quantum simulations with Rydberg arrays, enabling controlled exploration of non-
equilibrium phenomena previously out of reach. Beyond advancing experimental capabilities, they provide fundamental insights into highly correlated processes with implications that reach from
quantum magnetism and glassy dynamics to cosmological models of the early universe.
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All authors Philip Osterholz, Fabio Bensch, Shuanghong Tang, Silpa Baburaj Sheela, Björn Sbierski, Igor Lesanovsky, Christian Groß
Strongly Correlated Electrons · Cross-listed from quant-ph
Probing chiral topological states with permutation defects
Yarden Sheffer, Ruihua Fan, Ady Stern et al. (+2 more)
The hallmark of two-dimensional
chiral topological phases is the existence of anomalous gapless modes at the spatial boundary. Yet, the manifestation of this edge anomaly within the bulk ground-state wavefunction itself remains only partially understood. In this work, we introduce a family of multipartite
entanglement measures that probe chirality directly from the bulk wavefunction. Our construction involves applying different permutations between replicas of the ground state wavefunction in neighboring spatial regions, creating "permutation defects" at the boundaries between these regions. We provide general arguments for the robustness of these measures and develop a field-theoretical framework to compute them systematically. While the standard topological field theory prescription misses the
chiral contribution, our method correctly identifies it as the
chiral conformal field theory partition function on high-genus Riemann surfaces. This feature is a consequence of the bulk-edge correspondence, which dictates that any regularization of the theory at the permutation defects must introduce gapless boundary modes. We numerically verify our results with both free-
fermion and strongly-interacting
chiral topological states and find excellent agreement. Our results enable the extraction of the
chiral central charge and the
Hall conductance using a finite number of wavefunction replicas, making these quantities accessible to Monte-Carlo numerical techniques and noisy intermediate-scale
quantum devices.
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All authors Yarden Sheffer, Ruihua Fan, Ady Stern, Erez Berg, Shinsei Ryu
Statistical Mechanics
Persson's Theory of Purely Normal Elastic Rough Surface Contact: A Tutorial Based on Stochastic Process Theory
Yang Xu, Xiaobao Li, Qi Chen et al. (+1 more)
Persson's theory of purely normal rough surface contact was developed two decades ago during the study of tire-road interaction, and gradually became one of the dominant approaches to study the solid-solid interaction between rough surfaces. Contrary to its popular applications in various cross-disciplinary fields, the fundamental study of Persson's theory of contact attracted little
attention from the tribology and contact mechanics communities. As far as the authors know, many researchers struggle to understand the derivation of the theory. Few attempts have been made to clarify the oversimplified derivation provided by Persson (Persson, 2001). The present work provides a detailed tutorial on Persson's theory, which does not simply follow the commonly adopted derivation initiated by Persson. A new derivation is given based on
stochastic process theory, assuming that the variation of the random contact pressure with respect to scale is a Markov process. We revisit the essential assumptions utilized to derive the
diffusion equation, boundary conditions, drift and
diffusion coefficients, and closed-form results. This tutorial can serve as a self-consistent introduction for solid mechanicians, tribologists, and postgraduate students who are not familiar with Persson's theory, or who struggle to understand it.
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All authors Yang Xu, Xiaobao Li, Qi Chen, Yunong Zhou
Quantum Gases · Cross-listed from quant-ph
Probing False Vacuum Decay and Bubble Nucleation in a Rydberg Atom Array
Yu-Xin Chao, Peiyun Ge, Zhen-Xing Hua et al. (+8 more)
In
quantum field theory (QFT), the "
vacuum" is not just empty space but the lowest-energy state of a
quantum field. If the energy landscape has multiple local minima, the local ground states are the false
vacuum (FV) which can tunnel towards the global ground state (true
vacuum, TV). This process exhibits signature akin to classical supercooled gas transitions and many-body tunneling in discrete
quantum systems. Here, we study the FV decay and bubble nucleation in a Rydberg atom ring. The $1/r^6$ van-der-Waals interactions and individual-site addressability allow us to explore physics beyond the standard Ising model. We observe that the FV decay rate decreases exponentially with the inverse of the
symmetry-breaking field, directly mirroring QFT predictions. Moreover, we demonstrate that even minor deviations from the ideal metastable state can cause a stark departure from this universal scaling law. Extending beyond short-time decay dynamics, we also examine resonant bubble nucleation, a feature distinctive to systems with discrete energy spectra. Our findings and methods open avenues for future studies of many-body tunneling in higher dimensions or more complex geometries.
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All authors Yu-Xin Chao, Peiyun Ge, Zhen-Xing Hua, Chen Jia, Xiao Wang, Xinhui Liang, Zongpei Yue, Rong Lu, Meng Khoon Tey, Xiao Wang, Li You
Mesoscale and Nanoscale Physics
Hole to Electron Crossover in a (Cd,Mn)Te Quantum Well through Surface Metallization
Amadeusz Dydniański, Mateusz Raczyński, Aleksandra Łopion et al. (+5 more)
In this work we look into how the contact material influences the local charge properties of a p-type CdTe-based
quantum well. We study five metals deposited as 10 nm layers on the sample surface: Au, Ag, Cr, Ni and Ti. We use magneto-spectroscopy to discriminate their charge states through monitoring the Zeeman shifts at singlet-triplet transitions. Most tested metals retain the original p-type of the QW, while gold and nickel coverage flips the local doping to n-type. This is attributed to a robust bonding of these two metals to the
semiconductor, efficiently passivating its surface and thus improving electron
diffusion from the metal to the
quantum well.
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All authors Amadeusz Dydniański, Mateusz Raczyński, Aleksandra Łopion, Tomasz Kazimierczuk, Jacek Kasprzak, Karolina Ewa Połczyńska, Wojciech Pacuski, Piotr Kossacki
Strongly Correlated Electrons
Phase transitions on the dark side of the Gross-Neveu model: Spontaneous $\textrm{O}(4N)$ symmetry breaking at repulsive coupling
Gabriel Osiander Rein, Fakher F. Assaad and Igor F. Herbut
Gross-Neveu model in 2+1 dimensions exhibits a continuous transition from gapless Dirac semimetal to the gapped
quantum anomalous
Hall (QAH)
insulator at a finite (attractive) coupling, at which the inversion and time-reversal
symmetry become spontaneously broken, and the
flavor O($M$)
symmetry remains preserved. A unification of leading order parameters of 2+1 dimensional $N$ four-component Dirac
fermions collects all Lorentz-singlet mass-like
fermion bilinears, except the one condensing in the QAH state, into an irreducible representation of the O($M=4N$), and predicts another phase transition in the Gross-Neveu model to occur at a strong (repulsive) coupling. Here, a fermionic auxiliary-field
quantum Monte Carlo
algorithm is employed in order to study a
lattice realization of the Gross-Neveu field theory in the repulsive regime, where the sign problem is absent. We indeed find the O($4N$)
symmetry breaking transition out of Dirac semimetal to occur and to be weakly first-order for $N=2$, relevant to
graphene. The size of the discontinuity and the magnitude of the critical coupling, however, both grow with $N$. Adding a finite chemical potential is found to break the
symmetry and cause superconductivity. These results are in broad agreement with the predictions of the unified field theory. Our
lattice model also displays an interesting exact O($2N$)
symmetry, a subgroup of the low-energy O($4N$), and has the ordered ground state with the order parameter that belongs to its $N(2N-1)$-dimensional representation. Other order parameters are also examined, and a certain hierarchy among those that belong to different representations of the exact $O(2N)$ is observed.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Ground state energy and phase transitions of Long-range XXZ using VQE
Mrinal Dev and Shraddha Sharma
The variational
quantum eigen solver (VQE), has been widely used to find the ground state energy of different
Hamiltonians with no analytical solutions and are classically difficult to compute. In our work, we have used VQE to identify the phase transition boundary for an infinite order phase transition. We use long-range XXZ (LRXXZ) chain for our study. In order to probe infinite order phase transition, we propose to utilise the ground state energy obtained from VQE. The idea rests on the argument that VQE requires an ansatz
circuit; therefore, the accuracy of the VQE will rely on this ansatz
circuit. We have designed this
circuit such that the estimated ground state energy is sensitive to the phase it is evaluated in. It is achieved by applying the constraint that the net
spin remains constant throughout the optimisation process. Consequently, the ansatz works in a certain phase where it gives relatively small random error, as it should, when compared to the error in ground state energy calculations of the other phases, where the ansatz fails. By identifying these changes in the behaviour of the error in ground state energy using VQE, we were able to determine the phase boundaries. Using exact diagonalisation, we also compare the behaviour of the energy gradient and energy gap across both the phase transition boundaries for this model. Further, by increasing the depth of the optimisation
circuit, we also accurately evaluate the ground energy of the LRXXZ chain for the value of coupling constant, J equal to -1
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Materials Science · Cross-listed from physics.optics
Exceptionally high Verdet constant in gold nanodisc arrays
Gajendra Mulay, Shraddha Choudhary, Ashwin A Tulapurkar et al. (+4 more)
Magneto-optical effects in non-
magnetic noble metals can be greatly enhanced by leveraging the in-plane Lorentz force at engineered plasmonic resonances. We demonstrate a 2D array of gold nanodiscs designed to host a hybrid resonance of localized plasmon and surface
lattice modes. The structure exhibits a Verdet constant of 1.98e6 deg/T.m, corresponding to a Faraday rotation of -0.15 deg at a 1 T
magnetic field. This Verdet constant represents a 15-fold enhancement over unpatterned gold and is highly competitive with many plasmon-enhanced diamagnetic nanostructures. These findings offer new opportunities for harnessing strong magneto-plasmonic effects in optoelectronic devices by patterning common non-
magnetic metals.
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All authors Gajendra Mulay, Shraddha Choudhary, Ashwin A Tulapurkar, Daria O Ignatyeva, Vladimir I Belotelov, Shriganesh S Prabhu, Venu Gopal Achanta
Materials Science
Ab initio study of Coulomb drag driven electron-hole bifluidity in doped graphene
Dwaipayan Paul, Elena Trukhan and Nakib H. Protik
Motivated by the notion that a preponderance of Coulomb interactions might lead to hydrodynamics, we carry out an ab initio calculation of the charge carrier transport properties of the electron-hole
plasma of doped
graphene. We include both the
phonon and Coulomb interactions within a momentum and band resolved Boltzmann transport formalism. We find that, under suitable conditions, the strong Coulomb drag effect induces effects like negative conductivity and joint electron-hole hydrodynamics (bifluidity) in the
plasma. We also identify the exclusive electron or hole hydrodynamics. We find that there is a strong violation of the Wiedemann-Franz law in the low doped regimes. Our work elucidates the roles of the microscopic scattering mechanisms that drive these hydrodynamic phenomena.
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Soft Condensed Matter
A hybrid Green-Kubo (hGK) framework for calculating viscosity from short MD simulations
Akash K. Meel and Santosh Mogurampelly
Viscosity calculation from
equilibrium molecular dynamics (MD) simulations relies on the traditional Green-Kubo (GK) framework, which integrates the stress autocorrelation function (SACF) over time. While the formalism is exact in the linear response regime, the traditional approach often suffers from poor convergence and requires extensive phase space sampling, which is computationally demanding for soft matter and
polymer systems. In this Letter, we introduce a hybrid Green-Kubo (hGK) framework that alleviates these limitations by partitioning the SACF into two physically meaningful regimes: (i) a short time ballistic component extracted directly from short MD simulations, and (ii) a long time relaxation tail represented using analytically motivated functions, $\phi(\tau)$, fitted only to short trajectories. This strategy bypasses the need for extensive sampling while preserving the exact GK framework at short times. Benchmarking against SPC/E water confirms excellent agreement with established results, and we further demonstrate the efficacy of the method for challenging electrolyte systems (EC-LiTFSI and PEO-LiTFSI), for which the GK framework fails to converge. The computational savings are substantial, with reductions of several orders of magnitude in required sampling, achieved without compromising predictive accuracy. We also discuss the limitations of the hGK framework and outline clear avenues for refinement, including optimal tail selection and robust identification of relaxation regimes in noisy stress data. The hGK framework presented in this Letter provides a conceptually simple, broadly applicable, and computationally efficient route for viscosity prediction in molecular
liquids,
polymer melts, and ionically conducting soft materials.
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Strongly Correlated Electrons
Magnetocaloric effect measurements in ultrahigh magnetic fields up to 120 T
Reon Ogawa, Masaki Gen, Kazuyuki Matsuhira et al. (+1 more)
We report proof-of-concept measurements of the magnetocaloric effect (MCE) in ultrahigh
magnetic fields up to 120 T for the classical
spin-ice compound Ho$_{2}$Ti$_{2}$O$_{7}$.
Radio-frequency resistivity measurements using an Au$_{16}$Ge$_{84}$ thin-film thermometer enable us to detect a rapid change in the sample temperature associated with a
crystal-field level crossing in the high-field region in addition to a
giant MCE at low fields. We discuss a possible delay in the temperature response and outline prospects for more precise MCE measurements in destructive pulsed fields.
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All authors Reon Ogawa, Masaki Gen, Kazuyuki Matsuhira, Yoshimitsu Kohama