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Physics Condensed Matter

cond-mat Watch Condensed Matter

Monday 6 July

Mesoscale and Nanoscale Physics

Local Defects and the Topology of the Haldane Model

Vishesh Makwana and Eric Akkermans

We investigate the interplay between local defects and topology in the Haldane model within the framework of the tenfold classification. The Haldane model realizes a Chern-insulating phase characterized by an integer topological invariant ($C=\pm 1$) and supports chiral edge states. Introducing vacancies gives rise to localized states at the defect sites, classified by a $\mathbb{Z}_2$ invariant $\nu = C\cdot m,\mathrm{mod},2$, where $m=N_A-N_B$ is the net sublattice imbalance of the vacancy configuration: an odd imbalance hosts a protected zero-energy mode, whereas an even imbalance does not. We identify three independent experimental signatures that distinguish these topological defect states from trivial (adatom) defects. First, vacancy-induced states exhibit characteristic dislocations in their wavefunction profiles that track the phase winding associated with the defect. Second, a fractional charge of $e/2$ accumulates at vacancy sites, while no such charge appears at adatoms. Third, the probability current circulating around a vacancy-induced state flows in the opposite direction to that of chiral edge states, in direct analogy with the current reversal produced by a vortex in a $p$-wave superconductor. All three signatures are in quantitative agreement with the $\mathbb{Z}_2$ prediction.
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Mesoscale and Nanoscale Physics

Strain- and potential-controlled tunneling in monolayer MoS$_2$

Hasna Chnafa, Rachid El Aitouni, Clarence Cortes et al. (+2 more)

We present a theoretical study of spin- and valley-resolved quantum transport in monolayer MoS$_2$ under the combined influence of mechanical strain and an external scalar potential, a combination whose simultaneous unexplored. Within an effective massive Dirac Hamiltonian that incorporates intrinsic spin–orbit coupling, strain induces valley-dependent momentum shifts that lift the degeneracy between the $K$ and $K'$ valleys and strongly modify the transport characteristics. The scalar potential modifies the tunneling spectrum, leading to pronounced changes in resonant transmission, Fabry–Pérot interference, and conductance. We show that the interplay between strain and electrostatic potential enables efficient control of both valley and spin polarization of the transmitted current. In particular, we identify a dual-knob control scheme in which the barrier width governs the frequency of conductance oscillations while strain independently controls their phase and amplitude. Furthermore, we predict electrostatic spin inversion – a sign reversal of spin polarization achievable purely by gate tuning at finite strain, requiring no geometric reconfiguration. Depending on the strain orientation, the transmission probability and conductance can be selectively suppressed or enhanced, resulting in highly tunable valley- and spin-polarized transport. These findings demonstrate that strain and potential engineering provide orthogonal and independently operable mechanisms for controlling conductance as well as spin and valley degrees of freedom in monolayer MoS$_2$, offering promising prospects for spintronic and valleytronic device applications.
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All authors Hasna Chnafa, Rachid El Aitouni, Clarence Cortes, David Laroze, Ahmed Jellal

Mesoscale and Nanoscale Physics

On the $\mathrm{In_{x}Ga_{1-x}As}$ channel noise in InP HEMTs from 4 K to 300 K

Junjie Li, Justin H. Chen, Austin J. Minnich et al. (+1 more)

The InP high-electron-mobility transistor (HEMT) is indispensable for low-noise amplifiers (LNAs) in radio astronomy and quantum computing. The composition of the $\mathrm{In_{x}Ga_{1-x}As}$ channel in InP HEMT is known to influence the LNA noise performance. However, the various physical mechanisms responsible for noise generation are not fully characterized and understood. Here, we investigate the $\mathrm{In_{x}Ga_{1-x}As}$ channel noise from 4 K to 300 K for 100-nm gate-length InP HEMTs with channel indium content of 53%, 60% and 70%. Channel noise was quantified by extracting the equivalent drain noise temperature $\mathit{T}_{d}$ using both on-wafer and LNA-based measurements, covering 40-300 K and 4-40 K, respectively. The 60% indium channel InP HEMT exhibited the lowest channel noise across the full temperature range. The $\mathit{T}_{d}$ extracted from on-wafer characterization was found to obey a parabolic temperature dependence which predicted the $\mathit{T}_{d}$ at 4 K for all InP HEMTs in good agreement with LNA-based measurements. By expressing the channel noise as the sum of one thermal and one excess noise term, it was found that the former increased linearly with ambient temperature and dominated at 300 K. The channel noise at 4 K was determined by the excess noise term and exhibited a non-monotonic dependence on the channel indium content in the InP HEMT. The results suggest that the excess noise in the InP HEMT originates not only from temperature-independent shot noise but also from impact ionization and real-space transfer noise.
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All authors Junjie Li, Justin H. Chen, Austin J. Minnich, Jan Grahn

Mesoscale and Nanoscale Physics

Room-Temperature Nonlinear Hall Effect in Polycrystalline Magnetic Multilayers

Preet Kamal, Amiya Mondal, Kanupriya et al. (+3 more)

We report a zero-field nonlinear Hall effect in sputtered polycrystalline Ta/Pt/[Pt/Co/Fe/Ir]$_5$/Pt multilayers from 2 to 300 K. Angle-resolved transport reveals macroscopic in-plane anisotropy and a second-order response. The transverse voltage scales quadratically with current and remains unchanged across magnetization reversal. Conductivity scaling reveals strong scattering contributions, and first-principles calculations yield a symmetry-allowed Berry curvature dipole. Our findings support a mixed intrinsic-extrinsic response and establish a scalable platform for nonlinear electronics
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All authors Preet Kamal, Amiya Mondal, Kanupriya, Chirag Kalouni, Awadhesh Narayan, Debangsu Roy

Mesoscale and Nanoscale Physics

Tunable Nonlinear Landscapes in Graphene Nanoelectromechanical Systems

Ateesh K. Rathi, Rajan Singh, Javed A. Mondal et al. (+4 more)

Nonlinear nanomechanical resonators give convenient solid-state access to classical analogs of extreme nonlinear optics and to phononic signal processing. Here we report integer high-harmonic generation and phononic frequency combs in a suspended monolayer graphene drum. A gate voltage breaks the out-of-plane symmetry of the membrane and tunes its fundamental flexural mode onto a 1:2 internal resonance with a higher mode at twice the frequency, where the quadratic coupling between the two modes becomes large. A single drive tone then generates phase-locked integer harmonics in sequence, and at larger drive these fill in to a dense frequency comb. Raising the drive further, we find a reverse period-doubling transition: the comb spacing doubles, the line density halves, and energy flows back into the even-order comb lines. The measured spectra yield the quadratic ($\zeta$) and cubic ($\beta$) nonlinear coefficients of the membrane. These results show how the tunable nonlinear landscape of graphene supports distinct dynamical regimes on demand, allowing a single gated device to act in turn as a frequency multiplier, a broadband comb source, and a chaotic generator.
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All authors Ateesh K. Rathi, Rajan Singh, Javed A. Mondal, Arnab Sarkar, Ryan J.T. Nicholl, Kirill I. Bolotin, Saikat Ghosh

Strongly Correlated Electrons

Supercritical fluid of quantum electrons in three-dimensional superconducting fullerides

Xinying Li, Yuki Matsuda, Chongli Yang et al. (+10 more)

The supercritical fluid (SCF) of quantum electrons at the Mott metal-insulator transition without symmetry breaking is one of the most elusive phenomena in strongly correlated electron physics. Prior studies of Cr-doped V2O3 and organic Mott systems reported discrepant critical exponents. A key limitation is that the scaling analysis relies on a single experimental observable, leaving the roles of phase coexistence, inhomogeneity, and percolation unaddressed. Here we report the first experimental identification of a thermodynamically equilibrated SCF phase and its associated Mott endpoint in the three-dimensional superconducting fullerides CsxRb3-xC60, using two independent probes of electrical conductivity and magnetic susceptibility, which reveal two distinct metal-insulator transition lines converging at a single Mott endpoint. A hypothesis-free two-particle analysis of magnetic susceptibilities yields a metal-insulator coexisting SCF by exhibiting the maximum two-phase mixing entropy, in agreement with a picture of a thermodynamically equilibrated Widom line. Simultaneously, conductivity scaling yields a critical exponent in the regime of quantum critical predictions. Our new dual-probe approach provides a unified microscopic picture of the Mott SCF with a characteristic length scale below current diffraction resolution, in addition to a new interpretation on the origin of superconducting Tc-dome.
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All authors Xinying Li, Yuki Matsuda, Chongli Yang, Huaxue Zhou, Takuma Ogasawara, Qin Wang, Liguo Zhang, Hidekazu Shimotani, Hailiang Xia, Khuong K. Huynh, Panagiotis Kotetes, Satoshi Heguri, Katsumi Tanigaki

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Krylov complexity, mode-resolved complexity and entanglement entropy across phase transitions in the non-Hermitian extended Su-Schrieffer-Heeger model

Ling-Feng Zhang and Wing Chi Yu

We investigate phase transitions in the extended Su-Schrieffer-Heeger (SSH) model with next-nearest-neighbor hoppings and an imaginary staggered chemical potential. In the presence of small non-Hermiticity, exceptional points emerge in pairs from the gap-closing momenta near the topological phase boundaries of the Hermitian limit. Utilizing the Krylov spread complexity and entanglement entropy, we analyze two dynamical protocols: (i) preparing the non-Hermitian ground state via a unitary transformation, and (ii) evolving the system under the non-Hermitian Hamiltonian. We show that the spread complexity, and long-time spread complexity as well as entanglement entropy can effectively signal phase transitions in the first and second protocols, respectively. To unravel the detailed structure of the transitions, we introduce the momentum-resolved complexity that identifies the characteristic modes and tracks their evolution with the driving parameter. In the regime where the system possesses a purely imaginary spectrum, we further identify dynamical phases based on the saturation behavior of the spread complexity. The entanglement entropy is also found to exhibit similar saturation behavior, thereby providing a more experimentally accessible probe of the dynamical phases.
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Mesoscale and Nanoscale Physics

Quantum Geometric Friedel Oscillations

Xing-Lei Ma, Jinchao Zhao, Bo-Qing Wu et al. (+2 more)

In conventional Friedel oscillations, the real-space charge density oscillations induced by an impurity are characterized by an oscillation period set by the Fermi momentum. In this work, we demonstrate that in metals with an isolated (nearly) flat band at the Fermi energy, quantum geometry induces a distinct type of oscillations, which we call the quantum geometric Friedel oscillations (QGFOs). The period of the QGFOs is set by the momentum-space separation of the quantum metric hot spots of the isolated band. The conventional and quantum metric-induced oscillations can coexist at low temperatures. At higher temperatures, the conventional Friedel oscillation amplitudes away from the impurity site are set by the thermal length such that the oscillations can be easily washed out by temperature effects. Remarkably, the QGFOs decay length is set by the quantum metric length which is defined by the integration of the quantum metric of the isolated band. As a result, the QGFOs can persist even at temperatures much larger than the bandwidth of the isolated flat band. Moreover, the decay length is invariant for a wide range of temperature which is a striking result. In conclusion, we show that the quantum metric induces novel Friedel oscillations. Our work suggests that the measurement of the QGFOs is a powerful way to detect the quantum metric length (which is associated with the integral of the quantum metric) and the quantum metric hot spot separations (which are associated with the distribution of the quantum metric in the momentum space).
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All authors Xing-Lei Ma, Jinchao Zhao, Bo-Qing Wu, Patrick A. Lee, K. T. Law

Materials Science

Topological Electronic States and Phonon Mediated Superconductivity in Ru Based Ternary Pnictides: ZrRuAs and HfRuP

Jubair Hossan Abir, Tanvir Khan, Tauhidur Rahman et al. (+5 more)

This study investigates the structural, electronic, mechanical, optical, thermodynamic, and superconducting properties of ZrRuAs and HfRuP. Electronic band structure calculations reveal topological semimetallic behavior in both compounds with several bands crossing the Fermi level. The inclusion of spin orbit coupling lifts band degeneracies in both compounds. The Fermi surface shows both electron and hole segments. The estimated Pugh ratio, Poisson ratio and machinability index indicate that both compounds are ductile in nature and exhibit excellent machinability. Optical results show metallic reflectivity and notable absorption in the ultraviolet region. Thermodynamic analysis indicates stable behavior. The estimated superconducting transition temperatures are 9.75 K for ZrRuAs and 9.03 K for HfRuP that indicates strong coupling conventional superconductivity. The results provide a detailed view of the physical and superconducting properties of ZrRuAs and HfRuP and help to close the existing research gaps in these topological superconducting materials.
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All authors Jubair Hossan Abir, Tanvir Khan, Tauhidur Rahman, Md. Kamrul Hassan, Sraboni Saha Moly, Mst. Maskura Khatun, Raihana Shams Islam, Saleh Hasan Naqib

Soft Condensed Matter

Statistics of rupture in phantom chain network simulations

Yuichi Masubuchi, Takato Ishida and Takashi Uneyama

Phantom chain simulations have shown that the mean rupture properties of star polymer networks collapse onto master curves against the cycle rank density $\xi$. This study revisits this universality with a much larger ensemble than in earlier studies to discuss the statistics. Phantom Gaussian networks were made by end-linking star prepolymers, and 1,000 realizations were collected for each of 30 conditions with functionality $f=3$–$8$ and conversion $p=0.60$–$0.95$, giving 30,000 networks in total. For each realization, the breaking stretch $\lambda_b$, the breaking stress $\sigma_b$, the breaking energy $W_b$, and the cycle rank $\xi$ were recorded. The master curves are unchanged by the larger sample, demonstrating that the earlier conclusions reported for the averages of smaller ensembles hold. However, the individual realizations are inherently random, and their statistical properties, rather than the individual values, are examined. At fixed $f,p$, the fluctuation of $\xi$ is small, varying by less than 0.01, whereas $\lambda_b$, $\sigma_b$, and $W_b$ scatter by 0.05–0.3. The fluctuation of $\xi$ is almost uncorrelated with that of the breaking properties. In addition, the scatter has a definite structure; its magnitude decreases with the mean cycle rank density $\xi$, the $\lambda_b$–$\sigma_b$ correlation grows with $\xi$, and the distributions deviate from Gaussian. The $\lambda_b$ distribution is skewed to the right at small $\xi$, whereas $\sigma_b$ is skewed to the left at large $\xi$. These rupture statistics were discussed in the framework of extreme-value statistics to demonstrate that the observed trends are opposite to those of the random fuse model, in which strength decreases with size and weakest-link statistics appear for weak disorder. The difference may reflect the source of fluctuation, i.e., the cross-linking in the present networks.
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Superconductivity

Superconductivity on the verge of metal-insulator transition in Cu$_{1-x}$Zn$_x$Ir$_2$S$_4$ probed by $\mu$SR

K. M. Kojima, M. Miyazaki, M. Hiraishi et al. (+6 more)

The thiospinel CuIr$_2$S$_4$ undergoes a metal-insulator transition below $\approx$230 K, which is suppressed by substitution of Cu with Zn (Cu$_{1-x}$Zn$_x$Ir$_2$S$_4$) to induce superconductivity for $0.2\lesssim x\lesssim0.8$. We show that the temperature/field dependence of superfluid density in samples with $x = 0.3$ and 0.4 ($T_{\rm c} \approx 3$ K and 2.5 K) investigated by muon spin rotation and relaxation ($\mu$SR) is consistent with a fully gapped $s$-wave pairing. Meanwhile, the relatively high resistivity (10$^{-3}$-10$^{-2}$ $\Omega\:$cm) in their normal state suggests that the superconductivity is in the "dirty limit" where the mean free path is much shorter than the coherence length ($\ell \ll \xi_0$). This indicates that the potential anisotropy associated with unconventional pairing mechanisms expected under the strong electron correlations is smeared out by the electron scattering. Based on these observations, we discuss potential link between the Zn substitution-induced superconductivity and that recently discovered in CuIr$_2$S$_4$ under high pressure ($>18$ GPa) where the existence of strong electron scattering is also suggested.
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All authors K. M. Kojima, M. Miyazaki, M. Hiraishi, A. Koda, R. Kadono, C. Baines, Y. Tsuchiya, H. S. Suzuki, H. Kitazawa

Materials Science

VASP Plugins: Linking the Vienna ab-initio Simulation Package with Python

Sudarshan Vijay, Martijn Marsman, Georg Kresse et al. (+1 more)

Implementing novel features and experimental algorithms into widely adopted density functional theory (DFT) codes is frequently hindered by complex legacy architectures and the use of compiled languages such as Fortran. These production codes, while optimised for high-performance computing clusters, present significant hurdles for software development and rapid prototyping, often requiring deep expertise in the code's internal structure to modify. To address this challenge, we present a Python plugin infrastructure for the Vienna ab-initio Simulation Package (VASP) that combines computational efficiency with the flexibility of high-level scripting. Our architecture uses a C++ intermediate layer and pybind11 to expose VASP data as NumPy arrays via shared memory buffers, ensuring high performance without data duplication. We implement two categories of plugins: those that modify quantities at the end of each converged self-consistent field (SCF) cycle, such as structure and force_and_stress, and those that operate during the SCF cycle, such as local_potential and occupancies. We demonstrate the utility of our implementation through three applications, structure relaxation using the scipy library, implementing an implicit solvent model, and adding the DFT-D4 dispersion corrections. This infrastructure effectively bridges the gap between high-performance electronic structure routines and the widespread scientific Python ecosystem.
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All authors Sudarshan Vijay, Martijn Marsman, Georg Kresse, Martin Schlipf

Strongly Correlated Electrons

Orbital-Selective Mott and Antiferromagnetic Phases in Diagonally Compressed Kagome Lattice

Jiewei Ding, Ho-Kin Tang and Wing Chi Yu

We perform determinant quantum Monte Carlo simulations of the half-filled Hubbard model on a diagonally compressed kagome lattice, introducing exponential decay long-range hopping $t(r) = t_0 \exp\bigl(-r / r_0\bigr)$ to account for the evolving bond length. By varying the lattice angle $\theta$ and the on-site interaction $U$, double occupancy, charge compressibility, and spin-spin correlation functions of the whole system and each sub-lattice are measured. We find that geometric compression induces a clear sublattice differentiation: for $\theta\gtrsim52^\circ$, the A sublattice establishes long-range hoppings, which in turn suppresses the metallic behavior of the $B/C$ sublattice and drives a selective Mott transition; for $\theta\lesssim52^\circ$, the $B$-$C$ chains develop long-range antiferromagnetic correlations within the finite-size simulations, which in turn suppresses the metallic behavior of the $A$ sublattice and drives a selective Mott transition. The critical interaction $U^c_A$ for the $A$ sites decreases sharply near the onset of $B$-$C$ antiferromagnetic correlations, while $U^c_{B/C}$ increases. These competing orders give rise to an orbital-selective Mott phase and a rich $U$-$\theta$ phase diagram featuring paramagnetic-metal, paramagnetic-Mott, antiferromagnetic-metal, and antiferromagnetic-Mott states. Our results highlight the complex interplay between lattice geometry, magnetic frustration, and strong correlations in frustrated two-dimensional systems.
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Soft Condensed Matter

Synchro-nematic and -antinematic ordering of spheroidal circle swimmers

Anson G. Thambi, Alexander N. Dodge and William E. Uspal

Chirality gives a microswimmer something a straight-line swimmer lacks: a phase. This variable both modulates, and is affected by, the hydrodynamic interactions between microswimmers. Here we ask what collective order emerges when many such chiral swimmers are free to move, and how the shape and actuation anisotropies of an individual swimmer dictate the outcome. Using a kinetic theory for hydrodynamically interacting circle swimmers, we show that the interplay between intrinsic rotation, stresslet flows, and Jeffery-like reorientation generates effective phase-locking interactions. Asymmetries in the actuation are encoded through a non-axisymmetric stresslet tensor. At the pair level, pusher swimmers select one of two synchronized states depending on particle shape and actuation asymmetry: in-phase/anti-phase locking, or quarter-shifted locking. Extending the analysis to many-body systems, we find that these pair-level synchronization mechanisms drive emergent collective phases. The swimmers develop global synchro-nematic order when the hydrodynamic coupling favors parallel or anti-parallel phase locking, and synchro-antinematic local order where quarter-shifted locking prevails. A coarse-grained field theory predicts the onset of nematic order through a hydrodynamic instability criterion. In addition, we find that the collective states exhibit crystalline or disordered hyperuniform structure arising from period-averaged hydrodynamic interactions that are effectively repulsive between swimmers. Lattice Boltzmann simulations of chiral oblate squirmers, resolving finite-size and near-field flows, recover the synchro-nematic ordering. Together, these results show how a swimmer's geometric and actuation anisotropies can be leveraged to program synchronization and spatiotemporal order in chiral active matter.
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Sunday 5 July

Statistical Mechanics · Cross-listed from physics.chem-ph

Speed limits on biomolecular processes from fundamental physical constants

Dmitrii E Makarov

Many of the timescales of life have speed limits set by quantum-mechanical constraints along with non-fundamental quantities, such as the temperature of the environment, which are however bounded by anthropic considerations. Here, some of such speed limits are examined, including those for the rates of elementary chemical reactions and biomolecular folding. Limitations of simple back-of-envelope estimates are also discussed.
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Materials Science

Data-Driven Prediction of NaCl-Type Entropy-Stabilized Oxide Compositions from First-Principles and Supervised Learning

Sebastien Junier, Celine Barreteau, David Berardan et al. (+2 more)

Entropy-stabilized oxides (ESOs) open access to vast multicomponent compositional spaces, but identifying promising candidates remains challenging because of the large number of possible mixtures and the need to assess their stability against competing phases. In this work, we develop a high-throughput computational framework to screen equimolar quinary ESOs in the NaCl structure type by combining density functional theory (DFT), special quasirandom structures (SQS), convex-hull thermodynamics, and supervised machine learning. A consistent reference database of binary and ternary ordered oxides, including disordered phases such as all binary cation combinations in the NaCl-type oxide, is first constructed using GGA and meta-GGA calculations. Quinary disordered phases are then described by SQS supercells and used to train machine-learning models that predict the distance to the convex hull and the corresponding stabilization temperature over the full set of 4368 possible equimolar quinary compositions generated from 16 cation species. Among the tested models, an optimized multilayer perceptron provides the best predictive performance, with a test error of about 4 kJ/mol, while requiring explicit DFT calculations for only about 10% of the quinary systems. Comparison with experimental synthesis tests and computed decomposition paths further shows that the approach captures the main stability trends and the dominant competing phases, although absolute stabilization temperatures remain affected by systematic thermodynamic approximations. These results establish an efficient route for the data-driven exploration of multicomponent oxides and provide practical guidance for the experimental search for new ESOs.
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All authors Sebastien Junier, Celine Barreteau, David Berardan, Yann-Andrev Kerneur, Jean-Claude Crivello

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Where Does Surface $\chi^{(2)}$ Come From? A Systematic Derivation of Nonlinear Surface Susceptibilities from Bulk Nonlocal Response

Zolla Frederic

We extend the distributional framework developed in the companion paper [Zolla, arXiv:2605.15716] to the nonlinear case, focusing on the second-order ($\chi^{(2)}$) response responsible for second-harmonic generation (SHG). Starting from the most general tensorial nonlocal second-order constitutive relation and combining a spatial moment expansion with a distributional thin-layer limit, we show that the full complexity of the nonlinear interfacial response condenses, at leading order, into two scalars, the nonlinear surface susceptibilities $\chi^{(2),s}_\parallel$ and $\chi^{(2),s}_\perp$, associated with the tangential and normal components of the electric field, respectively. A key structural result is established: via a marginal integration over one field argument, the nonlinear surface problem reduces recursively to an effective linear one, whose surface susceptibility is determined by the bulk nonlinear kernel alone. Generalized nonlinear Maxwell boundary conditions are derived explicitly for planar and spherical interfaces, and curvature corrections are obtained systematically. The formalism is illustrated on Gaussian, Yukawa, and tensorial Lorentz kernels.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph

Controlling many-body quantum chaos in a dissipative optical cavity

Filippo Ferrari, Francesca Orsi, Ekaterina Fedotova et al. (+4 more)

Cavity quantum electrodynamics (QED) with ultracold fermions provides a promising platform for realizing many-body quantum chaos through disordered, photon-mediated long-range interactions. Such setups are inherently open and are therefore subject to dissipation arising from cavity photon loss and atomic spontaneous emission. In this article, we study the driven-dissipative dynamics of a typical cavity QED setting including controllable disorder and long-range interactions. We find that the two dissipation sources have qualitatively different structures. Cavity loss reduces to a single dephasing channel, whereas spontaneous emission in the experimentally relevant regime generates a collection of nonlocal dephasing channels. Cavity-induced dephasing preserves signatures distinguishing integrable from chaotic Hamiltonian dynamics in observables that depend linearly on the density matrix, while spontaneous emission suppresses these signatures. By contrast, quantities that probe the structure of the many-body state, such as the entanglement entropy, are strongly affected by both dissipation mechanisms. Assuming experimentally realistic parameters, we derive quantitative constraints for the observation and control of many-body quantum chaos in cavity-QED platforms.
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All authors Filippo Ferrari, Francesca Orsi, Ekaterina Fedotova, Óscar Rios Alves, Michał Zdziennicki, Jean-Philippe Brantut, Vincenzo Savona

Superconductivity · Cross-listed from nucl-th

Theory of Spinful Relativistic Superfluids

Dam Thanh Son

We construct an effective field theory description of relativistic superfluids with nonzero angular momentum density. At first order in the derivative expansion, the effective action contains a term with a quantized coefficient, which encodes the Berry phase for the angular momentum of the superfluid condensate. From this single term we derive a number of physical effects, including the relativistic Mermin-Ho relation, an anomalous Ettingshausen effect (exchangeable for an anomalous Hall effect), and an anomalous Hall viscosity.
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Superconductivity

Pseudo-superconducting-diode effect in ferroelectric Josephson junctions

Yaozu Tang, Nienke ten Haaf, Artem Bondarenko et al. (+2 more)

The superconducting diode effect (SDE), characterized by unequal critical supercurrents in opposite current directions, enables supercurrent rectification. We propose a magnetic-field-free pseudo-superconducting-diode effect in ferroelectric Josephson junctions with broken inversion symmetry. Using a coupled dynamical model that combines a polarization-dependent RCSJ description with Landau-Khalatnikov-Tani ferroelectric dynamics, we show that ferroelectric polarization switching induces asymmetric critical and retrapping currents under current sweeps. The resulting nonreciprocity is highly tunable via ferroelectric parameters and the sweep protocol and remains robust at finite temperatures. Our work identifies ferroelectric Josephson junctions as a promising platform for magnetic-field-free nonreciprocal superconducting devices.
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All authors Yaozu Tang, Nienke ten Haaf, Artem Bondarenko, Mazhar N. Ali, Yaroslav M. Blanter

Mesoscale and Nanoscale Physics

Quasi-two-dimensional Majorana zero modes from finite-size-coupled chiral hinge states

Wenhao Liang and Xun-Jiang Luo

Majorana zero modes (MZMs) in topological superconductors have attracted broad research interest for their potential applications in topological quantum computation. In this work, we propose a quasi-two-dimensional route to realize spatially separated MZMs in a chiral higher-order topological insulator (HOTI) proximitized by a conventional $s$-wave superconductor through a theoretical model study. In three dimensions, the chiral HOTI hosts gapless hinge states along the $z$ direction, arising from a mass term that anisotropically gaps the surface Dirac cones of a topological insulator. By confining the sample along the $x$ direction while keeping it extended along $y$ and finite along $z$, opposite $z$-directed chiral hinge states hybridize and effectively form one-dimensional helical channels. Incorporating the superconducting proximity effect into this quasi-two-dimensional system induces effective $p$-wave pairing in these helical channels, thereby opening a topological gap. A fully open-boundary sample then hosts four localized MZMs, one at each endpoint of the helical channels, realizing a second-order topological superconductor characterized by Majorana corner modes. In addition to MZMs, we also find that superconducting pairing in this model produces extended Majorana hinge modes in three dimensions. Furthermore, representative disorder calculations indicate that these Majorana corner modes are robust against weak-to-moderate disorder, provided the excitation gap remains open. These results establish finite-size-coupled chiral hinge states as a promising platform for engineering multiple MZMs via conventional superconducting proximity effect.
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Soft Condensed Matter

Mass weighting algorithm optimizes Fourier-based physics-informed neural network in adhesive contact mechanics

Yunong Zhou, Kaifeng Huang, Chaofan Du et al. (+2 more)

Physics-informed neural networks (PINNs) for elastic contact mechanics suffer from a spectral stiffness imbalance,that is, the elastic kernel grows linearly with wave number, causing short-wavelength modes to dominate gradient updates and stall convergence of the macroscopic deformation. We introduce a spectral preconditioning strategy that reweights loss gradients with respect to displacements in Fourier space before back-propagation, amplifying low wavenumber components through a mass weighting (MW) function while suppressing sub-grid noise via a built-in low-pass filter. Applied to adhesive line contact problems, the mass weighted PINN reaches machine-zero residual loss within $400$ Adam iterations for specified benchmark, whereas the reference benchmark stalls at three orders of magnitude higher loss. The converged displacement and contact stress fields agree quantitatively with Green's function molecular dynamics (GFMD) solutions for both smooth Hertz contact at pressures spanning tension to compression and rough surfaces with roughness covering several decades of wavelength. The method operates directly on a uniform real-space grid, requires no explicit Green's function integration or quadrature rules, and is formulated entirely in terms of minimising a scalar energy function. Extension to two-dimensional rough surfaces is direct, as both the Fourier elastic energy and the spectral preconditioner depend only on the wave-number magnitude.
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All authors Yunong Zhou, Kaifeng Huang, Chaofan Du, Yang Xu, Hengxu Song

Materials Science

First-principles Floquet analysis from real-time propagation

Ruipeng Li, Benshu Fan, Umberto De Giovannini et al. (+2 more)

We present a real-time Floquet analysis method for extracting quasi-energies and Floquet states directly from propagated wavefunctions. By reconstructing the one-period evolution operator from overlaps between time-evolved states, the method avoids the explicit construction of the enlarged Floquet Hamiltonian and adds negligible computational overhead to time-dependent simulations. To resolve the ambiguity inherent in the reduced-zone representation, we introduce an unfolding procedure based on the harmonic decomposition of Floquet states, which recovers their underlying equilibrium band character beyond the reduced Floquet Brillouin zone. The reconstructed wavefunctions further provide access to the symmetry properties of individual light-induced sidebands. We demonstrate the applicability and generality of the method in first-principles time-dependent simulations of real materials, ranging from two-dimensional monolayers to a three-dimensional bulk semiconductor, and including finite pulses without strict time periodicity. This framework directly connects real-time simulations with Floquet observables, enabling practical analysis of light-driven electronic structure in materials.
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All authors Ruipeng Li, Benshu Fan, Umberto De Giovannini, Hannes Hübener, Angel Rubio

Statistical Mechanics · Cross-listed from hep-th

Entanglement of excited states after measurements in conformal field theory

Hui-Huang Chen

We study the entanglement of low-energy excited states after a fixed-outcome projective measurement on a spatial interval in a (1+1)-dimensional conformal field theory (CFT). We restrict to post-selected measurement outcomes whose induced boundary condition flows in the infrared to a conformal boundary condition. Such an outcome is represented by a slit carrying that boundary condition, while excited states are introduced by operator insertions in the Euclidean path integral. After mapping the replicated slit geometry to a disk, the excited-state contribution to the post-measurement Rényi entropy is expressed as a normalized boundary-CFT correlation function. We apply this framework to the compact free boson CFT. For the chiral current excitation, the relevant ratios are given by current hafnians. We also study coherent superpositions of $J$ and $\bar J$, and of conjugate compact vertex operators. In the conjugate-vertex case, the ordinary-cylinder second Rényi ratio is independent of the relative phase, whereas the finite-slit post-measurement ratio contains phase-sensitive interference terms. Finally, we describe free-fermion and multi-Slater determinant methods for testing these predictions in the critical XX chain.
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Mesoscale and Nanoscale Physics

Phase-Factor-Controlled Interaction and Bonding between a Chiral Bobber and a Skyrmion String in the Conical Phase

Haijun Zhao, Tingting Yan and Shuai Dong

Skyrmion interactions govern the formation of skyrmion lattices, clusters, and particle-like growth patterns. In contrast, the interaction between a chiral bobber and a skyrmion string remains largely unexplored, despite the role of bobbers as intermediate states in skyrmion-string formation and annihilation. Here we show that this interaction is intrinsically phase dependent in the conical phase. Using three-dimensional micromagnetic simulations, we compute the locally relaxed constrained energy landscape as a function of the bobber–skyrmion separation $R$ and the surface phase factor $\phi_0$. We find that changing $\phi_0$ qualitatively reshapes the interaction, producing repulsive, attractive, and bonding-like regimes that cannot be reduced to a conventional distance-dependent potential. Real-space analysis shows that this behavior originates from phase-dependent reconstruction of nonaxisymmetric outer distortion shells. The phase-controlled interaction persists over a finite field range and follows the expected top–bottom phase relation of surface-sensitive conical textures. These results identify the conical phase direction, often hidden in projected or thickness-averaged descriptions, as a previously underappreciated degree of freedom in the interaction between skyrmion strings and finite-length chiral textures, as demonstrated here for chiral bobbers.
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Statistical Mechanics

Universal fluctuations of first discoveries in competitive exploration

Arthur Plaud, P. L. Krapivsky, S. Redner et al. (+1 more)

Random exploration is usually quantified by how fast new space is found, from the range of a single walker to the territory collectively covered by many walkers. In competitive exploration, first arrival secures an exclusive resource, as when foragers compete for food items or agents capture distributed targets. It is then no longer enough to know which sites have been discovered: one must determine, for each discovered site, which searcher reached it first. We introduce the discovery share $X_n$, the fraction of the first $n$ collective discoveries secured by a tagged searcher. For two identical competitors, exchange symmetry fixes $\langle X_n\rangle=1/2$, but the central question is whether this equal split emerges in each long exploration history or only on average, i.e. whether early competitive advantages are erased or persist. Here we show that the answer is controlled by the spectral dimension $d_s$, defined by the large-time decay of the probability that a single searcher is at its starting point after $t$ steps, $p_0(t)\sim t^{-d_s/2}$. Across ordinary diffusion, long-range superdiffusion and subdiffusion induced by crowding or memory, $d_s$ separates persistent randomness in recurrent exploration $(d_s<2)$, anomalously slow non-Gaussian concentration for $2\le d_s<3$, and Gaussian concentration, logarithmically corrected at $d_s=3$, for $d_s\ge3$. For $d_s\ge2$, we derive exact asymptotic variances, including prefactors, and the discovery scale on which competitive imbalances are erased. Two-point correlations of first-discovery labels identify the memory mechanism behind these regimes. The same phase structure persists under changes in geometry, competitor heterogeneity, number of competitors and memory, revealing a general fluctuation theory of first-arrival inequalities.
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All authors Arthur Plaud, P. L. Krapivsky, S. Redner, Olivier Bénichou

Materials Science

Tellurium sublattice instability driven amorphization in the chalcogenide AgSbTe2 under pressure

Baihong Sun, Zihan Zhang, Wei Luo et al. (+12 more)

Pressure provides a powerful thermodynamic route to access hidden structural states in functional materials, yet the microscopic origin of pressure-induced amorphization remains elusive in many complex chalcogenides. Here we report a detailed high-pressure structural study of AgSbTe2,combining synchrotron X-ray diffraction with density functional theory and molecular dynamics calculations up to 60 GPa. We uncover a pressure-driven transformation from the ambient R-3m phase to a fully disordered cubic Im3m phase, through an extended intermediate amorphous state. Enthalpy calculations reveal a near-degeneracy between the R3m and Im3m structures over a broad pressure range, dictating amorphization. Contrary to previously speculated cation vacancies, the amorphization is governed by a pronounced displacement instability of the Te sublattice. Remarkably, the time dependent decompression pathway controls the final structural state, resulting in either amorphous (slow decompression) or fully crystalline (fast decompression) states, indicative of a strong counterintuitive kinetic effect.
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All authors Baihong Sun, Zihan Zhang, Wei Luo, Sergei Grazhdannikov, Wenting Lu, Shiyu Feng, Haikai Zou, Chenxin Wei, Martin Kunz, Hirokazu Kadobayashi, Bihang Wang, Azkar Saeed Ahmad, Yaron Amouyal, Rajeev Ahuja, Elissaios Stavrou

Strongly Correlated Electrons

Cuprate d-wave superconductivity based on Non perturbative many body theory for spin fluctuation

Jianwei Gong, Junnian Xiong, Ruitao Xiao et al. (+4 more)

We employ the nonperturbative many-body spin GW method to compute the single-particle Green's function, and the covariance method to evaluate the two-body correlation functions, for the Hubbard model of superconductors. The method, benchmarked at strong coupling and low temperatures, allows simulations on lattices up to $64\times64$, thereby enabling access to the thermodynamic limit. We find the key transition temperatures—namely the Néel temperature and the superconducting critical temperature $T_c$—to be in quantitative agreement with experimental data. Above the $d$-wave superconducting dome, there exists a broad pseudogap region in which the normal-state excitations are suppressed. These results indicate our approach may offer a new route toward investigating strongly correlated systems, especially cuprate superconductors.
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All authors Jianwei Gong, Junnian Xiong, Ruitao Xiao, Hui Li, Ziyu Li, Huaqing Huang, Dingping Li

Materials Science

Emergent Fermi polarons in Dirac materials

Xin Chen, Eugen Dizer, Rafał Ołdziejewski et al. (+3 more)

We investigate band-structure effects on the absorption spectra of quantum impurities in Dirac materials. We uncover the formation of novel quasiparticles – Dirac-Fermi polarons – emerging from the dressing of impurities by excitations near the Dirac point. These quasiparticles are remarkably robust, persisting for both attractive and repulsive interactions, and across the full range of electron and hole doping. We show that their spectroscopic signature is a generic feature of Dirac materials, accessible with established techniques in both solid-state and ultracold atomic platforms. Our results establish polaron spectroscopy as a powerful probe of Dirac points at energies far from the Fermi surface, providing direct access to band-structure effects beyond conventional approaches.
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All authors Xin Chen, Eugen Dizer, Rafał Ołdziejewski, Kostya S. Novoselov, Marton Kanász-Nagy, Richard Schmidt

Disordered Systems and Neural Networks

Broken Ergodicity and the Violation of the Fluctuation-Dissipation Theorem Lead to Generalization Beyond Overfitting in Machine Learning

Chan Li and Nigel Goldenfeld

The remarkable ability of modern neural networks to generalize improves with increasing network capacity, even when the number of model parameters or effective degrees of freedom exceeds the number of training data points. This phenomenon is all the more surprising given that generalization error diverges when the number of model parameters approaches a critical value from below. Here we use dynamical mean field theory to show that this so-called "double descent" behavior is the outcome of a phase transition in the stochastic field theory describing the training process. We calculate the critical exponents and scaling function of the double descent phase transition, and show that it is marked by a breakdown of the fluctuation-dissipation theorem associated with broken ergodicity. The corresponding response function has the same functional form as the simple London model of the superconducting transition, with the rigidity of the wave function corresponding to the neural network's ability to generalize accurately.
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