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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 24 February

Strongly Correlated Electrons

Kondo breakdown as an entanglement transition driven by continuous measurement

Debraj Debata, Abhirup Mukherjee and Siddhartha Lal

We study the breakdown of Kondo screening by a local magnetic field from the perspective of a measurement-driven entanglement transition in a monitored quantum system. Here, the Kondo coupling leads to the growth in entanglement of an impurity spin with it's fermionic environment, while the local field plays the role of a continuous observer. Using a non-perturbative Unitary Renormalization Group (URG) approach, we derive coupled renormalization-group flow equations for the Kondo exchange and the local field, and obtain a field-dependent RG phase diagram. The RG flows separate a low-energy Kondo-screened phase, where the impurity is absorbed into the Fermi sea and forms an entangled singlet with the conduction bath, from a polarized local-moment phase in which screening is frustrated and impurity-bath entanglement is suppressed. We identify the fixed-point Hamiltonians governing the two phases and the critical regime, and relate the transition to the emergence of a novel non-Fermi liquid. Various impurity signatures such as the spectral function and thermalisation of impurity observables are used to characterise this entanglement transition. These results offer insight into the interplay of decoherence and measurement in governing the dynamics of a prototypical quantum system.
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Mesoscale and Nanoscale Physics

Effects of shear displacement on the conductance of monolayer/gapped bilayer/monolayer graphene junctions: Implications for ac-dc conversion

Ryo Tamura

Analytical treatments of tunneling in bilayer graphene have typically relied on minimal models including only the vertical interlayer hopping $\gamma_1$ and have been restricted to the weak interlayer-bias regime ($2\varepsilon \ll \gamma_1$). Consequently, they cannot adequately describe lattice deformations or strong electric-field effects. In this work, we present an analytical theory of evanescent states in electrically gapped bilayer graphene that overcomes both limitations. Our approach explicitly incorporates the skew interlayer hoppings $\gamma_3$ and $\gamma_4$ and remains valid even when the interlayer bias $2\varepsilon$ is comparable to $\gamma_1$. Focusing on low-energy electronic states near the charge neutrality point, we analytically derive the complex longitudinal wave numbers, the gap width, and the sublattice pseudospin within the electric-field-induced gap. We then systematically analyze the dependence of these quantities on the interlayer shear displacement $\vec{\delta}=(\delta_x,\delta_y)$, and find that skew interlayer hoppings, in particular $\gamma_3$, play an essential role. For transport along the zigzag ($x$) direction, the longitudinal wave vector becomes complex, whereas the transverse wave vector remains real. For a monolayer/bilayer/monolayer junction with transport along the zigzag direction, we find that $\delta_y$ has a significantly stronger impact on the conductance than $\delta_x$. Furthermore, we identify a shear-induced phase proportional to $\delta_y$ that appears universally in the analytical expressions for the gap width, the sublattice pseudospin, and the decay length. These results establish a unified framework for shear- and bias-controlled evanescent tunneling in bilayer graphene and suggest broader relevance to nonequilibrium transport phenomena in layered materials.
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Statistical Mechanics

Fluctuation theorems for a non-Gaussian system

A. Saravanan and I. Iyyappan

In this work, we numerically verify the Jarzynski equality and Crook fluctuation theorem for a Brownian particle diffusing in a heterogeneous thermal bath and hence having a non-Gaussian position distribution. We use the diffusing-diffusivity model to take the account of heterogeneity of the thermal bath where the mobility is considered as a fluctuating quantity. The Brownian particle is confined by a time-dependent harmonic potential. By changing the stiffness coefficient, we perform an isothermal process. We use the stochastic thermodynamics framework to calculate the work. We find that the Jarzynski equality and the Crook fluctuation theorem are convincingly satisfied for a non-Gaussion system. We also find that the work distribution is non-Gaussian for diffusing-diffusivity system even at a larger process time.
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Strongly Correlated Electrons

Real-space construction and classification for time-reversal symmetric crystalline superconductors in 2D interacting fermionic systems

Yi-Ming Liu, Wei-Qiang Chen and Zheng-Cheng Gu

Crystalline symmetry and time-reversal symmetry are commonly present in real superconducting materials. However, the topological classification of systems respecting these symmetries, particularly for interacting fermions, remains incomplete. In this work, we systematically classify time-reversal symmetry-protected crystalline topological superconductors in two-dimensional interacting fermionic systems using an explicit real-space construction. Among the resulting phases, we identify intrinsically interacting fermionic topological superconductors, i.e., phases that cannot be realized in either free-fermion or interacting bosonic systems. For spinless fermions with protecting symmetry group $C_4 \times Z_2^T$ or $D_4 \times Z_2^T$ (plus fermion parity), the intrinsic sector has a $Z_4$ classification. The corresponding root phases generating this $Z_4$ classification admit a transparent real-space construction in terms of decorated 1D blocks. These blocks are 1D fermionic symmetry-protected topological (FSPT) phases, realizable as double Majorana chains. We further find the corresponding $Z_4$ spinless intrinsic phases for wallpaper groups $p4$, $p4m$, and $p4g$. We also find an additional $Z_2$ intrinsically interacting phase for spinless fermions with wallpaper group $pm$, which is absent with the corresponding point-group symmetry alone. Moreover, these intrinsic phases naturally give rise to higher-order FSPT phases that support corner zero modes. Finally, we verify the crystalline equivalence principle for generic 2D interacting FSPT systems with both crystalline and internal symmetries.
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Materials Science

Design of Skyrmion Bags with Tunable Topology in Symmetry-Broken 2D Lattices

Junhuang Yang, Kaiying Dou, Ying Dai et al. (+2 more)

Magnetic skyrmion bags, as high-order topological swirling spin textures, offer rich fundamental physics and distinct advantages for spintronic applications; however, their realization remains a formidable challenge, especially in two-dimensional (2D) systems. Here, through model analysis, we propose a novel design principle for engineering skyrmion bags with tunable topology in symmetry-broken 2D ferromagnetic lattices. The physics correlates to the delicate interplay of isotropic exchange interaction, Dzyaloshinskii-Moriya interaction and magnetic anisotropy, which can stabilize a rich variety of high-order topological spin states as well as the intriguing skyrmionium with zero topological charge. We further validate this mechanism in monolayer CrInTe2 using first-principles calculations and atomistic spin model simulations, revealing the existence of field-free skyrmion bags. Furthermore, we find that a weak magnetic field triggers a transition to skyrmioniums that exhibit remarkable thermal stability up to 240 K. Our results provide a compelling platform for exploring high-order topological magnetism.
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All authors Junhuang Yang, Kaiying Dou, Ying Dai, Baibiao Huang, Yandong Ma

Other Condensed Matter · Cross-listed from physics.optics

Dynamic Lattice Disorder and Collective Dipole Coupling Give Rise to Dicke Physics in Perovskite Quantum Dots

Priya Nagpal and Patanjali Kambhampati

Halide perovskite quantum dots exhibit cooperative optical phenomena that are absent in conventional semiconductor nanocrystals, including exciton superradiance, superabsorption, and biexciton superradiance within individual dots. Here we develop a microscopic theory that identifies the physical origin of these Dicke effects and establishes how they can be controlled by materials parameters. The central result is that cooperative emission emerges from a competition between collective coupling of optical transition dipoles and lattice-induced disorder, with the balance governed by the Raman-derived phonon spectral density and the excitonic oscillator strength. At elevated temperature, strong Fröhlich coupling and glassy lattice dynamics produce dynamic disorder that suppresses dipole synchronization and yields incoherent emission. Upon cooling, lattice fluctuations freeze and cooperative coherence emerges when the collective coupling exceeds residual static disorder, defining size- and composition-dependent crossover temperatures that we map as phase diagrams. Extending the framework to biexcitons, we show that a confined biexciton constitutes a single correlated charge distribution dressed by a shared lattice configuration, enabling pathway-indistinguishable decay and cooperative radiative enhancement. The theory quantitatively accounts for observed size, composition, and temperature trends in radiative-rate constant ratios and biexciton binding energies, while explaining why full Dicke saturation is not universal. More broadly, the results establish Raman spectral weight and oscillator strength as design parameters for engineering cooperative quantum-optical behavior in quantum materials.
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Materials Science

Propagation of elastic waves in a flexomagnetic solid

Swarnava Ghosh

Flexomagnetism is the coupling between magnetism and strain gradients and is a technologically relevant phenomenon. We present a theory of elastic wave propagation in a linear elastic flexomagnetic material with microstructure and strain gradient elastic interactions. The expressions of frequency, phase velocity, and group velocity of longitudinal and transverse waves are derived and are shown to depend on the flexomagnetic coefficient and microstructure. We also show that the effect of flexomagnetism and microstructure can lead to some interesting phenomena in wave propagation, which are not observed in classical linear elasticity theory of waves. Specifically, in contrast to classical linear elastic materials, where wave propagation is non-dispersive, flexomagnetic materials with microstructure can exhibit both normal and abnormal dispersion. It is also noteworthy that, in flexomagnetic materials with gradient elasticity, the phase velocities of transverse waves can exceed those of longitudinal waves, which is atypical in classical elasticity. Furthermore, waves can also attenuate for a certain range of wavenumbers that depend on the flexomagnetic coefficient and microstructural parameters. Finally, we explore the possibility of waves exhibiting zero group velocity modes, where waves are non-propagating but have strong local energy confinement, negative group velocity modes, where the wave packet moves in the opposite direction to that of wave propagation, and the phenomenon of wave freezing, where a propagating wave stops in space without diffusing or spreading.
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Mesoscale and Nanoscale Physics

Omnidirectional magnetic imaging of magnetic anisotropy and phase transitions

Alexander J Healey, Kaijian Xing, Weiyao Zhao et al. (+7 more)

Micron scale imaging of magnetic fields is an important tool for understanding the evolution of magnetism through phase transitions and as a result of interactions inside of heterostructures. However, most imaging platforms, like the nitrogen-vacancy (NV) centre in diamond, are restricted to applying magnetic fields along the quantisation axis of the quantum sensor. This greatly restricts the utility of these systems for exploring materials that emit strong fields or exhibit variable response with respect to the applied field direction. Here we explore an alternative approach using weakly coupled spin-pairs in hBN that exhibit a spin-1/2-like behaviour and an isotropic response to magnetic field. We demonstrate that the spin-pair system can operate in the presence of strong fields from a thin film magnet which were incompatible with NV diamond imaging even with applied fields along the quantisation axis. Further, we demonstrate that using this platform allows for imaging with an arbitrary applied magnetic field direction, allowing us to probe the anisotropy and spin-reorientation transition in the ferrimagnet TbMn$_6$Sn$_6$. Finally, we propose an improved geometry for imaging small anisotropy contributions such as crystalline anisotropy. These results demonstrate how this or similar spin-1/2 systems might be used for imaging magnetic materials that are incompatible with other techniques despite the reduction in sensitivity compared with NV in diamond imaging.
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All authors Alexander J Healey, Kaijian Xing, Weiyao Zhao, Islay O. Robertson, Hark Hoe Tan, Mehran Kianinia, Igor Aharonovich, Jean-Philippe Tetienne, Julie Karel, David A. Broadway

Mesoscale and Nanoscale Physics

Magnetoelastic conversion in integrated YIG nanostructures

Artem V. Bondarenko, Fabian Engelhardt, Marios Kounalakis et al. (+5 more)

Motivated by the recent proposal of two-step transduction from microwave to optical domain using magnetic and elastic intermediate stages arXiv:2205.05088, we consider the coupling between resonant magnetic and elastic modes within a simple axially-symmetric nanodevice designed to host high-quality-factor acoustic modes: A suspended YIG ring structure supported by a central stem, fabricated from a continuous single-crystal film. We study the modes of the system with our custom finite element solvers. We identify the lowest order “breathing” mode of a magnetic vortex and the lowest order elastic breathing mode as having the largest mode overlap. For this pair of modes, the external out-of-plane magnetic bias field is critical for bringing them into resonance; however, we show that at the same time it also affects the strength of the coupling. To counteract this, we optimize the radius of the ring at fixed thickness. For the 100 nm-thick film the resonant coupling is maximized at $g/2\pi = 8\text{MHz}$ at $R\approx1.7\mu\text{m}$, indicating that the overlap integral approaches the idealized limit assumed in previous order-of-magnitude estimates. Our results pave the way for the design of tunable frequency-conversion devices based on magnetoelastics.
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All authors Artem V. Bondarenko, Fabian Engelhardt, Marios Kounalakis, Thierry Valet, Olivier Klein, Gerrit E. W. Bauer, Silvia Viola Kusminskiy, Yaroslav M. Blanter

Mesoscale and Nanoscale Physics

Photogalvanic effect in few layer graphene

Zhaohang Li, Kainan Chang, Haoyu Li et al. (+4 more)

We systematically investigate the nonlinear photogalvanic effect in few-layer graphene with various stacking orders, including AA- and AB-stacked bilayers, and AAA-, ABA-, and ABC-stacked trilayers. Using a tight-binding model to describe the electronic states, the shift current conductivity and jerk current conductivity are calculated over a broad spectral range from terahertz to visible frequencies. Our symmetry analysis reveals that a nonvanishing shift current emerges only in ABA-stacked trilayer graphene due to its broken inversion symmetry, with a peak conductivity reaching approximately $1.21 \times 10^{-13}$ A$\cdot$m/V$^2$ at optimal doping. In contrast, the jerk current, permitted in all structures, requires an in-plane static electric field and exhibits pronounced spectral tunability with chemical potential. These findings establish a comprehensive symmetry-band-field coupling paradigm for nonlinear photocurrents in layered graphene and provide design principles for tunable, polarization-sensitive photodetection and energy-harvesting devices based on van der Waals heterostructures.
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All authors Zhaohang Li, Kainan Chang, Haoyu Li, Yuxuan Gao, Wei Xin, Jinluo Cheng, Haiyang Xu

Soft Condensed Matter

Dynamic fragmentation of residually stressed solids: From microscopic instabilities to universal scaling

Vineet Dawara and Koushik Viswanathan

The dynamic fragmentation of residually stressed solids involves a complex interplay between stored elastic energy, stress wave propagation, and crack instabilities. In this work, we investigate the fracture mechanics of chemically toughened glass through high-velocity projectile impact experiments and a novel micromechanical network model. We rigorously incorporate residual stress into the discrete lattice framework via a prescribed inelastic strain (eigenstrain) distribution, formulated as equivalent body and surface forces to ensure mesh-independent fracture paths. Our experiments and simulations demonstrate that while the fracture topology shifts from coarse to fine with increasing impact energy, the cumulative fragment size distribution consistently follows an exponential decay. Crucially, we reveal a universal scaling law: fragment size distributions from diverse loading conditions and stress profiles collapse onto a single master curve when normalized by the mean fragment area. Furthermore, the model elucidates the determinants of fragmentation, showing that the resulting fragment size is governed not only by the magnitude of residual stress but also by the steepness of the stress gradient. At the microscopic scale, we identify a mechanism for dynamic instability where non-sequential bond breaking ahead of the crack tip leads to apparent local crack speeds exceeding the Rayleigh wave speed ($c_r$). These arrested micro-branches, analogous to the Burridge-Andrews mechanism, provide a physical explanation for the "tongue-like" features and hackle zones observed in post-mortem fractography.
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Materials Science

Autonomous epitaxial atomic-layer synthesis via real-time computer vision of electron diffraction

Haotong Liang, Yunlong Sun, Ryan Paxson et al. (+8 more)

Autonomous science platforms which make decisions on the fly are fundamentally changing the outlook for materials development. AI-driven schemes can effectively reduce the total number of iterations needed to arrive at the best stoichiometry for desired properties or optimum synthesis parameters by significant margins. Here, we demonstrate real-time closed-loop autonomous navigation of a multi-dimensional synthesis parameter space for fabricating phase-pure epitaxial films of a metastable functional oxide phase using pulsed laser deposition. Sequential growth iterations in search of the optimized recipe to stabilize the desired crystal phase were performed using frame-by-frame quantitative computer vision of electron diffraction images at the unit-cell level. Our scheme regularly resulted in > 30-fold reduction in the number of experiments compared to comprehensive parameter-space mapping. The real-time workflow developed here can be readily extended to other thin film synthesis platforms opening the door for self-driving atomic-level materials design as well as autonomous semiconductor manufacturing.
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All authors Haotong Liang, Yunlong Sun, Ryan Paxson, Chih-Yu Lee, Alex T. Hall, Zoey Warecki, John Cumings, Hideomi Koinuma, Aaron Gilad Kusne, Mikk Lippmaa, Ichiro Takeuchi

Monday 23 February

Soft Condensed Matter

Wet granular bed eroded by a dry granular flow

Lama Braysh, Patrick Mutabaruka, Farhang Radjai et al. (+1 more)

Using three-dimensional Discrete Element Method (DEM) simulations, we investigate the erosion dynamics of a cohesive bed composed of wet spherical particles subjected to the shear flow of an overlying non-cohesive granular layer. Cohesion is modeled through a capillary attraction law, where the erosion process is governed by the irreversible rupture of liquid bridges at the interface. By systematically varying the liquid-vapor surface tension and the inclination angle of the bed, we analyze the influence of cohesive strength and flow intensity on the mass entrainment rate. Our results identify two distinct erosion regimes: a slow, stochastic regime driven by granular temperature fluctuations, and a fast, collective regime characterized by a global mechanical instability of the interface. We propose a robust scaling law for the surface erosion rate in the fast erosion regime, based on the interplay between two dimensionless parameters: the inertial number ($I$) and the cohesion index ($\xi$). This framework reveals that the threshold for the fast erosion regime is determined by the ratio of the geometric mean of the driving stresses (kinetic and pressure) to the cohesive resistance. These findings provide a comprehensive description of the coupling between inertial and capillary forces, offering a predictive tool for the stability of cohesive interfaces in sheared granular flows.
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All authors Lama Braysh, Patrick Mutabaruka, Farhang Radjai, Serge Mora

Materials Science

Band-Like Transport and Cation Off-Centring in Ag/Bi-Based Solar Absorbers

Yi-Teng Huang, Yixin Wang, Georgia Fields et al. (+19 more)

Ag(I)-Bi(III)-based semiconductors have gained substantial attention as nontoxic, stable alternatives to lead-halide perovskites for optoelectronics, but are widely limited by carrier localization, which severely restricts diffusion lengths. The most efficient Ag/Bi solar absorber is AgBiS2, but diffusion lengths in nanocrystal films are <50 nm. Carrier localization in this rock-salt (Fm-3m) system is believed to arise from cation disorder, and so we herein investigate the layered cation-ordered analogue. Through beyond-DFT simulations combined with neutron and X-ray powder diffraction, we reveal that off-centring of Ag+ and Bi3+ cations is energetically-favoured in this cation-ordered phase. Despite local distortions in the AgS6 and BiS6 octahedra, band-like transport takes place, which, surprisingly, also occurs in the cation-disordered rock-salt phase when these materials are made as bulk powders. The cubic-phase powders have the same degree of cation disorder as the nanocrystals that have carrier localization, which suggests that extrinsic factors play a determining role. We ascribe the intrinsic band-like transport of both phases of AgBiS2 to its close packing, ensuring high electronic dimensionality. These insights offer pathways for designing solar absorbers avoiding carrier localization limitations, and call for future efforts to enhance the efficiency of AgBiS2 photovoltaics to focus on large-grained thin films, or improved nanocrystal surface passivation.
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All authors Yi-Teng Huang, Yixin Wang, Georgia Fields, Peixi Cong, Yongjie Wang, Jack E. N. Swallow, Avari Roy, Jack M. Woolley, Victoria Rotaru, Maxim Guc, Lars van Turnhout, Mohamed Aouane, Emmanuelle Suard, Dominik Kubicki, Alejandro Pérez-Rodríguez, Aditya Sadhanala, Akshay Rao, Dennis Friedrich, Robert S. Weatherup, Simon J. Clarke, Seán R. Kavanagh, Robert L. Z. Hoye

Quantum Gases

Revealing Pseudo-Fermionization and Chiral Binding of One-Dimensional Anyons using Adiabatic State Preparation

Brice Bakkali-Hassani, Joyce Kwan, Perrin Segura et al. (+5 more)

Fractional statistics give rise to quantum behaviors that differ fundamentally from those of bosons and fermions. While two-dimensional anyons play a major role in strongly correlated systems and topological quantum computing, the nature of their one-dimensional (1D) counterparts remains the subject of intense debate, with renewed interest fueled by recent experimental progress. Theoretically, 1D anyons are predicted to host exotic many-body phases and quantum phase transitions, yet experimental signatures have remained elusive. Using ultracold atoms in an optical lattice, we prepare two-body ground states of the 1D anyon-Hubbard model by combining Hamiltonian engineering via quasiperiodic drives and adiabatic state manipulation. We uncover the effects of statistical interactions that lead to pseudo-fermionization and to the formation of chiral bound states when particles remain close together. Our results establish a link between lattice and continuum realizations of anyon models, and mark important steps towards the precise control of 1D anyons in both equilibrium and out-of-equilibrium settings.
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All authors Brice Bakkali-Hassani, Joyce Kwan, Perrin Segura, Yanfei Li, Isaac Tesfaye, Gerard Valentí-Rojas, André Eckardt, Markus Greiner

Quantum Gases

Zero-point energy of a trapped ultracold Fermi gas at unitarity: squeezing the Heisenberg uncertainty principle and suppressing the Pauli principle to produce a superfluid state

D.K. Watson

The zero-point energy of a trapped ultracold Fermi gas at unitarity is investigated in relation to the combined effects of the Heisenberg uncertainty principle and the Pauli principle. This lowest allowed quantum state is a superfluid state which has been studied extensively both experimentally and theoretically. The method used for the current investigation is based on a recent series of papers that proposed microscopic dynamics based on normal modes to describe superfluidity instead of real-space Cooper pairs. This approach yielded excellent agreement with experimental data for multiple properties and allowed the microscopic behavior underlying these results as well as the basis of universal behavior to be analyzed in detail using the group theoretic basis of this general N-body approach. This microscopic picture is now used to illucidate the roles played by the uncertainty principle and the Pauli principle in determining the energy and character of the lowest allowed quantum state including the squeezed character of this superfluid state and the suppression of the Pauli principle.
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Mesoscale and Nanoscale Physics

Electronic dynamics in long linear and cyclic polyynes towards the carbyne limit

Soumyadip Bhunia, Yueze Gao, Jack Woolley et al. (+3 more)

Carbyne-the one-dimensional sp-hybridised allotrope of carbon-has long been predicted to exhibit unique properties, yet its synthesis remains elusive. To probe its behaviour, finite sp-carbon chains such as cumulenes and polyynes have been studied, but work to date has focused almost exclusively on short, linear systems far from the infinite carbyne limit and without considering topology. Here, we investigate long (48-carbon) linear and cyclic polyynes using steady-state and ultrafast, temperature- and polarization-resolved optical and vibrational spectroscopy. We find highly delocalized ground states in both topologies, with Peierls distortions markedly weaker than in short chains. In contrast, excited states undergo rapid self-localisation, with the localisation pathway and subsequent intersystem crossing strongly dependent on chain length and topology. Unlike shorter polyynes, excited-state structural rearrangements are minimal, and comparison with theoretical predictions shows that properties, such as Huang-Rhys factors, have plateaued by 48 carbons. Our results reveal how topology influences the electronic dynamics of long polyynes and refines our understanding of sp-carbon systems approaching the carbyne limit
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All authors Soumyadip Bhunia, Yueze Gao, Jack Woolley, Ross Milverton, Harry L Anderson, Raj Pandya

Statistical Mechanics · Cross-listed from stat.ML

Selecting Optimal Variable Order in Autoregressive Ising Models

Shiba Biswal, Marc Vuffray and Andrey Y. Lokhov

Autoregressive models enable tractable sampling from learned probability distributions, but their performance critically depends on the variable ordering used in the factorization via complexities of the resulting conditional distributions. We propose to learn the Markov random field describing the underlying data, and use the inferred graphical model structure to construct optimized variable orderings. We illustrate our approach on two-dimensional image-like models where a structure-aware ordering leads to restricted conditioning sets, thereby reducing model complexity. Numerical experiments on Ising models with discrete data demonstrate that graph-informed orderings yield higher-fidelity generated samples compared to naive variable orderings.
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Other Condensed Matter

Transient Plastic Spin Labeling with Chlorine Dioxide

Bence G. Márkus, Sándor Kollarics, Kristóf Kály-Kullai et al. (+5 more)

Plastic waste, being one of the most important problems for humankind, poses severe threats to ecosystems, wildlife, and human health. Tracing, quantifying, and identifying types of plastic waste is of crucial importance to understand its environmental pathways and develop targeted strategies for reduction, recycling, and remediation. To contribute to addressing this global issue, we investigated the spin-labeling capabilities of aqueous chlorine dioxide (ClO$_2$) radicals upon introduction into poly(ethylene terephthalate) and utilized electron spin resonance spectroscopy for detection. The technique is capable of identifying plastic species as the unpaired electron of the radical molecule is strongly sensitive to its local environment through its coupling parameters. Temperature-dependent measurements revealed that the molecules are immobilized at low temperatures and exhibit well-resolved anisotropic and hyperfine spectra that are quantitatively described by a model spin Hamiltonian. Even above the melting point of water, some degrees of freedom remain blocked as a result of the polymer matrix. Furthermore, employing a time-series measurement at room temperature enabled us to determine the diffusion coefficient of the molecule in the polymer.
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All authors Bence G. Márkus, Sándor Kollarics, Kristóf Kály-Kullai, Bernadett Juhász, Dávid Beke, László Forró, Zoltán Noszticzius, Ferenc Simon

Materials Science

Demonstration of High-Performance Ultra-Wide Bandgap SrSnO$_3$ Top-Gated MOSFETs

Junghyun Koo, Weideng Sun, Donghwan Kim et al. (+6 more)

We report the demonstration of high-performance top-gated metal-oxide-semiconductor field-effect transistors (MOSFETs) based on the ultra-wide bandgap perovskite oxide SrSnO$_3$ (SSO). Using hybrid molecular beam epitaxy-grown SSO channels and ALD-deposited HfO$_2$ gate dielectrics, the devices exhibit field-effect mobility exceeding 65 cm$^2$/V$\cdot$s, an on-state current up to 194 mA/mm, an on/off current ratio above $10^8$, and a contact resistance of 0.66 $\Omega\cdot$mm. The devices also show a near-ideal subthreshold slope of 68 mV/dec and negligible hysteresis, indicating a high-quality dielectric/semiconductor interface. These results establish SrSnO$_3$ as a promising ultra-wide bandgap oxide semiconductor platform for high-performance power electronic applications.
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All authors Junghyun Koo, Weideng Sun, Donghwan Kim, Hongseung Lee, Chengyu Zhu, Kiyoung Lee, Hagyoul Bae, Bharat Jalan, Gang Qiu

Superconductivity

Impact of magnetic field direction on anti-dot-based superconducting diodes

E. B. de Melo Junior, E. Strambini, F. Giazotto et al. (+1 more)

The superconducting diode effect (SDE) is a fundamental building block for dissipationless nonreciprocal electronics, yet its microscopic origins in thin films often involve competing mechanisms that remain debated. Here, we demonstrate that the SDE can be engineered in niobium films by patterning macroscopic asymmetric antidots, revealing distinct control mechanisms under in-plane and out-of-plane magnetic fields. We identify two dominant contributions to nonreciprocal transport: edge flux pinning, which governs the low-field and in-plane field regimes via surface-barrier asymmetry, and bulk flux pinning, which drives the high-field response and correlates directly with the geometric asymmetry of the antidots. Supported by time-dependent Ginzburg-Landau simulations and an analytical model, we provide a unified description of these regimes, linking the diode efficiency to the specific pinning landscape. These findings establish a flexible design principle for engineering superconducting diodes with tunable functionality, paving the way for their integration into next-generation quantum and cryogenic circuits.
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All authors E. B. de Melo Junior, E. Strambini, F. Giazotto, C. I. L. de Araujo

Quantum Gases

Equilibrium and dynamical quantum phase transitions in dipolar atomic Josephson junctions

Cesare Vianello, Giovanni Mazzarella and Luca Salasnich

An atomic Josephson junction realized with dipolar bosons in a double-well potential can be described by an extended Bose-Hubbard model in which dipolar interactions generate an effective on-site interaction and nearest-neighbor pair tunneling. Using mean-field theory and exact diagonalization, we investigate how this correlated process affects zero-temperature equilibrium and dynamical properties of the system. In equilibrium, we show that pair tunneling induces ground-state parity modulations and significantly reshapes the phase diagram, producing qualitative changes in the quantum phase transitions toward NOON and phase-NOON states, as well as quantitative shifts of the critical points. Out of equilibrium, we demonstrate that it modifies the conditions for macroscopic quantum self-trapping, and assess its impact by comparing mean-field and fully quantum evolution, including the emergence of dynamical quantum phase transitions.
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Statistical Mechanics

Mutual Linearity is a Generic Property of Steady-State Markov Networks

Robin Bebon and Thomas Speck

Understanding and predicting how complex systems respond to external perturbations is a central challenge in nonequilibrium statistical physics. Here we consider continuous-time Markov networks, which we subject to perturbations along a single edge. We find that in steady state the probabilities of any two states are linearly related to one another. We show that this mutual linearity of probabilities extends to a broad class of observables, including currents but also generic counting and state-dependent observables. Moreover, we derive an exact relation between the relative response of any state's probability and the ratio of two steady-state probabilities. Leveraging the Markov chain tree theorem, we further show that probabilities and the considered observables are constrained by the topological and kinetic properties of the network and provide analytical expressions in terms of spanning tree polynomials. Our results are general, holding for arbitrary rate parameterizations and extending far from equilibrium.
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Statistical Mechanics

Hyperuniformity in active fluids reshapes nucleation and capillary-wave dynamics

Raphaël Maire

While nucleation in typical active and driven fluids often appears equilibrium-like, striking departures emerge when large-scale fluctuations are strongly suppressed. Here, we investigate nucleation in nonequilibrium hyperuniform fluids by projecting the full density-field dynamics onto relevant collective variables. We demonstrate that nucleation is governed by a nonequilibrium quasipotential rather than the reversible work of formation. Surprisingly, because of the reduced hyperuniform fluctuations, the nucleation probability no longer separates into the usual surface and volume contributions. Furthermore, accounting for capillary waves reveals a clear breakdown of detailed balance driven by nonreciprocal dynamics. More broadly, our framework can be readily extended to identify nonequilibrium signatures in conventional active fluids.
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Statistical Mechanics · Cross-listed from quant-ph

Entanglement Barriers from Computational Complexity: Matrix-Product-State Approach to Satisfiability

Tim Pokart, Frank Pollmann and Jan Carl Budich

We approach the 3-SAT satisfiability problem with the quantum-inspired method of imaginary time propagation (ITP) applied to matrix product states (MPS) on a classical computer. This ansatz is fundamentally limited by a quantum entanglement barrier that emerges in imaginary time, reflecting the exponential hardness expected for this NP-complete problem. Strikingly, we argue based on careful analysis of the structure imprinted onto the MPS by the 3-SAT instances that this barrier arises from classical computational complexity. To reveal this connection, we elucidate with stochastic models the specific relationship between the classical hardness of the $\sharp$P $\supseteq$ NP-complete counting problem $\sharp$3-SAT and the entanglement properties of the quantum state. Our findings illuminate the limitations of this quantum-inspired approach and demonstrate how purely classical computational complexity can manifest in quantum entanglement. Furthermore, we present estimates of the non-stabilizerness required by the protocol, finding a similar resource barrier. Specifically, the necessary amount of non-Clifford operations scales superlinearly in system size, thus implying extensive resource requirements of ITP on different architectures such as Clifford circuits or gate-based quantum computers.
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Strongly Correlated Electrons · Cross-listed from hep-th

A Two-Point Hologram for Everything

Tamra Nebabu, Xiao-Liang Qi, Haifeng Tang et al. (+1 more)

Known holographic dictionaries, especially AdS/CFT, rely on symmetry matching between the bulk and the boundary. We take a step toward a holographic dictionary with no symmetry requirement and without assuming the geometry being asymptotically AdS. Starting from any interacting Majorana generalized free field on a $(0+1)$d boundary and its two-point function data, we derive a concise analytic formula for the dual $(1+1)$d bulk geometry, borrowing techniques from unitary matrix integral and inverse scattering. Using this formula, we compute the near-horizon curvature, give conditions for positive versus negative curvature, and identify simple boundary models with de Sitter or anti-de Sitter near-horizon duals. We also study the large-$q$ SYK model, finding an unusual temperature dependence of the near-horizon curvature, related to the discrepancy between physical temperature and the “fake disk” temperature. We also construct, directly from boundary operators, approximate algebras generated by null translations and boost that become exact at the bifurcate horizon.
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All authors Tamra Nebabu, Xiao-Liang Qi, Haifeng Tang, Huaijin Wang

Superconductivity

Superconductivity and magnetism in bilayer nickelates: itinerant perspective

Yi-Ming Wu, Tobias Helbig, Salahudin V. Smailagić et al. (+4 more)

We study superconductivity and magnetism in bilayer nickelates from an itinerant perspective. Starting from a tight binding fit to recent ARPES measurements on compressively strained thin films, we incorporate the standard set of onsite repulsive interactions among partially filled $e_g$ orbitals: intra-orbital $U$, inter-orbital $U'$, Hund's coupling $J_H$ and a pair hopping $J_P$. We obtain the effective pairing interaction by dressing these bare interactions with particle-hole fluctuations via the RPA. In the strong Hund's coupling regime, we find that $s$-wave superconductivity and $(\pi/2, \pi/2)$ SDW order are the favored ground states. With weaker Hund's coupling, we find that $d$-wave pairing and $(\pi, \pi)$ SDW are the leading ground states. Our results are qualitatively consistent with earlier DMRG studies, and point to the key role played by Hund's coupling in determining the nature of superconductivity and magnetism in this system.
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All authors Yi-Ming Wu, Tobias Helbig, Salahudin V. Smailagić, Hao-Xin Wang, Yijun Yu, Harold Y. Hwang, Srinivas Raghu

Superconductivity

Qubit Noise Spectroscopy of Superconducting Dynamics in a Magnetic Field

Jiajie Cheng, Jaewon Kim, Oriana K. Diessel et al. (+2 more)

An applied magnetic field affects a superconductor in two ways – by promoting pairing fluctuations, and by inducing topological defects called vortices that carry quantized magnetic flux. A quantitative characterization of the resultant field-induced superconducting dynamics with spatio-temporal resolution remains challenging, particularly in two-dimensional materials. In this work, we analyze magnetic noise measured by the depolarization rate of a proximate single spin qubit as a non-invasive probe of such dynamical fluctuations. We demonstrate that the temperature dependence of the magnetic noise spectrum near $T_c$ deviates from predictions based on quasiparticle excitations due to critical superconducting fluctuations, which in turn are enhanced by a weak applied field. By analyzing the magnetic noise due to vortex dynamics, we further show that noise spectroscopy is not only able to distinguish between different vortex phases, but also extract key physical quantities of interest, such as oscillation frequencies of pinned vortices, phonon dispersion of vortex lattices and vortex diffusivity in a vortex liquid. Complementing recent work on noise magnetometry of quasiparticle excitations and Berezinskii-Kosterlitz-Thouless transitions in two-dimensional superconductors without an applied field, our work highlights the ability of noise spectroscopy to reveal a wealth of superconducting dynamical phenomena in an applied field.
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All authors Jiajie Cheng, Jaewon Kim, Oriana K. Diessel, Chong Zu, Shubhayu Chatterjee

Soft Condensed Matter

Breakdown and Restoration of Hydrodynamics in Dipole-conserving Active Fluids

Anish Chaudhuri, Lokrshi Prawar Dadhichi and Arijit Haldar

We present a general hydrodynamic theory for active fluids, capable of describing living matter, that conserve center of mass or dipole moment. Imposition of dipole or center-of-mass conservation has been reported to yield peculiar behavior: breaking Galilean invariance in classical systems and potentially enabling exotic immobile excitations in quantum settings. In passive fluids, dipole conservation has been shown to cause a breakdown of linear hydrodynamics in all experimentally relevant dimensions. We show that introducing activity changes this picture: it can either restore or break linear hydrodynamics depending on spatial dimensions. Using our formulation, we predict universal dynamical scaling exponents for single-component active fluids in $d=1,2,3$ dimensions and find agreement with microscopic lattice-field simulations. Strikingly, for $d\geq 2$, activity revives linear hydrodynamics, while for $d<2$ it leads to a breakdown; both cases flow to previously unexplored universality classes. Our results suggest that dipole-conserving active fluids are far more experimentally accessible than their passive counterparts.
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Statistical Mechanics

Spectral Decimation of Quantum Many-Body Hamiltonians

Feng He, Arthur Hutsalyuk, Giuseppe Mussardo et al. (+1 more)

We develop a systematic theory of spectral decimation for quantum many-body Hamiltonians and show that it provides a quantitative probe of emergent symmetries in statistically mixed spectra. Building on an analytical description of statistical mixtures, we derive an explicit expression for the size of a characteristic symmetry sector (CSS), defined as the largest subsequence of levels exhibiting non-Poissonian correlations. The CSS dimension is shown to be the size-biased average of the underlying symmetry sectors, establishing a direct link between spectral statistics and Hilbert-space structure. We apply this framework to two paradigmatic settings: Hilbert-space fragmentation and disorder-induced many-body localization (MBL). In fragmented systems, the CSS reproduces the mixture prediction and isolates correlated subsectors even when the full spectrum appears nearly Poissonian. In the disordered Heisenberg chain, spectral decimation reveals the gradual emergence of integrability through a shrinking CSS, whose statistics exhibit signatures consistent with local integrals of motion. We introduce a characteristic symmetry entropy (CSE) as a finite-size scaling observable and extract, within accessible system sizes, the crossover exponents. Our results establish spectral decimation as a controlled, unbiased and computationally inexpensive diagnostic of hidden structure in many-body spectra, capable of distinguishing between chaotic dynamics, statistical mixtures, and emergent integrability.
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All authors Feng He, Arthur Hutsalyuk, Giuseppe Mussardo, Andrea Stampiggi