Mesoscale and Nanoscale Physics
Vortex-Beam-Driven Dirac Materials: Impurity and Polarization Effects on Light-Induced Vortex and Edge States
Trevor W. Walsh, Eric E. Caldwell, Nancy P. Sandler et al. (+1 more)
We study
impurity scattering and polarization detuning in finite-size
vortex-light-beam-driven massive Dirac systems. In finite geometries, circularly polarized
vortex light opens a dynamical gap where topological edge states coexist with photoinduced multiply quantized
vortex states. We analyze how finite-size effects, vorticity, and effective particle-hole
symmetry manifest in the quasienergy spectrum, real-space states, and local density of states. We show that angular-momentum mixing due to localized
impurities and
impurity clusters reshape
vortex states, while when produced by circular polarization, it leads to a gradual filling of the dynamical gap with bulk-derived states. Our results indicate that both
vortex and edge signatures remain observable in the presence of
impurities and realistic polarization deviations, providing guidance for experimental realizations.
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All authors Trevor W. Walsh, Eric E. Caldwell, Nancy P. Sandler, Mahmoud M. Asmar
Superconductivity · Cross-listed from quant-ph
Effects of Josephson Junction Non-idealities on Adiabatic Quantum Flux Parametron Circuits
Daryoush Shiri, Likai Yang, Mohamed A. Hassan et al. (+2 more)
Adiabatic
quantum flux parametron (AQFP) gate is a promising approach to scale up the cryogenic microwave electronics for superconducting
qubit multiplexed control. However, the performance of these
circuits depends on the quality of the Josephson junctions which are ideally
superconductor-
insulator-
superconductor (SIS) type following the ideal sinusoidal relation between current and
quantum phase. We demonstrate how the non-sinusoidal current-phase relation in
Superconductor-Normal metal-
Superconductor (SNS) and weak link (WL) junctions affects the speed, delay, and margin of the AQFP gates. The JJ models are defined in the Keysight ADS simulator using symbolically defined device (SDD) method.
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All authors Daryoush Shiri, Likai Yang, Mohamed A. Hassan, Philip Krantz, Eric T. Holland
Materials Science
Characterization of ultrathin nickel films deposited by thermal laser evaporation
David S. Catherall, Yifei Yan, Finley B. Donachie et al. (+2 more)
Thermal
laser evaporation is a physical vapor deposition technique of increasing interest because of its ability to evaporate essentially any solid element, even the most refractory such as W. However, many films deposited by this method, especially non-epitaxial films, remain to be characterized; further, key system components such as the
laser delivery system have not been described in detail. Here, we present the evaporation and characterization of ultrathin Ni films deposited with a home-built thermal
laser evaporation system. The system employs a continuous-wave 1 kW fiber
laser (1070 nm) focused to sub-millimeter diameter onto a Ni target rod mounted inside an ultrahigh-
vacuum chamber. The
laser heats the target to a temperature high enough to produce vapor for film deposition; for Ni, this temperature is around the melting point of 1725 K. We report the characterization of the surface roughness, composition, and room-temperature electrical properties of the films along with the design of the major components of our system. This work advances the growing consensus regarding the potential of thermal
laser evaporation for thin film deposition and epitaxy and provides the necessary design information to facilitate broader adoption of the technique.
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All authors David S. Catherall, Yifei Yan, Finley B. Donachie, Azmain A. Hossain, Austin J. Minnich
Materials Science
Robust Spin Splitting and Strain-Controlled Optical Response in Monolayer CrC2N4 for Valleytronic and Optoelectronic Applications
Md. Samrat, Vivek Chowdhury, Sake Wang et al. (+1 more)
Monolayer CrC2N4 recently emerged as a promising two-dimensional
semiconductor, yet its
spin-orbit-coupled (SOC) physics and strain-tunable optical response remained largely unexplored. Here, we investigated the electronic, valley, charge-transfer, and optical properties of pristine and biaxially strained monolayer CrC2N4 using first-principles calculations. The monolayer exhibited a direct band gap at the K/K' valleys. SOC produced valley contrasting out-of-plane
spin polarization, yielding a moderate valence band
spin splitting of 51.9 meV and a small conduction band
spin splitting of 1.7 meV. Orbital-resolved analysis showed that the edge states were mainly governed by Cr-d and N-p hybridization, while Bader analysis indicated polar-covalent bonding through charge transfer toward N atoms. Biaxial strain in the range of -4% to +4% tuned the band gap from 1.987 to 1.421 eV and drove an indirect-to-direct gap transition near -1% strain. Tensile strain enhanced the Berry
curvature and red-shifted the optical response toward the visible-near-infrared region. These results suggested monolayer CrC2N4 as a promising platform for strain-engineered valleytronic and optoelectronic device applications.
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All authors Md. Samrat, Vivek Chowdhury, Sake Wang, Ahmed Zubair
Strongly Correlated Electrons
Emergent Antiphase Stacking in a Transient Charge Density Wave
Jade Stanton, Gal Orenstein, Ryan A. Duncan et al. (+14 more)
Photoexcitation can induce novel states in materials that are inaccessible in
equilibrium, a recent example being the light-induced charge density wave (CDW) observed in $\text{LaTe}_3$. Here, we investigate this transient CDW using infrared-pump x-ray-probe scattering at a free-electron
laser, with high momentum and time resolution. We find that the transient CDW Bragg peak is broad in reciprocal space, indicating a highly disordered state. The ordering wavevector of the transient state is different from the
equilibrium orders that develop in this class of materials - the transient peak appears near (2/7, 0, 0) reciprocal
lattice units, whereas the
equilibrium $a$ order and $c$ order occur at $\approx (5/7, 0, 0)$ and $(0, 0, 2/7)$, respectively. The transient CDW is therefore distinct from the
equilibrium $a$ order, differing in the relative phase of the CDW displacement between the two equivalent nearly-square Te-Te nets in the conventional unit
cell. Our work highlights how photoexcitation can access states with no
equilibrium analog, and how x-ray scattering can provide microscopic insight into such elusive phases.
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All authors Jade Stanton, Gal Orenstein, Ryan A. Duncan, Gilberto A. de la Peña Muñoz, Yijing Huang, Viktor Krapivin, Quynh Le Nguyen, Samuel Teitelbaum, Anisha G. Singh, Roman Mankowsky, Henrik Lemke, Mathias Sander, Yunpei Deng, Christopher Arrell, Ian R. Fisher, David A. Reis, Mariano Trigo
Strongly Correlated Electrons
II. Exploring the role of the Crystal Electric Field in the vicinity of a Quantum Critical Point
Julian G. Sereni, Ivan Curlik, Slavo Gabani et al. (+1 more)
Very low temperature thermodynamic properties of the Yb$M_{5-x}X_x$ (with $M$= Ni, Cu, and $X$= Cd, Mg, Au, Zn, Ag) cubic compounds are analyzed covering a broad range of behavior between
magnetic and
Fermi-
liquid ground states GS using the chemical doping: $\zeta$ as control parameter. This allows to gain insight into the
evolution of the GS behavior including a
quantum critical point QCP. Doniach-Lavagna phase diagram limitations are improved by taking into account
crystal electric field CEF splittings. Three regions are recognized as a function of $\zeta$: i) a
magnetic one with long range
magnetic order and $T_{ord}\propto T_N \approx 1$\,K, that weakens the interactions between $0.8\,K \geq T_m\geq 0.4$\,K, exhibiting very low Kondo temperature $T_K^{GS}$ in respective doublets GS. Then, for $T_Q\leq 0.4$\,K,
quantum fluctuations start to dominate the scenario with the specific heat $C_{4f}/T(T\geq T_Q)$ showing $T$ power law dependencies, and a very heavy-
fermion plateau below $T_Q$. ii) beyond the QCP the typical Non-
Fermi-
Liquid logarithmic $T$ dependence: $C_{4f}/T \propto \ln(T/T_0)$, with traces of
magnetic order. At the non-
magnetic limit: iii) the
alloys behave as valence-fluctuation systems with growing $T_K$ that overcomes the CEF splitting. With this experimental information, a realistic phase diagram can be drawn around the QCP where the scenario is dominated by low lying
quantum fluctuations, without $C_{4f}/T|_{Lim T\to 0}$ divergences but a clear drop entering into the non-
magnetic phase.
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All authors Julian G. Sereni, Ivan Curlik, Slavo Gabani, Mauro Giovannini
Materials Science
Dislocation-templated antiferromagnetic domains in epitaxial NiO
Alexandra Fonseca Montenegro, Justin Michel, Fengyuan Yang et al. (+1 more)
Controlling
antiferromagnetic domains is essential for spintronics, yet predictable manipulation remains challenging due to their lack of net magnetization. Here, we utilize scanning electron microscopy electron channeling contrast imaging (ECCI) to observe the formation of nanoscale
antiferromagnetic domains in epitaxial NiO/MgO(001) at interface dislocations. Thermal cycling across the Néel temperature reveals that while domain contrast vanishes in the paramagnetic phase, the features re-emerge at identical spatial locations upon cooling. Diffraction-vector-dependent ECCI imaging, governed by a relative tilt contrast model, indicates that the domains stem from localized rhombohedral distortions of volumetric twin-type $T$-domains. These $T$-domains are stabilized by the long-range shear stress field of interface misfit dislocations (MDs). By tracking a film thickness series from 23 to 46~nm, we resolve a transition in
oxide relaxation mechanics from primary $60^\circ$ interface MDs along $\langle110\rangle$ to a cross-slipped network of pure edge $90^\circ$ MDs deviated toward $\langle100\rangle$. We demonstrate that ECCI identifies the Burgers vector and line direction of these MDs via strict $\vec{g} \cdot (\vec{b} \times \vec{u})$ invisibility criteria, and an Eshelby interaction energy model accurately predicts the asymmetric nucleation of specific $T$-domains along MD flanks. Quantitative image analysis shows $T$-domain volume fractions track the spatial configuration of the evolving MD networks, providing a framework for defect-engineering
antiferromagnetic textures using one-dimensional defects.
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All authors Alexandra Fonseca Montenegro, Justin Michel, Fengyuan Yang, Roberto C. Myers
Mesoscale and Nanoscale Physics
Room-temperature tuning and probing of Fermi polarons in atomically thin semiconductors on a plasmonic metasurface
Tingting Wu, Francesca Maria Marchetti, Antonio Tiene et al. (+9 more)
The
Fermi polaron, arising from interactions between a mobile
impurity and a degenerate
Fermi sea, is a many-body quasiparticle that provides a sensitive probe of strongly correlated electronic phases in atomically thin
semiconductors. In doped transition-metal dichalcogenides, the attractive and repulsive polaron branches are well established in monolayers. However, extending active control and quantitative, branch-resolved probing to stacked geometries has remained elusive because spectral quenching and weak optical contrast restrict access to
Fermi polaron signatures. Here, we integrate electron-doped WS$_2$ flakes from monolayer to quadrilayer with a strain-tunable plasmonic metasurface, enabling high-contrast scattering readout at room temperature through coupling between
Fermi polaron resonances and surface plasmons. This platform enables quantitative extraction of polaron branch spectral weights and coupling strengths across different layer numbers. We uncover a systematic thickness dependence of the spectral-weight distribution and demonstrate continuous and fully reversible spectral-weight transfer between attractive and repulsive branches in
bilayers and quadrilayers, with near-complete transfer achieved in
bilayers. By identifying layer number and strain as complementary control parameters for
Fermi polarons, our results establish metasurface-enabled scattering spectroscopy as a practical route to resolve and manipulate many-body resonances in stacked van der Waals
semiconductors, bridging idealized monolayer polaron physics and device-relevant architectures.
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All authors Tingting Wu, Francesca Maria Marchetti, Antonio Tiene, Antonio I. Fernández-Domínguez, Miao Qi, Zhe Wang, Lin Liu, Lei Wei, Francisco J. Garcia-Vidal, Mengxiao Chen, Qi Jie Wang, Yu Luo
Superconductivity
Tunable Superconductivity in 1313-La$_3$Ni$_2$O$_7$: Suppressed under Compression and Possible $s^{\pm}$ Pairing under Tension
Yang Zhang, Ling-Fang Lin, Adriana Moreo et al. (+2 more)
Motivated by recent progress in the 1313-La$_3$Ni$_2$O$_7$ nickelate thin films (Nie et al., Nature 652, 628 (2026)), we systematically investigate the effects of both compressive and tensile strain in this system. Self-doping effects between the single-layer (SL) and trilayer (TL) blocks are observed in our studies in both cases, but are most pronounced under tensile strain. We find that superconductivity is unlikely to emerge in the 1313 film on the LSAO substrate even with further hole doping. Remarkably, within the random-phase approximation, under tensile strain, a robust $s^{\pm}$-wave pairing state emerges in the TL subsystem with sign changes between the small electron-like $\sigma$ pocket at the $\Gamma$ point and the small hole-like $\gamma$ pocket at the M point. These pockets are connected by a wave vector close to $(\pi,\pi)$. Our calculations also suggest that superconductivity in 1313-LNO requires an optimally sized $\gamma$ pocket, because an oversized $\gamma$ pocket suppresses pairing formation. Overall, our results predict strain-dependent electronic reconstruction in 1313-La$_3$Ni$_2$O$_7$ and provide guiding principles for engineering superconductivity under ambient pressure conditions.
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All authors Yang Zhang, Ling-Fang Lin, Adriana Moreo, Thomas A. Maier, Elbio Dagotto
Materials Science
General Method for Evaluation of Stop-Bands of Periodic Structures with Symmetric Unit Cells
Alexander Hvatov, Mariia Krasikova, Aleksandra Pavliuk et al. (+1 more)
The mirror
symmetries of a periodic unit
cell are exploited to decompose the standing-wave eigenproblem at the high-
symmetry vertices of the Brillouin zone into four independent sub-problems on a quarter-
cell, each governed by Neumann (sound-hard) or Dirichlet (sound-soft) boundary conditions. Sorting and pairing the resulting eigenfrequencies by index along each segment of the irreducible Brillouin zone boundary yields an explicit formula for the stop-band intervals without computing the full dispersion diagram. The decomposition is exact, following directly from the representation theory of the little group at each high-
symmetry point. It applies to any unit
cell whose material distribution is invariant under the mirrors normal to the
cell faces. The method is validated on two configurations: a phononic
crystal of lead cylinders in an epoxy
matrix, analyzed using the plane-wave expansion, and a
lattice of coupled C-shaped Helmholtz resonators, analyzed using finite-element analysis. For both systems, the reconstructed stop-band boundaries agree with the full Floquet dispersion calculation to within 1% for the lowest bands, requiring
eigenvalue solutions at only three discrete wavevectors. Avoided crossings within a Brillouin zone segment can cause bands to exhibit non-monotone behavior, rendering the pairing rule approximate; the spectral conditions for this are identified. Flat bands common to both boundary-condition types are identified as bound states in the continuum.
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All authors Alexander Hvatov, Mariia Krasikova, Aleksandra Pavliuk, Steffen Marburg
Superconductivity · Cross-listed from physics.app-ph
Coupled-Mode Equations with Arbitrary Mode Combinations for Kinetic-Inductance Superconducting Traveling-Wave Parametric Devices: Theory and Experimental Validation
F. Patricio Mena, Camilo Espinoza, Ryan O. Berriel et al. (+2 more)
The coupled-mode equations (CMEs) have proven very successful in describing parametric processes in nonlinear optics. More recently, the same formulation has been used to model microwave superconducting parametric amplifiers and frequency multipliers. However, when applied to the microwave regime, not all assumptions remain valid and losses play a more dramatic role. Here, we revisit the CMEs applied to traveling-wave superconducting amplifiers to include losses and provide a formulation that enables their systematic derivation for any combination of traveling waves. As examples, we discuss the impact of unwanted harmonics and intermodulation products on parametric amplification, as well as harmonic generation. We verify that, if not properly accounted for, device performance can deviate considerably from the ideal case. Furthermore, using a superconducting CPW-based artificial transmission line and combining an independent experimental determination of its nonlinear parameter $I'_*$ with simulations of its linear properties, we obtain a parameter-free validation of this formulation. The nonlinear parameter was determined to be $I'_* \approx 27$ mA which, surprisingly, scales with the theoretical depairing current and not with the much smaller critical current of the device. For the validation, we measured multiple-harmonic generation and found excellent agreement between theory and experiment. The fact that $I'_* \gg I_C$ has direct implications for device design.
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All authors F. Patricio Mena, Camilo Espinoza, Ryan O. Berriel, Ricardo Finger, David J. Thoen
Disordered Systems and Neural Networks
Stochastic Thermodynamics of Score Matching in Diffusion Models
Xuehao Ding, H. T. Quan and Yuhai Tu
Score-based
diffusion models are a powerful class of generative AI systems capable of sampling from complex, high-dimensional probability distributions. Their dynamics consist of a forward
diffusion process that transforms data into noise and a learned reverse process that reconstructs data by reversing the probability flow. Here, we develop a
stochastic thermodynamic framework for
diffusion models and their score-matching objective. We introduce a trajectory-dependent quantity, time-asymmetry
entropy production (TAEP), defined from the forward and reverse
diffusion dynamics, and show that it obeys exact fluctuation
theorems. Remarkably, Hyvärinen's implicit score-matching kernel emerges naturally as a fluctuating component of TAEP, while the average TAEP is exactly proportional to the score-matching objective. We further show that fluctuations of TAEP quantify sampling unevenness and provide a thermodynamic measure of data-
manifold coverage. These results yield a quantitative explanation for the superior sampling diversity of
diffusion models and reveal a thermodynamic mechanism by which
stochastic gradient descent favors flatter, more generalizable solutions. By uncovering the entropic nature of score matching, our work establishes fundamental statistical-mechanical principles underlying
diffusion-based generative AI.
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Quantum Gases · Cross-listed from quant-ph
Post-Selection Probability and Fidelity of Bidirectional Teleportation
Ning Sun, Lei Feng and Pengfei Zhang
Understanding the scrambling of
quantum information is central to many areas of
quantum physics, including
quantum thermalization,
entanglement growth, and
quantum information processing. Insights from these studies have, in turn, inspired the development of novel
quantum protocols and
algorithms. Recently, a bidirectional teleportation protocol was proposed to implement a digital SWAP operation between
qubits by leveraging chaotic
Hamiltonian evolution combined with measurement and post-selection. In this work, we provide a comprehensive study of two central quantities that characterize the protocol, the post-selection probability and the fidelity, taking into account possible errors in time-reversed dynamics. We show that these quantities can be expressed in terms of standard diagnostics in
quantum dynamics, including the Loschmidt echo and its subsystem variant. The results unveil (1) the initial-state dependence of the fidelity and (2) the stability of the post-selection probability in integrable models. Our findings offer practical guidance for the implementation of the protocol on realistic
quantum devices.
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Quantum Gases
Spin effects in the particle current of Bose-Einstein condensates in synthetic gauge fields
Hugo Bencomo Martín and Antonio Muñoz Mateo
Spin reveals the rotational features of a system independently of its state of motion. Hence, it is not a relativistic quantity, despite giving rise to effects that emerge naturally from relativistic equations only. Within a non-relativistic framework these effects are not inherently captured, and have to be added by resorting to
symmetry principles or to the asymptotic limit of the corresponding relativistic framework. We report on one of these effects: the divergenceless
spin term in the particle current density of spinor Bose-Einstein condensates. It could be observed in the setup of a synthetic
Hall system made with non-relativistic pseudospin-1/2 bosonic particles. By tuning the interaction strength, the system can show how the
spin term in the particle current is needed for the local matching of classical drift velocity in the ground state of the non-interacting system, whereas for increasing interparticle interactions the
spin-to-orbital current ratio decreases. In either case, since the overall particle velocity changes with the
spin term contribution, so does its circulation in a loop, which in turn has physical consequences for its relationship with the Aharonov-Bohm phase shift.
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Strongly Correlated Electrons
Antisite-disorder driven tuning of magnetic properties and exchange-bias in Nd$_{2-x}$Sr$_{x}$CoMnO$_{6-\delta}$ $(0 \leq x \leq 1)$ ($\delta \sim 0.5$) double perovskites
Kazi Parvez Islam, Jayjit Kumar Dey, Sourav Chowdhury et al. (+8 more)
We demonstrate precise control of exchange bias (EB) in the Nd$_{2-x}$Sr$_x$CoMnO$_{6-\delta}$ ($0 \leq x \leq 1$) double-perovskite series through Sr$^{2+}$ induced hole doping, unveiling a remarkable transition between normal and inverse EB states. Employing
neutron powder diffraction and X-ray absorption spectroscopy, we reveal a structural
evolution from a B-site-ordered monoclinic ($P2_1/n$) phase to a disordered rhombohedral ($R\overline{3}c$) phase with increasing $x$, accompanied by a shift in the effective Co valence from +2 toward +3, while the Mn valence remains essentially unchanged. DC magnetization measurements indicate a gradual suppression of ferromagnetism with hole doping, whereas AC susceptibility measurements at $x = 0.75$ reveal pronounced cluster-glass behavior and the highest EB field of $\sim 4$ kOe at 8 K under a 6 T cooling field. After correcting for minor-loop effects, we identify robust inverse EB at $x = 0.75$, persisting even under a cooling field of 6 T. We attribute this phenomenon to competing
ferromagnetic–
antiferromagnetic and
ferromagnetic–glassy interfaces, governed by strong
magnetic frustration and the magnetocrystalline anisotropy associated with rare-earth 4$f$ electrons. These findings elucidate the pivotal role of doping-induced structural and
magnetic competition in tailoring EB behavior in rare-earth double perovskites, providing new insights for the design of advanced
magnetic materials.
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All authors Kazi Parvez Islam, Jayjit Kumar Dey, Sourav Chowdhury, Samyabrata Paria, Flora Banerjee, Suryakanta Mishra, Suman Kalyan Samanta, Moritz Hoesch, Robert Dankelman, Indu Dhiman, Debraj Choudhury
Materials Science
Physics-Informed Attention Mechanism and Generalization Capability of Deep Learning-Based Grain Growth Evolution Prediction
Pungponhavoan Tep and Marc Bernacki
Machine Learning (ML) models for grain growth prediction are typically trained on idealized synthetic data, yet practical applications require generalization to conditions outside the training distribution. This study evaluated the Out-Of-Distribution (OOD) generalization capability of the trained model from our previous study across three test cases, including experimental microstructures, microstructures characterized by a bimodal grain size distribution, and abnormal grain growth. To further probe whether physics-informed architectural design could improve robustness under these different conditions, a boundary-masked
attention mechanism was proposed specifically for grain growth, constraining
attention to grain boundary pixels. Both the baseline and the proposed physics-informed
attention model were evaluated without retraining or fine-tuning on the OOD data. Both models successfully generalized to all three test cases, yet the boundary-masked
attention mechanism provided substantial improvements, with the most notable gains for microstructures characterized by a bimodal grain size distribution, where Structural Similarity Index Measure (SSIM) improved from \num{0.6221} to \num{0.7609} and mean grain size ($\overline{R}$) error decreased from \SI{8.75}{\percent} to \SI{3.57}{\percent}. The
attention heatmap analysis revealed that the boundary-masked
attention model learned to concentrate
attention on large grain boundaries in a manner consistent with
curvature-driven grain growth physics, emerging from training without being explicitly encoded into the architecture. These results indicate that models trained on synthetic data can generalize to diverse OOD conditions without retraining, and that physics-informed
attention may improve accuracy when the boundary morphology matches the training domain.
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Mesoscale and Nanoscale Physics
Kohn–Luttinger Superconductivity in Flat Chern Bands
Nianlong Zou, Cheng Xu, Yafis Barlas et al. (+1 more)
Recent observations of superconductivity near correlated topological phases in flat bands suggest a facile link between flat-band geometry and electron pairing. In this work, we reveal a geometry-driven Kohn–Luttinger mechanism in which Landau-level-like form factors align the attractive lobe of the RPA-screened Coulomb interaction with the form-factor peak, generating an anomalously strong attractive channel near local band extrema. Using the Skyrmion
lattice model as a minimal realization, we show that for
spin-unpolarized pairing the form-factor magnitude enforces an emergent momentum-space translational
symmetry and selects an extended-$s$ instability concentrated at small
Fermi pockets, while for
spin-polarized pairing the form-factor phase drives
chiral $p$- and $f$-wave order without invoking
spin fluctuations. The band-extrema enhancement persists in higher Landau-level analogs and survives finite-temperature screening and Berezinskii–Kosterlitz–Thouless phase fluctuations. Our work establishes
quantum geometry as a key organizing principle for unconventional pairing in flat Chern bands.
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All authors Nianlong Zou, Cheng Xu, Yafis Barlas, Yang Zhang
Superconductivity
How twist angle inhomogeneity masks the BKT transition and the order parameter symmetry
Ilaria Maccari, Louk Rademaker and Giulia Venditti
Two-dimensional
superconductors, including twisted multilayer
graphene, should exhibit a BKT transition, and the $T$-dependence of the superfluid stiffness should distinguish between nodal or gapped order parameter
symmetries. However, this picture dramatically changes when spatially correlated disorder is taken into account. Such correlations naturally arise in moiré systems due to twist angle inhomogeneities, which we model using elasticity theory. Using a random impedance network based on realistic disorder in the local $T_c$, we show that the finite-frequency conductance reveals a smeared percolative transition instead of a BKT transition. At low temperatures, the disorder can effectively obscure the distinction between nodal and fully gapped superconducting order parameters. We propose that the real part of the conductivity can be used as a key diagnostic observable to probe the relevance of correlated disorder.
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Materials Science
Machine learning insights into band gap properties in halide-based perovskites
Chadawan Khamdang and Mengen Wang
Halide perovskites show great promise for applications in optoelectronic devices. The lead-free perovskites are attracting increasing interest due to their low toxicity and motivate the exploration of alternative compositions and structures, including A$_2$BX$_6$, A$_2$BB$^\prime$X$_6$, A$_3$B$_2$X$_9$, and A$_4$BX$_6$. Accurate predictions of a wide range of band gap energies are important for designing new materials. It is also desired to generate a direct relationship between the structural and elemental descriptors and the band gap energies. In this work, we develop machine learning models to predict band gap energies across various types of halide perovskites based on atomic and structural properties.
Algorithms including ensemble tree-based methods, random forest regression (RFR), gradient boosted regression trees (GBRT), and extreme gradient boosting (XGB) showed strong predictive accuracy. We also analyzed feature importance to identify key descriptors, including B-site and X-site elemental properties, as well as the number of A- and B-site atoms, as primary factors influencing band gap energies. These results improve our understanding of the ML models and provide guidance for designing new halide perovskite materials.
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Statistical Mechanics
Why dimensional analysis works: general classification of self-similarity based on scale-invariance
Hirokazu Maruoka
In this work, we formulate self-similarity from the perspective of scale invariance, where a self-similar form is understood as the transformation of a function into a form invariant under scale transformations. By applying this formulation to physical parameters, which consist of numerical values and units, it is demonstrated that dimensional analysis works for physical problems because scale invariance is partially shared between units and physical parameters. This naturally leads to the distinction between similarity of the first kind and similarity of the second kind according to whether the scale functions induced by units and those associated with physical parameters are equivalent or not. Self-similar solutions of the second kind can be further classified according to whether the power exponents of the similarity parameters include functions of dimensionless numbers. This leads to the conclusion that there are three kinds of self-similar solutions. The present work provides a unified framework for understanding dimensional analysis and a universal classification of self-similarity in physical problems.
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Superconductivity
Hybrid Ferromagnet-SNSPDs: Single photon induced order-to-disorder transition in ferromagnets coupled to thin film superconductors
Leif Bauer, Daien He, Sathwik Bharadwaj et al. (+1 more)
The development of midwave and longwave infrared single
photon detectors is crucial for their emerging applications in spectroscopy, remote sensing,
exoplanet detection, and free space
quantum communications. However, existing sensors need to be operated at extremely low temperatures (0.08-0.9K) to reduce dark noise and hence require the use of advanced cryogenics such as dilution refrigerators or $^3$He cryogens, significantly limiting applications. Here we propose a
vortex-engineering approach based on a hybrid phase transition in a ferromagnet/
superconductor bilayer to increase the operating temperature of infrared single
photon detectors up to 3.75K. We show that the introduction of a
ferromagnetic layer produces a local
magnetic field which impedes
vortex crossing in the
superconductor, reducing dark noise. When a single
photon is incident, the
photon-induced hotspot causes an order-to-disorder transition in the ferromagnet, leading to a
vortex-induced phase transition in the superconducting layer. By engineering the ferromagnet's Curie temperature to be close to the device's operating temperature, single
photon sensitivity can be achieved at increased operating temperatures. We predict at midwave/longwave infrared wavelengths (3-14$\mu$m) the operating temperature can be raised to 3.25-3.75K, enabling significantly simpler cooling systems.
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All authors Leif Bauer, Daien He, Sathwik Bharadwaj, Zubin Jacob
Statistical Mechanics · Cross-listed from hep-th
Thermal One-point Functions and Asymptotic CFT Data: QFT in AdS
Ilija Burić, Francesco Mangialardi, Francesco Russo et al. (+2 more)
We investigate the thermal partition and one-point functions of the three-dimensional conformal field theory dual to a massive interacting scalar field in AdS$_4$. Using thermal inversion formulas, we determine the asymptotic behaviour of the spectral density and OPE coefficients involving heavy operators at fixed
spin. We first analyse these CFT data for the generalised free field, corresponding to the non-interacting bulk theory. Then we compute the first-order perturbative corrections induced by the cubic and quartic bulk interactions. The thermal observables considered here probe a sector associated with operators of large dimension and, in the bulk description, a regime dominated by states with large particle number. This regime remains comparatively unexplored even in generalised free field theory. Remarkably, the asymptotic formulas obtained from thermal inversion remain quantitatively accurate far from the asymptotic regime, describing CFT data reliably already at intermediate conformal weights. Our results show that this feature survives the inclusion of bulk interactions and provide new analytic control over heavy-state data in conformal field theories.
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All authors Ilija Burić, Francesco Mangialardi, Francesco Russo, Volker Schomerus, Alessandro Vichi
Strongly Correlated Electrons
Exotic magnetism and persistent spin dynamics in a frustrated Jeff = 1/2 triangular lattice antiferromagnet
M. Barman, K. Jaksetič, M. Pregelj et al. (+3 more)
The delicate interplay between competing degrees of freedom, anisotropy, and frustration-induced strong
quantum fluctuations in pseudospin-$J_{\rm eff}=1/2$ rare-earth triangular-
lattice antiferromagnets offers a promising platform for the experimental realization of exotic states with nontrivial low-energy excitations. Here, we present thermodynamic, inelastic
neutron scattering (INS), and
muon spin relaxation ($\mu$SR) investigations of the frustrated magnet K$_3$NdTe$_2$O$9$, in which Nd$^{3+}$ ions constitute a structurally perfect triangular
lattice with no detectable site disorder. The experiments reveal the realization of a Kramers doublet ground state with $J{\rm eff}=1/2$ moments, well separated from the first excited state, which interact antiferromagnetically with an exchange interaction of $\sim$0.6 K between the Nd$^{3+}$ moments in the triangular plane. The absence of oscillations and the so-called 1/3 plateau in the zero-field $\mu$SR asymmetry down to 50 mK rules out long-range
magnetic ordering and
spin freezing on the $\mu$SR time scale, respectively. The temperature dependence of the zero-field $\mu$SR relaxation rate is well described by the Orbach relaxation mechanism, indicating the existence of fluctuating moments in the ground state of this frustrated magnet. Our results demonstrate exotic magnetism and persistent
spin dynamics down to 50 mK. These observations establish this new family of frustrated rare-earth triangular-
lattice antiferromagnets as a promising venue for the experimental realization of nontrivial
quantum states with exotic low-energy excitations.
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All authors M. Barman, K. Jaksetič, M. Pregelj, M. D. Le. P. J. Baker, A. Zorko, P. Khuntia
Statistical Mechanics · Cross-listed from hep-th
The Helical SYK Model and Emergent Infrared Integrability
Gustavo Valdivia-Mera, Bhavay Tyagi, Eric R. Bittner et al. (+1 more)
We construct a helical generalization of the Sachdev-Ye-Kitaev (SYK) model in $1+1$ dimensions, built from left- and right-moving Majorana
fermions with local quartic interactions and random couplings in
flavor-chirality space. These interactions organize into a
symmetry-controlled hierarchy of quartic chirality sectors. At the most restrictive end of this hierarchy,
symmetry forces the quartic structure into a density-density form, which admits an exact solution using bosonization, rendering the theory integrable. Once the full quartic helical interaction space is allowed, including purely
chiral, chirality-balanced, and chirality-imbalanced sectors, this
symmetry-protected integrable structure is lost. Nevertheless, the large-$N$ infrared limit remains analytically tractable through short-distance selection rules and disorder averaging. Using conformal perturbation theory about the free fixed point, we show that the entire interaction space is marginally irrelevant, and the theory thus becomes free and integrable in the IR.
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All authors Gustavo Valdivia-Mera, Bhavay Tyagi, Eric R. Bittner, Pavan Hosur
Superconductivity
Superconductivity from emergent dipolar interactions in a fractionalized Fermi liquid
Mina-Lou Schleith, Arthur Bril and Nick Bultinck
Starting from the
spin-
fermion model or Hertz-Millis theory describing electrons coupled to anti-
ferromagnetic spin fluctuations we develop a theory to describe the transition from a fractionalized
Fermi liquid into a $d_{x^2-y^2}$
superconductor. We focus on small electron doping on top of the half-filled state. The doped electrons enter the system as spinon-chargon bound states, which form a small, reconstructed
Fermi surface. The bound states are neutral under the emergent U(1) gauge
symmetry of the fractionalized
Fermi liquid, but interact via a dipolar two-body potential. We show that because of the projective action of translation
symmetry on the spinons and chargons, the
Fourier components of this repulsive dipolar interaction are peaked at the anti-
ferromagnetic wave vector, thereby providing a robust microscopic mechanism for $d_{x^2-y^2}$ pairing in a fractionalized metal.
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Quantum Gases · Cross-listed from quant-ph
Fermionic Hamiltonian engineering with local control
Özgün Kum, Matthias Zipper, Ludwig Mathey et al. (+1 more)
Quantum simulators enable the exploration of complex
quantum phenomena in condensed-matter systems by reproducing their dynamics on controllable
quantum devices. However, experimental constraints often restrict the class of
Hamiltonians that can be realized natively.
Hamiltonian engineering addresses this limitation by expanding the set of accessible
Hamiltonians beyond the fixed system
Hamiltonian provided by the hardware. We introduce a framework for fermionic
Hamiltonian engineering based on interleaving free
evolution under the system
Hamiltonian with a sequence of experimentally feasible local fermionic
unitaries. The required sequences and free-
evolution times are obtained efficiently through a linear program, enabling effective time
evolution under a broad class of target
Hamiltonians. In particular, our method realizes arbitrary complex tunnelling coefficients, constrained only by the connectivity of the underlying system
Hamiltonian. We further show that
symmetries of the
Hamiltonian engineering task can be exploited to drastically reduce the cost of computing the control parameters, and that errors arising from finite pulse times can be compensated within the same framework through a simple modification of the linear program. To our knowledge, this is the first automated method to realize locally tunable artificial gauge fields in interacting fermionic
lattice models using only site-resolved energy shifts as control. We demonstrate the method by engineering the dynamics of interacting
Fermi-Hubbard chains with complex tunnelling coefficients and of the Harper-Hofstadter model on a 1088-mode
lattice. For the latter, we exploit the translation
symmetry of the model to determine a provably optimal six-pulse sequence that produces the desired dynamics independent of the
lattice size.
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All authors Özgün Kum, Matthias Zipper, Ludwig Mathey, Martin Kliesch
Statistical Mechanics
Derivation of height field theory for the two-dimensional classical dimer model from a Grassmann-integral representation
Stephen Powell
The classical dimer model on bipartite
lattices hosts a Coulomb phase, characterized by algebraic correlations and topological order. Its long-wavelength properties can be described by the fluctuations of a vector field with zero divergence, which, in two dimensions, is equivalent to a continuum height model. We show how this field theory can be derived constructively for both square and honeycomb
lattices, starting from an exact representation of the dimer model in terms of Grassmann integrals. Taking the continuum limit gives a massless Dirac
fermion in two-dimensional Euclidean space, which, using bosonization in the path integral representation, maps exactly to the well-known height field theory, incorporating the relationship between its boundary discontinuity (or "tilt") and the flux. By including source terms coupling to the flux density and the local valence-bond-solid order parameter, which we show are the only ones required to describe the asymptotic long-distance correlations, we derive expressions for the dimer observables in terms of the height.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Projected logical ensembles in surface codes via the random-matrix theory of quantum dots
Mircea Bejan, Jan Behrends, Max McGinley et al. (+1 more)
Measurements underpin active
quantum error correction (QEC) and have been recognized as a source of novel measurement-induced many-body phenomena. Here, we study the statistical properties of post-measurement logical states arising in QEC on topological codes subject to deterministic transversal
unitary gates. Upon syndrome extraction followed by maximum-likelihood decoding, a Born-weighted ensemble arises which we dub the "projected logical ensemble" (PLE). Focusing on surface codes subject to uniform single-
qubit Pauli-$X$ rotations, we characterize the measurement-induced randomness of the PLE. To this end, we show that for a code with a single logical
qubit, the PLE is isomorphic to an ensemble of scattering
matrices describing mesoscopic
quantum dots obtained from a 2D Majorana network model with suitable boundary conditions. We uncover regimes where these
quantum dots are chaotic such that their scattering
matrices are well-described by random
matrix theory. In these regimes, the PLE approaches a universal ensemble that is maximally random up to
symmetry and decoder-induced constraints. The
symmetry constraints, set by stabilizer and logical operator weights, realize Altland-Zirnbauer classes D or DIII, which we both illustrate. Our results establish a fundamental connection between emergent universality concepts in mesoscopic physics,
quantum many-body systems, and QEC.
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All authors Mircea Bejan, Jan Behrends, Max McGinley, Benjamin Béri
Materials Science
Chiral Phonons Enable Ultrafast Magnetization Switching via Magnetoelastic Coupling
Weiwei He, Muhammad Hamza Asim, Mara Strungaru et al. (+3 more)
Phonons are desirable for current-free energy-efficient
spin manipulation and harnessing their chirality to achieve ultrafast magnetization switching remains actively pursued. Here we demonstrate that terahertz-driven
chiral phonons enable faster magnetization switching than linear
phonons through the purely magnetoelastic coupling that transfers both energy and angular momentum. Only one
phonon handedness efficiently transfers angular momentum to the
spin system, which we explain by a large fictitious kinematic Barnett-like field at THz frequencies that destabilizes
spin precession for the opposite chirality. Considering different regions of the spinwave spectrum, we find that switching conditions can be realized near the {\Gamma}-point where strong energy transfer and spinwave excitation dominate, and near the P-point which offers minimal energy loss. Our results establish
phonon chirality as a decisive and previously overlooked parameter in
spin-
lattice dynamics within the magnetoelastic coupling mechanism, offering a promising avenue for ultrafast low-energy spintronic devices.
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All authors Weiwei He, Muhammad Hamza Asim, Mara Strungaru, Roy Chantrel, Min Yi, Oksana Chubykalo-Fesenko
Strongly Correlated Electrons
Compact Spin-Charge Separated Neural Quantum States for Valence-Bond States
Ang-Kun Wu, Louis Primeau, Yixin Zhang et al. (+3 more)
Neural-network
quantum states (NQS) provide a flexible nonlinear representation of
quantum many-body wavefunctions, but their efficiency depends sensitively on whether the architecture reflects the sign structure and constrained
Hilbert space of the target state. In this work, we propose a solvable-point-guided strategy: design the architecture at an exactly solvable point where the correct local rules can be read off, then refine to the non-exact regime by enlarging only the kernel size and hidden dimension. The strategy is built from four physics-motivated designs: a stride-matched local-rule convolution,
geometric pooling, a sign-resolving $\tanh(x^{2k+1})$ activation, and explicit
spin-hole sector separation. We test this approach on quasi-one-dimensional valence-bond-solid (VBS) states and their doped
soliton variants (sVBS), the exact ground states of a $t$-$J$-like model with a single mobile hole. In finite-size
benchmarks, this architecture reaches high fidelity for the exact sVBS state with substantially fewer parameters than generic fully connected, convolutional, and
transformer baselines tested under the same setup. For the
spin sector, the learned local rule transfers from small to larger systems without retraining. Away from the solvable point, increasing kernel size and hidden dimension systematically improves accuracy, and the model shows approximately $L^2$ parameter scaling in the gapless regime for system size $L$, compared with approximately $L^4$ for
matrix-product states in the same regime. Our work establishes a recipe for compact NQS in sign-structured, constrained
Hilbert spaces and paves the pathway to physics-informed architectures for the broader $t$-$J$ and Hubbard families.
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All authors Ang-Kun Wu, Louis Primeau, Yixin Zhang, Jingtao Zhang, Adrian Del Maestro, Yang Zhang