Disordered Systems and Neural Networks
Learning constructive models of emergent systems
Bipul Pandey, Caden Proctor, Vinay Ramanathan et al. (+2 more)
Emergent systems - systems with multiscale interactions - arise through iteration than forward design, leaving principles for building them under-explored. Current artificial intelligence architectures, while useful for generation, provide no logic for construction. Inspired by statistical phylogenetics, we show that inferring scales of system
entropy then constraining information from low to high entropic scales yields stepwise constructive models. We term this architecture the Layer-Restricted Boltzmann Machine (LRBM). Applied identically to digit images, natural
language, and enzyme sequences, LRBMs follow a common hierarchical logic: lower layers encode global structure, higher layers fine-grained features. As a stringent test, we assayed 160 synthetic chorismate mutase (CM) constructive trajectories alongside 1,130 natural homologs in vivo. Designed CMs functioned up to 53% divergent from nearest natural homolog. Fold emerged at intermediate layers while function required all layers, illustrating that fold was necessary but insufficient for function. Our results demonstrate a shared, learnable logic for constructing emergent systems.
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All authors Bipul Pandey, Caden Proctor, Vinay Ramanathan, Nico Roth, Arjun S. Raman
Strongly Correlated Electrons · Cross-listed from hep-lat
Searching for symmetric mass generation with staggered fermions in four dimensions
Nouman Butt, Simon Catterall, Gwen Hartshaw et al. (+1 more)
We conduct numerical simulations to map out the phase diagram and critical behavior of a
lattice Higgs model composed of two massless staggered
fermion fields forming a doublet under a global $SU(2)$ and coupled to a scalar field in the adjoint representation of the group. The scalar action consists of a potential comprising quadratic and quartic terms and a scalar kinetic term. At fixed quartic coupling we explore a two-dimensional parameter space finding a massless symmetric phase at weak coupling and a massive symmetric phase (SMG phase) at strong coupling. An intermediate anti-
ferromagnetic phase separates these two regimes. These results are consistent with leading order weak and strong coupling expansions. We find that the critical lines bounding the intermediate phase merge at a unique point where all
fermion bilinear condensates vanish but
fermion susceptibilities diverge as non-trivial powers of the
lattice size. We
conjecture that this merged point corresponds to a multicritical point and may describe a phase consisting of a condensate of certain topological defects.
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All authors Nouman Butt, Simon Catterall, Gwen Hartshaw, Anna Hasenfratz
Mesoscale and Nanoscale Physics · Cross-listed from hep-ph
Towards Quantum-Dot Detectors as Barcodes for Dark Matter Interactions
Marek Matas, Andrea Gallo Rosso, Antonio Cammarata et al. (+6 more)
Quantum dots are tunable
semiconductor nanocrystals that can be produced at industrial scales. We present the first ab initio calculation of the scattering of dark matter on electrons bound in
quantum dots. The momentum-dependence of a
quantum dot's electronic response depends on its morphology and on the dark matter mass, interaction operator, mediator coupling, and mediator mass. Therefore, the relative rates across an array of distinct
quantum dot targets form a “barcode” that carries information about the nature of the dark matter interaction. We project the sensitivity of a detector concept in which a collection of independent target subunits, each loaded with silicon
quantum dots of a particular morphology, are read out by Skipper CCDs. Given a future signal, this barcode could discriminate between interaction operators and mediator types. We quantify the discrimination power for a
benchmark pair of models as a function of readout noise and exposure.
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All authors Marek Matas, Andrea Gallo Rosso, Antonio Cammarata, Nora Hoch, Carlos Blanco, Jan Conrad, Rouven Essig, Tim Linden, Lindley Winslow
Strongly Correlated Electrons
Chern insulator boundary criticality
Benjamin Moy and Eduardo Fradkin
We investigate signatures of chirality at Chern
insulator transitions in the presence of a boundary. The transition between a trivial
insulator and a Chern
insulator with Chern number $C=1$ is described by a massless Dirac
fermion whose parity anomaly gives a critical
Hall conductivity $\sigma_{xy}=\frac{1}{2}\frac{e^2}{h}$. Using a Dirac mass domain wall construction, we show that the
chiral edge mode delocalizes into the bulk at criticality, but the boundary
fermion correlation function retains a
chiral structure and acquires the scaling dimension of the bulk
fermion. We compute current correlation functions and demonstrate that the anomaly of the bulk
Hall response is matched by delocalized
chiral modes near the boundary. Using only the residual conformal
symmetry of a (2+1)d conformal field theory (CFT) in a half-space, we identify parity-odd terms in current and energy-momentum tensor correlation functions that encode these modes and determine their electromagnetic and gravitational anomaly coefficients. Our analysis therefore applies to general time-reversal breaking (2+1)d CFTs, beyond the free Dirac transition. In particular, the analysis of the gravitational anomaly is also applicable to the free Majorana CFT governing the transition between a trivial
superconductor and a topological
superconductor. We also extend our results to more general Chern number changing transitions and to the transition between a (3+1)d topological
insulator and a trivial
insulator.
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Materials Science
Breaking the mutual exclusivity between metallicity and ferroelectricity in a non-polar covalent semiconductor via orbital selective doping
Hui Li, Yunfan Yang, Junquan Huang et al. (+18 more)
The mutual exclusion of ferroelectricity and metallic conductivity is a long-standing tenet because itinerant electrons screen long-range Coulomb forces that stabilize the bulk polar order. Here, we break this paradigm by heavily doping a non-polar covalent
semiconductor of cubic silicon carbide (3C-SiC) with nitrogen. This introduces heavy electron doping, inducing
metallicity and driving a structural transition from the non-polar F-43m to the polar R3m
symmetry via the pseudo-Jahn-Teller effect. Remarkably, we provide direct, atomic-scale visualization of about 180{\deg} polarization reversal under an external voltage bias in a ferroelectric metal. The strongly directional character of antibonding orbitals occupied by conduction electrons prevents them from screening the local Si-C polarization, resulting in the coexistence of
metallicity and ferroelectricity. Ferroelectric tunnel junctions demonstrate nonvolatile
memory properties with a well-defined high-resistance state (HRS) and low-resistance state (LRS), an ultrahigh response speed (~50 ns), an ultralow operating voltage (1 V), an endurance exceeding 85927 cycles, and a projected retention time of 100 years. Our results provide a novel strategy for pioneering ferroelectricity in a metal, a new ferroelectric metal platform for exploring exotic properties, and a ferroelectric device with high performance that meets the requirements for low consumption and high-speed non-volatile devices.
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All authors Hui Li, Yunfan Yang, Junquan Huang, Yukun Feng, Guobin Wang, Qinci Wu, Jun Deng, Zhaolong Liu, Subi Du, Dongliang Gong, Zaihui Shen, Anmin Nie, Yang Xu, Junwei Yang, Zesheng Zhang, Huaping Song, Jiangang Guo, Wenjun Wang, Hailin Peng, Yongjun Tian, Xiaolong Chen
Quantum Gases · Cross-listed from physics.atom-ph
Ultrafast and high resolution spatial light modulation for cold atoms
Alexander Dennisovich Deters, Yanfei Li, Alexander Douglas et al. (+2 more)
Programmable arrays of ultracold atoms are a leading platform for
quantum computation and simulation, enabling state-of-the-art implementations of
quantum error correction, and analog simulations of Hubbard models that address open problems in condensed matter physics. In these systems, all local control is mediated through precisely shaped optical fields, and so the challenge of managing many-body
quantum states becomes an exercise in optical design. In particular, one wishes for fast, flexible control with low disorder and heating, and access to large arrays with many atoms. An ideal optical system therefore must generate arbitrary patterns with high spatial resolution and low disorder, and alter these patterns on a timescale that is faster than the relevant atomic dynamics. Here, we present an optical system that is comparable to previous approaches in scale, while advancing all other axes. We demonstrate arbitrary pattern generation with $10^{-3}$ intensity resolution, a frame rate of $>84$ MFPS (megaframes per second), and a spatial resolution of $83 \times 52$ beam waists (with $11 \times 52$ waists accessible via a single $40$ GHz electro-optic modulator). These capabilities unlock a new class of experiments. We develop and numerically validate a scheme for fully programmable Hubbard models, with time-dependent control over local chemical potentials, tunneling amplitudes, on-site interactions, and patterns of artificial
magnetic flux. The same architecture performs fast, arbitrary permutations of tweezers in 2D, decoupling optical constraints from the design of high-rate error-correcting codes.
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All authors Alexander Dennisovich Deters, Yanfei Li, Alexander Douglas, Markus Greiner, Aaron W. Young
Disordered Systems and Neural Networks
Quantum Geometric Tensor Preconditioning for Stable Training of Recurrent Neural Quantum States
Adil Attar, Amine M. Aboussalah and Mohamed Hibat-Allah
Neural
Quantum States (NQS) provide a powerful neural network-based variational framework for representing many-body wave functions and solving for ground states. Recurrent Neural Networks (RNNs) are particularly promising owing to their relatively low computational cost and their autoregressive property, which enables perfect sampling. Recently, RNNs have been reported to be unstable under
curvature-based optimizers such as the minimum-step
stochastic reconfiguration (minSR) method. In this paper, we address this perceived limitation and show that minSR can be stabilized through simple regularization techniques, enabling robust training of RNN-based NQS with only a few samples. Our approach outperforms the Adam optimizer on the one-dimensional transverse-field Ising model and the one-dimensional cluster state, and provides competitive results on the two-dimensional Heisenberg and $J_1-J_2$ models. This work offers a promising pathway for using modern optimization techniques with autoregressive NQS to address open questions in
quantum simulation.
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Materials Science · Cross-listed from physics.app-ph
Achieving Long Retention in Area-Dependent Resistive Memory with Phase-Separated Amorphous Tantalum Oxide
Sangyong Lee, Anton V. Ievlev, Dongjae Shin et al. (+2 more)
Resistive random-access
memory (ReRAM) is a promising future nonvolatile
memory technology. Most ReRAM exhibit a fundamental tradeoff: filament-type ReRAM provides long data retention but suffers from poor uniformity and high switching current, whereas nonfilamentary ReRAM shows lower-current, area-dependent switching but generally poor retention. No two-terminal device has been able to overcome this tradeoff. In this work, we present a two-terminal Ta2O5/ TaOX resistive
memory cell that achieves both nonfilamentary switching and long retention. Electrical measurements and composition depth profile show that the switching is not confined to a single filament but is instead uniform across the entire switching region. Despite the nonfilamentary switching, this device can retain information for over 22 hours at 190 {\deg}C, which is comparable to the best filamentary devices. We propose that this long retention arises from composition phase separation in amorphous tantalum
oxide. Our work shows that the fundamental tradeoff between information retention and switching uniformity can be overcome, and thereby provides a pathway toward more uniform and reliable
oxide memory devices.
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All authors Sangyong Lee, Anton V. Ievlev, Dongjae Shin, Jingxian Li, Yiyang Li
Mesoscale and Nanoscale Physics
Electronic Reconstruction at the Quasicrystal-Moiré Crossover in Twisted Bilayer Graphene
Kuo-En Chang, Aitor Garcia-Ruiz, Ta-Lei Chou et al. (+11 more)
Large twist angles in twisted
bilayer graphene are widely expected to be electronically trivial, with negligible interlayer coupling and no electronic reconstruction, in contrast to the rich moiré-driven band reconstruction and correlated physics that emerge at small twist angles. Here, we show that this paradigm breaks down near a twist angle of 29{\deg}, where the system crosses over between quasicrystalline and commensurate order. Atomic-resolution transmission electron microscopy directly reveals the coexistence of near-dodecagonal quasicrystalline
symmetry and emerging moiré periodicity, indicating an intermediate, nonperiodic structural regime. Magnetotransport measurements uncover strong interlayer hybridization mediated by Umklapp scattering, manifested by magneto-intersubband oscillations and a highly unconventional Landau-level spectrum. Remarkably, the Landau-level degeneracy evolves from 4- to 12-fold with increasing temperature, a behavior incompatible with two decoupled
graphene monolayers. These findings establish large-angle twisted
bilayer graphene as a platform where quasiperiodic
symmetry fundamentally reshapes low-energy electronic states beyond the conventional moiré framework.
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All authors Kuo-En Chang, Aitor Garcia-Ruiz, Ta-Lei Chou, Yen-Ting Liu, Sheng-Chin Ho, Yu-Chiang Hsieh, Ching-Hua Kao, Chiu-Hua Huang, Ying-Mei Yang, Kenji Watanabe, Takashi Taniguchi, Ming-Wen Chu, Ming-Hao Liu, Tse-Ming Chen
Mesoscale and Nanoscale Physics
Long-time fermionic quantum transport with controlled full-state error using an adaptive reservoir-mode window
Mikhail Umanskii, Nataliya Arefyeva, Georgy Sultanov et al. (+2 more)
Real-time simulations of interacting nanostructures coupled to fermionic reservoirs can require a growing number of environmental degrees of freedom to retain long-lived correlations. We introduce tape-recorder coarse graining, which reorganizes each noninteracting lead into incoming, active, and outgoing modes. The device is propagated with the active modes, while outgoing modes are stochastically sampled and removed once their remaining integrated coupling falls below a prescribed threshold. For each outgoing-mode truncation, we derive a nonperturbative upper bound on the infidelity between the exact and truncated full device-reservoir states over any prescribed finite interval. The bound depends on the mode's remaining coupling weight and finite-interval response factors. Numerically, the active-mode count saturates in time at fixed relative threshold and grows logarithmically as the threshold is reduced. We
benchmark the method on a two-site
quantum point contact at zero temperature and maximal bias. For Lorentzian reservoirs, the dynamics agrees with converged HEOM calculations and the steady-state current with the Landauer-Büttiker result. For flat-band reservoirs with algebraically decaying correlations, it agrees with direct Schrödinger
evolution before finite-size recurrences and reproduces the Landauer-Büttiker stationary current, while finite exponential HEOM decompositions remain unconverged. For interacting contacts, the method yields Coulomb-blockade peak splitting. In the noninteracting driven limit, it agrees with an exact Floquet Green-function calculation and reproduces coherent current suppression under periodic driving, which persists at finite Coulomb repulsion. Together, these
benchmarks show that tape-recorder coarse graining enables practical long-time simulations of the full device-reservoir state in interacting fermionic transport.
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All authors Mikhail Umanskii, Nataliya Arefyeva, Georgy Sultanov, Alexey Rubtsov, Evgeny Polyakov
Mesoscale and Nanoscale Physics
Dynamics of Majorana tetron qubits under quasiparticle poisoning
Sauri Bhattacharyya and Bernard van Heck
We study the dissipative dynamics of a Majorana tetron
qubit in the presence of extrinsic quasiparticle poisoning due to the coupling to external leads. From the Bloch-Redfield equation describing a finite-size topological
superconductor hosting four Majorana zero modes and tunnel-coupled to fermionic reservoirs, we recover analytical expressions for the decoherence rate of a Majorana
qubit at arbitrary values of the charging energy. The analysis shows that the exponential suppression of the decoherence rate is gradually removed by the energy splitting of the
qubit states. These results can be useful to understand time-domain experimental data in Majorana
qubit prototypes.
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Statistical Mechanics
Critical behavior and crossover scaling in the Light-Heavy model
Shilpa Prakash, Mustansir Barma and Kabir Ramola
The Light-Heavy (LH) model involves two species of particles (light and heavy) coupled with a fluctuating surface (described by tilts). The dynamics include the inherent
diffusion of the particles (or tilts) as well as the drive provided by the tilts (or particles). When the two are of similar magnitude, the system lies in the unscaled (uLH) regime, while a significantly weaker drive leads to the scaled (sLH) regime. In the unscaled limit, the model exhibits an order-disorder transition characterized by the fluctuation-dominated phase ordering (FDPO). In this state, interestingly the dynamics is driven by multiple modes, giving rise to dynamic clusters. Away from the critical regime the disordered phase retains vestiges of FDPO behavior on length scales smaller than the correlation length. We examine this local FDPO-like behavior by using a scaling function that links the off-critical and critical regimes. We next turn to the scaled model and show that the multi-mode dynamics present in the unscaled regime is replaced by dynamics that is effectively controlled by a single dominant mode in the scaled regime. Concurrently, the two-point correlations change from the $\mathcal{O}(1)$ FDPO form to an anomalous long-range form that decays as $1/\sqrt{L}$. Drawing on the analogy with the sABC model, where similar anomalous correlations appear at criticality, we derive an analytical expression for the two-point correlation function using the same approach used for that model.
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Materials Science
Energy-efficient, Reconfigurable Optoelectronic Artificial Synapses Based on MoWS$_2$ Alloy for Pattern Recognition and Color Image Filtering Applications
Deepak Kumar Sahu, Santu Kumar Ghosh, Sagarneel Ghoshal et al. (+2 more)
Two-dimensional transition-metal dichalcogenide
alloys are potential candidates for advanced optoelectronic and neuromorphic applications due to their strong light-matter interactions and controllable defect properties. However, large-area growth of such
alloys remains challenging, while the correlation between their physical and neuromorphic properties remains largely unclear. In this work, we present an innovative microcavity chemical vapor deposition (CVD) reactor pathway to grow uniform, and large-area MoWS$_2$ mono- and few-layer
alloy films for demonstrating optoelectronic synaptic functionalities. Driven by growth-induced intrinsic sulfur vacancies, as confirmed by XPS, KPFM, and STEM measurements, our optoelectronic synaptic device (OSD) successfully emulates essential biological synaptic features, such as excitatory postsynaptic currents (EPSC), paired-pulse facilitation (PPF~170%), and stimulus-dependent short- and long-term plasticities (STP & LTP). With picojoule-order energy consumption per synaptic event and nanoampere-order dark current, the device enables low-power neuromorphic learning, including emulation of Pavlovian associative learning. Furthermore, the experimentally measured conductance weight-update characteristics enabled an artificial neural network (ANN) simulation to achieve 92.43% recognition accuracy on the MNIST handwritten digit
dataset. Finally, we demonstrate advanced neuromorphic visual processing by executing color image filtering based on the device's wavelength-selective photoresponse characteristics. This simple, yet multifunctional device architecture provides a promising path toward energy-efficient, spectral-selective neuromorphic
vision applications.
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All authors Deepak Kumar Sahu, Santu Kumar Ghosh, Sagarneel Ghoshal, Saranya Das, Samit K. Ray
Quantum Gases · Cross-listed from quant-ph
Dressed magnon dynamics in a Bose-Hubbard bath: retardation, pairing, entanglement and two-magnon scattering
Andrés N. Cáliz, Arnau Riera, Enrique Rico et al. (+2 more)
We study one- and two-
magnon dynamics in a
spin-$1/2$ XX chain coupled to a tunable Bose-Hubbard bath. The XX
Hamiltonian transports the
magnons, while the bath dresses their motion and mediates an effective attraction. A single
magnon forms a mobile polaron whose retarded bosonic cloud reduces its velocity below the static Lang-Firsov prediction and generates
magnon-
boson entanglement. In the weak-dressing, off-resonant mobile regime, the residual velocity deficit and
entanglement are governed by the excitation weight of the cloud, as captured by perturbation theory and tensor network-based real-time simulations. Transport therefore provides a model-calibrated proxy for
entanglement without joint-state reconstruction. When two clouds overlap, the bath mediates a finite-range attraction, yielding finite-size evidence for a compact two-
magnon bound state and a transient post-scattering signature. On-site bath interactions suppress local
boson number fluctuations and stiffen the bath response, reducing
entanglement and weakening ground-state binding. Bath deformability thus emerges as a common control parameter for
magnon transport,
entanglement, and bath-mediated pairing.
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All authors Andrés N. Cáliz, Arnau Riera, Enrique Rico, João Barata, Marcin Płodzień
Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Simplicial closure fragments the explosive cooperation transitions in higher-order public goods games
Wenjia Rao and Jianneng Huang
Hypergraph (HG) and simplicial complex (SC) are two common representations of higher-order networks, and are often expected to differ mainly quantitatively when they encode comparable group interactions. Here we show that this expectation fails in evolutionary cooperation dynamics. Using a controlled higher-order public goods game (PGG) with minimal ad hoc parameters, we compare cooperation transitions on randomized HG and SC constructed from the same triangular backbone. We find that the impact of simplicial closure is selective: when the cooperation transition is continuous-like on HG, imposing simplicial closure mainly broadens the transition without changing its qualitative nature; however, when the transition is explosive and first-order-like on HG, simplicial closure will fragment the compact low/high bistability into a broad ensemble of metastable final states. Detailed analysis reveals that this selective effect arises from the dual role of simplicial closure in cooperative-
nucleus dynamics: it promotes the survival of local cooperative
nuclei while suppressing their conversion into system-wide cascades. Further experiments confirm that this fragmentation is not tied to a specific payoff form, but is a generic feature of explosive cooperation transitions in higher-order PGGs.
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Soft Condensed Matter
Topology of Nonequilibrium Currents Controls Active Transport
A. Escobar, G. Geva, A. Alexander-Katz et al. (+3 more)
Structured environments repeatedly redirect active particles, producing transport pathways that cannot be readily inferred from individual trajectories. Here, we show that the large-scale organization of these transport pathways is governed by topological constraints. Hydrodynamic scattering generates nonequilibrium current fields whose defect structure, characterized by integer indices, constrain transport pathways and renders them robust to smooth perturbations. This principle is demonstrated with rotating colloids in obstacle arrays and extended to stokeslet and force-dipole flows, thereby linking microscale transport to the
topology of hydrodynamically generated nonequilibrium currents.
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All authors A. Escobar, G. Geva, A. Alexander-Katz, L.R. Arriaga, J.V. Alvarez, J.L. Aragones
Disordered Systems and Neural Networks
Dephasing-induced distinct mobility edges in a dimerized off-diagonal quasicrystal
Ming-Jie Tao, Yi-Ting Wang, Jing Li et al. (+3 more)
Anderson localization and the mobility edge (ME) have been extensively studied in isolated aperiodic systems. Conventional theory suggests that dephasing and decoherence should disrupt localization and facilitate transport. In this work, we investigate localization behaviors in a dimerized off-diagonal Aubry-Andre-Harper (AAH) quasicrystal subject to on-site pure dephasing. In the strong-dephasing limit, we apply adiabatic elimination within the Lindblad master equation framework to derive an effective classical Markov transition
matrix that governs the dissipative relaxation dynamics. Counterintuitively, we demonstrate that pure dephasing can induce distinct MEs, including both conventional MEs separating extended and localized states and anomalous MEs separating multifractal critical states from localized states, even when all eigenstates of the original closed coherent system are delocalized or multifractal. Using fractal dimension finite-size scaling, wave-packet spreading dynamics, and energy spectrum statistics, we numerically verify the coexistence of fully extended, multifractal critical, and localized regions within the relaxation spectrum of the dissipative system, and construct the global dissipative phase diagram. These findings reveal that dephasing can see as a powerful mechanism for controlling localization transitions, thus enhancing our understanding of dissipative quasicrystal systems.
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All authors Ming-Jie Tao, Yi-Ting Wang, Jing Li, Hongsheng Hou, Xiang-Ping Jiang, Lei Pan
Statistical Mechanics · Cross-listed from math.PR
Near-unit-root persistence of symmetric and asymmetric stable autoregressive sequences
José Ricardo G. Mendonça and Boubaker Smii
For an AR($1$) sequence with coefficient $0 < a < 1$, the probability of staying above zero decays exponentially in the number of steps; at the unit root $a=1$ it decays polynomially, with order $n^{-1/2}$ for symmetric increments. We study this transition for AR($1$) sequences driven by symmetric and asymmetric $\alpha$-stable innovations. We write $\Lambda(a,\alpha)$ for the symmetric exponential persistence rate and $\Lambda(a,\alpha,\rho)$ for the rate of a strictly stable law with positivity parameter $\rho$. The entire chain admits an exact representation through a single stable Lévy process observed on a geometrically expanding time grid. In the symmetric case, comparison with continuous half-line survival gives $\Lambda(a,\alpha) \leq \frac{\alpha}{2}\log{(1/a)}$. For $0 < \alpha < 2$, this bound disproves the stable specialization of a
conjecture of Hinrichs, Kolb and Wachtel concerning regularly varying innovation tails. Combining stable closure under subsampling with a monotonicity coupling yields a lower bound of the same near-unit order. This proves $\Lambda(a,\alpha) \asymp \log{(1/a)}$ as $a \uparrow 1$ and shows that $\Lambda(a,\alpha)/\log{(1/a)}$ converges to a limit in $(0,\alpha/2]$ equal to the supremum of that ratio over $0 < a < 1$. A Lamperti transformation reduces identification of this constant to a dense-sampling problem for a stationary stable Ornstein-Uhlenbeck process. Existing Gaussian theory determines the sharp value at $\alpha=2$; for $0 < \alpha < 2$, rescued crossings between observations remain the obstacle. For asymmetric strictly stable innovations with $\alpha \neq 1$ and admissible $\rho\in(0,1)$, the corresponding bounds are $\Lambda(a,\alpha,\rho) \leq \alpha(1-\rho)\log{(1/a)}$ and $\Lambda(a,\alpha,\rho) \asymp \log{(1/a)}$. At $\alpha=2$, only the symmetric case $\rho=1/2$ occurs.
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Statistical Mechanics
Heat capacity as a marker for shape and jamming transitions in active systems
Ion Santra
Persistence influences the stationary states of active particles, producing boundary accumulation at the single-particle level, and clustering or jamming in interacting systems. These features disappear as the persistence decreases and the system approaches a more passive-like stationary state. We show that these transitions have a distinct calorimetric signature. Using a
lattice run-and-tumble dynamics, consistent with local detailed balance, we compute the nonequilibrium heat capacity from the excess heat released following a small temperature perturbation. For a single particle confined between reflecting boundaries, the heat capacity develops a maximum in the persistence regime corresponding to shape transition. Adding an exclusion interaction to the active particles on a periodic
lattice, the reorganization of jammed clusters produces a corresponding peak in the thermal response. We also discuss the impact of the time-symmetric part of the transition rates, and show the possibility of seeing the same signatures of heat response in experiments by AC calorimetry. Our results show that nonequilibrium heat capacities can serve as calorimetric probes of nonequilibrium phase transitions.
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Disordered Systems and Neural Networks
Hidden Unbounded Potential and Re-Entrant Multifractalization in a Generalized Su-Schrieffer-Heeger Model
Yun-Yan Chen, Jia-Ming Zhang and Zhi Li
We study the multifractal criticality in a generalized Su-Schrieffer-Heeger model. The results show that the system supports not only critical phases but also re-entrance multifractalization (REM). By mapping the hopping term to an effective potential, we analytically prove that although the model has no explicit unbounded potential, a hidden unbounded potential is actually present-this is the key mechanism driving the emergence of multifractal critical phases. Moreover, one can get a condition where the competition between the explicit and hidden unbounded potentials is exactly balanced. Under this condition, the multifractal critical phase vanish, and the system returns to the extended phase. Based on this mechanism, we achieve both demultifractalization and re-entrant multifractalization. Finally, we double check the theoretical predictions through wave packet dynamics, and the numerical results are consistent with our theoretical analysis. This work broadens our understanding of how unbounded potentials induce multifractal critical phases, providing a theoretical basis for designing new systems with multifractal critical phases.
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Materials Science
Optical decoherence in Er$^{3+}$-doped CeO$_2$ spin qubit platforms
Vrindaa Somjit, Ignas Masiulionis, Gregory D. Grant et al. (+7 more)
Erbium ions (Er$^{3+}$) in cerium dioxide (CeO$_2$) represent a promising
spin-
photon interface for
quantum communication, but the mechanisms limiting their optical coherence remain poorly understood. Using periodic hybrid density functional theory calculations with finite-size corrections, we identify Ce$^{3+}$ polarons and their complexes with oxygen vacancies and Er$^{3+}$ dopants as likely sources of optical decoherence. These defects exhibit finite photoionization cross-sections at 0.8 eV, coinciding with both the
laser excitation energy used experimentally and the emission energy of Er$^{3+}$. This resonance enables photoionization of the polarons and photoluminescence quenching of Er$^{3+}$, leading to the broadening of optical linewidths, shortening of excited-state lifetimes, and introduction of charge noise. Our concentration-dependent photocurrent measurements in Er$^{3+}$-doped CeO$_2$ films under 0.8 eV illumination validate the predicted decoherence pathway. Our combined computational and experimental results identify a concrete defect-engineering target for improving the Er$^{3+}$-doped CeO$_2$ platform, and point to a decoherence mechanism likely relevant to other Er$^{3+}$-doped multivalent-
oxide quantum platforms.
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All authors Vrindaa Somjit, Ignas Masiulionis, Gregory D. Grant, Weiguo Jing, Matteo Giantomassi, Supratik Guha, Gian-Marco Rignanese, F. Joseph Heremans, Jiefei Zhang, Giulia Galli
Soft Condensed Matter
A solid-state theory for dense cylindrical packings of balls
Luke K. Davis and Alexander R. Klotz
We develop an analytical theory for the dense packing of hard spheres in cylinders. Physically, our theory consists of a finite cylindrical masking of a close-packed three-dimensional solid and covers the entire range of cylinder aspect ratios, thus going beyond efforts that are focused on very tall cylinders in a narrow range of widths. We explicitly derive an exact equation for resulting packing fractions, valid for any regular
lattice, and it provides a basis to understand the oscillations and scaling of volume fractions that have appeared in previous works. Our analytical relation serves as a rigorous lower bound and to tighten it we derive, and implement, an efficient mathematical procedure to optimize the orientation of the cylinder. Furthermore, we suggest simple techniques to improve on the predicted packings. Overall, we provide a general theoretical foundation for the packing of balls in cylinders, valid for all container sizes.
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Mesoscale and Nanoscale Physics
The Deformed Image Vortex Ansatz: A Perturbation-Aware Description of Magnetic Vortices in In-Plane Fields
Thomas G. Coppée, Colin Ducarme, Simon de Wergifosse et al. (+1 more)
Thiele-based descriptions of
magnetic vortex dynamics in thin
ferromagnetic nanodots rely on magnetization ansätze that describe the
equilibrium texture but cannot represent perturbation-induced deformations. We introduce the Deformed Image
Vortex Ansatz (DIVA): a perturbation-aware ansatz in which the response to an external perturbation is built into the magnetization profile itself, rather than appended to the dynamics as a correction. Here, we demonstrate the concept for a uniform, stationary in-plane field applied to a Permalloy nanodot, for which the deformation is analytically tractable. A
symmetry-based perturbative expansion identifies the leading deformation as a single $m = 1$ harmonic around the disk, while energy minimization and a dominant-balance analysis yield a closed-form interpolant for the radial profile. Benchmarked against micromagnetic simulations on Permalloy disks of aspect ratio $t/R = 0.1$ and $0.0125$, this realization reduces the disk-averaged angular deviation by a factor of 3 to 6 relative to the two-
vortex ansatz, depending on geometry and field, and reduces the total-energy deviation by about a factor of six in the thicker disk.
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All authors Thomas G. Coppée, Colin Ducarme, Simon de Wergifosse, Flavio Abreu Araujo
Statistical Mechanics
Frustration without Glass: A Non-Abelian Gauge Model of Network Compatibility
Xuanhua Wang
We formulate a non-Abelian theory of network compatibility in which dynamical transformations reside on the links. Gauge covariance follows from the freedom to choose local representation frames, while plaquette holonomies quantify the incompatibility of closed-loop transformations. For an SU(2) model on the complete simplicial 2-complex with quenched random plaquette couplings, parallel-tempering simulations reveal a continuous disorder-driven phase transition characterized by the network compatibility $M_P$. As the disorder strength approaches the critical value, the compatibility drops rapidly to a value that decreases with system size, while the frustration energy of the network sharply rises. Moreover, analysis of connected replica-overlap width provides no evidence for thermodynamic replica-
symmetry breaking. Instead, the high-disorder regime sustains a nearly constant integrated adjacent correlation as the system size increases. Therefore, rather than a frozen gauge glass or a featureless disordered “gas” phase, dense topological frustration produces a non-glassy correlated gauge
liquid in which individual pair correlations are geometrically diluted while a finite integrated correlation survives.
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Materials Science
Electron transport in amorphous materials: from localization to predictive transport modeling
Yeonghun Lee
Amorphous materials are disordered solids without long-range structural order, making them useful systems for studying electron transport beyond the crystalline picture. This review discusses how structural disorder changes the spatial character of electron wavefunctions and how these changes govern carrier transport in amorphous materials, especially amorphous
semiconductors. Basic concepts of Anderson localization, mobility edges, diffusive transport, and hopping transport are first reviewed, followed by representative amorphous
semiconductors, including amorphous silicon and amorphous
oxide semiconductors. Computational approaches are then discussed, from conventional Boltzmann and Green's-function-based transport theories to real-space Kubo-Greenwood simulations combined with molecular dynamics. The discussion focuses on localization, spectral broadening, finite-temperature
lattice fluctuations, and electron-
phonon interactions. Recent progress and remaining issues in predictive transport modeling of amorphous materials are then outlined.
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Mesoscale and Nanoscale Physics
Elizaveta Morozova, Xin Zhang, Utso Bhattacharya et al. (+9 more)
Understanding collective phases of strongly correlated
quantum magnets relies on theoretically tractable model systems with precise microscopic control.
Antiferromagnetic spin ladders provide such a setting, hosting field-tunable gapped and gapless phases at half filling and unconventional pairing tendencies upon doping. Here, we realize a programmable Heisenberg
spin ladder in a half-filled germanium
quantum dot array featuring site-resolved, continuously tunable exchange interactions. Under a fixed
magnetic field, we vary the rung and leg coupling to map the rung-singlet, canted
antiferromagnetic, and fully polarized phases.
Hamiltonian-learning protocols combining
equilibrium and dynamical measurements quantitatively characterize the ladder, incorporating
spin-orbit interactions to reproduce the observed crossover behavior. Measurements of higher-order
spin correlators – including four-point correlations inaccessible to conventional bulk probes – reveal signatures of the underlying phase structure despite the finite size. Our results establish germanium
quantum dot arrays as a controllable platform for
quantum magnetism, opening routes to investigate unconventional superconductivity in doped ladders.
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All authors Elizaveta Morozova, Xin Zhang, Utso Bhattacharya, Pablo Cova Fariña, Daniel Jirovec, Alexander Nico-Katz, Stefan D. Oosterhout, Sougato Bose, Giordano Scappucci, Menno Veldhorst, Eugene Demler, Lieven M. K. Vandersypen
Materials Science
Defect Geometry Selects Polar and Anomalous Hall Phases in Two-Dimensional Altermagnets
Xujia Gong, Amar Fakhredine, Hosein Alavi-Rad et al. (+6 more)
Point defects in altermagnets can create phases absent in the pristine host by selectively breaking
crystal symmetries. Combining
symmetry analysis, first-principles calculations, and
Hamiltonian modeling, we identify how point
impurities modify the altermagnetic phase. Using the pristine d- wave altermagnetic monolayer V2Se2O as a testbed, we identify three distinct classes of
impurities: those that preserve
spin-momentum locking, those that induce a hybrid-parity state associated with Edelstein
spin conversion, and those that produce a metallic ferrimagnetic state with an anomalous
Hall effect. We further discuss the robustness of two-dimensional altermagnets against point
impurities. Results for other two-dimensional systems, such as Mn4N2 and 2H-FeBr3, reveal the same
symmetry-based control across distinct
lattices and parent
spin harmonics, establishing defect geometry as a general route for engineering
spin textures and transport properties.
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All authors Xujia Gong, Amar Fakhredine, Hosein Alavi-Rad, Mahyar Hassani-Vasmejani, Xing Ming, Xiangang Wan, Carmine Autieri, Meysam Bagheri Tagani, Sahar Izadi Vishkayi
Materials Science
Polarization-Dependent Raman Selection Rules in Sb$_2$S$_3$ from First Principles and Experiment
Tobias Dierke, Michael Hüttenkofer, Stefan Wolff et al. (+4 more)
Antimony sulfide (Sb$_2$S$_3$) is a
semiconductor composed of quasi-one-dimensional ribbon-like structural units, which give rise to pronounced structural anisotropy in the bulk
crystal. Despite growing interest in Sb$_2$S$_3$, in particular Sb$_2$S$_3$ thin films, a detailed understanding of its
symmetry-based
lattice dynamics remains incomplete. Here, we present a combined experimental and theoretical study of polarization-dependent Raman scattering in Sb$_2$S$_3$ thin films. We derive the Raman selection rules from the
crystal symmetry and calculate the zone-center
phonon modes and corresponding Raman tensors using density functional theory. The calculated polarization dependencies are systematically compared with polarization-dependent Raman measurements performed on oriented crystalline domains of Sb$_2$S$_3$ thin films. This combined analysis enables reliable mode assignments, elucidates the anisotropic Raman response associated with the ribbon-like
crystal structure, and demonstrates the sensitivity of polarized Raman spectroscopy to
crystal orientation and structural order in antimony chalcogenide (Sb$_2$S$_3$, Sb$_2$Se$_3$) as well as isostructural Bi$_2$S$_3$ thin films.
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All authors Tobias Dierke, Michael Hüttenkofer, Stefan Wolff, Mingjian Wu, Julien Bachmann, Erdmann Spiecker, Janina Maultzsch
Superconductivity
Entropy mapping under uniaxial pressure utilizing the elastocaloric effect
Zhenhai Hu, You-Sheng Li, Aleksei V. Frolov et al. (+8 more)
Uniaxial pressure is a powerful tuning parameter for
quantum materials, but conventional thermodynamic probes such as specific heat are difficult to realize in the constrained geometries of strain apparatus. We develop a quantitative analysis framework for a.c. elastocaloric effect measurements that enable the reconstruction of the absolute
entropy and hence specific heat across complex phase diagrams. The absolute accuracy is achieved by combining measurements in the strong coupling regime at low frequencies with high signal-to-noise measurements in the quasi-adiabatic regime at high frequencies. Applying the approach to the correlated
superconductor Sr$_2$RuO$_4$, we obtain an absolute
entropy map across the phase diagram including across phase transitions deep into the superconducting state. We demonstrate that from such data one can derive the absolute specific heat which is currently not possible through other approaches. This data reinforces the finding that the quenching of
entropy within the
superconductor Sr$_2$RuO$_4$ is strongest at the critical strain consistent with the superconducting gap being maximized at the Van Hove singularity (VHs). Furthermore, we demonstrate that, although $\Delta c /(\gamma T) $ does increase at the VH strain, this increase is much weaker than previously inferred from more indirect caloric experiments.
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All authors Zhenhai Hu, You-Sheng Li, Aleksei V. Frolov, Fabian Jerzembeck, Manuel Brando, Naoki Kikugawa, Dmitry A. Sokolov, Hilary M. L. Noad, Andrew P. Mackenzie, Michael Nicklas, Andreas W. Rost
Soft Condensed Matter
Rheology and Dynamic Arrest in Colloidal Depletion Gels Mediated by Surface Brush Density
Ziye Zhuang, Robert A. Campbell, Safa Jamali et al. (+1 more)
We use the density of surface-grafted
polymers as a geometry-preserving control parameter for tuning the rheology of colloidal depletion gels. Reducing brush density accelerates gelation and produces gels with higher plateau storage modulus and yield stress. This mechanical enhancement is not accompanied by increased local densification; low-brush networks exhibit lower average contact number and reduced spatial heterogeneity while displaying stronger elastic responses than their high-brush counterparts. Our findings demonstrate a reduced coordination threshold to form elastic nodes in the low-brush gel network. In addition, low-brush gels relax more slowly, accumulate less creep deformation, and exhibit lower effective noise temperatures within the Soft Glassy Rheology framework. These results establish surface-brush density as an experimentally accessible control parameter for colloidal depletion gel rheology with coupled changes in effective attraction, network architecture, and contact kinematics.
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All authors Ziye Zhuang, Robert A. Campbell, Safa Jamali, Ali Mohraz