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Physics Condensed Matter

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Tuesday 30 June

Soft Condensed Matter · Cross-listed from physics.soc-ph

Synchronization and Swarming of Two-Mode Stochastic Oscillators

Synchronization and swarming are canonical manifestations of self-organization, observable across scales from cellular processes to animal flocks. This study investigates the collective dynamics of a novel agent-based model where individuals exhibit both spatial mobility and internal, two-mode stochastic oscillatory states. By introducing a local, distance-dependent coupling between the agents' spatial configuration and their internal state transitions, we establish a mutual feedback loop that drives complex pattern formation. Through large-scale numerical simulations, we identify seven distinct morphological configurations, ranging from stationary Filled-disk states to highly disordered Intense-motion regimes. By performing a rigorous quantitative analysis of the rotational energy and radial dispersion, we transcend simple morphological classification and demonstrate that the system organizes into discrete, quantized topological attractors. We derive a macroscopic scaling law, $\Omega \propto r^{-1/2}$, which proves that the emerging rotating states are not rigid-body rotations, but rather composite differential vortex structures characterized by spontaneous chiral symmetry breaking. Our results suggest that these stable, quantized dynamical states are fundamental features of systems governed by bidirectional spatial-phase feedback, offering a robust framework for designing autonomous, decentralized robotic swarms.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Superconducting Spiral Inductors for RF Reflectometry: Operation at Elevated Temperatures and Magnetic Fields

Superconducting spiral inductors are emerging as key components for radio-frequency (RF) reflectometry, a widely used readout technique for semiconductor spin qubits. Future scalable quantum-computing architectures are expected to operate at elevated temperatures and magnetic fields, placing new demands on the performance and stability of superconducting circuit elements. Here, we present a systematic study of NbTiN spiral inductors under temperatures of several kelvin and magnetic fields approaching 1 T. By combining weakly coupled resonator measurements with independent two-port inductance extraction, we separate inductive and capacitive contributions to device behaviour and directly identify the origin of resonance shifts and quality factor degradation. Furthermore, we establish practical design metrics linking geometry, temperature sensitivity, and magnetic-field robustness. These results provide a general framework for benchmarking superconducting inductors and guiding the design of future RF-reflectometry circuits for practical quantum technologies.
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All authors Euan Parry, Murat Cubukcu, Patrick Reuvekamp, Manoj Stanley, Jonathan D. Fletcher, Alessandro Rossi

Disordered Systems and Neural Networks · Cross-listed from cs.LG

Scaling Up Thermodynamic AI Models

Thermodynamic computing devices based on the Ising model show great promise for low-power AI inference and edge computing, but scalable methods for training large models for such hardware remain limited. Prior theory shows that the time-averaged behavior of high-temperature Gibbs-sampled Ising systems can implement feed-forward neural inference. We turn this theoretical correspondence into a scalable and purely backpropagation-based algorithm for training deep convolutional networks for thermodynamic inference on Ising machine hardware. Our image classification models achieve accuracies of 94.9% on CIFAR-10 and 76.0% on CIFAR-100 under binary Gibbs sampling. We then develop and experimentally validate a mathematical theory relating inference cost to accuracy and controlling autocorrelation times. Subsequently, we calculate asymptotic results showing that inference cost is bounded by a well-controlled tradeoff with performance and exhibit algorithms for computing optimal inference schedules. Finally, we discuss implications for hardware development and the future of high-temperature thermodynamic AI models.
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Materials Science

Topological Hall plateau in quasi-2D kagome magnet YMn$_6$Sn$_6$

We examine the impact of the Dzyaloshinskii–Moriya interaction (DMI) in kagome magnets and show that a predominantly planar DMI together with ferromagnetic exchange stabilizes a disordered skyrmion phase in quasi-two-dimensional (2D) YMn$_6$Sn$_6$. Within an {\it{ab initio}} framework combining density functional theory and spin-dynamics simulations, we generate realistic spin textures of disordered skyrmion and find that this phase persists for $B_{\rm ext} \leq 0.5$~T, with a decreasing skyrmion size as magnetic field increases. We demonstrate the emergence of topological Hall plateau in the range $-0.5 \leq B_{\mathrm{ext}} \leq 0.5$~T, driven by nearly uniform scalar spin chirality and the resulting constant real-space Berry curvature. This response is anti-symmetric with magnetic field while magnitude and sign of these plateau are determined by a complex interplay between Hund's coupling strength and chemical potential signifying the role of Dirac points and van Hove singularities. In addition, we reveal topological magnon excitations in the disordered skyrmion phase of quasi-2D YMn$_6$Sn$_6$.
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All authors Sambit Jena, Nastaran Salehi, Manuel Pereiro Lopez, Olle Eriksson, Narayan Mohanta, Karthik V Raman, Tanay Nag, Banasree Sadhukhan

Strongly Correlated Electrons

Gibbs-state phases beyond microscopic symmetry breaking: A phase invariant for the 3D toric code

Do phases of Gibbs states admit a classification beyond symmetry breaking? We study the three-dimensional toric code with transverse and longitudinal fields that explicitly break both microscopic higher-form symmetries. We introduce the connected correlation $f_W$ of two locally decoded winding Wilson loops. Nonzero asymptotic $f_W$ rules out shallow local preparation from product states. An asymptotic optimization over the observables and physical recovery channels defines an invariant $\mathcal{F}$, which we prove constant within phases defined by two-way local channels with product ancillas and sublinear causal radius. The invariant equals one for the canonical zero-temperature state of the field-free toric code. Quantum Monte Carlo tests the conjectured thermodynamic values $f_W=1$ at weak fields and low temperature and $f_W=0$ elsewhere. The fixed-decoder correlation provides a lower bound on $\mathcal{F}$, so the results suggest an extended region with $\mathcal{F}=1$. Product states, including the infinite-temperature state and fully polarized infinite-field limits, have $\mathcal{F}=0$ exactly and therefore lie in a different phase from states with $\mathcal{F}=1$.
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Statistical Mechanics · Cross-listed from quant-ph

Work Statistics Under Quantum-Jump and Quench Dynamics in Monitored Ising Chains

We investigate work statistics in monitored transverse-field Ising chains subjected to both a quantum quench of the transverse field and either stochastic quantum jumps or controlled measurement sequences. For generalized measurements, we derive a trajectory-resolved generating function for work statistics in the two-point energy measurement scheme. Evaluating it using a fermionic Gaussian-state formalism, we show that, under stochastic jump dynamics, the work distribution crosses over from a comb-like structure to an essentially Gaussian form with shrinking sub-Gaussian tails, as the number of detection events grows. For controlled jump protocols, the energy added by each jump is constant when successive jumps are causally disconnected but decreases and then saturates when they lie within each other's light cone, leading to linear growth of average work in the former case and a transient sublinear regime followed by linear growth with a reduced slope in the latter. For monitored quenches, continuous observation washes out the fine structure of the isolated-quench distribution and again drives the statistics toward Gaussian behavior. Together, these results establish work statistics as a trajectory-resolved diagnostic of measurement-induced energy injection and of the emergence or breakdown of additivity in monitored many-body dynamics.
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Statistical Mechanics · Cross-listed from hep-lat

Monte Carlo reconstruction of symmetry-twisted partition function ratios: the critical 3D Ising

We introduce a Monte Carlo strategy for directly estimating partition function ratios between distinct global sectors of a lattice theory. It enlarges the configuration space to sample an interpolating family whose endpoints are the desired sectors, and uses flat histogram methods to reconstruct the corresponding free energy difference. Although the construction is more general, we focus here on the three-dimensional Ising model on the slab $\mathbb{R}^{2}\times S^{1}_{L_{z}}$ at the bulk critical point, comparing the untwisted periodic sector with the $\mathbb{Z}_{2}$-twisted antiperiodic sector. A large-volume and aspect ratio extrapolation gives the symmetry-twisted thermodynamic Casimir difference $\Delta_{\mathbb{Z}_{2}}=0.327(2)$ directly, without lattice derivatives or bulk subtractions. This provides an independent twisted sector probe of tensions observed in periodic sector thermodynamic Casimir observables. More generally, the method gives direct but selective numerical access to CFT compactification data, including estimates of the effective thermal screening scale and the $\mathbb{Z}_{2}$-odd sector energy gap on $T^{2}$.
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Mesoscale and Nanoscale Physics

An analog ac voltage amplifier based on a single straintronic magnetic tunnel junction

Magnetic tunnel junctions (MTJs) are known for their digital applications (memory and logic). A special class of them called "straintronic" magnetic tunnel junctions (s-MTJ) has lately emerged as a potential platform for analog applications because their conductance can be varied continuously with mechanical strain generated with a gate voltage. The conductance versus gate voltage (transfer) characteristic always has a linear region and that can be leveraged for a variety of analog applications. Here, we discuss one such application, namely analog voltage amplification. If the s-MTJ's gate voltage is fixed around the midpoint of the linear region and a small ac voltage is superimposed on it, then the ac voltage can be amplified without distortion as long as its amplitude is small enough to avoid gate voltage excursion beyond the linear region. Unlike a transistor-based voltage amplifier whose amplification is determined solely by the transistor's internal parameters - namely the transconductance and Early resistance - here the amplification can be varied by an external power supply voltage. We examine the maximum allowed amplitude and frequency of input signal for distortion-free amplification by modeling the magnetization dynamics and derive an expression for the amplification.
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Strongly Correlated Electrons

Single-worldline theory for a dissipative Mott transition

In one dimension at zero temperature, local baths with spectral exponent $s$ can stabilize a compressible, non-superfluid dissipative phase between the Mott insulator and Luttinger liquid. The dissipative-to-Mott transition is accessible neither to perturbative renormalization-group methods nor to the free-fermion description of the conventional Mott transition. Here, we show it is governed by the worldline of a single doped excitation, whose geometrical roughness determines the critical exponents. Without dissipation, this worldline undergoes Brownian motion, recovering $\beta=\nu=1/z=1/2$. Dissipation turns it into a long-range interacting interface, yielding continuously varying exponents $\beta=\nu=1/z=s-1$ for $1<s<3/2$, and $\beta=\nu=1/z=0$ for $s<1$. The same theory identifies $s=3/2$ as the threshold above which the dissipative phase disappears. Large-scale Monte Carlo simulations of both the single-worldline theory and the original many-body model quantitatively support these predictions.
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Strongly Correlated Electrons · Cross-listed from hep-th

Toward Hamiltonian simulations of Maxwell-Chern-Simons theory: constant modes and gauge field truncation

Maxwell-Chern-Simons (MCS) theory in $2+1$ dimensions provides a paradigmatic example of a topological gauge theory with both dynamical and topological degrees of freedom. Its Euclidean formulation suffers from a sign problem, making Hamiltonian numerical approaches particularly attractive. As a first step toward the non-perturbative Hamiltonian study of MCS theory, we investigate the constant mode sector on a spatial torus. Being analytically solvable in the continuum, it provides an ideal benchmark for understanding how the topological properties of the theory are encoded in a finite-dimensional lattice Hilbert space. We construct a finite-dimensional discretization of the torus of flat connections and show that the resulting lattice problem maps onto a generalized Harper-Hofstadter model with twisted boundary conditions. We identify the commensurability conditions under which the finite lattice exactly reproduces the magnetic translation algebra and the topological degeneracy of the continuum theory. A systematic analysis of gauge field truncation and its convergence toward the continuum limit is then presented.
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All authors Andrea Bulgarelli, Maria Cristina Diamantini, Nico Dichter, Lena Funcke, Tobias Hartung, Karl Jansen, Enrique Rico Ortega, Simran Singh, Lorenzo Spera

Statistical Mechanics

Exactly solvable non-unitary conformal interfaces in unitary CFTs

We construct directly on the lattice a class of non-unitary interfaces that are both exactly conformal and exactly solvable, and establish their corresponding boundary and interface conformal field theory (CFT) descriptions. The construction is obtained by analytically continuing the scattering data of known exact unitary conformal interfaces on the lattice, yielding an $SL(2,\mathbb C)$-parametrized family, which is non-compact and breaks probability-current conservation. Exploiting the exact lattice-continuum correspondence, we derive the conformal boundary states in the folded picture. We show that a proper definition of the Hilbert space in the closed-string channel requires the incoming and outgoing boundary states to be specified independently by boundary data associated with a pair of dual biorthogonal bases, in close analogy with the right and left eigenvectors of a non-Hermitian Hamiltonian. This requirement determines a consistent CFT construction of non-unitary boundaries and interfaces, and leads to a non-unitary generalization of the conventional Cardy's condition for unitary boundary CFT. Beyond their formal construction, these non-unitary interfaces are shown to exhibit logarithmic entanglement scaling governed by an effective central charge that is generally complex. For the $SU(1,1)$ subclass, the effective central charge remains real but grows without bound as the transmission coefficient increases. This result is demonstrated through analytical and numerical lattice calculations, as well as an interface CFT analysis in the unfolded picture. Finally, we present a general CFT analysis of a class of global quantum quenches whose initial states are prepared with non-unitary boundaries. We relate their effective temperature to the conformal dimension of the boundary-condition-changing operators associated with non-unitary boundary conditions.
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Statistical Mechanics

Multifractal Scaling in Hi-C Maps

The three-dimensional organization of the genome exhibits rich, scale-dependent structure, as revealed by both chromosome contact maps (e.g., Hi-C maps) and chromatin density measured by microscopy. Recent studies have reported multifractal scaling in these data. Yet, the origin of this scaling behavior remains unclear: existing efforts describe it through postulated models. Here, we show that the multifractal structure of Hi-C maps is a direct consequence of the power-law contact probability $P(s)$, which is itself an empirical observable measured from Hi-C maps. Starting from $P(s)$ with a single exponent $\gamma$, we analytically derive the mass exponent $\tau(q)$, which characterizes how the $q$-th moment of contact density scales with box size $l$ used to coarse-grain the genomic coordinate. This multifractal behavior reflects the geometric competition between intra- and inter-segment contacts. We find that the slope of $\tau(q)$ at large $q$ is given by $2 -\gamma$ when $\gamma <1$, and by $1$ when $\gamma \geq 1$. We further show that this behavior is robust to noise and consistent across diverse organisms, indicating that it is a universal feature of chromatin organization. We extend our analysis into double-exponent $P(s)$, and show the $l$ dependence in multifractal behavior. Taken together, these results provide a physical explanation for multifractal scaling and establish a direct link between the multifractality in Hi-C maps and polymer contact statistics, with the large-$q$ slope of $\tau(q)$ mapping onto a known polymer contact exponent.
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All authors Seong-Gyu Yang, Lucas Hedström, Jan Smrek, Ludvig Lizana

Statistical Mechanics

Exploring the entropic asymmetry on logical stochastic resonance with energetically equivalent intrinsic outputs

Small-scale systems are inherently subject to environmental noise that can be harnessed constructively to realize reliable logic operations – a phenomenon known as logical stochastic resonance (LSR), where a bistable system produces correct logical outputs within an optimal window of noise intensity. The Brownian dynamics governed by appropriate inputs inside a double-well potential, modeling the bistable system, mimic the logic operations. The two wells of this potential represent two distinct logical output states 0 and 1. Asymmetry in this potential is known to be essential for improving logical reliability. However, prior studies have focused on energetic asymmetry, characterized by unequal depths of the two wells of the potential. This left the role of the width asymmetry in the potential, unexplored. This latter class of asymmetry emerges due to the dissimilar widths of the two wells of the potential. It can be classified as the entropic asymmetry between the two logical output states. Here, we systematically investigate the effect of width or the entropic asymmetry in the system on the logical response for OR and AND gate operations. Unlike energetic asymmetry, width asymmetry preserves the energetic equivalence of the two intrinsic logical output states, making it a geometric effect. We find that increasing width asymmetry consistently improves the optimal P(logic), the quantifier measuring the successful logical outcome. Moreover, when it is combined with an energetic bias, it produces reliable logic gate operation at a significantly reduced energetic cost compared to the symmetric case. The requirement of this energy bias also diminishes gradually with the increasing degree of width asymmetry in the potential.
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Statistical Mechanics

Non-Maxwellian Velocity Statistics in Supercooled Liquids and Their Possible Relation to Super-Arrhenius Viscosity

For particles of fixed mass, classical equilibrium statistical mechanics dictates a Maxwellian velocity distribution determined solely by the temperature, regardless of the interactions, density, or structure. Supercooled glass forming liquids realize long lived metastable states that evade equilibrium crystallization and may thus violate assumptions underlying Maxwellian statistics. We numerically demonstrate that supercooled liquids can exhibit persistent non-Maxwellian velocity distributions with deviations connected to their exceptionally slow super-Arrhenius relaxation. Our work is motivated by a general result establishing that long lived metastable states may exhibit finite width distributions of intensive variables. A distribution of temperatures implies non-Maxwellian velocity statistics. We test this prediction by introducing stochastic thermostats that generate stationary states while, unlike conventional thermostats, not imposing Maxwellian velocity distributions. Simulations with these thermostats yield long lived states that have, by comparison to Maxwellian velocity distributions, an excess kurtosis $0<\kappa\lesssim0.3$. Crystallization is strongly impeded with increasing $\kappa$. In a minimal description, temperature fluctuations are characterized by a dimensionless width $\overline{A}$ with $\kappa\simeq3\overline{A}^{2}$. The nearly constant $\overline{A}$ (of an average value $0.08$ and standard deviation $0.03$) found in viscosity data collapse across $45$ glass formers and in specific heat signatures is consistent with kurtosis found in our simulations. Long time non-Maxwellian velocity statistics may thus link slow relaxation, transport, and thermodynamic measurements. Independent of the tested theory, the stochastic thermostats that we introduce offer a molecular dynamics route to non-Maxwellian velocity statistics.
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Disordered Systems and Neural Networks · Cross-listed from q-bio.NC

Stationary covariance spectra of discrete-time non-normal random recurrent dynamics

Principal component analysis is widely used to characterize structure in the dynamics of recurrent neural networks. For stationary noise-driven dynamics, the distribution of variance among the principal components is determined by the spectrum of the stationary covariance matrix. While the spectral properties of this matrix are well-understood for linear networks with normal synaptic weight matrices, our understanding of the stationary covariance spectrum for random non-normal dynamics remains incomplete. In this note, we use a free-probability approach to formally derive a closed functional equation for the moment generating series of the limiting stationary covariance spectrum of discrete-time dynamics with random non-normal Gaussian weights. This characterization allows us to analyze the behavior of tail eigenvalues in the critical regime: they decay with the inverse-square of their rank. In contrast, applying the same approach to the analogous continuous-time dynamics leads to an infinite hierarchy of Schwinger-Dyson equations, rather than a closed scalar equation. We conclude with some comments regarding the relevance of these results to comparisons of models of non-normal dynamics to neural data.
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Statistical Mechanics · Cross-listed from q-bio.PE

Invasion with size-dependent dispersion range

The coalescing colony model provides a minimal framework for biological invasions with long-range dispersion. In its standard formulation, the dispersion range is assumed independent of the size of the invading population. Here, we relax this assumption and consider size-dependent dispersal: a main colony of linear size $r$ emits secondary colonies at distance $r^\mu$, with $0 \leq \mu \leq 1$. We derive the generalized dynamical equations for this extended model and map out the growth phase diagram for the leading order contribution. Depending on $\mu$, the main colony exhibits distinct regimes: linear expansion, power-law growth, exponential regime and finite-time blow-up. We confront these theoretical predictions with a spatially explicit physical model. While the coalescing colony approach correctly captures the scaling of the perimeter, it fails to predict the scaling of the volume. We trace this discrepancy to an effective breakdown of circular symmetry in the morphology of the main colony. Finally, we quantify temporal evolution of the population fraction residing outside of the main colony. The coalescing colony model predicts its decay to~$0$ like a power-law when~$\mu<1$, and a macroscopic amount of the population remains in the secondary colonies at~$\mu=1$. Simulations of the physical model reveal a persistent satellite population not captured by the theory at~$\mu>\mu^*\approx 0.7$. Broadly, our findings highlight how coupling dispersal range to population size fundamentally alters invasion dynamics, with implications for biological invasions, metastatic growth, and urban expansion.
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Mesoscale and Nanoscale Physics

Untangling 3D atomic reconstruction in twisted bilayer 2D crystals via dark field transmission electron microscopy

Reconstruction of the atomic crystal structure in twisted 2D materials has been demonstrated to be responsible for multiple exciting phenomena in van der Waals heterostructures, from the appearance of flat bands in twisted bilayer graphene to Wigner crystallization in transition metal dichalcogenides (TMDs). However, there are still no experimental methods for accessing the 3D atomic distributions nor models that describe the exact atomic shifts in such reconstructed structures, which significantly impedes the development of the field. Dark field (DF) transmission electron microscopy (TEM) has been conventionally employed to visualize the local in-plane atomic displacements. Here we expand this method to obtain a full description of the reconstructed atomic systems and demonstrate the quantitative relations between the local stacking and the intensity in the DF image. We show how local 3D atomic displacements and the interlayer distance can be extracted from a DF image.
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All authors Pankaj Kumar, Michel Bosman, Nikolai Lavrentev, He Zheng, Ding Peng, Kostya S. Novoselov, Tatiana Latychevskaia

Statistical Mechanics · Cross-listed from hep-th

Fate of "Space-like singularities" in $c=1$ Matrix Model

A class of time dependent backgrounds in two dimensional String Theory leads to superluminal Liouville walls on the worldsheet. In the dual double scaled $c=1$ matrix model these backgrounds involve eigenvalues leaking out to infinity, and the collective field fluctuations become strongly coupled along space-like regions, resembling singularities. We realize these backgrounds as results of quantum quenches in the matrix model, retaining non-linear terms in the matrix potential, thus departing from a double scaling limit. Working in the fermion picture in a Thomas-Fermi approximation, we show that while the early time behavior of the phase space density near the maximum of the potential agrees with that obtained in the double scaled theory, at times of the order $(\log N)$ the effect of the IR wall becomes significant. At later times, with a characteristic winding time of order $(\log N)^2$, folds on the fermi surface proliferate and eventually cover the allowed region in phase space densely. Using action-angle variables, we show that the phase space density oscillates around a time independent and angle independent value rapidly at late times. A coarse-grained density in the angle space relaxes to a time independent equilibrium value as a power law with an exponent largely independent of the details of the initial state. Thus, the appearance of a space-like singularity is an artifact of the strict double scaling limit. We comment on the interpretation of the final state in String Theory.
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All authors Sumit R. Das, Shaun D. Hampton, Sinong Liu, Gautam Mandal

Materials Science

What enables GaOx as hole transport layer for a 16 percent 1.0 eV CuInSe2 Bottom Cells with VOC above 550 mV?

Among the highly efficient photovoltaic technologies, that do not rely on epitaxy, only chalcopyrites have a bandgap tunable down to 1.00 eV, the ideal for tandem applications. This is obtained with a pure CuInSe2 absorber without Ga. GaOx has been shown to be an efficient hole transport layer that prevents recombination at the metallic back contact. On the other hand, GaOx has proven detrimental, when it forms on In containing transparent back contacts in bifacial solar cells. Here, we investigate the conditions that make the GaOx layer conductive. We employ a GaOx hole transport layer that is formed through ion exchange during co-evaporation of the low band gap absorber layer. We find that no additional Cu is needed, and that Na is not necessary for a conductive GaOx. Nor did we find a systematic influence of oxygen flow during the sputtering process of the oxide layer. The GaOx layer is partly crystalline. The optimized passivating hole transport layer enables a CuInSe2 bottom solar cell, without any addition of Ag or heavy alkalis, with an active area efficiency above 16% and a record-certified open-circuit voltage VOC of 552meV
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All authors Francesco Lodola, Zhuangyi Zhou, Boaz Koren, Saeed Bayat, Alessandro Magon, Yucheng Hu, Adrian-Marie Philippe, Michele Melchiorre, Hasan Arif Yetkin, Gunnar Kusch, Nathalie Valle, Rachel A. Oliver, Susanne Siebentritt

Soft Condensed Matter

Drift-diffusion interplay in active Brownian particles under orienting field

Magnetic active particles offer a versatile route to externally controlled microscale transport by combining self-propulsion with field-tunable orientation, as realized in both synthetic and living magnetic microswimmers. Here, we develop a theoretical framework for three-dimensional active Brownian motion in a uniform magnetic field, incorporating coupled translational and rotational dynamics and providing analytical approximations for low-order displacement moments. At long times, the system dynamics reduces to a combination of enhanced diffusion and permanent drift absent in regular active Brownian particles. The field acts as an external controller, channeling activity toward one of these two types of motion. At intermediate time scales, the interplay between rotational noise, self-propulsion, and magnetic alignment results in pronounced non-Gaussian displacement statistics. First-passage properties exhibit strong field sensitivity, highlighting the potential of magnetic guidance to optimize search processes and targeted delivery in active matter systems. Theoretical predictions are validated by numerical simulations.
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All authors Andrey A. Kuznetsov, Vittoria Sposini, Sofia S. Kantorovich, Aleksei V. Chechkin

Soft Condensed Matter

Self-Generated Electric Fields in Polyelectrolyte Gradients Increase Microparticle Transport

There are many situations in nature and industry where small particles are exposed to gradients of charged polymers, such as enzymes in biological gradients of DNA or RNA, virus particles in respiratory droplets, and colloidal particles in stratifying paint layers. Here, we study the phoretic propulsion of charged microparticles in a polyelectrolyte gradient. We theoretically predict the emergence of a macroscopic electric field from charge-separation dynamics in a polyelectrolyte gradient under a continuous diffusive driving force. We confirm the presence of this self-generated electric field experimentally and show that it significantly increases the phoretic velocity of the microparticles. Finally, for high molecular weight polyelectrolytes we observe that propulsion becomes gradient-independent, consistent with diffusiophoretic predictions for asymmetric electrolytes. Our results show that self-generated electric fields in polyelectrolyte gradients can enhance microparticle transport, with potential applicability wherever charged species of different mobility are continuously driven out of equilibrium.
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All authors Max Huisman, Ali Azadbakht, Patrick B. Warren, Daniela J. Kraft

Materials Science

Proximity-Induced Skyrmion Stabilization at the Cu2OSeO3/Bi2Se3 Interface

We investigate proximity-induced magnetic interactions at the interface between the topological insulator Bi2Se3 and the chiral magnetic insulator Cu2OSeO3, with particular focus on the low temperature skyrmion phase. Broadband ferromagnetic resonance spectroscopy reveals enhanced stability of noncollinear spin textures in the Cu2OSeO3/Bi2Se3 heterostructure compared with bare Cu2OSeO3. In addition to an extra resonance mode in the tilted conical phase that is absent in bare Cu2OSeO3, field cycling resolves two counterclockwise skyrmion resonance branches separated by approximately 238 MHz, consistent with the coexistence of a bulk skyrmion lattice and an interfacial skyrmion phase stabilized by proximity-induced exchange coupling and enhanced interfacial Dzyaloshinskii-Moriya interactions. The finite frequency separation indicates that the two skyrmion phases occupy distinct magnetic energy landscapes while retaining similar resonance character. Resonant elastic x-ray scattering measurements further confirm that the interfacial skyrmion phase spans a broader magnetic-field range than the bulk phase, demonstrating enhanced stability and ordering of topological spin textures at the interface. These findings establish interface engineering as a promising route for extending the stability regime of skyrmion and tilted-conical phases in topological-magnetic heterostructures.
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All authors Sina Mehboodi, Victor Ukleev, Chen Luo, Radu-Marius Abrudan, Jie Xiao, Ronny Golnak, Florin Radu, Matthias Kronseder, Christian H. Back, Aisha Aqeel

Materials Science

Giant perpendicular Edelstein polarization in 2D compensated magnets via bichromatic Floquet driving

While unconventional $p$-wave magnets can generate nonrelativistic Edelstein polarizations, spin-group symmetries strictly forbid these responses in unconventional magnets with higher-order harmonics, such as $d$-wave altermagnets. Here, we demonstrate that combining Rashba spin-orbit coupling with bichromatic Floquet driving activates giant perpendicular Edelstein polarizations (PEPs) across 2D altermagnets and broader classes of unconventional spin-polarized magnets – a feat monochromatic driving cannot achieve. By dynamically breaking two-fold rotational symmetry, the two-frequency drive (including bilinear, bicircular, and circular-linear configurations) induces a stray-field-free in-plane Zeeman-like field that generates orbitally dominated PEPs (0.5–1.5 $\mu_{\rm B}$). This massive response is governed by universal selection rules tied to the system's magnetic parity and the second beam's harmonics. These emergent PEPs provide a powerful mechanism for perpendicular memory writing.
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All authors Mohsen Yarmohammadi, Daegeun Jo, Marco Berritta, Libor Šmejkal, James K. Freericks, Peter M. Oppeneer

Superconductivity

Anomalous Hall Effect Driven by Chiral Superconductivity

Direct dc-current signatures of unconventional superconductivity remain scarce. Existing probes of unconventional pairing are typically indirect, relying on phase-diagram anomalies, responses to external fields, or optical measurements. Here we propose a zero-field Hall drag effect as a direct transport signature of chiral superconductivity. The effect arises from Coulomb drag between quasiparticles in a chiral superconductor and those in an adjacent time-reversal-symmetric normal layer. We develop a minimal hydrodynamic theory that includes both quasiparticle normal current and condensate supercurrent in the superconducting layer. In an open-circuit superconducting layer, the condensate generates a counterflowing supercurrent that cancels the net layer current, while a finite quasiparticle current remains and mediates the transverse drag response. This results in anomalous Hall voltage signal appearing abruptly when $T$ is lowered below $T_c$, of the sign reflecting the sign of the superconducting order parameter phase winding.
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Superconductivity

Universal Spectral Mirage Gaps in Superconductors with Time-Reversal-Symmetric Spin-Orbit Coupling

Spectral mirage gaps, regarded as evidence of finite-energy pairing correlations, have so far been mainly studied in superconductors with Ising spin-orbit coupling (SOC). Here, we show that superconductors with any time-reversal-symmetric SOC can generate mirage gaps near the SOC energy scale when the applied magnetic field has a component perpendicular to the SOC texture, whereas the parallel component produces Zeeman-split spectral features near the superconducting gap. We demonstrate this general principle in superconductors with Rashba and Rashba-Ising SOC. These universal field-dependent signatures establish superconducting spectroscopy as a powerful probe of SOC textures and strengths.
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Soft Condensed Matter

Designing topological edge currents in chiral active matter

Achieving robust functionality in active matter driven away from thermal equilibrium is a current theoretical and experimental challenge. Several recent studies have reported edge currents–persistent transport along walls and density inhomogeneities–in chiral active matter. Yet, the microscopic rules that render these edge currents robust with respect to the confinement geometry and defects remain elusive. Here, we introduce a simple particle model of two-dimensional chiral active swimmers that undergo chirality switching and demonstrate that the model exhibits robust edge currents, i.e., when a single particle is confined, edge currents arise regardless of the confinement geometry or the presence of defects. We also investigate the collective behavior of interacting particles in bulk and find that chirality switching induces phase separation accompanied by edge currents along interfaces. This phase separation is distinct from motility-induced phase separation and is qualitatively explained by an effective hydrodynamic theory derived via bottom-up coarse-graining. Furthermore, by analyzing the topological properties of the linearized hydrodynamic equations, we show that the edge currents in our system are genuine topological edge modes. Notably, phase separation induced by chirality switching can be regarded as the coexistence of two topologically distinct domains. Our results provide guidelines for designing robust edge currents in active matter systems.
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All authors Yuta Kuroda, Ellen Meyberg, Gaurav Gardi, Thomas Speck, Saeed Osat

Soft Condensed Matter

Optimal interactions for addressable self-assembly

Addressable self-assembly asks that each building block assemble into a particular location in a target structure. Although particles may all be distinct, achieving high yield is a challenge because of monomer depletion: more target structures can nucleate than there are building blocks for, so they form partial fragments which cannot complete growth. We ask how to design the interactions between building blocks to achieve the highest yield in a given time. Using reaction equations describing all the intermediate steps of assembly, combined with numerical optimization, we show that the optimal interactions are such that (i) all bonds are either very strong or very weak, and (ii) the strong bonds form a spanning tree of the target structure. We then prove that when interactions form a spanning tree, monomer depletion cannot occur: assembly can always proceed downhill in energy space, with no kinetic traps. This result is a combinatorial property of the underlying interaction graph, and does not depend on the particular model for the kinetics. It suggests a robust design principle: create a network of strong interactions that has no loops, and make all other interactions much weaker. We validate this principle in numerical simulations of larger structures, and we further show that spanning trees that are more compact have typically better yield. Our results suggest a new framework for understanding monomer depletion and addressable self-assembly, which may be applied to DNA nanotechnology and which may give insight into the assembly pathways of certain multiprotein complexes.
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All authors Tighe McAsey, Sushrut Tadwalkar, Ali Fele-Paranj, Miranda Holmes-Cerfon

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

Navigating committor landscape of biomolecules with a general pairwise interaction model

Sampling rare conformation transitions between metastable states is a central challenge in atomistic simulations. While the committor function serve as an ideal reaction coordinate for driving enhanced sampling, their high-dimensional inputs and complex functional forms limit the efficacy of standard feedforward neural networks in modeling them. Inspired by recent breakthroughs in biomolecular structure prediction, we propose a novel committor learning framework grounded in the AlphaFold 3 paradigm. By integrating a lightweight, differentiable atom-level embedding with a simplified Pairformer architecture, our method inherently captures intricate dynamical features of diverse biosystems without requiring specialized prior knowledge. We demonstrate the superior expressiveness and accuracy of the proposed framework across multiple atomistic processes. For the folding of the chignolin mini-protein, our model reveals the finer-grained structure of its transition state ensemble (TSE) and a detailed bifurcated reaction mechanism. Furthermore, for calixarene host-guest systems, we develop a unified committor model that elucidates how ligand substituents regulate the ratio between distinct binding pathways, offering new perspectives for structure-based drug design.
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All authors Jintu Zhang, Zichang Jin, Huifeng Zhao, Kai Zhu, Bowei Zhao, Xujun Zhang, Peilin Kang, Tingjun Hou

Materials Science

A technical report on the surface-energy and morphology-based screening for electrode/electrolyte interface compatibility in SOFC/ReSOC materials

The performance and durability of solid oxide fuel cells and reversible solid oxide cells are strongly affected by the electrode-electrolyte interface, where charge transfer, ionic transport, adhesion, morphology and thermomechanical stability interact. Early-stage compatibility screening is usually based on electrochemical or compositional criteria, whereas surface-related descriptors are rarely included in a unified framework. This work proposes a surface-based methodology to assess the expected compatibility of candidate electrode-electrolyte pairings. Contact-angle measurements with water and glycerol are used to determine total, dispersive and polar surface free energy components through the Owens-Wendt-Rabel-Kaelble method. Confocal topography is used to extract ISO 25178 roughness parameters, including average roughness, peak-to-valley height, valley depth, skewness, kurtosis and surface slope. A compatibility matrix is constructed by combining energetic affinity and morphological suitability, with emphasis on the electrolyte surface, since the electrode is deposited directly onto the electrolyte substrate. The results indicate that the most promising interfaces are not necessarily those with the highest surface free energy, but those combining high adhesion work, low interfacial energy and a substrate morphology suitable for continuous electrode deposition. The proposed approach provides a rational pre-electrochemical screening tool to prioritize electrode-electrolyte combinations for subsequent validation by electrochemical impedance spectroscopy, area specific resistance, electrical contact resistance, microstructural analysis and durability testing. Although it does not replace electrochemical characterization, it offers a physically grounded way to connect surface chemistry, topography and interface formation in solid oxide cell materials.
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Strongly Correlated Electrons

The exceptional origin of the strange metal and the LFL-HFL transition

We propose an algebraic framework for the strange metal regime of strongly correlated electrons. We show that the exceptional superconformal algebra $D(2,1;\alpha)$ admits two distinct contractions of its conformal sector: one to a pair of canonical fermions, the underlying degrees of freedom of the Landau–Fermi liquid (LFL), and one to the algebra of Hubbard operators, which characterise a distinct metallic regime, the Hubbard–Fermi liquid (HFL). We argue that competition between these two metallic states drives the emergence of the strange metal as a $0+1$D superconformal bath. We analyse the resulting thermodynamics, and at leading order obtain a parameter-free prediction, $4\pi^2\gamma^{-1} =\chi_s^{-1} + \chi_c^{-1}$, relating the Sommerfeld coefficient to the static spin and charge susceptibilities. We further show that the LFL-HFL transition is discontinuous at low temperature, forced by an algebraic constraint on the Hubbard contraction, and map out the resulting phase diagram. We connect the framework to microscopic lattice models and to the phenomenology of correlated insulators.
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