Materials Science
Surface Equilibration Mechanism Controls the Stability of a Model Co-deposited Glass Mixture of Organic Semiconductors
Shinian Cheng, Yejung Lee, Junguang Yu et al. (+2 more)
While previous work has identified the conditions for preparing ultrastable single-component organic glasses by physical vapor deposition (PVD), little is known about the stability of co-deposited mixtures. Here, we prepared binary PVD glasses of organic
semiconductors, TPD (N,N-Bis(3-methylphenyl)-N,N-diphenylbenzidine) and m-MTDATA (4,4,4-Tris[phenyl(m-tolyl)amino]triphenylamine), with 50:50 mass concentration over a wide range of substrate temperatures (Tsub). The enthalpy and kinetic stability are evaluated with differential scanning calorimetry and spectroscopic ellipsometry. Binary organic
semiconductor glasses with exceptional thermodynamic and kinetic stability comparable to the most stable single-component organic glasses are obtained when deposited at Tsub=0.78-0.90Tg (where Tg is the conventional glass transition temperature). When deposited at 0.94Tg, the enthalpy of m-MTDATA/TPD glass equals that expected for the
equilibrium liquid at that temperature. Thus, the surface equilibration mechanism previously advanced for single-component PVD glasses is also applicable for these co-deposited glasses. These results provide an avenue for designing high-performance organic electronic devices.
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All authors Shinian Cheng, Yejung Lee, Junguang Yu, Lian Yu, M. D. Ediger
Soft Condensed Matter
Overaging with stress in polymer glasses? Faster segmental dynamics despite larger yield stress!
Masoud Razavi, Enran Xing and M.D. Ediger
It is well known that physical aging of
polymer glasses increases their yield stress and affects their failure behavior. Studies indicate that application of moderate levels of stress during aging results in higher yield stress compared to aging in the absence of stress (quiescent aging). This has been interpreted to indicate that stress accelerates physical aging, and has been described as overaging. In this study, we age PMMA glasses under stress, and carry out direct measurement of segmental dynamics during and after aging by using a probe reorientation technique. We observe that samples aged under stress, despite having higher yield stress, have faster segmental dynamics after stress release than quiescently aged samples. This contradicts the overaging interpretation, for the range of conditions explored here. Our results indicate that yield stress is not a simple function of structural relaxation time and theoretical models based on this understanding need to be revised.
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Materials Science
Fractional Spin Ferroelectric and Sliding Spin Current in Magnetic Sliding Ferroelectrics
Yilin Han, Lei Li, Chaoxi Cui et al. (+3 more)
We investigate the fractional
spin ferroelectric (FSFE) in
magnetic sliding ferroelectrics (SFEs), where ferroelectric switching is characterized not only by the reversal of the out-of-plane electric polarization but also by a variation of fractional in-plane
spin electronic polarization. We show that interlayer sliding in FSFEs can naturally lead to a
symmetry-protected pure
spin current, termed the sliding
spin current here. The underlying mechanism is that, during switching, the contributions of valence electrons and ions to the in-plane charge transfer cancel each other, whereas the in-plane
spin transfer, which stems solely from valence electrons, persists, leading to a pure
spin current. We demonstrate our ideas in various material candidates, including $H$-stacked
bilayer CrI$_3$, whose few-layer form has been experimentally confirmed to be a
magnetic SFE, and $R$-stacked
bilayers $2H$-V$X_2$ ($X=$ S, Se, Te), which have been experimentally synthesised. For a typical switching time of about $1$ ns, the estimated
spin-current densities for
bilayer CrI$_3$ and V$X_2$ reach $10^9 (\hbar/2e)\mathrm{A/m^2}$ and $10^8 (\hbar/2e)\mathrm{A/m^2}$, respectively. This means that by applying a periodic out-of-plane electric field, a significant alternating
spin current can be generated in
magnetic SFEs. Thus, our findings propose a compelling new mechanism for the all-electrical generation of pure
spin current, and predict concrete realistic materials for experimental verification.
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All authors Yilin Han, Lei Li, Chaoxi Cui, Run-Wu Zhang, Zhi-Ming Yu, Yugui Yao
Statistical Mechanics · Cross-listed from hep-th
Critical dynamics of a scalar field near four spatial dimensions
Laura Batini and Eduardo Grossi
The critical dynamics of a non-conserved order parameter is generally expected to become overdamped at long distances, even when propagating modes occur at microscopic or intermediate scales. We investigate the critical dynamics of a scalar field theory in thermal
equilibrium which, in addition to local friction and noise, also contains a time-dependent second-order kinetic term. We show how to build a supersymmetric field-theory formulation. Using a two-loop expansion about four spatial dimensions, we show that the propagating and strictly overdamped limits share the same static Gaussian and Wilson-Fisher fixed points but realize distinct dynamical scaling regimes. The overdamped limit reproduces Model A. On the surface where local friction and noise vanish, the theory instead supports an interacting propagating fixed point whose dynamic exponent receives corrections at two loops. We demonstrate that coarse-graining does not generate a local dissipative operator on this surface, which therefore remains invariant under the RG flow. Local dissipation is nevertheless relevant at the propagating fixed point: an arbitrarily small
equilibrium friction-noise perturbation drives the flow away from propagating scaling. Propagating critical dynamics thus defines a consistent but fine-tuned regime that is unstable to local
equilibrium dissipation.
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Materials Science
Homojunction-induced thermopower enhancement in polymer films
Zhen Xu, Hui Li, Guangzheng Zuo et al. (+7 more)
It has been more than twenty years since conductive
polymers began to receive
attention as an emerging thermoelectric material. However, the trade-off between electrical conductivity ({\sigma}) and thermopower (S) has proven to be a major challenge that has obstructed their use in actual devices. Here we report the discovery that the thermopower of the p- and n-type legs of organic thermogenerators can be substantially enhanced, without significant deterioration of {\sigma}, by constructing an in-plane segmented structure consisting of a homojunction with different doping levels on either side. In such segmented layers, the S is abnormally higher than the average value of the constituent parts when applying a forward temperature gradient (heating the heavily doped counterpart), while it is lower upon a reverse temperature gradient. Typically, for a two-stage segmented film of p-type PDPP-Se, an abnormally large S of 210 uV K-1 and {\sigma} of 2.5*10^4 S m-1 are obtained, resulting in a large power factor (PF) of 1100 uW m-1 K-2 and a record ZT of 1.36 at room temperature. The enhanced thermopower is attributed to an additional voltage developed at the homojunction under heating as explained by kinetic Monte Carlo simulations. This finding provides a breakthrough approach to the modulation of thermoelectric transport properties of conductive
polymers.
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All authors Zhen Xu, Hui Li, Guangzheng Zuo, Xiaojuan Dai, Jincheng Liao, Guofeng Cheng, Jian Song, Wenqing Zhang, Martijn Kemerink, Lidong Chen
Quantum Gases
Crossing over universal scaling laws in two-dimensional driven dissipative condensates
Q. Fontaine, F. Helluin, M. Escalera et al. (+8 more)
In low dimensional systems, fluctuations are enhanced and prevent the spontaneous breaking of continuous
symmetries. As a result, spatial and temporal correlation functions decay at large distances and long times. A well established example is given by two-dimensional bosonic condensates at
equilibrium, which do not display long-range order of the coherence but algebraic decay belonging to the Berezinski-Kosterlitz-Thouless universality class. In contrast, the universal behaviors of non-
equilibrium bosonic condensates are more diverse and many open questions remain. Here, we explore the spatio-temporal coherence properties of two-dimensional driven-dissipative polariton condensates in
semiconductor optical microcavities. By tuning microscopic parameters, we observe a cross-over between two scaling laws that we attribute to the Edwards-Wilkinson (EW) and the Kardar-Parisi-Zhang (KPZ) universality classes. We demonstrate the collapse of the measured first-order correlations onto the EW and KPZ universal scaling functions and obtain critical exponents, well matching the values predicted theoretically. Our results highlight the intrinsic non-
equilibrium nature of polariton condensates and establish them as a platform of choice for controlled exploration of the two-dimensional KPZ universality class.
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All authors Q. Fontaine, F. Helluin, M. Escalera, D. Pinto Dias, A. Lemaître, M. Morassi, M. Wouters, A. Minguzzi, L. Canet, S. Ravets, J. Bloch
Superconductivity
Emergent magnetic pseudogap from phase fluctuations and hierarchy of scales in two-dimensional superconductors
Xu-Cheng Wang and Yang Qi
Preformed pairs and phase fluctuations are believed to play a vital role in predicting the charge pseudogap in the normal state of two-dimensional
superconductors. In this work, we extend this idea and further identify the emergent
magnetic pseudogap from pure phase fluctuations without invoking any competing order. We examine the NMR relaxation rate $1/T_1T$ by evaluating the bubble contribution and leading-order vertex correction within perturbation theory. It is found that the
magnetic pseudogap, manifesting as a smooth suppression of $1/T_1T$ in the normal state, is characterized by a temperature scale $T_\text{mPG}$ distinct from the superconducting gap $\Delta_\text{SC}$ and transition temperature $T_c$. The onset scales of both charge and
magnetic pseudogap are dominated by the competition of BKT correlation length $\xi(T)$ and BCS coherence length $\xi_\text{BCS}$. Moreover, the vertex correction is shown to be irrelevant for $d$-wave pairing, while it becomes prominent in $s$-wave systems and drives a coherent enhancement of $1/T_1T$ at lower temperatures just above $T_c$. We attribute this normal-state enhancement of $1/T_1T$ to the diverging coherence peak at the $s$-wave superconducting gap edge, which shares the same spirit as the celebrated Hebel-Slichter peak in the BCS theory. Analogous to the coherent Hebel-Slichter peak, regularization by
Fermi-
liquid-like scatterings is important and is characterized by a scattering length $\ell$. The normal-state coherent enhancement of $1/T_1T$ is hence described by the competition of $\xi(T)$ and $\ell$, through which the coherence scale $T_\text{coh}$ is determined. As a result, the complete
evolution of $1/T_1T$ is understood quantitatively in a unified picture as the interplay among hierarchy of scales $\xi(T)$, $\xi_\text{BCS}$ and $\ell$.
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Mesoscale and Nanoscale Physics
Perfect absorption by metal-contacted two-dimensional systems with ultra-proximate reflectors
Kirill Kapralov, Vladislav Atlasov, Alina Khisameeva et al. (+2 more)
Electromagnetic absorbance by most two-dimensional electron systems is typically well below unity, which hinders both practical applications in photodetection and fundamental studies of their optical properties. Here, we show that a periodic structure comprised of narrow two-dimensional sections connected with wide perfectly conducting metal sections enables large absorbance. It reaches 50 % provided the filling factor by the two-dimensional system $f$ equals its dimensionless conductivity $\eta=\sigma Z_0/2$, where $Z_0$ is the free-space impedance. The absorbance is further raised to 100 % if the periodic structure is placed above a perfectly conducting electromagnetic reflector, and provided $f=2\eta$. Surprisingly, the optimal distance between two-dimensional system and reflector may fall well below the quarter of incident wavelength $\lambda_0/4$, which was assumed as conventional absorption enhancement condition in optics. For low filling factors $f\ll1$, large dielectric constants of the substrate, and grating periods comparable with $\lambda_0$, the optimal distance to reflector tends to zero. Above the critical values of the grating geometrical parameters, the absorbance maximum ceases to exist. The critical behavior manifests as a large-amplitude resonance in 'dirty' two-dimensional system with purely real conductivity, while enhancement of carrier momentum relaxation time lowers the resonant peak. Such resonance mimics the plasmonic one, but does not rely on high electron mobility.
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All authors Kirill Kapralov, Vladislav Atlasov, Alina Khisameeva, Viacheslav Muravev, Dmitry Svintsov
Quantum Gases
Observation of far-from-equilibrium scaling in the transient dynamics of 2D quantum magnets
Fabio Bensch, Umberto Borla, Federico Balducci et al. (+7 more)
The transient regime of far-from-
equilibrium quantum many-body dynamics lacks the established organizing principles that universality and scaling provide in
equilibrium. It is least understood for two-dimensional short-range interacting systems, where mean-field arguments are not expected to hold, controlled theoretical descriptions are few, and fluctuations are strong. Here we investigate the quench dynamics of the transverse-field Ising model using programmable Rydberg-atom arrays realizing honeycomb, square, kagome, and triangular
lattices. Starting from a fully magnetized state, we observe a pronounced softening of the dominant collective magnetization oscillation accompanied by a maximum in the damping rate, signaling a crossover between interaction- and field-dominated transient dynamics. Even though the microscopic
lattice geometries are different, both the oscillation frequencies and the damping rates collapse onto common curves after being rescaled by the coordination-number-weighted interaction strength. Our findings show that a mean-field description effectively reproduces the magnetization oscillations. The importance of correlated
quantum fluctuations is underlined by the failure of the discrete truncated Wigner approximation to predict the damping for strong interactions, while tree-tensor-network simulations reproduce the dynamics accurately. These results reveal a robust scaling regime governing the transient dynamics of short-range interacting two-dimensional
quantum magnets. They reveal that the dominant transient dynamics is governed by a simple collective description despite the presence of strong
quantum fluctuations — an important insight in the quest to uncover organizing principles in far-from-
equilibrium quantum matter.
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All authors Fabio Bensch, Umberto Borla, Federico Balducci, Philip Osterholz, Shuanghong Tang, Silpa Baburaj Sheela, Anushya Chandran, Roderich Moessner, Jad C. Halimeh, Christian Groß
Statistical Mechanics
Distribution of the Radius of Gyration for an ISAW
Antony Lesage, Vincent Dahirel, Jean-Marc Victor et al. (+1 more)
We aim at calculating an explicit expression for the finite-size probability distribution of the radius of gyration $R$ of an Interacting Self-Avoiding Walk (ISAW), as a function of chain length $N$ and monomer-monomer interaction energy $\varepsilon$. We first derive the explicit free energy expression for a non-interacting Self-Avoiding Walk, introducing a new natural scale variable $t = \rho^g$ expressed as a power of the density $\rho$. Then, thanks to a cumulant expansion approach introduced by Lhuillier, Victor and coworkers, we extend it to the interacting case, capturing both the coil-globule transition and finite-size corrections to scaling, including entropic and surface-energy contributions. The radius of gyration distribution determined by the new free energy expression is then compared, using
Bayesian inference to estimate the model parameters, to results from extensive Monte Carlo simulations of three-dimensional ISAWs, showing excellent agreement except very close to the $\Theta$-point, where finite chain lengths limit the accessible scaling regime. This validates our resulting free energy expression and allows us, as an application, to construct a phase diagram of the coil-globule transition.
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All authors Antony Lesage, Vincent Dahirel, Jean-Marc Victor, Maria Barbi
Statistical Mechanics
Statistical stability of random potentials to thermal and quantum activation
Luis Filsinger and Roland Willa
In numerous physical, chemical, and biological systems the dynamics can be reduced to the motion of state variables in a complex potential landscape. In case the
manifold is known, the motion and response of the embedded object can be described deterministically up to
stochastic effects usually associated with a noise. In contrast, if the
manifold is unknown, the static and dynamic response of the state variable may be used as a spectroscopic tool to characterize the potential landscape. Inspired by a seminal work of L.\ Embon and co-workers, [Sci.\ Rep.\ 5, 7598 (2015)] we investigate the statistical properties of potential minima, in particular, their stability to thermal and
quantum activation. For Gaussian random
manifolds, we derive an algebraic expression to evaluate the statistical probability of the potential character (value, slope,
curvature, ...). With this tool, we compute the expectation value for the rate of thermal and
quantum activation and link these findings to the principal characteristics of the Gaussian potential, i.e., its Green's function. This link provides the opportunity to access information on the potential's Green's function by studying the activation behavior of an object in this
manifold.
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Statistical Mechanics · Cross-listed from gr-qc
Anomaly quenching and dynamical cooling of Hawking evaporation in Horndeski gravity
Amogh Srivastav and S. Shankaranarayanan
We investigate the semiclassical Hawking evaporation of a two-dimensional Callan-Giddings-Harvey-Strominger (CGHS) black hole perturbed by first-order Horndeski scalar-tensor couplings. By evaluating the exact scalar
curvature invariants, we demonstrate that coordinate singularities near the apparent horizon parametrize a physical deformation of the surface
gravity while preserving a strictly regular event horizon. In the linear-order $\gamma_3 \Phi X$ coupling sector, the surface
gravity and correspondingly the Hawking temperature decreases dynamically as the black hole loses mass. Extrapolating this cooling effect via a resummed temperature equation suggests that evaporation halts, potentially leaving behind a stable, macroscopic cold remnant at the boundary of perturbative control. Utilizing both the conformal trace anomaly and the Robinson-Wilczek gravitational anomaly, we establish that the asymptotic radiation flux identically reflects this
geometric shift. Consequently, the fine-grained
entanglement entropy of the Hawking radiation departs from linear growth and transitions to an asymptotic logarithmic regime. This indicates that
quantum information may be permanently retained within the remnant, altering the standard semiclassical Page curve without requiring a breakdown of horizon regularity.
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Materials Science · Cross-listed from quant-ph
Exploring the Relaxation Landscape of a 2D Quantum Magnet on a 256-Qubit Processor
Tiago Mendes-Santos, Joseph Vovrosh, Sergi Julià-Farré et al. (+33 more)
How
quantum matter relaxes far from
equilibrium is a central open problem in many-body physics, and one for which analog
quantum simulators are well positioned to move from confirming theory to discovering new physics. Here, we use a two-dimensional Rydberg atom array of 256
qubits to map the relaxation landscape of the two-dimensional transverse-field Ising model across its phase diagram. Beyond the expected rapid thermalization, we identify two further regimes. The first is a prethermal regime whose dynamics are governed by an effective XY model. The second, and most unexpected, is a crossover regime characterized by a slowdown in relaxation. This slowdown occurs precisely where state-of-the-art classical tensor-network methods lose control at late times, whereas the
quantum simulation remains consistent across system sizes. These results establish Rydberg atom arrays as a platform for scientific discovery in nonequilibrium
quantum many-body dynamics.
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All authors Tiago Mendes-Santos, Joseph Vovrosh, Sergi Julià-Farré, Dorian Claveau, Guillaume Villaret, Lucas Béguin, Lucas Leclerc, Laurin Brunner, Wladislaw Krinitsin, Matthias Hecker, Fergus Hayes, Boris Albrecht, Lilian Bourachot, Clémence Briosne-Frejaville, Antoine Cornillot, Julius de Hond, Djibril Diallo, Clément Dupays, Robin Dupont, Thomas Eritzpokhoff, Loïc Henriet, Lucas Lassablière, Arvid Lindberg, Yohann Machu, Hadriel Mamann, Thomas Pansiot, Julien Ripoll, Bruno Ximenez, Henrique Silvério, Joseph Tindall, Markus Schmitt, Markus Heyl, Adrien Signoles, Constantin Dalyac, Antoine Browaeys, Alexandre Dauphin
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Transient Electrical Response Beyond Quasistatic Capacitance at Mechanically Excited Droplet–Dielectric Interfaces
Pramodt Srinivasula, Rameez Raja Khan, Diwakar Singh et al. (+1 more)
Dynamic electrowetting of conducting droplets under mechanical deformation is conventionally modeled as a quasi-static variable-capacitance system, in which the electrical response is assumed to be governed solely by the
evolution of the droplet–electrode contact area. Under the assumption of instantaneous charge equilibration, this framework successfully describes the cyclic steady-state electromechanical response of the system. However, its validity for transient interfacial electrical dynamics remains largely unexplored. Here, the transient electrowetting response of mercury droplets confined between a polymeric dielectric-coated electrode (PTFE or PVDF) and an opposing copper electrode is investigated under periodic mechanical excitation with multiple waveforms at 2 Hz. The measured contact area and corresponding capacitance evolve closely as predicted from instantaneous surface-energy minimization, confirming that the
liquid-interface mechanics remain quasi-static. In contrast, the measured transient current and instantaneous electrical power exhibit pronounced asymmetric excitation and relaxation phases that are independent of the excitation waveform, demonstrating that transient charge
evolution cannot be inferred from the instantaneous
geometric capacitance alone. This transient behavior is phenomenologically interpreted using constituent first-order interfacial dielectric charge-relaxation kinetics, indicating that the measured current arises from slow dielectric charging followed by dielectric relaxation over the timescale of the imposed periodic mechanical oscillations during discharging. These findings establish that transient electrowetting is governed by the coupled interplay of droplet electrohydrodynamics and dielectric interfacial polarization, requiring a constitutive description beyond quasi-static variable-capacitance models based solely on contact-line dynamics.
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All authors Pramodt Srinivasula, Rameez Raja Khan, Diwakar Singh, Gaurav Bhutani
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Many-Body Localization Induced by Correlated Disorder in Interacting Superconducting Qubits
Thiago R. Girão Souza, Andreia Saguia, Alan C. Santos et al. (+1 more)
The failure of
quantum thermalization due to Many-Body Localization (MBL) has evolved from a theoretical concept in
spin chains to an experimental reality in synthetic
quantum platforms, most notably superconducting
circuits based on transmon
qubits. Despite its significance, the MBL transition has been studied primarily under purely random disorder and local couplings, leaving more complex and realistic configurations largely unexplored. Here, we investigate the
quantum dynamics of transmon networks subject to the unavoidable competing effects of correlated disorder and network-mediated non-local interactions. First, we show how to engineer the physical parameters of the
quantum hardware to systematically control the correlated disorder patterns emerging in the system. Then, we demonstrate that the MBL phase transition is robust against such correlations, which is essential for tuning localization properties in realistic transmon devices. This robustness is established through the analysis of the block
entanglement entropy variance across disorder realizations, which precisely locates the MBL critical point. Independently, we introduce a local
memory parameter, whose dynamics at long
evolution times reveals
memory retention in the localized phase and yields a critical point consistent with the
entropy analysis. These results provide a framework for understanding localization in complex
quantum network
topologies, with potential implications for multi-
qubit processor design.
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All authors Thiago R. Girão Souza, Andreia Saguia, Alan C. Santos, Marcelo S. Sarandy
Materials Science
Morphology Engineering of Mixed Ionic Electronic Conductors through Aqueous Phase Separation
Siqi Wang, Maria Restrepo, John Linkhorst et al. (+1 more)
The performance of organic electrochemical transistors (OECTs) is fundamentally governed by the interplay between ionic accessibility and electronic transport within organic mixed ionic-electronic conductors. Although increasing channel thickness enhances transconductance, it also prolongs ion transport, resulting in the well-known gain-speed trade-off. Here, we demonstrate that engineering the internal morphology of PEDOT:PSS:PEI films through pH-induced aqueous phase separation provides an effective route to mitigate this limitation. The resulting interconnected pore network promotes electrolyte penetration and increases the electrochemically addressable volume, while DMSO treatment and annealing enhance the continuity and ordering of the PEDOT-rich electronic phase. Consequently, porous OECT channels achieve a transconductance of 30 mS and a response time of 13 ms at an ultralow gate voltage of 0.05 V despite channel thicknesses exceeding 100 um. Comparison of films with comparable electronic conductivity but different pore architectures identifies morphology as the dominant factor governing device performance, supporting a transition from predominantly surface-limited modulation toward spatially distributed mixed ionic-electronic transport. Beyond demonstrating a scalable water-based fabrication strategy, this work establishes internal morphology as a design parameter that complements molecular structure and device geometry in organic mixed conductors, providing a general framework for the development of high-performance OECTs, soft bioelectronics, and future neuromorphic materials.
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All authors Siqi Wang, Maria Restrepo, John Linkhorst, Matthias Wessling
Materials Science · Cross-listed from quant-ph
Niobium Titanium Nitride as a High Tensile Stress Material for Nanomechanics
Korbinian Rubenbauer, Burak E. Bülbüloglu, Thomas Luschmann et al. (+6 more)
Over the past decades, high-coherence mechanical resonators have been continuously pushed to new limits, using techniques such as dissipation dilution and clamp-tapering to enhance their quality factor beyond intrinsic material limitations. Today, these mechanical resonators are often fabricated from silicon-nitride, silicon-carbide or aluminum. Recently, however, interest in novel material platforms has grown, especially those allowing for the integration within superconducting
circuits. Among these, superconducting nitrides stand out as particularly promising due to their high transition temperatures compared to elementary
superconductors. Here, we introduce them as nanomechanical resonators and report on the fabrication and characterization of highly stressed, doubly clamped niobium titanium nitride (NbTiN) nanostring resonators. Using optical interferometry, we determine the elastic properties and mechanical quality factor from room temperature to 13 K. We observe high tensile stress up to 0.81 GPa along with a Young's modulus of 181 GPa and an intrinsic mechanical quality factor up to 850. With these favorable mechanical properties, NbTiN constitutes a promising material platform for future applications in cavity electro- and nanomechanics.
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All authors Korbinian Rubenbauer, Burak E. Bülbüloglu, Thomas Luschmann, Manuel Müller, Stephan Geprägs, Witlef Wieczorek, Eva M. Weig, Matthias Althammer, Hans Huebl
Statistical Mechanics · Cross-listed from nlin.CD
Learning a quantitative criterion for distinguishing chaos from noise
Jaesung Choi, Athokpam Langlen Chanu and Jong-Min Park
Distinguishing chaos from noise using time-series data is fundamentally challenging because both exhibit irregular fluctuations and share many statistical and dynamical characteristics. Existing methods face two key limitations: temporally correlated noise can yield spurious signatures of chaos, and analyses of scalar time series often require explicit choices of
embedding parameters. Here, we propose a purely data-driven method for distinguishing chaos and noise based on a reservoir-computing framework with a cross-prediction scheme. In the proposed approach, the model is trained to predict the future change of a variable from its current value, thereby combining a short-term predictability test with a test of the smoothness of deterministic flows. The recurrent structure of reservoir computing enables effective prediction of high-dimensional chaotic dynamics even from scalar time series without explicit delay-coordinate reconstruction, while the cross-prediction framework strongly suppresses spurious predictive correlations arising from noise. We apply the proposed method to diverse synthetic and empirical time series. Chaotic systems consistently yield strong correlations between the true and predicted future changes, whereas noise processes remain clearly separated in a low-correlation regime. The method also exhibits substantial robustness to practical limitations in empirical data, including measurement noise, limited data length, and increasing prediction lag. These results demonstrate that the squared Pearson correlation coefficient provides a simple quantitative criterion for distinguishing chaos from noise directly from observed time-series data.
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Superconductivity
Origin of the superconductor-insulator transition in disordered two-dimensional films
Alexander Weitzel, Lea Pfaffinger, Animesh Panda et al. (+8 more)
Theory predicts the
superconductor-to-
insulator transition (SIT) to emerge from the competition between Anderson localization, which tends to localize single-particle wavefunctions, and superconductivity, which establishes long-range correlations in the superconducting order parameter. In two-dimensional (2D) superconducting films, the transition temperature $T_\text{c}$ at which resistance vanishes, $R_\Box(T_\text{BKT}){=}0$, is set by the Berezinskii-Kosterlitz-Thouless (BKT) mechanism and satisfies $T_\text{BKT}< T_{c0}$, where $T_{c0}$ is the mean-field transition temperature. In weakly disordered samples $T_\text{BKT}\lesssim T_{c0}$, whereas increasing disorder drives $T_\text{BKT}\ll T_{c0}$ near the SIT. Whether the finite-temperature transition retains its BKT character throughout this crossover remains an open question. Here, we investigate the
evolution of both sheet resistance $R_\Box(T)$ and superfluid stiffness $J_s(T)$ over a wide range of disorder strength $W$. We establish that even near the SIT, the finite-temperature transition from the superconducting to the resistive state remains of BKT type. However, as disorder approaches the critical value, the zero temperature superfluid phase stiffness, $J_s(0)$, is found to vanish rapidly while $T_{c0}$ remains finite, which we attribute to
quantum phase fluctuations as the drive for the zero-temperature transition. Three decades after its experimental discovery by Haviland, Liu, and Goldman, our measurements clarify the origin of the SIT in 2D films.
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All authors Alexander Weitzel, Lea Pfaffinger, Animesh Panda, Arpan Das, Ilaria Maccari, Simon Reinhardt, Sven Linzen, Evgenii Il'ichev, Nicola Paradiso, Ferdinand Evers, Christoph Strunk
Mesoscale and Nanoscale Physics
Topological surface altermagnets in SSH-stacked magnetic layers
Rui Chen, Bin Zhou and Dong-Hui Xu
Surface altermagnetism opens new avenues in spintronics by unlocking altermagnetic
spin-splitting at the boundaries of conventional antiferromagnets, bypassing the strict
symmetry requirements of bulk altermagnets. In this work, we propose creating topological surface altermagnet by stacking
magnetic layers in a Su-Schrieffer-Heeger pattern. We show that while the bulk of the system is a standard antiferromagnet with degenerate bands protected by $PT$
symmetry, breaking the local
symmetry at the boundary gives rise to a topologically protected surface altermagnetic state residing within the topological gap. Furthermore, we propose that this effect can be experimentally detected by applying a perpendicular electric field. Besides, this approach can be readily generalized to surface altermagnetism of different types. Our work establishes topological boundaries as a natural platform for surface altermagnetism, offering a distinct route for realizing and manipulating topological surface altermagnets.
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Materials Science
Net and Hidden Spin-Valley Locking Enable Ultrahigh Hole Mobility in Covalent Bulk WN$_2$
Rong-Tian Pang, Zhongjuan Han, Jiayi Gong et al. (+3 more)
High carrier mobility at room temperature underpins high-performance electronics, yet high hole mobility remains rare in bulk
semiconductors.
Spin-valley locking can suppress intervalley scattering and enhance mobility, but it is limited to materials with broken inversion
symmetry. Hidden
spin polarization offers a possible route beyond this constraint, although whether its compensated
spin textures could protect charge transport remains unclear. Using ab initio electron-
phonon and transport calculations, we show that the two hexagonal phases of bulk WN$_2$ realize net and hidden
spin-valley locking and exhibit ultrahigh room-temperature hole mobilities. In non-centrosymmetric $\alpha$-WN$_2$, a large valley
spin splitting produces net
spin-valley locking that nearly eliminates
phonon-mediated intervalley scattering. In centrosymmetric $\beta$-WN$_2$, hidden Zeeman-type
spin polarization yields a compensated, sector-resolved
spin texture that reverses between valleys and suppresses intervalley scattering as effectively as the net locking does. The stiff W-N/N-N covalent network further keeps the remaining intravalley scattering weak. Our results establish hidden
spin polarization as an effective transport-protection mechanism and extend
spin-valley engineering to centrosymmetric bulk
semiconductors.
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All authors Rong-Tian Pang, Zhongjuan Han, Jiayi Gong, Jiangang He, Jin-Jian Zhou, Yugui Yao
Disordered Systems and Neural Networks
Many-Body Mobility Edge and Non-Hermitian Skin Effect in an Interacting Quasi-Periodic Spin Chain
Lavoisier Wah, Ayan Banerjee and Flore K. Kunst
Non-Hermitian many-body physics reveals a rich interplay between
topology, localization, and boundary effects, yet their collective behavior in interacting disordered systems remains largely unexplored. In this work, we study an interacting non-Hermitian
spin chain subject to a quasi-periodic longitudinal field, providing a unified and controlled setting, where non-Hermitian dynamics, interactions, and localization mechanisms intertwine. Remarkably, we discover a "D-shaped" many-body mobility edge that separates extended and localized eigenstates, while simultaneously delineating regimes of many-body localization and the many-body skin effect (where many-body eigenstates acquire an anomalous drift towards a boundary under open boundaries) emerging from the combined action of interactions, non-Hermiticity, and driving amplitude. We demonstrate that the skin effect induces multifractal scaling in the non-Hermitian eigenstates, providing a clear signature of the many-body skin effect. Employing diagnostics such as the fractal dimension, complex
eigenvalue fractions, and many-body inverse participation ratios, we map out a unified phase diagram in which all measures consistently identify the "D-shaped" mobility edge. Finally, we probe this interplay using both complex level-spacing statistics and dynamical observables such as density imbalance,
entanglement growth, and wave-packet
evolution, culminating in a rich many-body mobility phase diagram that captures both the many-body skin effect and localization transitions. Our results identify a clear, defining signature of the "D-shaped" many-body mobility edge, and underscore its pivotal role in shaping the physics of open
quantum many-body systems.
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Materials Science
Local lattice dynamics of hcp zinc from EXAFS and machine-learning interatomic potentials
Vitalijs Dimitrijevs, Pjotrs Žguns, Inga Pudza et al. (+2 more)
The
lattice dynamics of hexagonal close-packed (hcp) zinc, a prototypical anisotropic metal, is studied using temperature-dependent Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy combined with atomistic simulations. The reverse Monte Carlo method enable the extraction of mean-square relative displacements (MSRDs) for eight coordination shells, providing a shell-resolved description of thermal motion. The MSRD temperature dependence, analysed using the correlated Einstein model, yields effective interatomic force constants and reveals pronounced anisotropy between in-plane and out-of-plane interactions. This anisotropy is further quantified by the ratio of MSRDs for the first and second coordination shells, which closely matches the anisotropic displacement parameters from diffraction experiments. Molecular dynamics simulations using the CHGNet universal machine-learning interatomic potential show that the original model overestimates thermal disorder, while a fine-tuned version substantially improves agreement with experimental EXAFS spectrum and radial distribution function. Overall, EXAFS-informed analysis is effective for validating and refining machine-learning interatomic potentials.
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All authors Vitalijs Dimitrijevs, Pjotrs Žguns, Inga Pudza, Aleksandr Kalinko, Alexei Kuzmin
Materials Science · Cross-listed from math-ph
Effective mass density for wave propagation in periodic layered media in the elasto-acoustic transition
Gabriel Núñez, William J. Parnell and Raphaël C. Assier
This article investigates the effective mass density for acoustic and elastic wave propagation in layered media, with emphasis on its transition between these regimes. Conventionally, it is possible to recover the governing equations of acoustics from those of elasticity via the no-shear limit. However, when considering an effective medium, the anisotropic effective mass density typically obtained for acoustics differs from the isotropic one found in elasticity. Furthermore, direct investigation of this limit is hindered by the fact that the effective mass density is independent of the shear modulus $\mu$. To tackle this problem, a transfer
matrix approach is combined with Bloch's
theorem to derive the effective wavenumber for a periodic material whose unit
cell consists of two layers with different densities. The effective mass density is obtained analytically from the wavenumber, allowing for its evaluation in both regimes. Moreover, for the first time, a description of the transition from isotropic elastic to anisotropic acoustic effective density in a periodic layered medium is provided. Additionally, the existence of band structure in $\mu$-space is demonstrated, along with exceptional points, where compressional and shear modes coalesce and waves become evanescent, which heavily affects the behaviour of the effective density in the elasto-acoustic transition.
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Soft Condensed Matter
Active Brownian motion in a single-relaxation viscoelastic fluid
Sanatan Halder and Manas Khan
Active Brownian particles (ABPs) in viscoelastic (VE) media exhibit fascinating dynamical phenomena set by self-propulsion, thermal fluctuations, and fluid viscoelasticity. We extend our model, in which the Brownian dynamics within a slowly diffusing harmonic well emulates that in a single-relaxation VE fluid, to study active Brownian motion in such media. Consequently, the resultant dynamics is governed by the interplay of the characteristic timescales of the systems: the crossover and equilibration times of the VE fluid, $\tau_k$ and $\lambda$, respectively, and the persistence time of the ABP, $\tau_{\mathrm{R}}$. Following analytical predictions and simulations, we study two practically relevant regimes where the dynamics is dominated by the persistence of active motion and the elastic confinement of the VE fluid, with a phoretically active Pt-coated Janus colloid in a dynamic optical trap, and show quantitative agreement with the simulations. This approach provides a VE environment with tunable VE properties that remain unaffected by the strength of self-propulsion, allowing us to systematically investigate active Brownian motion in VE media in ways that are not otherwise possible with physical VE fluids.
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Mesoscale and Nanoscale Physics
Magneto-optical signal from $\mathrm{Co_2Mn}$-based Heusler thin films in MOKE and BLS
Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher et al. (+3 more)
$\mathrm{Co_2Mn}$-based Heusler compounds offer a versatile, composition-tunable platform for magnonics and spintronics. Among them, the half-metallic $\mathrm{Co_2MnSi}$ is of particular interest for magnonics owing to its ultralow Gilbert damping, yet its weak magneto-optical response in the visible challenges optical probing such as Brillouin light scattering (BLS). We study the magneto-optical response of epitaxial $\mathrm{Co_2Mn}X$ films ($X = \{\mathrm{Al}_x\mathrm{Si}_{1-x}, \mathrm{Ga}_x\mathrm{Ge}_{1-x}, \mathrm{Sn}\}$) by magneto-optical Kerr effect (MOKE) spectroscopy and BLS. Angle-resolved MOKE resolves a significant, wavelength-dependent quadratic MOKE (QMOKE) only for $\mathrm{Co_2MnSi}$, whereas $\mathrm{Co_2MnAl}$, $\mathrm{Co_2MnGa}$ and $\mathrm{Co_2MnSn}$ respond dominantly linearly. Comparing BLS intensities of thermal
magnons at two wavelengths, $\mathrm{Co_2MnSi}$ gives the weakest signal at 532 nm yet among the strongest at 457 nm, tracking the spectral dependence of its Kerr angle. These results emphasise the relation between the two magneto-optical techniques, guiding the choice of probing wavelength for $\mathrm{Co_2Mn}$-based Heusler compounds.
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All authors Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher, Sébastien Petit-Watelot, Stéphane Andrieu, Philipp Pirro
Mesoscale and Nanoscale Physics
Out-of-equilibrium spin-valley dynamics of ferromagnets in topological Chern bands
J. James, I. Krastilevskiy, F. Pichler et al. (+8 more)
Understanding
quantum matter far from
equilibrium is a central goal of modern physics. Twisted MoTe2
bilayers constitute a promising platform for exploring this frontier by combining strong Coulomb interactions, nontrivial band geometry, and optical control. Here, we exploit this setting to investigate the role of
topology and many-body correlations in the out-of-
equilibrium dynamics of ferromagnets in Chern bands. Using a focused circularly polarized light pulse, we create a local
magnetic domain oriented opposite to an external
magnetic field and directly image its subsequent
spin-valley relaxation in spatially and time-resolved low-temperature experiments. We demonstrate that in the vicinity of both integer and fractional Chern insulating states, the dynamics is governed by qualitatively different mechanisms than in
ferromagnetic metals. Whereas metallic domains collapse by shrinking, Chern domains melt via thermal activation, resulting in drastically different temporal
spin evolution and orders-of-magnitude longer relaxation times. These findings demonstrate the influence of
topology and strong correlations on far-from-
equilibrium collective
spin phases, opening new opportunities for dynamical control of ferromagnets in the
quantum Hall regime.
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All authors J. James, I. Krastilevskiy, F. Pichler, L. Wang, A. Iafarova, F. Menzel, K. Watanabe, T. Taniguchi, C. Kuhlenkamp, M. Knap, T. Smoleński
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Multimode phonon-mediated enhancement of entanglement and competing synchronization in cavity magnomechanics
Z.Imara, Jia-Xin Peng, E.K. Berinyuy et al. (+2 more)
The generation of
quantum correlations in hybrid
quantum systems remains a central challenge due to the intrinsic limitations of linear interactions. In cavity magnomechanical platforms, the cavity-
magnon coupling gives rise to hybridized cavity-
magnon polaritons (CMPs). However, as a beam-splitter-type interaction, it does not by itself generate
entanglement between the polariton modes in the absence of additional nonlinear or parametric processes. Here, we propose a mechanism based on multimode
phonon mediation, in which multiple vibrational modes act as parallel scattering channels that couple the polaritons through Stokes and anti-Stokes processes. We show that , in the parameter regime explored here, the presence of multiple
phonon modes leads to a monotonic enhancement of steady-state
entanglement, thereby going beyond the limitations of conventional single-mode schemes. Furthermore, we demonstrate that
quantum synchronization between the polariton modes originates from the same underlying scattering processes responsible for
entanglement generation, yet exhibits an opposite scaling behavior with increasing
phonon number for the phase quadrature, while the amplitude synchronization reveals collective squeezing that grows with the number of
phonon channels. Our results provide new insights into the role of multimode interactions in shaping
quantum correlations and establish a viable pathway for controlling
entanglement and collective dynamics in hybrid magnomechanical platforms.
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All authors Z.Imara, Jia-Xin Peng, E.K. Berinyuy, S.K. Singh, A. El Allati
Strongly Correlated Electrons
Local magnetic properties of the rare-earth intermetallics $R$Mn$_2$Ge$_2$ ($R$=Ce, Pr, Nd)
N. P. Bentley, T. L. Breeze, A. Hernández-Melián et al. (+9 more)
We present an investigation of the rare-earth intermetallic materials, $R$Mn$_2$Ge$_2$ ($R$=Ce, Pr, Nd), reported to host a
lattice of skyrmionic bubbles at room temperature. The magnetism of all three materials is characterised by the onset of local fluctuations as the
magnetic state changes from a conical
magnetic structure to a collinear
antiferromagnetic one as temperature $T$ is increased. In this $T$ regime, where skyrmion-bubble textures have been reported, we see dynamics similar to those observed in other skyrmion-hosting materials. The level of disorder above this transition increases across the series from $R$=Ce to Nd. At low temperatures the magnetism is affected by the ordering of the rare-earth ions, resulting in distinct behaviour for the different members of the series.
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All authors N. P. Bentley, T. L. Breeze, A. Hernández-Melián, M. J. Pearce, T. J. Hicken, M. T. F. Telling, B. M. Huddart, G. D. A. Wood, D. A. Mayoh, G. Balakrishnan, S. J. Clark, T. Lancaster
Statistical Mechanics · Cross-listed from quant-ph
Fugacity-Resolved Stabilizer Entropy in Critical Quantum Chains: Discrete Selberg Sums and Exactly Solvable Rényi Indices
Reyhaneh Khasseh and M. A. Rajabpour
Stabilizer Rényi
entropy quantifies the nonstabilizerness of a
quantum state through Rényi moments of its Pauli expectation-value distribution. Its standard form sums over Pauli-string degrees and retains only the total Rényi weight. We introduce a fugacity-resolved partition function for the critical transverse-field Ising chain that resolves this degree in the balanced Majorana representation and generates its full counting statistics. This Ising problem extends beyond a single model: exact decimation identities and the correspondence with the half-filled \(XX\) chain establish it as a common finite-size building block for stabilizer and computational-basis Shannon–Rényi
entropies. We map the fugacity-resolved all-minors sum, for every positive Rényi index, to a checkerboard-weighted discrete Selberg ensemble on a half-filled doubled root
lattice. For positive integer indices, it reduces to a finite aliased Dyson constant term. At \(\alpha=\tfrac12,1,2\), determinant and Pfaffian compressions yield product formulas. At \(\alpha=4\), the generic-fugacity problem admits an exact inverse Jack–Kostka representation, while at unit fugacity a complementary middle-minor identity relates it to the square of the \(\alpha=2\) result. These generating functions determine the balanced-degree statistics. Complement
symmetry makes the distribution symmetric about \(k=L/2\), with an index-dependent width. It is exactly binomial at \(\alpha=1\), has variance proportional to \(L\) at \(\alpha=\tfrac12\), and develops an \(L\log L\) enhancement at \(\alpha=2\). After variance rescaling, the centered distributions converge to Gaussian limits at all three indices. Beyond these solvable cases, finite-size numerics reveal an
evolution from a central peak to a symmetric bimodal profile and eventually to endpoint dominance as the Rényi index increases.
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