Statistical Mechanics
Uphill transport in competitive drift-diffusion models with volume exclusion
Francesco Casini, Cristian Giardinà, Jacopo Nicolini et al. (+2 more)
This paper addresses uphill transport (defined as a regime in which particle flow is opposite to the prescriptions of Fick's
diffusion) in drift-
diffusion particle transport constrained by volume exclusion. Firstly, we show that the stationary hydrodynamic limit of a multispecies, weakly asymmetric exclusion process (SHDL) naturally predicts precisely characterized uphill regimes in the space of external drivings. Then, with specific reference to systems of oppositely charged particles, we identify well-defined model hypotheses and extensions whereby the SHDL converges to the modified Poisson-Nernst-Planck model, thus bridging the gap between exclusion-based particle models and continuum descriptions commonly used in engineering. The merits and limitations of the models in describing the particle fluxes and predicting uphill transport conditions are investigated in detail with respect to the adopted approximations and simplifications. The results demonstrate the persistence of uphill transport phenomena across modeling scales, clarify the conditions under which they occur, and suggest that uphill transport may play a significant role in nanoscale electrolytes, confined ionic and iontronic devices, and membrane-based technologies.
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All authors Francesco Casini, Cristian Giardinà, Jacopo Nicolini, Luca Selmi, Cecilia Vernia
Disordered Systems and Neural Networks
Percolation and Threshold-like Behavior in Multiple Sclerosis Progression
Nikola Mirkov, Dušan S. Radivojević and Slobodan Maletić
In this study we investigate the Percolation Hypothesis for Multiple Sclerosis Progression. The methodology relies on cross-reference analysis centered around a question: What is the evidence for a Percolation/phase-transition hypothesis in Multiple Sclerosis (MS), especially the idea that the RRMS dynamic balance can abruptly break akin to crossing a percolation threshold into SPMS? We identify theoretical models invoking percolation/critical thresholds, network/connectome studies assessing percolation robustness or threshold-like behavior, clinical markers showing thresholds or early-warning signals, and counter-evidence arguing for gradual/continuum transitions.
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Strongly Correlated Electrons
Orientation-driven route to an intrinsic insulating ferromagnetic state in manganite superlattices
Priyanka Aggarwal, Kirill B. Agapev, Sagar Sarkar et al. (+3 more)
Increasing precision in the growth of superlattices sparks hope in applications that may arise from engineering layered structures. Heterostructuring and functionalization of
magnetic oxides have been very popular due to their versatility and readiness for integration in modern electronics. In this study, we provide yet another example of this phenomenology by predicting that an insulating
ferromagnetic state can be realized in superlattices of LaMnO$_3$ and SrTiO$_3$ oriented along the (111) direction. In strike contrast with respect to other orientations, these properties are not of extrinsic origin but arise from the interplay of structural order, strain and
quantum confinement. The bandgap is shown to be either direct and indirect, depending on the precise composition, which can be explained in terms of the geometrical properties of (111)-oriented
bilayers of LaMnO$_3$. The electronic structure shows narrow bands indicating localized $e_g$ states for all the investigated superlattices. These features and the analysis of the inter-atomic
magnetic coupling suggest that the investigated superlattices behave as a Kugel-Khomskii material, at least for the explored compositions. Our results provide not only a new route to an insulating ferromagnet, but also novel insight into the intricate interplay between
lattice symmetry, Hubbard physics and Hund's coupling to be exploited in next-generation spintronic applications.
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All authors Priyanka Aggarwal, Kirill B. Agapev, Sagar Sarkar, Biplab Sanyal, Igor Di Marco, Fabrizio Cossu
Materials Science
Precipitation induced recrystallisation (PIX) in a Ti-Fe-Mo bcc-superalloy driven by lattice misfit
Neal M. Parkes, Kan Ma, Ben Poole et al. (+2 more)
Beta-Ti bcc-superalloys, comprising an A2 beta-Ti
matrix reinforced by ordered intermetallic B2 beta-
prime-TiFe precipitates, exhibit an unusual recrystallisation that occurs with no externally applied strain (i.e. no thermomechanical processing). Thermal ageing at 750 degrees Celsius for 72 h results in refinement of the grain size from 364 um to 30 um. This grain refinement is driven by discontinuous precipitation of beta-
prime-TiFe lamellae with the beta-Ti
matrix from grain/phase boundaries, which is associated with significant misorientation and increased dislocation density, attributed as precipitation induced recrystallisation (PIX).
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All authors Neal M. Parkes, Kan Ma, Ben Poole, Chris Hardie, Alexander J. Knowles
Soft Condensed Matter
Homing through Reinforcement Learning
Riya Singh, Pratikshya Jena, Anish Kumar et al. (+1 more)
Homing and
navigation are fundamental behaviors in biological systems that enable
agents to reliably reach a target under uncertainty. We present a Reinforcement Learning (RL) framework to model adaptive homing in continuous two-dimensional domain. In this framework, the
agent's state is given by its angular deviation from home, actions correspond to
alignment or
stochastic reorientation, and learning is driven by a radial-distance-based cost that penalizes motion away from the target, where the cost also acts as an effective signal guiding the
agent towards the home. For a single self-propelled
agent moving with constant speed, we find that the mean homing time $\langle T_{\mathrm{home}} \rangle$ exhibits a non-monotonic dependence on the rotational
diffusion strength $D_r$, with an optimal noise level $D_r^\ast$, revealing a subtle interplay between exploration and goal-directed correction. Extending to two
agents with soft repulsion, one
agent consistently reaches home faster than the other, while in multi-
agents system, repulsion ensures separation and the fastest
agent becomes progressively faster as group size increases. Finally, we have compared the homing time obtained from the RL
agent with that of an Active Brownian Particle (ABP) with resetting and a pure ABP (without resetting) under identical conditions. The RL-based
agent consistently achieves shorter homing times with trajectories that are less noisy and more directed than both cases, while the pure ABP typically continues wandering near the target without reliable localization. Our results show that cost-driven learning,
stochastic reorientation, and inter-
agent interactions enable efficient adaptive
navigation, linking individual and collective homing. This RL framework captures key biological features such as feedback-based route learning, randomness to escape unfavorable orientations, and mutual coordination.
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All authors Riya Singh, Pratikshya Jena, Anish Kumar, Shradha Mishra
Materials Science
Hidden in-plane long-range order in an amorphized crystal
Yin Chen, Anthony E. Phillips, Cheng Fu et al. (+12 more)
Solid materials are commonly classified as crystalline or amorphous based on the presence or absence of long-range order.Metal-organic frameworks (MOFs), like other solids,also display markedly different properties and functions in these two phases. Here, we identify a previously unrecognized structural state that retains long-range in-plane translational order while losing order along the stacking direction. Hypothesized since 1941 but not experimentally verified, this intermediate phase emerges in a crystalline MOFs via controlled thermal desolvation, which selectively disrupts the intrinsically weak interlayer interactions while preserving macroscopic structural coherence. Although the resulting material appears amorphous under conventional characterization, systematic synchrotron PXRD, total X-ray scattering, and low-dose high resolution TEM reveal clear in-plane periodicity. This material spontaneously delaminates in water into uniform, high-quality two-dimensional crystalline nanosheets, forming stable colloidal suspensions and exhibiting superlubricity comparable to
graphene - but at less than 0.1% of the production cost. Our discovery finds a missing link within the long-standing crystalline-amorphous dichotomy, while providing an inherently scalable route to high-quality 2D
crystals, and offering a conceptual and practical advance in phase engineering.
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All authors Yin Chen, Anthony E. Phillips, Cheng Fu, Volodymyr Bon, Lei Liu, Xiaoxu Sun, Jiahui Wang, Na Lin, Ruize Xie, Guanqun Cai, Yutong Wang, Jing Ma, Yuhong Liu, Yu Han, Stefan Kaskel
Materials Science
Pressure induced electronic band evolution and observation of superconductivity in the Dirac semimetal ZrTe5
Sanskar Mishra, Nagendra Singh, Vinod K. Gangwar et al. (+8 more)
We report a comprehensive investigation of the pressure effects on the magnetotransport properties of the topological material ZrTe5 within 1 to 8 GPa pressure range. With increasing pressure, the characteristic peak (Tp) in its electrical resistivity first shifts to higher temperature and then moves quickly towards the lower temperature before disappearing eventually at 6 GPa. Beyond 6 GPa, the system exhibits metallic behavior across the entire temperature range, and superconductivity emerges below Tc = 1.8 K at 8 GPa. Based on the systematic magnetotransport measurement under pressure, we demonstrate that the superconductivity occurs following a significant electronic structure modulation possibly due to pressure induced structural changes near 6 GPa, which coincides with dramatic enhancement of the magnetoresistance (MR) reaching up to 1400 percent. Our experimental results are substantiated by density functional theory calculations as the application of pressure drastically alters the density of states near the
Fermi level. Notably, multiple hole pockets emerge at the
Fermi level from 4 GPa onward, and their contributions are further enhanced with increasing pressure. The combined experimental and theoretical investigation reveals a comprehensive
evolution of electronic structure of Dirac semimetal ZrTe5 under pressure and suggest a possible link between the
Fermi surface reconstruction in the pressure range of structural transition and emergence of superconductivity
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All authors Sanskar Mishra, Nagendra Singh, Vinod K. Gangwar, Rajan Walia, Jianping Sun, Genfu Chen, Dilip Bhoi, Sandip Chatterjee, Yoshiya Uwatoko, Jinguang Cheng, Prashant Shahi
Soft Condensed Matter
Coarse grained modeling of self assembled DNA 3D structure using pragmatic soft ellipsoid contact potential
Abhirup Das and Jayashree Saha
In this paper, we employ the soft ellipsoid contact type potential (ECP) in a generic coarse grained model of DNA and study the renaturation process. The interactions between the bases are modeled using our ECP type potential, along with other interactions to capture bending, dihedral and solvent effects implicitly. Structure and helix formation is primarily driven by non-spherical geometry of the bases and excluded volume effects. Simulation results demonstrate that two isolated strands in a random initial configuration undergo spontaneous helix formation during annealing. The model captures the qualitative features of the coil-helix transition as well as the morphology of the helical structure. However, the present parameterization of our model does not yet capture the proper right chirality and detailed helical geometry associated with DNA. Thus, its capability for making any quantitative predictions remains limited. Statistical and physical properties of our model are discussed in detail.
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Materials Science
Coupling between CaWO$_4$ phonons and Er$^{3+}$ dopants
Mikhael T. Sayat, Federico Pisani, Hin Lok Chang et al. (+8 more)
We investigate the
lattice dynamics of CaWO$_4$, a promising host
crystal for erbium-based
quantum memories, using inelastic
neutron scattering together with density-functional perturbation theory. The measured
phonon dispersion along the (100), (001), and (101) reciprocal space direction reveals
phonon bands extending up to 130 meV, with a gap between 60 and 80 meV, in good agreement with our calculations. From a
symmetry analysis of the
phonon eigenmodes, we identify eight Raman-active modes that can couple directly to the Er$^{3+}$
crystal-field operators, including a low-energy $B_g$ mode at 9.1 meV that is expected to play a dominant role in
phonon-assisted
spin-
lattice relaxation. These results provide a microscopic description of the
phonon bath in CaWO$_4$ and establish a basis for engineering phononic environments to mitigate the loss of stored
quantum states and optimize Er-doped CaWO$_4$ for
quantum-
memory applications.
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All authors Mikhael T. Sayat, Federico Pisani, Hin Lok Chang, Yaroslav Zhumagulov, Kirrily C. Rule, Tom Fennell, Jakob Nunnendorf, Chee Kwan Gan, Oleg V. Yazyev, Ping Koy Lam, Jian-Rui Soh
Materials Science
Inverse orbital Hall effect induced terahertz emission enabled by a ferromagnet with quenched orbital moment in Fe/Pt/W trilayers
Chao Zhou, Lei Hao, Shaohua Zhang et al. (+10 more)
The inverse orbital
Hall effect (IOHE) has recently attracted considerable
attention as an emerging mechanism for terahertz (THz) emission based on ultrafast angular-momentum-to-charge conversion. Most experimental studies have focused on materials with strong
spin-orbit coupling or pronounced orbital character, where sizable orbital
Hall responses are expected. Elemental ferromagnets such as Fe are generally regarded as quenched orbital sources and are not expected to exhibit orbital-dominated THz emission. Here, we report a pronounced enhancement of THz emission in Fe/Pt/W trilayer
heterostructures, despite the absence of detectable orbital contributions in the corresponding Fe/Pt and Fe/W
bilayers. Thickness-dependent measurements reveal long-distance signal persistence, systematic delay accumulation, and pronounced pulse broadening with increasing W thickness. These features are inconsistent with diffusive
spin transport and indicate that orbital angular momentum transport in the W layer, converted into charge current via the IOHE, becomes a dominant channel for THz emission in the trilayer configuration. Our results demonstrate that strong IOHE can emerge in
heterostructures incorporating a quenched orbital ferromagnet, providing an effective route to enhance spintronic THz emitters through orbital
Hall physics.
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All authors Chao Zhou, Lei Hao, Shaohua Zhang, Yaxuan Jin, Xianguo Jiang, Ning Yang, Li Zheng, Hao Meng, Chao Lu, Wendeng Huang, Yizheng Wu, Yan Zhou, Jia Xu
Materials Science · Cross-listed from math.CV
Mellin-Space Prony Representability of Linear Viscoelastic Models
Dimiter Prodanov
Linear viscoelastic materials are commonly described by continuous relaxation spectra, yet practical measurements and simulations employ discrete Prony series. In the Laplace frequency domain, the distinction is well understood: rational transfer functions admit finite Prony representations, while fractional models with branch cuts do not. This work provides a complementary and structurally deeper characterization in the Mellin transform domain. We prove that a viscoelastic modulus admits an exact finite Prony series if and only if the arithmetic pole
lattices of its Mellin kernel align with the integer
lattice of the constitutive kernel, and the associated residues satisfy decoupled first-order recurrences along aligned sublattices. Unlike the Laplace-domain rational/non-rational dichotomy, the Mellin criterion reveals the arithmetic geometry underlying finite representability, which requires Diophantine
alignment of infinite pole progressions and the compatibility of their residues. Applying this criterion yields a complete model taxonomy. Classical spring-dashpot networks (Maxwell, standard linear solid) satisfy the
alignment and recurrence conditions. In contrast, fractional models (power-law, Cole-Cole, Havriliak-Negami, Zener) and log-normal spectra violate one or both conditions and require infinite Prony ladders for exact representation. The framework thus shifts the question of finite network realizability from an algebraic condition on rational functions to a
geometric condition on pole
lattices, offering both a theoretical classification and a practical computational test.
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Statistical Mechanics
Preserving Hamiltonian Locality in Real-Space Coarse-Graining via Kernel Projection
Sun Haoyuan
Numerical simulations of critical
lattice systems are fundamentally limited by critical slowing down, as long-range correlations are typically established through slow temporal equilibration. A physically constrained generative framework that replaces temporal relaxation with a spatial projection mechanism for critical systems is proposed. Using the two-dimensional Ising model at criticality as a
benchmark, we introduce an energy-constrained kernel that synthesizes large-scale configurations from compact equilibrated seeds by enforcing
Hamiltonian-level observables. The generated configurations are projected onto the nearest-neighbor energy
manifold, ensuring thermodynamic consistency while retaining universal critical properties. We show that the resulting configurations reproduce scale-invariant
spin correlations, Binder cumulants, and isotropic structure factors for
lattice sizes exceeding 10,000, without iterative Monte Carlo equilibration. While not a strict renormalization group transformation, and motivated by renormalization ideas, the method provides a practical inverse mapping that retains universal features of criticality and enables efficient GPU-parallel generation of ultra-large critical ensembles.
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Materials Science
Giant Magnetocaloric Effect in a High-Spin Shastry-Sutherland Dipolar Magnet
Jianjian Gong, Junsen Wang, Junsen Xiang et al. (+15 more)
The Shastry-Sutherland
lattice is a prototypical frustrated
quantum magnet. It is notable for its exactly solvable dimer-singlet ground state and hosts a wealth of
magnetic phenomena under external fields. Here, this work investigates the high-
spin (S = 7/2) Eu-based magnet Eu2MgSi2O7 (EMSO) using low-temperature magnetothermal measurements and Monte Carlo simulations, revealing a
giant magnetocaloric effect (MCE) in this Shastry-Sutherland compound. The
entropy change peak value is found to be 55.0 J kg-1 K-1 under a field change of B = 0-4 T, approximately 1.5 times larger than the commercial Gd3Ga5O12 (GGG). Adiabatic demagnetization refrigeration achieves a lowest temperature of 151 mK, deeply into the sub-Kelvin regime. Furthermore, a distinctive cooling effect persists below about 1 T, a characteristic absent for conventional
magnetic coolants. A dipolar Shastry-Sutherland model is introduced as a minimal model to describe this system; in particular, the experimentally revealed 1/3 magnetization pseudo-plateau can be ascribed to the presence of dipolar couplings between Eu2+ ions, further stabilized by the thermal fluctuations, explaining the persistent cooling effect. This work establishes EMSO as a novel platform for exploring the dipolar Shastry-Sutherland system and for sub-Kelvin adiabatic demagnetization refrigeration.
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All authors Jianjian Gong, Junsen Wang, Junsen Xiang, Zhaojun Mo, Lei Zhang, Xinyang Liu, Xuetong He, Lu Tian, Zhixing Ye, Huicai Xie, Xucai Kan, Xinqiang Gao, Zhenxing Li, Peijie Sun, Shouguo Wang, Wei Li, Baogen Shen, Jun Shen
Mesoscale and Nanoscale Physics
Observation of e/4 charge at $\nu=1/2$ in GaAs
Tomer Alkalai, Emily Hajigeorgiou, Adbhut Gupta et al. (+9 more)
Even-denominator fractional
quantum Hall states (FQHSs) fall outside the standard Laughlin's and Jain's odd-denominator hierarchy. In this work, we study the FQHS $\nu=1/2$ in the lowest Landau level. The state is confined within a 70 nm-wide GaAs
quantum well, where the electrons exhibit a
bilayer-like charge distribution. Inter-layer interactions stabilize the $\nu=1/2$ FQHS, which is predicted to host quasiparticles with charge e/4 - with either Abelian or non-Abelian topological order. Here, we report on shot-noise measurements of partitioned quasiparticles at $\nu=1/2$, where charge partitioning is generated by a unique etch-defined
quantum point contact. Our measurements were performed on two nominally identical devices, at two independent experimental setups. Analysis of shot noise in the weak-backscattering regime in each device reveals quasiparticles with charge e/4. These observations provide a clear
benchmark for future studies aimed at probing the topological order of the $\nu=1/2$ FQHS and its quasiparticles' exchange statistics.
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All authors Tomer Alkalai, Emily Hajigeorgiou, Adbhut Gupta, Tapas Senapati, Priya Tiwari, Chia-Tse Tai, Siddharth Kumar Singh, Kirk W. Baldwin, Loren N. Pfeiffer, Mansour Shayegan, Mitali Banerjee, Moty Heiblum
Materials Science
Ozonation of Dielectric Fosters Self-Healing Efficiency in Metalized-Film Capacitors: Quantum-Chemical Simulation
Nadezhda A. Andreeva, Cuixia Liu and Vitaly V. Chaban
Metalized-film capacitors (MFCs) employ
polymer organic dielectrics like polypropylene (PP) and polyimide (PI), in which self-healing is seen as a key advantage. However, the performance of self-healing depends on specific chemical mechanisms involved. The formation of semiconductive carbonaceous soot represents a critical failure risk. This study investigates how oxygen atom impregnation through ozonation of the dielectric material tunes the composition and electrical conductivity of breakdown products in the PP and PI systems with aluminum-zinc electrodes. We revealed, at the atomistic level, that oxygen atoms tend to remove a fraction of carbon atoms from the semiconductive soot by oxidizing carbon into carbon monoxide in both
polymers. In PP, oxygen fraction linearly increases gas mass fraction, thereby reducing soot fraction. In PI, the gas/soot ratio effect of oxygen content is less drastic, still clearly positive. The PP soot conductivity decreases uniformly as larger fractions of oxygen atoms are added. In turn, the PI conductivity drops to ~1500 S/m quickly. The PI soot exhibits narrower band gaps compared to that of PP. The oxygen fraction non-monotonically tailors band gaps, which generally increase. To summarize, ozonation enhances MFC reliability by increasing gas species fraction and reducing soot conductivity. We hereby provide numerical molecular-level insights to rationalize self-healing performance enhancement through
polymer ozonation.
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Soft Condensed Matter
Shear-Induced Collective Shape Oscillations in Dense Soft Suspensions
Ioannis Hadjifrangiskou, Rahil N. Valani and Diogo E. P. Pinto
Dense suspensions of deformable particles can exhibit rich nonequilibrium dynamics arising from complex flow-structure coupling. Using a multi-phase field model, we show that steady shear drives an initially disordered, dense, soft suspension into a positionally and orientationally ordered state, within which particles undergo robust self-sustained shape oscillations. These oscillations originate from repeated T1 neighbor exchanges that force the ordered particle
lattice to cyclically traverse different ordered configurations, coupling particle deformation to evolving
lattice topology. By identifying the
lattice angle as a key variable, we construct a minimal one-degree-of-freedom model that quantitatively captures the limit cycle oscillation. Because these mechanisms rely only on deformability, packing, and shear, they provide a generic route to collective time-dependent behavior in dense soft suspensions.
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Quantum Gases
Long-lived oscillations of an attractive polaron in a Bose gas
Saptarshi Majumdar and Aleksandra Petković
We study the out-of-
equilibrium dynamics of an attractively interacting
impurity suddenly immersed with a nonzero initial velocity into a system of one-dimensional weakly interacting homogeneous
bosons. We uncover and characterize different dynamical regimes in the parameter space. Especially interesting is the relaxation of a fast
impurity with a mass close to or exceeding the critical one, where the
impurity exhibits undamped temporal long-lived velocity oscillations before reaching a stationary state. The underlying mechanism is the transient localization of a
boson depletion cloud near the
impurity, that oscillates around the
boson density peak situated at the
impurity position. The lifetime of this oscillating state increases with the absolute value of the
impurity-
boson coupling. Cold atomic gases provide an ideal playground where this phenomenon can be probed.
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Statistical Mechanics
Exact Stationary State of a $d$-dimensional Run-and-Tumble Particle in a Harmonic Potential
Mathis Guéneau, Satya N. Majumdar and Grégory Schehr
We derive the exact nonequilibrium steady state of a run-and-tumble particle (RTP) in $d$ dimensions confined in an isotropic harmonic trap $V(\mathbf r)=\mu r^{2}/2$, with $r=\|\mathbf r\|$. Rotational invariance reduces the problem to the stationary single-coordinate marginal $p_X(x)$, from which the radial distribution $p_R(r)$ and the full joint stationary density follow by explicit integral transforms. We first focus on a generalized trapped RTP in one dimension, where post-tumble velocities are drawn from an arbitrary distribution $W(v)$. Using a Kesten-type recursion, we represent its stationary position in terms of a stick-breaking (or Dirichlet) process, yielding closed-form expressions for its distribution and its moments. Specializing $W(v)$ to the projected velocity law of an isotropic RTP, we reconstruct $p_R(r)$ and the full joint distribution of all the coordinates in $d=1,2,3$. In $d=1$ and $d=2$, the radial law simplifies to a beta distribution, while in $d=3$, we derive closed-form expressions for $p_R(r)$ and the stationary joint distribution $P(x,y,z)$, which differ from a beta distribution. In all cases, we characterize a persistence-controlled shape transition at the turning surface $r=v_0/\mu$, where $v_0$ is the self-propulsion speed. We further include thermal noise characterized by a
diffusion coefficient $D>0$, showing that the stationary law is a Gaussian convolution of the $D=0$ result, which regularizes turning-point singularities and controls the crossover between persistence- and
diffusion-dominated regimes as $D \to 0$ and $D \to \infty$ respectively. All analytical predictions are systematically validated against numerical simulations.
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Disordered Systems and Neural Networks
Analysis of the Hopfield Model Incorporating the Effects of Unlearning
Shuta Takeuchi, Takashi Takahashi and Yoshiyuki Kabashima
We analyze a variant of the Hopfield model that incorporates an unlearning mechanism based on
spin correlations in the high-temperature regime. In the large system limit where extensively many patterns are stored, we employ the replica method under the replica symmetric ansatz to characterize the model analytically. Our analysis provides a systematic and self-consistent framework that yields order-parameter equations and stability conditions at finite temperatures over a wide range of parameter settings. The resulting theory accurately captures the behavior of the signal-to-noise ratio, the
memory capacity, and the criteria for selecting optimal hyperparameters, in agreement with the qualitative findings of Nokura (1996 J. Phys. A: Math. Gen. 29 3871). Moreover, the theoretical predictions show good agreement with numerical simulations, supporting the conclusion that unlearning enhances
memory capacity by suppressing spurious
memories.
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Statistical Mechanics
Stationary densities in a weakly nonconserving asymmetric exclusion processes with finite resources
Sourav Pal and Abhik Basu
Asymmetric exclusion process (TASEP) along a one-dimensional (1D) open channel sets the paradigm for 1D driven models and nonequilibrium phase transitions in open 1D models. Inspired by the phenomenologies of an open TASEP with Langmuir kinetics (Lk) and with finite resources, we study the stationary densities and phase transitions in a TASEP with Lk connected to a particle reservoir at its both ends. We calculate the stationary density profiles and the phase transitions. The resulting phase diagrams in the plane of the control parameters are significantly different from their counterparts in an open TASEP with Lk. In particular, some of the phases admissible in the open TASEP with Lk model are no longer possible. Intriguingly, our model that is closely related to a TASEP coupled with Lk on a ring with a point defect, admits more phases than the latter. Phenomenological implications of our results are discussed.
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Mesoscale and Nanoscale Physics
Highly Polarized and Long Range Dissipationless Spin Transport Due to Counterflowing Electron and Hole Edge Channels
Maxen Cosset-Chéneau, Boxuan Yang and Bart J. van Wees
The presence of edge channels in the
quantum Hall regime leads to dissipationless charge transport over long distances. When
graphene is interfaced with a
magnetic material, the exchange interaction lifts the Landau levels
spin degeneracy. This causes the presence of counterflowing edge channels with opposite
spin polarization. We show theoretically that the
spin-flip scattering between these edge channels enables a dissipationless
spin transport with larger than 100%
spin polarization of the charge current. It also allows the transport of
spin over macroscopically long distances, even in the absence of an applied charge current.
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Materials Science
2D ferroelectric narrow-bandgap semiconductor Wurtzite' type alpha-In2Se3 and its silicon-compatible growth
Yuxuan Jiang, Xingkun Ning, Renhui Liu et al. (+17 more)
2D van der Waals ferroelectrics, particularly alpha-In2Se3, have emerged as an attractive building block for next-generation information storage technologies due to their moderate band gap and robust ferroelectricity stabilized by dipole locking. alpha-In2Se3 can adopt either the distorted zincblende or wurtzite structures; however, the wurtzite phase has yet to be experimental-ly validated, and its large-scale synthesis poses significant challenges. Here, we report an in-situ transport growth of centimeter-scale wurtzite type alpha-In2Se3 films directly on SiO2 substrates using a process combining pulsed
laser deposition and chemical vapor deposition. We demonstrate that it is a narrow bandgap ferroelectric
semiconductor, featuring a Curie tem-perature exceeding 620 K, a tunable bandgap (0.8-1.6 eV) modulated by charged domain walls, and a large optical absorption coefficient of 1.3 times 10 powers 6 per centemeter. Moreover, light absorption promotes the dynamic conductance range, linearity, and
symmetry of the synapse devices, leading to a high recognition accuracy of 92.3 percent in a supervised pattern classification task for neuromorphic computing. Our findings demonstrate a ferroelectric polymorphism of In2Se3, highlighting its potential in ferroelectric synapses for neuromorphic computing.
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All authors Yuxuan Jiang, Xingkun Ning, Renhui Liu, Kepeng Song, Sajjad Ali, Haoyue Deng, Yizhuo Li, Biaohong Huang, Jianhang Qiu, Xiaofei Zhu, Zhen Fan, Qiankun Li, Chengbing Qin, Fei Xue, Teng Yang, Bing Li, Gang Liu, Weijin Hu, Lain-Jong Li, Zhidong Zhang
Disordered Systems and Neural Networks
Thermodynamic modes of a quasiperiodic mobility-edge system in a quantum Otto cycle
Ao Zhou, Shujie Cheng and Gao Xianlong
We investigate thermodynamic operation of a quasiperiodic
lattice with an exact mobility edge, described by the Biddle–Das Sarma model. We use this model as the working medium of a
quantum Otto cycle and map its operating mode as a function of the hopping-range parameter $p$, the initial and final potential strengths $V_i$ and $V_f$, and two idealized protocols for the isolated strokes. In a near-adiabatic (state-frozen) protocol, where the density
matrix is approximately unchanged during the isolated strokes, the cycle supports only two modes: a heater and an accelerator. In an adiabatic protocol, where level populations are preserved while the spectrum is deformed, two additional modes appear: a heat engine and a refrigerator. Our results show that mobility-edge systems can realize multiple thermodynamic functions within a single platform and provide guidance for switching between modes by tuning $p$, $V_i$, and $V_f$.
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Soft Condensed Matter · Cross-listed from physics.flu-dyn
High-resolution numerical simulations of turbulent non-catalytic reverse water gas shift
Nils Erland L. Haugen, Axel Brandenburg, Ewa Karchniwy et al. (+5 more)
A green transition in aviation requires a drastic upscaling of Sustainable Aviation Fuel (SAF). The power-to-
liquid process for the production of CO2-neutral jet fuel via electricity, called e-SAF, directly replaces fossil jet fuel without having to change infrastructure, aeroplanes, or jet-engines. The process combines green hydrogen with industrial exhaust gas, or captured carbon dioxide, in a circular economy concept. A key element of the e-SAF production plant is the reactor where syngas is produced. Traditional reactors use catalytic technology, which faces severe challenges due to the reduced performance over time because of catalyst degradation, clogging, and breakup due to embrittlement. A high-potential alternative is the catalyst-free reverse water-gas-shift (RWGS) reactor concept. The primary aim of this paper is to investigate the fundamental aspects of the catalyst-free RWGS process, such as reaction kinetics and the interactions between
turbulence and chemistry. The secondary aim is to identify how a typical combustion subgrid scale models for Large Eddy Simulations (LES) perform when the chemical reactions are endothermic, in contrast to the strong endothermicity associated with classical combustion. It is found that even small traces of O2 in the CO2 stream can significantly increase the production rate of CO. This is attributed to the increased pool of OH. The effect is strongest at atmospheric pressure and less pronounced at higher pressure. By using the temporal jet framework to study
turbulence-chemistry interactions, an algebraic equation for the prediction of the CO conversion time in a turbulent flow as a function of Damkohler number and chemical timescale is employed. Finally, it is concluded that the PaSR LES subgrid model designed for combustion reactions perform well also for the endothermic reverse water-gas-shift reaction.
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All authors Nils Erland L. Haugen, Axel Brandenburg, Ewa Karchniwy, Ole Hauke Heinz Meyer, Åsmund Ervik, Hursanay Fyhn, Ladan Samaei, Bjørn Bringedal
Strongly Correlated Electrons
Direct Evidence of a Near-Ideal Jeff = 1/2 Ground State in Triangular-Lattice Na2BaCo(PO4)2
M. M. Ferreira-Carvalho, S.H. Chen, Y. C. Ku et al. (+7 more)
We investigated the local Co 3d electronic structure of Na2BaCo(PO4)2 using polarization-dependent X-ray absorption spectroscopy (XAS) in combination with full multiplet cluster calculations. We employed the line-fitting inverse partial fluorescence yield (IPFY) technique to obtain accurate XAS spectra from strong insulating materials. Our combined experimental and theoretical analysis reveals a very small effective trigonal distortion of only 11 meV in the CoO6 octahedra, indicating a close to ideal condition to render a ground state with the Jeff = 1/2 character. With our cluster model we were also able to simulate
magnetic susceptibility measurements along different directions in the
crystal. These findings highlight Na2BaCo(PO4)2 as a promising platform for exploring exotic
magnetic phenomena associated with Jeff = 1/2 ground states on triangular
lattices.
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All authors M. M. Ferreira-Carvalho, S.H. Chen, Y. C. Ku, Anagha Jose, Ryan Morrow, C. Y. Kuo, C. F. Chang, Z. Hu, M. W. Haverkort, L. H. Tjeng
Superconductivity
Intimate relationship between spin configuration in the triplet pair and superconductivity in UTe$_2$
Hiroki Matsumura, Yuki Takahashi, Riku Matsubayashi et al. (+16 more)
Spin-triplet superconductivity is an intriguing
quantum coherent state with both
spin and orbital degrees of freedom, which holds significant potential for future applications in
quantum technology. However, how the
spin of the triplet pairs responds to an external
magnetic field remains poorly understood. This is mainly due to the absence of suitable
spin-triplet
superconductors. Here, we report results of Knight-shift and ac-susceptibility measurements on UTe$_2$. We demonstrate that the
spin susceptibility, which slightly decreases compared to the normal-state value below the superconducting (SC) transition temperature $T_{\rm c}$, is rapidly restored and nearly recovers to the normal-state values around 5 T, well below the SC upper critical field $H_{c2}$ when the
magnetic field is applied along the $c$ axis ($H \parallel c$). In addition, we found that $H_{\rm c2}$ of superconductivity becomes larger when the SC
spin aligns with the
magnetic field. By considering the results on $H \parallel b$, our results suggest the presence of a close relationship between the
spin configuration of the triplet pair and $H_{\rm c2}$, as well as the anisotropic pinning interaction acting on the triplet pairs. These phenomena, which have never been observed in
spin-singlet
superconductors, represent characteristic features unique to
spin-triplet
superconductors. We discuss the similarities between superconductivity in UTe$_2$ and superfluid $^3$He, focusing on their
spin-triplet pairing states.
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All authors Hiroki Matsumura, Yuki Takahashi, Riku Matsubayashi, Katsuki Kinjo, Shunsaku Kitagawa, Kenji Ishida, Yo Tokunaga, Hironori Sakai, Shinsaku Kambe, Motoi Kimata, Ai Nakamura, Yusei Shimizu, Yoshiya Homma, Dexin Li, Fuminori Honda, Atsushi Miyake, Dai Aoki, Tetsuya Furukawa, Takahiro Sasaki
Statistical Mechanics
Variational Method for Interacting Surfaces with Higher-Form Global Symmetries
Kiyoharu Kawana
We develop a variational method for interacting surface systems with higher-form global
symmetries. As a natural extension of the conventional second-quantized
Hamiltonian of interacting
bosons, we explicitly construct a second-quantized
Hamiltonian formulated in terms of a closed surface operator $\hat{\phi}[C_p^{}]$ charged under a $p$-form global
symmetry. Applying the variational principle, we derive a functional Schrödinger equation analogous to the Gross-Pitaevskii equation in conventional bosonic systems. In the absence of external forces, the variational equation admits a uniform solution that is uniquely determined by a microscopic interaction potential $U(\psi^*\psi)$ and the chemical potential. This uniform solution describes a uniform gas of bosonic surfaces. Using the obtained energy functional, we show that low-energy fluctuations contain a gapless $p$-form field $A_p^{}$ when the $p$-form global
symmetry is $\mathrm{U}(1)$, whereas the $p$-form field becomes massive for discrete
symmetries, whose low-energy limit is described by a $\mathrm{BF}$-type topological field theory. As a consequence, the system exhibits abelian topological order with anyonic surface excitations. In the presence of external forces, however, solving the functional equation in full generality remains challenging. We argue, however, that the problem reduces to solving the conventional Gross-Pitaevskii equation when external forces act separately on the center-of-mass and relative motions. In addition, we present analytic solutions for topological defects as analogs of
vortex and domain-wall solutions in conventional bosonic systems. Finally, as a concrete microscopic model, we study a $\mathbb{Z}_N^{}$
lattice gauge theory and apply our variational method to this system.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Room Temperature Collective Blinking and Photon Bunching from CsPbBr3 Quantum Dot Superlattice
Qiwen Tan, Sudipta Seth, Boris Louis et al. (+7 more)
Development of
quantum light sources and search for
quantum systems capable of supporting collective many-body states are crucial for further progress of modern
quantum technologies. Metal halide perovskite
quantum dots (QDs) have emerged as a promising candidate for
quantum light sources, as individual QDs are reliable single
photon emitters even at room temperature. However,
photon bunching, a key signature of collective many-body states, has been so far largely observed at cryogenic temperatures in perovskite materials, limiting their applications under ambient conditions. Here, we report the observation of collective blinking and
photon bunching in perovskite QD superlattices at room temperature. Sub-wavelength-sized (100 - 500 nm) CsPbBr3 QD superlattices, fabricated via a self-assembly process, exhibit an unusual two-level blinking behavior similar to that of single QDs, and demonstrate
photon bunching with a degree of up to 2.75. Time-resolved photoluminescence (PL) measurements and super-resolution imaging reveal that the superlattices have a significantly longer PL lifetime than individual QDs and that their emission is spatially confined to regions tens of nanometers in size. These observations suggest long-range
exciton migration to a localized energy trap within the superlattice. Excitation power dependent degree of bunching and analysis of the bunching dynamics indicate that the
photon bunching originates from
exciton-biexciton cascade emission, a key mechanism for generating entangled
photons. These findings establish perovskite QD superlattices as a promising platform for room-temperature collective optical phenomena and
quantum light generation, advancing scalable
quantum photonic technologies.
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All authors Qiwen Tan, Sudipta Seth, Boris Louis, Xiayan Wu, Nithin Pathoor, Toranosuke Takagi, Shun Omagari, Takumi Sannomiya, Johan Hofkens, Martin Vacha
Soft Condensed Matter
Quo vadis biophotonics? Wearing serendipity and slow science as a badge of pride, and embracing biology
G.E. Schroeder-Turk
This article is a reflection on the themes of the Faraday Discussion meeting on "Biological and bio-inspired optics" held from 20 to 22 July 2020. It is a personal perspective on the nature of this field as a broad and interdisciplinary field that has led to a sound understanding of the material properties of biological nanostructured and optical materials. The article describes how the nature of the field and the themes of the conference are reflected in particular in work on the 3D bicontinuous biophotonic nanostructures known as single gyroids and in bicontinuous structures more broadly. Such single gyroid materials are found for example in the butterfly Thecla opisena, where the questions of biophotonic response, of bio-inspired optics, of the relationship between structure and function, and of the relationship between natural and synthetic realisations are closely interlinked. This multitude of facets of research on single gyroid structures reflects the beauty of the broader field of biophotonics, namely as a field that lives through embracing the serendipitous discovery of the biophotonic marvels that nature offers to us as seeds for in-depth analysis and understanding. The meandering nature of its discoveries, and the need to accept the slowness that comes from exploration of intellectually new or foreign territory, mean that the field shares some traits with biological
evolution itself. Looking into the future, I consider that a closer engagement with living tissue and with the biological questions of function and formation, rather than with the materials science of biological materials, will help ensure the continuing great success of this field.
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Soft Condensed Matter
Mixing properties of bi-disperse ellipsoid assemblies: Mean-field behaviour in a granular matter experiment
F.M. Schaller, H. Punzmann, G.E. Schröder-Turk et al. (+1 more)
The structure and spatial statistical properties of amorphous ellipsoid assemblies have profound scientific and industrial significance in many systems, from
cell assays to granular materials. This paper uses a fundamental theoretical relationship for mixture distributions to explain the observations of an extensive X-ray computed
tomography study of granular ellipsoidal packings. We study a size-bi-disperse mixture of two types of ellipsoids of revolutions that have the same aspect ratio of alpha approximately equal to 0.57 and differ in size, by about 10% in linear dimension, and compare these to mono-disperse systems of ellipsoids with the same aspect ratio. Jammed configurations with a range of packing densities are achieved by employing different tapping protocols. We numerically interrogate the final packing configurations by analyses of the local packing fraction distributions calculated from the Voronoi diagrams. Our main finding is that the bi-disperse ellipsoidal packings studied here can be interpreted as a mixture of two uncorrelated mono-disperse packings, insensitive to the compaction protocol. Our results are consolidated by showing that the local packing fraction shows no correlation beyond their first shell of neighbours in the binary mixtures. We propose a model of uncorrelated binary mixture distribution that describes the observed experimental data with high accuracy. This analysis framework will enable future studies to test whether the observed mean-field behaviour is specific to the particular granular system or the specific parameter values studied here or if it is observed more broadly in other bi-disperse non-spherical particle systems.
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All authors F.M. Schaller, H. Punzmann, G.E. Schröder-Turk, M. Saadatfar