Materials Science
High-throughput computational discovery of CuI-based ternary $p$-type transparent conductors
Michael Seifert, Miguel A. L. Marques and Silvana Botti
P-type transparent conducting materials (TCMs) remain scarce, limiting progress in transparent electronics and tandem photovoltaics. Here, we perform a high-throughput computational search across CuI-based ternary X–Cu–I compounds using the minima hopping method combined with density functional theory. Filtering for thermodynamic stability, optical transparency, and light hole effective mass, we identify 58 candidate p-type TCMs, of which 49 are previously unreported. Twenty are p-type degenerate
semiconductors with intrinsic hole carriers, including Cu$_2$FI$_2$ (calculated gap 3.75 eV, hole effective mass $0.262\,m_0$). We further use this
dataset to revisit the chemical modulation of the valence band (CMVB) design rules, originally formulated for Cu-based delafossite oxides. Four generalizations emerge: linear Cu coordination is not required, as tetrahedral coordination (CN = 4) is compatible with p-type TCM character; the mechanism extends to halide-based systems with I $5p$ anion states; the Cu $d$ state energy center $\epsilon_d$ is a quantitative descriptor for valence band dispersion; and Cu undercoordination in monovalent-anion hosts drives intrinsic p-type carrier generation through stoichiometric charge balance. These results establish a generalized computational framework for the design of p-type halide TCMs.
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Materials Science
Multiscale computational study of the dielectric response of semi-crystalline polyethylene with chemical defects
Roshal Perepadan Shaju, Guido Roma and Xavier Colin
Polymers are widely used as functional insulating materials, but predicting their dielectric behavior is challenging because multiple mechanisms, acting across different spatial and temporal scales, contribute to their response. In polyethylene (PE), one of the most common
polymers, electronic, atomic, and mesoscale dynamics must all be considered. In this work, semicrystalline models of polyethylene were developed and investigated using a multiscale approach.
Quantum simulations were employed to describe electronic and vibrational contributions to the dielectric response, while classical molecular dynamics simulations captured the behavior of
polymer chains at room temperature and frequencies down to the 10-100 MHz range. The study focuses on the impact of
radio-oxidation defects on the dielectric properties of polyethylene.
Quantum calculations reveal how electronic and vibrational contributions depend on the local atomic environment surrounding these defects. Comparison with molecular dynamics results highlights the influence of temperature on the static dielectric constant. Structural analyses further assess the effect of each defect type on PE crystallinity. Analysis of dipolar correlation functions shows that different defects interact with one another and with the
polymer matrix in distinct ways, affecting permittivity and dielectric loss peaks. For all defect types, defect-defect interactions provide the largest contribution to dielectric response. While most oxidized groups exhibit positive coupling with the PE
matrix, alcohol defects display a negative cross-correlation, partially offsetting their impact on the dielectric properties. Our results also show that ketone groups produce the largest dielectric loss between the defects studied.
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Soft Condensed Matter
Vibrational Mpemba relaxation in a linear damped elastic system
Kiwamu Yoshii and Satoshi Takada
We show that a linear damped elastic system can display a Mpemba-like reversal of vibrational relaxation without any nonlinear constitutive response or amplitude-dependent damping. The mechanism is purely modal. For a one-dimensional Kelvin–Voigt elastic medium, the decay rate of the $n$-th vibrational mode scales as $\gamma_n\propto n^2$. We formulate relaxation in terms of a positive modal envelope energy, thereby excluding crossings caused merely by oscillation phase. A one-parameter family of initial states is then constructed such that increasing the initial elastic excitation simultaneously reduces the projection onto the slow fundamental mode. In the invariant two-mode subspace, the relaxation-order crossing is obtained analytically and, for this family, occurs at a universal dimensionless time independent of the selected pair of initial states. In the limiting case where the slowest mode is absent, the dominant relaxation rate changes discontinuously, yielding a direct vibrational analogue of the strong Mpemba effect. We further show that the same relaxation-order reversal occurs in the ordinary mechanical vibrational energy, which decreases monotonically despite retaining the oscillatory dynamics of the underlying modes.
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Quantum Gases
Electron lattice potentials for ultracold atoms using circular Rydberg orbitals
Aileen A. T. Durst, Einius Pultinevicius, Homar Rivera-Rodríguez et al. (+3 more)
Recent advances in experiments using individually trapped atoms have enabled precise control over circular Rydberg electrons with exceptionally long lifetimes. We show that these giant and stable electron orbits can form toroidal
lattice potentials for ultracold atoms with a period set by the electron's de Broglie wavelength. Unlike conventional static optical
lattices, this electron
lattice is formed via the electron-atom interaction, which mixes Rydberg circular states with opposite azimuthal phase winding into a standing electronic matter wave. The
lattice phase is thereby intrinsically coupled to the atom position. For a pair of atoms, this results in ballistic tunneling motion in the two-atom spatial correlations along the ring, while the single particle dynamics is essentially free rotation. We simulate the dynamics for an experimentally realistic setting that exploits optical tweezers for individual atom control. Our results open a route toward incorporating long range atom-atom interactions mediated by a single electron and, ultimately, realizing small Bose and Fermi gases confined in these microscopic electronic atom traps.
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All authors Aileen A. T. Durst, Einius Pultinevicius, Homar Rivera-Rodríguez, Tilman Pfau, Matthew T. Eiles, Florian Meinert
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Steady–State Current Signatures of Strong Light–Matter Coupling in Single–Molecule Junctions
Kritanjan Polley and Norah M. Hoffmann
Strong light-matter coupling offers exciting opportunities for controlling molecular properties, yet resolving single-molecule behavior from collective effects remains a challenge. Recent experiments in scanning tunneling microscope break junctions (STM-BJs) have demonstrated strong light-matter coupling at the single-molecule level. Because STM-BJs provide direct access to molecular-junction currents, we investigate whether strong coupling leaves a measurable fingerprint in transport, potentially probing polaritonic states beyond optical spectroscopy. Using a semiclassical mapping approach for nonequilibrium
quantum transport, we find that steady-state current indeed carries a direct signature of single-molecule strong coupling. We test the robustness of this signature against electrode connectivity, nuclear motion, spatially structured electromagnetic modes, and solvent effects. While environmental factors and nuclear motion reshape the signature, the current is not a passive response but is actively influenced by coupled molecular dynamics. Our work establishes current as a tool to interpret and control strong light-matter interactions in nanoscale junctions.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
A General Non-Markovian Electronic Friction and Langevin Dynamics Framework for Nonequilibrium Systems
S. L. Rudge, R. J. Preston, D. S. Kosov et al. (+1 more)
We present a general framework for simulating the nonequilibrium vibronic dynamics of molecules interacting with metal surfaces, which utilizes non-Markovian electronic friction and the corresponding generalized Langevin equation. The method employs a Markovian
embedding scheme to sample coordinate-dependent
quantum colored noise, with the underlying
memory kernels represented systematically by exponential decompositions obtained directly from the electronic forces. In doing so, the approach extends the widely used electronic friction and Langevin dynamics formalism beyond the conventional Markovian approximation while retaining the coordinate dependence of the electronic back-action. We demonstrate the method for nonequilibrium charge transport through a vibrationally coupled molecular junction, where comparisons with numerically exact hierarchical equations of motion simulations show that the non-Markovian formulation is both more accurate and more robust than its Markovian counterpart. In particular, we find that non-Markovian electronic forces play a decisive role in the nonequilibrium vibrational dynamics, stabilizing regimes in which the conventional Markovian approximation fails.
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All authors S. L. Rudge, R. J. Preston, D. S. Kosov, M. Thoss
Materials Science
First-principles calculations of the thermodynamic factor of multicomponent alloys
Damien K. J. Lee, Shashank Saxena, Anton Van der Ven et al. (+1 more)
Computing non-dilute
diffusion coefficients from Onsager transport coefficients of a multicomponent
alloy requires the thermodynamic factor, which measures the
curvature of the free energy with respect to composition. As
diffusion in metals is mediated by vacancies, the
curvature that matters is not that of the vacancy-free
alloy, which is straightforward to compute, but that of an
alloy carrying a dilute concentration of vacancies. The resulting
matrix is nearly singular, and composition fluctuations from which it is obtained converge slowly in Monte Carlo simulations. Here we develop two routes that avoid sampling vacancy composition fluctuations. The first constructs the thermodynamic factor from two quantities, the free-energy
curvature of the vacancy-free
alloy and the vacancy concentration. The second truncates the semi-grand canonical partition function at a single vacancy and recovers the full thermodynamic factor of the vacancy-containing
alloy. The same separation shows that the largest
eigenvalue of the
diffusion matrix is the vacancy tracer
diffusion coefficient for any number of components and any degree of non-ideality, while the remaining
eigenvalues scale with the vacancy concentration. Across binary through quinary
alloys of the Hf–Mo–Nb–Ti–Zr system, both routes reproduce
eigenvalues and eigenvectors of
diffusion matrices obtained from fully converged Monte Carlo simulations. The single-vacancy expansion reaches this accuracy with roughly one tenth of the sampling effort. A scaling relation extends both routes to local vacancy chemical potentials away from
equilibrium, without additional simulations. These results allow thermodynamic descriptions from atomistic models or CALPHAD assessments to be used directly in mesoscale simulations of mass transport.
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All authors Damien K. J. Lee, Shashank Saxena, Anton Van der Ven, Anirudh Raju Natarajan
Soft Condensed Matter
The Paper-Stack Trampoline: Acoustic Restitution in Layered Media
Manou Liesker, Colton Kawamura, Maria Kieft et al. (+2 more)
A ball bouncing on a thicker cushion should bounce less. We show that this is not always so . Measuring the coefficient of restitution $e$ of a steel ball dropped on a stack of $N$ sheets of standard A4 printer paper, we find that $e$ first drops, then rises to a pronounced maximum, and only then decreases towards a minimum. The maximum occurs where the acoustic round trip through the stack matches the contact time of the impact. For a contact set by the stack itself, one recovers the classical bar-impact condition of a stack-to-ball mass ratio of order one. Bar impact, however, predicts only a weak recovery, insensitive to the surrounding gas. For paper stacks, the recovery is large and no maximum is resolved when the stack is evacuated: the air trapped between the sheets, not the paper alone, makes the stack a trampoline.
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All authors Manou Liesker, Colton Kawamura, Maria Kieft, Joshua A. Dijksman, Antoine Deblais
Materials Science
Electron paramagnetic resonance of Dy${^3+}$-doped CaWO$_4$: spin Hamiltonian, crystal-field analysis, and linear electric field effect
Achuthan Manoj Kumar, Larissa Aboudem-Joumessi, Remy Dassonneville et al. (+6 more)
We report an electron paramagnetic resonance (EPR) study of Dy${^3+}$ in CaWO$_4$ single
crystals spanning dopant concentrations from 80~ppb to 247~ppm. The $g$ factors of the ground Kramers doublet at the $S_4$ point-group site, $g_\parallel = 7.22 \pm 0.01$ and $g_\perp = 5.45 \pm 0.01$, and the hyperfine constants of \ce{^{161}Dy} and $^{163}$Dy are determined with an order-of-magnitude improvement in precision over the only previous report. A
crystal-field analysis constrained jointly by published optical levels and by the measured $g$ tensor identifies the ground doublet as the lower branch of an anticrossing between the near-degenerate $\|{\pm}11/2>$ and $\|{\mp}13/2>$ states, and explains why optical data alone left the $g$ values unconstrained. \add{The same parameter set, tested on the excited multiplets of the $^6H$ term, reproduces the ${}^6H_{13/2}$
crystal-field levels better than the optical parameters themselves.} The angular dependence of the linewidth in the $ab$ plane reveals broadening by random internal electric fields through the linear electric field effect. Calibrating these fields with the residual Er$^{3+}$ present in the same
crystals yields the first electric-field coupling parameters of Dy$^3+$, $(B_{31}^2+B_{36}^2)^{1/2} = (34\pm5)\times10^{-6}$~cm/V, three times the Er$^{3+}$ value and the largest reported for a rare-earth ion in this host.The residual linewidth and the concentration-dependent lineshape asymmetry follow the quadratic field scaling expected for a second-order Stark shift, which escapes the inversion-site cancellation constraining the linear effect. Both couplings trace back to the $\sim 20$~cm$^{-1}$ gap to the first opposite-
symmetry doublet, a consequence of the dense
crystal-field structure of the $J=15/2$
manifold.
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All authors Achuthan Manoj Kumar, Larissa Aboudem-Joumessi, Remy Dassonneville, Adrien Savoyant, Karolina Waszowska, Pengrui Jiao, Patrice Bertet, Philippe Goldner, Sylvain Bertaina
Mesoscale and Nanoscale Physics
Orbital photoinduced Faraday effect in a lattice of conducting disks
A. A. Gunyaga and M. V. Durnev
We present a theoretical study of pump-induced Faraday and Kerr rotation in a two-dimensional
lattice of conducting disks. We propose a mechanism of Faraday and Kerr responses in which a circularly polarized pump directly induces a high-frequency Hall component $\sigma_{xy}=-\sigma_{yx}$ of the electron conductivity tensor at the probe frequency. Microscopically, $\sigma_{xy}$ originates from the third-order nonlinear response of the electron gas rather than from the real
magnetic field created by solenoidal charge currents in the inverse Faraday effect. We show that the Faraday and Kerr rotation angles are significantly enhanced when the pump and probe frequencies are tuned close to the plasmon resonance of the disks, reaching $\sim 0.1^\circ$ per 1~kW/cm$^2$ of incident pump intensity in the terahertz range. This mechanism can explain recently observed giant pump-induced Faraday rotation in
graphene disk
lattices.
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Materials Science
Current-voltage characteristics and resistive switching in epitaxial La$_{0.67}$Sr$_{0.33}$MnO$_3$/SrMnO$_3$/La$_{0.67}$Sr$_{0.33}$MnO$_3$ multilayer
A. G. A. Rahman, R. K. Patel, Chandrani Nath et al. (+1 more)
In present study, we investigate the structural properties and current-voltage ($I$-$V$) characteristics of an epitaxial multilayer composed of La$_{0.67}$Sr$_{0.33}$MnO$_3$ (25 nm)/SrMnO$_3$ (70 nm)/La$_{0.67}$Sr$_{0.33}$MnO$_3$ (25 nm), grown on different substrates i.e., SrTiO$_3$(100), LaAlO$_3$(100), Si (100). The used substrates not only have different chemical compositions in line with the film materials, also they have different
lattice parameters which would tune the material chemistry and
lattice strain at the interface significantly. Our $I$-$V$ measurements reveal distinct electrical behaviors depending on the substrate. The multilayers grown on oxide SrTiO$_3$(100) and LaAlO$_3$(100) substrates exhibit regular $I$-$V$ with slight nonlinearity at low applied voltages. In contrast, $I$-$V$ in multilayer with Si(100) substrate exhibits large asymmetry and notable resistive switching (RS) behavior at room temperature, where a resistance ratio around 10 between the high resistance state (HRS) and low resistance state (LRS) is observed. While the observed $I$-$V$ behavior is sensitive to substrate-induced interfacial disorder and formation of trap bands within bandgap of SrMnO$_3$, the present results have potential applications in future
memory and memristive devices.
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All authors A. G. A. Rahman, R. K. Patel, Chandrani Nath, A. K. Pramanik
Materials Science
Modern triad for magnetic material science: geometric shape, electronic bands and spin textures
Denys Makarov, Oleksandr Pylypovskyi, Rui Xu et al. (+1 more)
To enable novel concepts in nanotechnologies, it is insightful to design materials with qualitatively new performances originating from recent discoveries in fundamental material science and physics. Curvilinear magnetism emerged as a tool to design chiral and anisotropic responses of materials at the nanoscale using the effects of the
geometric shape and
topology of the object. This concept is distinct yet complementary to material screening, which is primarily based on the optimization of intrinsic microscopic properties to modify
magnetic textures for specific applications. Contemporary curvilinear magnetism focuses on mean-field micromagnetics, while the explicit contribution of the
lattice structure and electronic degrees of freedom remains beyond consideration. In this review, we will emphasize on the effects which appear when this coupling is accounted for and that have resulted in novel concepts for the design of “metageometric” materials. Further development of this field will provide appealing technological prospects for fundamental understanding of curvilinear
magnetic nanostructures and their applications in energy efficient and scalable nanoelectronics.
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All authors Denys Makarov, Oleksandr Pylypovskyi, Rui Xu, Carmine Ortix
Statistical Mechanics
Slow-fast dynamics of the McKean model with stochastic resetting and diffusion
Jude Swaby and Paul C. Bressloff
In this paper we investigate the combined effects of
stochastic resetting and
diffusion on a slow–fast dynamical system given by the piecewise-linear McKean model. That is, the fast variable $v$ is subject to Gaussian white noise with effective diffusivity $D$ and is reset to a fixed value $v_r$ at a random sequence of times generated from a Poisson process with rate $r$. Assuming that resetting occurs on the fast timescale, we freeze the slow variable \(w\) under an adiabatic approximation and determine the resulting non-
equilibrium stationary state (NESS) of the fast variable as the solution of a modified Fokker–Planck equation. We show that the NESS can be expressed in terms of parabolic cylinder functions, whose asymptotic behavior allows us to recover the corresponding NESS without
diffusion in the small-
diffusion limit. The NESS is used to derive an averaged equation for the slow dynamics, whose solution converges to a stable fixed point \(w^*\) that depends on \(D\), \(r\) and \(v_r\). This fixed point effectively determines the long-time behaviour of the full system. Finally, we analyze the regime in which resetting occurs on the same timescale as the slow variable. We show how the slow variable now undergoes noisy oscillations due to resetting-induced switching between branches of the fast nullcline and derive the corresponding NESS for $w$ in the non-diffusive case.
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Materials Science · Cross-listed from quant-ph
Phase-accumulating hyperfine strain sensing with rare-earth-ion phase memories
Mustafa Gündoğan
Long-lived hyperfine coherences in rare-earth-ion
crystals provide controlled phase
evolution windows for metrology. We use this resource to propose an experimental protocol for accessing strain shifts of ground state hyperfine transitions in non-Kramers rare-earth-ion doped (REID) materials, a quantity that is difficult to access directly with conventional spectroscopic methods. Starting from the
crystal field
Hamiltonian, we relate the response to strain-dependent effective quadrupole and Zeeman tensors, including changes in electronic wave functions, virtual electronic admixtures, and the bare nuclear quadrupole interaction. The protocol optically prepares a selected hyperfine class, uses a phase-controlled rf $\pi/2$ pulse to create the sensing coherence, and applies synchronized dynamical decoupling pulses during the phase
evolution interval so that a coherent ac strain drive accumulates phase rather than averaging away. The accumulated phase is then retrieved by Raman heterodyne readout. The resulting framework provides a route to understanding strain-induced hyperfine couplings in non-Kramers REID systems.
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Quantum Gases
Rydberg-Atom-Mediated Strong Antisymmetric Spin Exchange in Molecular Arrays
Yunqing Jiao, Jin-Zhu Jiang, Bo-Wen Guan et al. (+6 more)
Ultracold molecular systems have recently emerged as a versatile platform for
quantum computation and simulation.
Spin-exchange interactions arising from direct molecular dipolar interactions constitute the key mechanism for generating
quantum entanglement and simulating
quantum spin models. However, the relatively small electric dipole moments result in weak
spin-exchange couplings, fundamentally limiting the speed of
quantum information processing and interaction cycle of many-body dynamics. Here, we introduce a framework that employs Rydberg atoms with large electric dipole moments to mediate strong interactions between molecules in optical tweezer arrays that enables individually
laser addressing both the Rydberg atom and molecules. Our result reveals that the mediated coupling can realize an effective molecular
spin-exchange interaction with an intrinsic Dzyaloshinskii-Moriya character, with the Rydberg atoms dynamically decoupled from the molecular degrees of freedom, and the effective interaction strength enhanced by up to three orders of magnitude. We further demonstrate its versatility through rapid
entanglement generation, high-fidelity two-
qubit gate operations, and the realization of non-
equilibrium symmetry-protected topological phase with long-lived edge coherence. Our work establishes a route toward strong molecular
spin interactions and opens opportunities for fast, scalable
quantum information processing and
quantum simulation of long-time non-
equilibrium quantum many-body physics in optical tweezer arrays of ultracold molecules.
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All authors Yunqing Jiao, Jin-Zhu Jiang, Bo-Wen Guan, Jie Ma, Liantuan Xiao, Chi Zhang, Weibin Li, Feng Mei, Suotang Jia
Soft Condensed Matter
S. Biswas, W. S. Fall and H. H. Wensink
Weakly flexible, directed
polymers can adopt a potentially infinite variety of conformations, some of them chiral. We develop a second-virial theory for semi-rigid
polymers embedded in a nematic environment based on the assumption that the chains possess no intrinsic molecular chirality but can take on weakly helical conformations of either handedness. We demonstrate how these transient helical fluctuations can be exploited to predict the degree of chain stiffening induced by molecular crowding. The theoretical predictions are in good agreement with large-scale molecular dynamics simulations of bead-spring
polymers with tunable backbone flexibility. Although both theory and simulations rule out spontaneous global chiral
symmetry breaking imparted by chain conformations alone, they do reveal that
polymers can develop pronounced enantiomeric shapes. Nematic fluids of semi-rigid
polymers can be viewed as compensated cholesterics composed of transiently helical
polymers with zero enantiomeric excess. By quantifying the degree of compensated chiral order developed over a broad range of concentrations and persistence lengths, two distinct regimes of weak and strong enantiomerism can be identified. A crossover between the two occurs when the chain persistence length drops below roughly three times the contour length.
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Materials Science · Cross-listed from cs.AI
AtomWorld-Mem: Memory-Restored World States for Long-Horizon Atomistic Evolution
Tian Luo, Ruge Zhang, Haozhi Han et al. (+5 more)
High-fidelity atomistic
evolution over long timescales requires more than observing the current
crystal configuration. Instantaneous atomistic snapshots are often incomplete: locally similar configurations can correspond to different hidden dynamical contexts, future event preferences, and waiting-time scales. We argue that this snapshot ambiguity makes long-horizon atomistic
evolution fundamentally a
memory-based world-state restoration problem. To address this, we introduce AtomWorld-Mem, a
memory-restored atomistic world model that recovers the latent world state missing from instantaneous
crystal snapshots. AtomWorld-Mem treats the evolving
alloy as an AtomWorld: spatial encoders write multi-scale atomistic keyframes from dense local
topology and sparse long-range defect context, while short-term event
memory and long-term structural
memory integrate these keyframes across time to restore a future-predictive evolutionary state. The restored state is used to prioritize legal vacancy-mediated events under single-event Kinetic Monte Carlo (KMC) constraints, while event legality, physical execution, and residence-time updates remain governed by the underlying simulator. Empirically, AtomWorld-Mem improves long-horizon atomistic progress under fixed microscopic event budgets while maintaining high-fidelity
evolution across energetic, structural, and vacancy-transport observables. It further transfers zero-shot across diverse unseen
alloy-temperature AtomWorlds, suggesting that the learned
memory-restoration mechanism captures reusable principles of hidden-state inference rather than a system-specific local energy heuristic. These results position
memory-restored world-state modeling as a promising route toward efficient, physically grounded, and transferable atomistic
evolution.
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All authors Tian Luo, Ruge Zhang, Haozhi Han, Yifeng Chen, Yunquan Zhang, Yunxin Liu, Ting Cao, Kun Li
Soft Condensed Matter · Cross-listed from physics.optics
From OpenSPIM to FlowSPIM: Enhancing the versatility of a light sheet microscope through an iterative design process
Endre Joachim Lerheim Mossige, Sergey Ponomartsev, Natalia Smirnova et al. (+12 more)
Light sheet microscopy is ideal for the 3D imaging of large biological specimens, yet systematic documentation on adapting microscope designs to diverse experimental requirements remains limited. We present the iterative process used to design and build a modular light-sheet microscope and adapt it to different sample types and experimental conditions. Starting from a stripped-down OpenSPIM platform, we gradually make our microscope more versatile by implementing new hardware, such as additional
laser channels and optical filters, and new protocols for sample handling. In its final iteration, FlowSPIM is a new flow-based incubation technique for 3D tissue culture.
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All authors Endre Joachim Lerheim Mossige, Sergey Ponomartsev, Natalia Smirnova, Wietske van der Ent, Siri Andresen, Xian Hu, Felix Margadant, Rainer Heintzmann, Roland Kádár, Kesavan Sekar, Helene Knævelsrud, Camila Vicencio Esguerra, Stefan Krauss, Dag Kristian Dysthe, Alexander Refsum Jensenius
Disordered Systems and Neural Networks
A Flatness-Generalization Relation in the Teacher-Student Tree-Committee Machine
Brandon Livio Annesi, Davide Straziota and Enrico Maria Malatesta
The flatness of the loss landscape at a minimizer is a widely used heuristic for
reasoning about neural-network generalization, yet evidence for this relation is mostly empirical and controversial. We study this relation in a teacher-student tree committee machine, where both the ERM
estimator and the Hessian spectrum are analytically tractable in the proportional high-dimensional limit. First, we use a zero-temperature Gibbs formulation to obtain predictions for the observables of the typical minimizers of the empirical loss. Secondly, we use Edwards-Jones formalism to derive the limiting Hessian resolvent around these typical minimizers. All predictions agree with finite-size gradient-descent simulations. Finally, we study three measures of flatness, namely the left and right edges and the spectral mean, and check if a decrease in generalization error as the
dataset size is increased corresponds to an increase in flatness. We find that the answer strongly depends on the learning task and on the ratio of the number of parameters to the number of data points. In regression, the spectral mean and right edge correlate with the generalization error, while the left edge does so only in the overparametrized regime. In classification this correlation reliably holds only in the highly overparametrized phase, while for underparametrized networks it can even reverse.
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Statistical Mechanics
Thermodynamics of the $q$-deformed Kittel–Shore model for spin-1 particles
V. Mariscal and J. J. Relancio
Quantum algebras ($q$-
algebras) have been used in the literature to deform
spin-chain models. In particular, in previous works by the present authors, the Kittel–Shore
Hamiltonian was deformed using $\mathfrak{su}_q(2)$
algebra. The deformed
Hamiltonian was presented for a general
spin, and the thermodynamic properties were studied for
spin-1/2 particles. In this paper, we focus on the $q$-deformation of the Kittel–Shore model for
spin-1 systems. We analyse the impact of this deformation on the thermodynamic properties and phase transitions of the system as a function of the deformation parameter $q$. Specifically, we study the specific heat,
magnetic susceptibility, and magnetisation, including a detailed analysis of the Curie temperature characterising the ferromagnetic phase. Furthermore, a finite-size scaling analysis is conducted for both the ferromagnetic and antiferromagnetic cases. Results are systematically compared with those of the undeformed model to reveal the physical effects of the $q$-deformation.
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Statistical Mechanics
2D target search with boundary-induced resetting
Kevin Chen and Paul C. Bressloff
Most studies of
stochastic search processes with resetting focus on spontaneous resetting events that occur at a random sequence of times typically generated by a Poisson process. One of the major consequences of spontaneous resetting is that it yields a finite mean first passage time (MFPT) in unbounded domains, resulting in an optimal resetting rate that minimises the MFPT. An optimal resetting rate can also occur in bounded domains provided that the reset point is not too far from the target. Recently, there has been growing interest in event-based rather than spontaneous resetting, where resetting is triggered when a specific threshold is reached. Identifying the threshold with a physical non-target boundary then leads to so-called boundary-induced resetting. In this paper, we explore the effects of boundary-induced resetting on single-particle diffusive search in a two-dimensional (2D) bounded domain $\Omega$ containing one or more small interior targets. The interior target boundaries are totally absorbing, whereas the exterior boundary $\partial \Omega$ is sticky. That is, whenever the particle reaches a point on $\partial \Omega$ it remains attached for a random waiting time $\tau$ after which it immediately resets to a fixed interior point $\x_0\in \Omega$. Using renewal theory, matched asymptotic analysis and Green's functions we calculate the unconditional MFPT for absorption by any of the targets and compare this with the corresponding MFPT of a search process on the same domain with a reflecting surface $\partial \Omega$ and no resetting. We show that boundary-induced resetting only reduces the MFPT relative to the no resetting case if the searcher's reset point $\x_0$ is sufficiently close to one of the targets.
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Materials Science
Unraveling the electronic structure and the oxygen $K$-edge x-ray absorption near-edge structure spectrum of DyFeO$_3$
G. Gebreyesus, Eric Macke, Pietro Delugas et al. (+5 more)
Rare-earth orthoferrites such as DyFeO$_3$ exhibit a rich interplay between localized rare-earth and transition-metal moments, giving rise to complex
magnetic phases and magnetoelectric phenomena. Understanding their electronic and spectroscopic properties from first principles requires an accurate description of the localized Fe-$3d$ and Dy-$4f$ states and their hybridization with O-$2p$ states. Here, we combine first-principles calculations and x-ray absorption near-edge structure (XANES) measurements to investigate the electronic structure and the O $K$-edge spectrum of DyFeO$_3$. We employ density-functional theory (DFT) with Hubbard $U$ corrections (DFT+$U$) determined from first principles using density-functional perturbation theory, the HSE06 hybrid functional, and orbital-resolved DFT+$U$ with Hubbard parameters calibrated to reproduce the electronic structure computed using HSE06. We find that standard DFT+$U$, despite improving the band gap, substantially underestimates the
crystal-field splitting of the unoccupied Fe-$3d$ states and consequently fails to accurately reproduce the separation of the two lowest-energy features in the O $K$-edge spectrum. HSE06 provides a more balanced description of the relevant electronic states, including the Fe-$3d$
crystal-field splitting. Mapping the corresponding electronic structure onto orbital-resolved DFT+$U$ yields a spectrum that remarkably reproduces the two lowest-energy experimental features and captures the main characteristics of the spectrum at higher energies. These results establish the low-energy O $K$-edge features as a sensitive probe of the Fe-$3d$
crystal-field splitting, while showing that the localized Dy-$4f$ states leave no distinct spectral fingerprints despite their importance for the
magnetic properties.
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All authors G. Gebreyesus, Eric Macke, Pietro Delugas, Weiguo Jing, Banani Biswas, Carlos A. F. Vaz, Christof W. Schneider, Iurii Timrov
Mesoscale and Nanoscale Physics
Plasmonic Modes in hybrid Josephson Junction Arrays
Alex Kirchner, Simon Feyrer, Vjeko Dimić et al. (+9 more)
We present microwave characterization measurements of Josephson junction arrays (JJAs) based on epitaxial Al-InAs
quantum well
heterostructure. The Josephson inductance of the constituent planar junctions can be derived by probing the low-energy plasmon modes of these devices. Applying an out-of-plane
magnetic field gives rise to a Fraunhofer-like diffraction pattern, from which the current-phase relation and the effective transparency can be extracted. JJAs can be used to achieve high inductances, suitable for the implementation of
quantum circuits. They also provide an excellent test-bed for studying the microscopic excitations of hybrid
superconductor-
semiconductor devices associated with the presence of Andreev states. Here, we demonstrate their tunability over a broad range of out-of-plane
magnetic fields.
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All authors Alex Kirchner, Simon Feyrer, Vjeko Dimić, Johanna Berger, Davide Curcio, Giorgio Biasiol, Michael Prager, Matthias Kronseder, Dominique Bougeard, Nicola Paradiso, Christoph Strunk, Leandro Tosi
Quantum Gases
Synthetic Berry curvature in atom-cavity systems
Zheng Tang, Rui-Lin Zhang, Xiaotian Nie et al. (+2 more)
In atom-cavity systems, mean field theory is widely used, in which the
quantum cavity operator is replaced by a classical amplitude. Then the problem is converted into atoms moving in a self-consistent potential. The mean field treatment captures the physics of cavity mediated interactions, and predicts the self-organized superradiant phase. In this work, however, we show that it fails for certain atom-cavity coupling: it predicts zero ground state atomic current where the fully
quantum calculation exhibits a finite one. We find that the origin of this failure is the non-zero Berry
curvature in the synthetic dimension spanned by the
photon Fock ladder and real space. In this synthetic picture, the atomic current can be understood as Hall response of cavity detuning, whereas mean field collapses this dimension and discards the atom–
photon correlations required for its Hall response. The same beyond-mean-field geometry predicts Laughlin-like
photon generation under adiabatic flux insertion. Our work identifies synthetic Berry
curvature as a concrete mechanism for the breakdown of static mean field in atom–cavity physics.
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All authors Zheng Tang, Rui-Lin Zhang, Xiaotian Nie, Li Chen, Wei Zheng
Statistical Mechanics
The renormalization group for a slab model of the spin reorientation transition
D. Pescia
In 1975, Polyakov invented a renormalization group
algorithm for treating the problem of a classical isotropic planar Heisenberg ferromagnet. Here we define a tool - "parallel transport of frames" - that extends Polyakov's original renormalization group method to local
magnetic anisotropies and, most significantly, the non-local dipolar interaction. We apply this tool to the problem of the
spin reorientation transition in an ultrathin ferromagnetic slab with finite thickness. We find that integrating out the short wavelength
spin wave fluctuations generates two local anisotropies that are absent from the microscopic dipolar energy
Hamiltonian. Taking them into account yields the correct
topology of the
spin reorientation transition line, as observed experimentally and in numerical simulations.
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Materials Science
Experimental realization of the minimal two-dimensional multi-orbital kagome model
Bing Liu, Arka Bandyopadhyay, Manish Verma et al. (+11 more)
Kagome materials have emerged as a major platform for correlated and topological
quantum matter, hosting flat bands, Dirac dispersions and van Hove singularities rooted in frustrated
lattice geometry. While their essential physics is epitomized by the canonical single-orbital kagome model, real kagome materials are intrinsically multi-orbital and typically chemically and structurally complex, with additional three-dimensional coupling making kagome geometry and orbital degrees of freedom difficult to disentangle. Here we realize a truly two-dimensional, elemental two-orbital kagome system in monolayer Sb on SiC(0001). Substrate-induced orbital filtering isolates the in-plane Sb p_x/p_y orbitals into a six-band kagome
manifold, establishing a chemically simple, minimal platform for multi-orbital kagome physics. We demonstrate two consequences that distinguish this system from the canonical single-orbital model. First, chemically enforced half filling pins the Fermi level to a closed nodal line, whose finite density of states drives a unit-
cell-conserving breathing instability and opens a giant insulating gap. Second, we uncover orbital-resolved atomic obstruction: individual orbital-derived
manifolds realize obstructed atomic limits, whereas their combined half-filled valence
manifold is non-obstructed. Our results establish kagome antimonene as a
benchmark system for exploring orbital-driven electronic, structural and topological kagome physics in the genuine two-dimensional limit.
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All authors Bing Liu, Arka Bandyopadhyay, Manish Verma, Jonas Erhardt, Tim Wagner, Jing Qi, Kilian Strauß, Domenico Di Sante, Carmine Ortix, Simon Moser, Jörg Schäfer, Ronny Thomale, Giorgio Sangiovanni, Ralph Claessen
Soft Condensed Matter
Collective order reorganizes dissipation and powers an active engine
Michael Riedl, Vincent Wattiez, Étienne Fodor et al. (+2 more)
Motile active matter systems, from animal groups to synthetic particles, exhibit spontaneous self-organized transitions between disordered and ordered collective states. These transitions are driven by continuous energy injection, yet how energy consumption and dissipation change during these transitions remains poorly understood due to the challenge of measuring individual energetic fluxes. Here, we introduce a minimal experimental system of synthetic motile spheres that enables the first time-resolved power-budget characterization of collective motion. We show that the transition to an ordered state is accompanied by increased locomotion efficiency and a reorganization of dissipation pathways, shifting dissipation from internal friction to external slip with the environment. Leveraging this energetic reorganization, we construct an active engine powered by collective motion, capable of performing mechanical work against an external load. These findings establish energetic fluxes as quantitative observables for understanding collective state transitions and demonstrate how collective order can be harnessed for work extraction in active matter.
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All authors Michael Riedl, Vincent Wattiez, Étienne Fodor, Jan Brugués, Francesco Romanò
Mesoscale and Nanoscale Physics
Measurement protocol for non-adiabatic geometric phases of Floquet states
Carlos Martín-Fernández, Gloria Platero and Sigmund Kohler
Periodically time-dependent
quantum systems have Floquet solutions. They consist of a phase factor and a Floquet mode which shares the periodicity of the driving. Consequently, any such solution possesses a non adiabatic
geometric phase known as the Aharonov-Anandan (AA) phase. It is gauge-invariant and, therefore, is experimentally accessible. We propose a protocol for the measurement of AA phases based on the adiabatic change of the phase of the non-adiabatic driving. We argue that the experimental requirements of the protocol are those of previous measurements of adiabatic phases.
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Materials Science
Binary magnetism and directional magnon transport in alkali-doped CrI$_3$
Cihan Bacaksiz, Maarten Soenen, Denis Sabani et al. (+2 more)
The recent realization of two-dimensional (2D) magnets, with CrI$_3$ as a pioneering example, has opened new avenues in the fields of 2D materials and magnetism. This breakthrough has been followed by extensive efforts to manipulate and exploit their
magnetic properties. In this work, we investigate the adsorption of alkali-metal atoms as a route to control the
magnetic behavior of monolayer CrI$_3$. We show that, upon adsorption, alkali-metal atoms donate an electron to the CrI$_3$ layer, leading to the formation of inequivalent Cr sites, with one Cr atom exhibiting an enhanced
magnetic moment of $4~\mu_B$, while the other retains its typical $3~\mu_B$ moment. These modifications significantly alter the
magnetic exchange interactions, including the emergence of anisotropic exchange and Dzyaloshinskii–Moriya interactions (DMI). Consequently, the doped systems exhibit non-collinear
magnetic ground states, modified temperature-dependent magnetism, and anisotropic
spin-wave propagation, with a preferred propagation direction that becomes increasingly pronounced with increasing dopant size. Furthermore, an asymmetry between
spin-wave propagation in opposite directions is observed, giving rise to a diode-like effect, particularly for heavier dopants. This behavior is attributed to the enhanced DMI, which breaks the
symmetry of the
magnon dispersion. These results demonstrate that alkali-metal doping provides an effective route to tune anisotropic and nonreciprocal magnonic properties in two-dimensional
magnetic materials.
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All authors Cihan Bacaksiz, Maarten Soenen, Denis Sabani, Rai Maciel de Menezes, Milorad V. Milosevic
Mesoscale and Nanoscale Physics
Electrically controlled spin-splitting and asymmetric tunnel magnetoresistance in anti-altermagnets
Abhiram Soori
Anti-altermagnets (AAMs) are a recently identified class of layered
magnetic materials where opposite
spin-splitting in adjacent layers creates a globally
spin-degenerate band structure, rendering conventional spectroscopic detection highly difficult. In this paper, we theoretically demonstrate an all-electrical method to manipulate and probe this hidden
magnetic order using a dual-gated transport junction. By applying a perpendicular displacement field, we break the spatial inversion
symmetry of the
lattice, explicitly lifting the global
spin degeneracy. We attach ferromagnetic (FM) leads on either side of the AAM. Using
quantum transport calculations, we show that this gate-induced
spin-splitting manifests as a strongly asymmetric tunnel magnetoresistance (TMR) as a function of the lead magnetization. We identify specific crystallographic orientations where the TMR retains its
symmetry despite the fully split bands, a direct consequence of exact momentum-space compensation. We further reveal that Rashba
spin-orbit coupling guarantees robust, highly directional transport asymmetries even in the absence of an explicit chemical potential mismatch between the layers. Our findings establish a clear, electrically tunable framework for exploiting AAMs in next-generation spintronic architectures.
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