Materials Science
Exciton-induced magnons carrying orbital angular momentum in CrI3
Martin Pavelka, Vishal Shokeen, Ruslan Chulkov et al. (+15 more)
Magnons are collective
spin excitations that contain and transport
spin angular momentum in
magnetic materials. It has been suggested that they can also carry orbital angular momentum in analogy to the electronic motion around the
nucleus. We explore the real-space
topology of
magnon wave-packets emanating from atomic-like
excitons in the
ferromagnetic insulator CrI3 and demonstrate the existence of orbital angular momentum in such wave-packets. We reveal that orbital angular momentum of
magnons is nearly equal to their
spin angular momentum and compensates the latter. This illustrates the existence of an unexplored internal angular momentum balance and demonstrates that the magnetization can be quenched without the need of angular momentum exchange with the
lattice.
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All authors Martin Pavelka, Vishal Shokeen, Ruslan Chulkov, Soma Dutta, David Muradas Belinchón, Ulrich Noumbe, Mahmoud Abdel-Hafiez, M. Venkata Kamalakar, Mathias Augustin, Vitaliy Goryashko, Torstein Hegstad, Johan H. Mentink, Jamal Berakdar, Oscar Grånäs, Anders Bergman, Olle Eriksson, Anna Delin, Hermann A. Durr
Mesoscale and Nanoscale Physics
Extracting higher-order nonlinearities in nanomechanical resonators using the backbone relation
Maria Kallergi, Daniel K. J. Boneß, Maximilian Seitner et al. (+2 more)
Nanomechanical resonators are a powerful platform for studying nonlinear dynamics with high sensitivity and precision. We explore the nonlinear response of a high-Q nanomechanical string resonator in and beyond the Duffing regime and introduce a robust framework for accurately extracting its conservative nonlinearities. The method is based on the backbone curve obtained from ringdown measurements, making it inherently resilient to small frequency fluctuations while explicitly accounting for both
symmetry-breaking and non-
symmetry-breaking nonlinearities. To validate the approach, we perform complementary ringdown and frequency-response measurements on the nanostring resonator and
benchmark the backbone-based extraction against established frequency-response techniques. The comparison confirms the accuracy of the proposed framework and demonstrates its advantages over conventional methods for nonlinear characterization.
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All authors Maria Kallergi, Daniel K. J. Boneß, Maximilian Seitner, Wolfgang Belzig, Eva M. Weig
Quantum Gases
Benchmarking the fermionic quasi-1D many-body problem
Ekaterina Gradova and Frédéric Chevy
We investigate the validity of effective one-dimensional models for quasi-1D fermionic systems by benchmarking a coupled-channel approach against the exact low-energy theory derived from the underlying three-dimensional problem in the weakly and strongly attractive limits. We show that reproducing the exact two-body scattering amplitude is insufficient to construct the correct effective low-energy theory of quasi-1D
fermions. In the weakly attractive regime, it does not capture the emergent three-body interaction induced by transverse excitations. In the strongly attractive regime, it yields an atom-dimer scattering length with an incorrect dependence on the three-dimensional scattering length. These results demonstrate the limitations of effective one-dimensional descriptions based solely on two-body physics and highlight the need to explicitly include few-body correlations in quasi-1D systems.
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Superconductivity
Spin Josephson diode effect induced by higher-harmonic spin Josephson currents in a diffusive Josephson junction
Shin-ichi Hikino
We theoretically investigate the
spin Josephson diode effect (SJDE) in a diffusive Josephson junction with a Rashba metal layer under a
ferromagnetic exchange field. Within the quasiclassical Green's function framework, we derive analytical expressions for the first- and second-harmonic
spin Josephson currents. The interplay between Rashba
spin-orbit interaction and the exchange field breaks inversion and time-reversal
symmetries, generating additional cosine terms in the
spin current-phase relations and a finite phi0 phase shift. This phase shift induces an intrinsic asymmetry between forward and backward
spin currents, leading to the SJDE without an external
magnetic field. Numerical results show that the efficiency decreases with increasing metal thickness due to suppression of the second-harmonic component, while its dependence on
spin-orbit interaction strength reflects competing effects between phase shift enhancement and harmonic suppression. These findings demonstrate that the interplay between harmonic components provides a mechanism for nonreciprocal
spin transport without requiring suppression of
spin-singlet correlations.
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Materials Science
Resonantly-enhanced Raman response in graphene-capped bismuthene on SiC
Lukas Gehrig, Cedric Schmitt, Erica Fragomeni et al. (+15 more)
Two-dimensional
quantum spin Hall insulators based on atomic monolayers offer a promising route toward dissipationless electronics, yet their practical use is often limited by environmental instability. Encapsulating the system with a
graphene capping layer has been shown to be a reliable method to prevent oxidation and degradation. However, the confirmation of a successful encapsulation still relies on ultra-high
vacuum techniques, that considerably slow the process. Here, we present an ex situ, rapid, nondestructive and spatially resolved Raman characterization of
graphene-capped bismuthene, a honeycomb monolayer of Bi on SiC. A pronounced Raman scattering peak at around 122 cm-1 is identified as the E2g
phonon of bismuthene, via a comparison with density functional perturbation theory calculations. We use excitation-energy and polarization-dependent Raman measurements to enable an unambiguous assignment of the spectral features. Tuning the excitation energy close to the excitonic transition in pristine bismuthene, we observe a strong enhancement of the Raman response and the emergence of additional scattering peaks. In this regime, higher-order
phonon features, as well as interfacial modes between bismuthene and the SiC substrate, become visible, suggesting the involvement of resonant scattering processes. Our results establish Raman micro-spectroscopy as a versatile tool for probing
graphene-protected
quantum materials, providing access to
lattice dynamics and interlayer coupling.
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All authors Lukas Gehrig, Cedric Schmitt, Erica Fragomeni, Simone Sotgiu, Stefan Enzner, Tommaso Venanzi, Bing Liu, Kilian Strauß, Jonas Erhardt, Martin Kamp, Elena Stellino, Paolo Postorino, Jörg Schäfer, Simon Moser, Christoph Stampfer, Giorgio Sangiovanni, Ralph Claessen, Leonetta Baldassarre
Soft Condensed Matter
A numerical study to analyze the interplay of Weissenberg number and viscosity ratio in a log-strain tensorial model for viscoelastic fluids
Nehal Dash, Ramon Codina and Giulio G. Giusteri
We present a computational study aimed at exploring the different and independent roles of the Weissenberg number and of the ratio between the polymeric and solvent viscosity contributions in a viscoelastic fluid model. The tensorial model under investigation, recently proposed, is based on a logarithmic relation between the elastic (or recoverable) strain and the elastic stress. In this model, the elastic strain plays the role of a conformation tensor and its
evolution equation inherently preserves its determinant and positive definiteness. These properties are also enforced in the computational method employed in the study. A finite-difference discretization in time is combined with a stabilized mixed finite element formulation based on the Variational Multiscale method for the spatial discretization and with a generalized Lie derivative approach for the advection terms. The behavior of the model is analyzed in paradigmatic pressure-driven flows and we find that the value of the viscosity ratio is crucial in determining to which extent non-Newtonian flow profiles are observed upon increasing the Weissenberg number. By comparing the solutions of the log-strain tensorial model with those of a suitable Generalized Newtonian Fluid model, we show that flow-type dependence plays a significant role even in the simple planar flow past a cylinder.
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Statistical Mechanics · Cross-listed from quant-ph
Optimality of Gaussian Entanglement of Formation
Gerardo Adesso
We prove that the
entanglement of formation of every two-mode Gaussian state coincides with its Gaussian restriction, solving a longstanding open problem in continuous variable
quantum information theory. The key result is a sharp affine relation between
entanglement and a generalized Einstein–Podolsky–Rosen observable, valid for arbitrary pure two-mode states, including non-Gaussian ones. We further prove that the
entanglement of formation is additive on arbitrary tensor products of two-mode Gaussian states, and hence coincides with the
entanglement cost, settling the latter for all two-mode Gaussian states. As a consequence, we obtain in closed form the
entanglement cost of thermal-loss, thermal-amplifier and additive-noise bosonic channels. Our results, which also extend to bisymmetric multimode states, establish that no two-mode state is less entangled than the Gaussian state with the same covariance
matrix, yielding measurable lower bounds on both the
entanglement of formation and the
entanglement cost of arbitrary non-Gaussian states.
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Materials Science
Machine Learning Assisted Design of Complex and High Entropy Alloys by Hybrid HiPIMS/Pulsed-DC PVD Process for Low Carbon Energy Applications in Extreme Environments
Paul Foulquier, Ryma Haddad, Ali Mahmoud et al. (+4 more)
Complex and high
entropy alloys are attracting much
attention currently thanks to their mechanical and corrosion resistance properties in harsh environments, in particular needed for carbon-free energy applications. However, their elaboration in bulk and in thin film form in a trial-and-error approach is impractical due to their complexity and the cocktail effect. The recent development of artificial intelligence brings a new possibility for their elaboration and adjustment of their properties. Firstly, we present an overview of Materials and data science research. Then we describe how DIADEM - French initiative for Materials and Data science convergence - tackles the development of innovative coatings for carbon-free energy applications (
nuclear, high temperature electrolysis, ...) thanks to the development of a nationwide network of synthesis and characterization platforms - the DIADEM discovery hub. We describe in particular DIADEM-2D, an AI-driven Hybrid HiPIMS/Pulsed-DC PVD process using 4 cathodes in confocal combinatorial configuration. We present the high
entropy alloy determination using data from the literature for corrosion resistance in molten salt media and
nuclear accidental conditions. An element-independent model gathering deposition parameters and coating properties has been implemented allowing the design of protective coatings with a particular composition. We demonstrate the feasibility of this process and its accuracy.
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All authors Paul Foulquier, Ryma Haddad, Ali Mahmoud, Eric Monsifrot, Fanny Balbaud-Celerier, Jean-Philippe Poli, Frederic Schuster
Mesoscale and Nanoscale Physics
Wannier-Stark localization, confinement and edge states
N. Aucar Boidi, A. Aharony, O. Entin-Wohlman et al. (+1 more)
The boundary between a system's bulk and the
vacuum can be modeled by a potential which confines the electrons to the bulk. Here we present the example of the Wannier-Stark linear potential, generated by an electric field along one axis of a two-dimensional
lattice. Along that axis, the potential generates electronic states which are localized around each
lattice site, with eigenenergies which form the Wannier-Stark ladder. In the transverse direction, the states are governed by a tight binding model with free Bloch states. In the ground state, filling these states under the Pauli principle generates an insulating bulk and an edge which can be metallic in the transverse direction. This paper explains the concepts of localization, localization length, filling and confinement. The paper also acquaints the readers with the use of Bessel functions in the solution of a simple physical model. These topics can be easily included in courses on solid state physics, and only require prior knowledge of
quantum mechanics.
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All authors N. Aucar Boidi, A. Aharony, O. Entin-Wohlman, C.Proetto
Strongly Correlated Electrons
Microscopic magnetic phase evolution in the Weyl semimetal Mn$_3$Sn revealed by $\mu^+$SR
U. Miniotaite, O. K. Forslund, H. Luetkens et al. (+8 more)
We report a comprehensive
muon spin relaxation ($\mu^+$SR) and bulk magnetization study of the
antiferromagnetic (AFM) Weyl semimetal Mn$_3$Sn (composition Mn${2.99}$Sn). Mn$3$Sn is reported to exhibit a commensurate inverse triangular (IT) AFM phase, an incommensurate (IC) helical AFM phase, and a proposed low-temperature
spin-glass-like state. In our sample, we identify the characteristic temperatures associated with these regimes as N'eel temperature ($T\mathrm{N} = 418$ K), a macroscopic bulk transition temperature between IT-AFM to IC helical phase ($T\mathrm{t} \approx 275$ K), and low-temperature transition $T_\mathrm{f} = 21$ K. Investigating the low-temperature regime below $T_\mathrm{f}$, we find no evidence of a static
spin-glass state. Instead, the sample exhibits an increasing
ferromagnetic (FM) component accompanied by a localized slowing of
spin fluctuations, indicating that these phenomena may be decoupled. In the IC helical AFM phase, the zero-field (ZF) spectra are best described by damped oscillations with an empirical phase offset, consistent with anharmonic and amplitude-modulated order reported by scattering studies. Upon warming above 150 K, a continuous redistribution of
muon spectral weight reveals a broad, homogeneous
magnetic crossover between the IC helical and IT-AFM phases. In the commensurate IT-AFM phase above $T_\mathrm{t}$, a persistent missing fraction in the initial asymmetry indicates that a subset of implanted
muons, corresponding to roughly 20% of the sample-related asymmetry, undergoes unresolved ultrafast depolarization. Finally, we observe temperature-driven shifts in
muon site populations above 325 K. Ultimately, our results show a highly dynamic
magnetic landscape in Mn$_3$Sn, demonstrating how its complex
magnetic orders often coexist and evolve continuously with temperature.
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All authors U. Miniotaite, O. K. Forslund, H. Luetkens, V. Rai, J. Persson, G. D. Morris, D. Zuhair, D. W. Tam, S. Nandi, Y. Sassa, M. Månsson
Strongly Correlated Electrons
Diodes and capacitors for the transport of monopoles in fragmented spin ice
Anoop Raj, Sumiran Pujari and Ludovic D.C. Jaubert
Spin-ice materials are famous for their quasi-particle excitations that behave like
magnetic monopoles. Magnetricity is the concept that these monopoles can conduct an AC
magnetic current, in analogy with conduction electrons. While monopole dynamics has been intensively studied and is reasonably well understood, very little has been done to design devices in order to control magnetricity. Here we develop a theoretical proof of concept for the design of diodes and capacitors for the transport of monopoles. We use the property of systems with
magnetic fragmentation, where
spin-ice physics co-exists with long-range
antiferromagnetic order. The key point is that
magnetic order allows for the existence of domain walls. Under certain conditions of preparation, this domain wall is equivalent to an asymmetric filter for monopoles. In a given direction, positive charges can go through while negative ones are repelled; the opposite applies in the opposite direction. This asymmetry effectively functions like a diode for monopole current. Successive domain walls separate positive from negative charges with a
vacuum of charge in between, producing a capacitor for monopoles. Once the capacitor is charged, it can in principle be used as a battery for monopoles. All microscopic mechanisms are explained and our proof of concept is validated by simulations of more than a million
spins. Application to experiments are discussed for rare-earth pyrochlore
oxides and artificial
spin ice. Finally, we discuss in general terms how a domain wall in fragmented
spin ice can also be seen as an emergent boundary separating two mirror "worlds" separated by time-reversal
symmetry. Beyond
spin ice, our work opens a promising direction of investigation for the dynamics of emergent quasi-particles crossing domain walls in
chiral and nematic
spin liquids, which also possess a broken
symmetry.
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Statistical Mechanics
Gap distributions between successive personal bests in cricket: Data and Models
Priyanka D. Bhoyar and Prashant M. Gade
Successive personal best performances provide a natural measure of progression in an athlete's career. Classical record theory predicts a universal gap distribution, $P(g)\sim 1/g$, for independent and identically distributed (i.i.d.) sequences. However, sporting careers are shaped by learning, aging, changes in ability, and external influences that violate these assumptions. We investigate the statistics of inter-record gaps, defined as the number of innings between successive personal best scores, in cricket. Using career records of leading Test, ODI, and T20 players obtained from ESPN Cricinfo. We find that the empirical distributions are well described by truncated power law $P(g) \propto g^{-\alpha} e^{-\lambda g}$ with exponents in the range (0.799 $\leq \alpha \leq$ 0.843). Much of this deviation disappears when the temporal ordering of innings is destroyed, indicating that career
evolution plays a key role in shaping record occurrence. Bootstrap-shuffled careers, which preserve individual score distributions and career lengths while removing temporal ordering, yield significantly larger exponents ($\alpha \approx 0.939\text{--}0.979$). These findings show that the progression of personal best performances retains information about the temporal organization of a player's career and cannot be fully explained by simple
stochastic record processes. More generally, they illustrate how record statistics are altered in nonstationary and path-dependent systems.
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Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Local network growth: How simple rules drive network complexity
Alexei Vazquez
The Internet, a living
cell, a circle of friends, a billion-dollar construction project: these systems share almost nothing – yet, drawn as networks, they look astonishingly alike. Each has a few
giant hubs among a multitude of sparsely connected nodes, short paths between any two parts, dense local clustering, communities, and many redundant routes. For two decades such patterns have been credited to "preferential attachment," the rich getting richer – a rule that, taken literally, asks every newcomer to survey the whole network before it links. This book makes a simpler case, and defends it one mechanism at a time: the global regularities of real networks are not imposed from above but emerge from purely local rules, in which each new node acts only on a node it has reached and that node's immediate neighbours. A surfer following links, a friend introducing a friend, a gene copied with its connections – none consults the network as a whole, yet each builds, in the aggregate, the full and unmistakable signature of a real complex system. Written for the curious reader as much as the specialist, with the ideas told in plain
language and the mathematics set aside in boxes that can be skipped, it shows how citation graphs, the web, social ties,
protein interactions, and project schedules all grow themselves from the same handful of local rules – one local decision at a time.
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Strongly Correlated Electrons
Topological Defects in Triple-$Q$ Magnetic Orders: A Fixed-Lattice Homotopy Classification
Jin-Tao Jin and Yi Zhou
Multiple-$Q$
magnetic orders combine continuous
spin rotations with discrete crystalline sectors associated with translations and point-group transformations, producing a richer defect structure than conventional single-$Q$ magnets. We classify the bulk defects of all seven stable phases for $N=2$ and $3$ in the $M$-point triple-$Q$ Ginzburg–Landau theory with $(\Vfour\rtimes\Dthree)\times\OO(N)$
symmetry, where $\Vfour$ is the translation-generated Klein four-group. The atomic
lattice is treated as a prescribed background, with
lattice dislocations and disclinations excluded and the three
Fourier fields retaining their physical $M$-point labels. The parent-group transformations continuously connected to the identity form $G_0=\{e\}\times\SO(N)$. For a reference-state stabilizer $H$, the connected component containing the reference state is $G_0/(H\cap G_0)$, not the quotient obtained by projecting $H$ onto
spin space. This distinction gives the orthogonal triple-$Q$ phase the full
manifold $\OO(3)$, with chirality walls and Abelian $\ZZ_2$ frame
vortices rather than non-Abelian binary-polyhedral
vortices. Every connected component of the $\OO(2)$ phases supports an integer $2\pi$
vortex, whereas fractional windings close only when attached to a discrete-domain wall and are linearly confined at nonzero wall tension. Translation
symmetry further forbids cross-gradient bilinears, reducing the quadratic elastic sector to an isotropic and an $M$-point-locked anisotropic stiffness. The classification separates free internal defects, crystalline domain walls, and wall-bound composites in triple-$Q$ magnets.
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Disordered Systems and Neural Networks
Tunneling the Loss Landscape: Bypassing Memorization with Monte Carlo Parameter Swapping
Lai Shun Chan, Xiaotian Zhang, Yue Shang et al. (+2 more)
Grokking is a striking phenomenon in neural network training, where a model can undergo a prolonged period of pure memorization before abrupt generalization. While previous works have attempted to interpret it through classical machine learning mechanisms like weight norm, recent research draws an analogy from statistical physics, framing grokking as a form of computational glass relaxation. This theory defines the initial memorization as a result of `fast cooling' where the training loss is reduced so quickly that a glass state is formed, followed by a `slow relaxation' towards final generalization. Although providing a unifying framework for representative grokking theories, this perspective has remained largely at the theoretical on macroscopic level without direct empirical validation on training dynamics. Here we introduce a three-component framework to directly characterize the training dynamics via parameter mobility (PM), and two representative measurements from glassy dynamics: replica correlation (RC) and fractal dimension (FD). We demonstrate that standard optimization presents clear signatures of glass dynamics and inherently traps the grokking network in a kinetic arrested memorization state with a collapsed mobility, strong history dependence, and channel-like motions. This quantitative agreement motivates us to introduce State-Aware Monte Carlo Parameter Swapping (SAM-Swap), an optimization plug-in that can accelerate generalization, inspired by swap Monte Carlo
algorithm widely used in glass dynamics. Comparing SAM-Swap, weight decay, and Gaussian gradient noise, we find that accelerated generalization is consistently associated with random exploration in the parameter space, similar to
diffusion in physics.
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All authors Lai Shun Chan, Xiaotian Zhang, Yue Shang, Ge Zhang, Entao Yang
Strongly Correlated Electrons
Emergent modular Luttinger liquid from spin-partitioned entanglement in the one-dimensional Hubbard model
Ádám Bácsi, Catalin Pascu Moca and Balázs Dóra
We study the
spin-partitioned
entanglement Hamiltonian of the one-dimensional repulsive Hubbard model. By combining bosonization with exact diagonalization, we show that tracing out one
spin species produces a modular Luttinger
liquid, whose properties fundamentally differ from those of the physical system. While the modular spectrum is fully dispersionless and possesses a momentum-independent
entanglement gap, its eigenstates exhibit algebraic correlations governed by a single effective Luttinger parameter equal to the
geometric mean of the charge and
spin Luttinger parameters. The resulting
entanglement spectrum displays a universal branching hierarchy in excellent agreement with exact diagonalization. We further demonstrate that the modular ground state is nearly identical to that of the spinless Luttinger
liquid. These results uncover a universal modular structure in interacting one-dimensional fermionic systems.
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Materials Science
Dual-Mode Exciton Coupling in Epitaxially Registered Organic-Inorganic 2D Heterocrystals
Eunbeen Jeon, Kihyun Lee, Jieun Yeon et al. (+5 more)
Two-dimensional (2D) heterocrystals comprising molecules and
semiconductors can serve as an ideal platform for studying interfacial
excitons and for future optoelectronic applications, yet the energy and charge flow across these atomically sharp interfaces remain unclear. In this work, we investigated PTCDA-MoS2 as a prototypical 2D organic-inorganic
heterostructure and revealed dual-mode
exciton coupling between the constituent
crystals. Monolayer-resolved PTCDA molecular
crystals were grown on monolayer MoS2 via physical vapor assembly, and their crystallographic details, including the stacking angle, were determined by electron diffraction. Upon the formation of the
heterostructures, PTCDA's photoluminescence was completely quenched because of organic-to-inorganic hole transfer, whereas that of MoS2 increased markedly with PTCDA thickness. Using differential reflectance and photoluminescence excitation spectroscopy, we found that the enhancement arises from two distinct mechanisms. Ground-state charge transfer injects holes into MoS2, which suppresses negative trion formation and enhances the radiative recombination of neutral
excitons. In addition, resonant energy transfer, enabled by spectral overlap between PTCDA and MoS2, diverts excitation energy from PTCDA to MoS2. Our findings reconcile previously proposed mechanisms and establish a unified framework in which charge and energy transfer cooperate to govern
exciton coupling at organic-inorganic interfaces.
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All authors Eunbeen Jeon, Kihyun Lee, Jieun Yeon, Juseung Oh, Kenji Watanabe, Takashi Taniguchi, Kwanpyo Kim, Sunmin Ryu
Statistical Mechanics
Universal Scaling of the Magnetocaloric Effect in 2D Ising Monolayers and Bilayer
Basit Iqbal and Kingshuk Sarkar
We report a Monte Carlo study of the magnetocaloric effect (MCE) in two-dimensional
ferromagnetic Ising models on square, honeycomb, and triangular
lattices with monolayer and
bilayer configurations. Using Binder cumulant analysis, we determine the critical temperature ($T_c$) of each structure and find that $T_c$ increases with coordination number, from the honeycomb ($r=3$) to the triangular ($r=6$)
lattice. In contrast, the
magnetic entropy change ($-\Delta S_M$) decreases with coordination number, reaching its maximum for the honeycomb
lattice. After normalization by their peak values and appropriate temperature scaling, both $-\Delta S_M$ and the field exponent $n$ collapse onto universal master curves for different
magnetic fields and across all six
lattice structures at a fixed low field. This demonstrates universal MCE scaling independent of coordination number and layer count. Critical scaling analysis further supports the observed universality and power-law behavior. Unlike $-\Delta S_M$, the adiabatic temperature change ($\Delta T_{ad}$) increases with coordination number, whereas the
magnetic Grüneisen parameter ($\Gamma_M$) follows the same trend as $-\Delta S_M$. Although the peak value of $-\Delta S_M$ decreases with coordination number, the relative cooling power and cooling capacity remain nearly unchanged due to compensating broadening of the $-\Delta S_M$ curves. The field dependence of $-\Delta S_M$, relative cooling power, and cooling capacity follows power laws up to $\sim2.6$ T (assuming $J\approx1$ meV). Hysteresis analysis shows that
lattices with lower coordination numbers exhibit a faster reduction in loop width with increasing temperature. These results establish the universal scaling behavior of the magnetocaloric effect in two-dimensional monolayer and
bilayer magnetic lattices and provide guidelines for designing
magnetic refrigerants.
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Soft Condensed Matter
Fluid-structure coupling governs a dynamic transition in foam scraping
Rei Kurita and Masaya Endo
Foam scraping exhibits a dynamic transition between a slip state, in which the foam moves beneath a plate, and a scraping state, in which the foam is expelled from the confined region. Although this transition has been associated with the propagation of local T1 rearrangements, the physical parameter controlling their propagation remains unclear. Here, we investigate the dependence of the critical scraping velocity on the
liquid fraction, bulk viscosity, and surfactant system. For all examined conditions, the critical capillary number follows $\mathrm{Ca}_c\propto\phi^{-1}$, apart from a solution-dependent prefactor. We propose a local fluid–structure-coupling model in which viscous work transmitted through the Plateau-border network competes with the effective energetic cost required for one T1 event to trigger the next. The observed scaling implies an effective energetic cost governed by the Laplace pressure and is consistent with a small local compressive component of the bubble deformation. These results identify local coupling between interstitial flow and bubble deformation as a mechanism controlling the macroscopic slip–scraping transition.
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Soft Condensed Matter
Impedance of an electric double layer capacitor with a multi-component electrolyte
David Fertig
I derive the impedance response of an ideal electrolyte containing an arbitrary number of mobile ionic species between blocking planar electrodes, described by the Poisson–Nernst–Planck equations. By transforming the linearized equations to a charge–salt basis, the response is written in terms of a multi-component
diffusion–migration
matrix and its
eigenvalues/eigenvectors. When all diffusivities are equal, the charge mode decouples from the neutral concentration subspace and the classical binary-electrolyte result is recovered. In contrast, unequal diffusivities couple charge relaxation to one or more neutral composition modes. For a ternary electrolyte with two cations and one anion, this coupling produces additional diffusive features and broadens the crossover between resistive and capacitive regimes. The results found in this paper provide a minimal continuum explanation for why mixed electrolytes can display impedance spectra that cannot be interpreted as a simple binary electrolyte with an averaged
diffusion coefficient.
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Statistical Mechanics · Cross-listed from quant-ph
Validation and calibration of quantum hardware through the many-body quantum Mpemba effect
Francesco Campaioli, Marco Avesani, Oren Raz et al. (+2 more)
We introduce a validation process that harnesses engineered many-body relaxation to control and calibrate
quantum hardware. On two independently developed neutral-atom processors, we realize the many-body
quantum Mpemba effect in an open system for the first time. Initial-state engineering creates fast and slow relaxation pathways: the fast pathway opens access to unreachable mixed-state physics before hardware noise obscures the target dynamics, whereas the slow pathway amplifies hidden imperfections in preparation and control. Computational-basis measurements directly and independently
benchmark dynamical reliability, revealing each processor's actual operating window as a many-body simulator. The processors are thus judged by the very dynamics they are built to reproduce. Complementary responses disentangle control errors and drive an adaptive, time-resolved scheme that supplies hardware developers directly actionable corrections, enhancing faithful reproduction of the target dynamics. These results establish many-body relaxation as a transferable validation and calibration tool for programmable
quantum processors.
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All authors Francesco Campaioli, Marco Avesani, Oren Raz, Roderich Moessner, Gianluca Teza
Mesoscale and Nanoscale Physics
Non-linear spin current in the surface states of topological insulators
Srijan Chatterjee and Tarun Kanti Ghosh
Spin Hall effect is one of the primary sources of pure
spin current in spintronic devices, observed in
spin-orbit coupled materials. In this work, we investigate linear and non-linear pure
spin currents in the hexagonally warped surface states of topological
insulators like $\rm Bi_2Te_3$, using the formalism of conserved
spin transport. The hexagonal warping effect enables the application of this formalism by providing a well-defined Berry
curvature without breaking the time-reversal
symmetry. The absence of in-plane
spin currents in the linear response motivates the extension of the formalism to the non-linear regime, by combining the perturbation of Bloch states with the Boltzmann transport equation. The second-order response exhibits both intrinsic and extrinsic in-plane
spin currents induced by the
spin-weighted Berry
curvature, Berry connection polarizability (BCP) dipole and Berry
curvature dipole (BCD) respectively. The band anisotropy due to the $C_{3v}$
symmetry of the material ($\rm Bi_2Te_3$) propagates through the
spin textures and the band
geometric quantities, resulting in the selection of certain components of the
spin conductivity tensors.
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Materials Science
Machine-Learning-Accelerated Metallene Stabilization from High-Throughput Sandwich Modeling
Mohammad Bagheri and Pekka Koskinen
Metallenes have appealing properties, but stabilizing them in a monolayer phase poses challenges for their synthesis. A recent experiment showed that the van der Waals squeezing method can stabilize certain metallenes in a MoS2 sandwich. This pioneering work motivates systematic studies, but such studies are experimentally impractical, while first-principles modeling remains prohibitive. Here, armed with universal machine-learning interatomic potentials, we constructed 1620 metallene sandwich
heterostructures containing 6 different sandwich layers and 45 metals. We performed
phonon calculations, which revealed 1208 dynamically stable structures. We found that transition-metal dichalcogenides, particularly MoSe2, are highly effective in stabilizing metallenes. Specifically, buckled hexagonal and honeycomb
crystal lattices exhibit the greatest stability. We further evaluated the thermal stability of selected
heterostructures with density-functional theory molecular dynamics simulations at room temperature. By uncovering the physical and chemical factors governing the stabilization of metallenes, our results provide systematic insights to guide and accelerate synthesis for future applications.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Tip-Enhanced Vibrational Ladder Climbing in Surface Molecular System
Tatsuto Mochizuki, Shota Takahashi, Atsunori Sakurai et al. (+1 more)
Achieving high-lying vibrational states is essential for actively controlling molecular reactions. We demonstrate vibrational ladder climbing of CO adsorbed on Pt(111) within the plasmonic tip-substrate nanogap formed in a scanning tunneling microscope, detected via tip-enhanced sum-frequency generation (TE-SFG). As the infrared pulse energy increases, hot-band peaks appear sequentially up to the 3-4 transition, indicating the stepwise population of higher vibrational states. Numerical analysis using the optical Bloch equations captures the observed energy dependence of these features. These results demonstrate the capability of TE-SFG to probe vibrational ladder climbing in surface molecular systems and suggest a promising route toward accessing high-lying vibrational states and controlling vibrational excitation at the nanoscale.
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All authors Tatsuto Mochizuki, Shota Takahashi, Atsunori Sakurai, Toshiki Sugimoto
Quantum Gases
Fate of moiré flat bands for a weakly repulsive Bose-Einstein condensate in one-dimensional $\mathcal{PT}$-symmetric bichromatic optical lattices
Enhong Cheng, Yu Tan, Yanzhen Xu et al. (+1 more)
One-dimensional (1D) superlattices provide one simplified platform for exploring moiré physics from a low-dimensional perspective, with the ratio of
lattice constants playing a role analogous to the twist angle in two-dimensional
bilayers. Here, we propose a 1D $\mathcal{PT}$-symmetric bichromatic optical
lattice for a weakly repulsive Bose-Einstein condensate and investigate how the interplay of dissipation and interaction impacts the lowest moiré flat band. Without interaction, we find that the lowest-band flatness induced by commensurate ratios exhibits a parity-dependent response to the $\mathcal{PT}$-symmetric imaginary potential due to the distinct $\mathcal{PT}$ pairing mechanism for the energy spectrum. For ratios with even denominators (i.e., even parities), the level attraction and thus the $\mathcal{PT}$-
symmetry breaking occur within the lowest two bands, leading to a monotonic broadening of the lowest flat band, whereas odd denominators (i.e., odd parities) yield a nonmonotonic response due to the $\mathcal{PT}$-
symmetry breaking within the second and the third lowest bands instead while the lowest band remains purely real. This parity-dependent phenomenon can be understood by the perturbation theory. Furthermore, by solving the Gross-Pitaevskii equation, we also find that although the weak repulsive interaction can broaden the moiré bands alone, the combined effects of interaction and imaginary potential also lead to parity-dependent behaviors. For even parities, band flattening is consistently diminished, whereas for odd parities, the imaginary potential can either enhance or reduce the degree of flattening. These results pave the way for experimental studies of dissipation and interaction effects on band flatness in moiré systems.
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All authors Enhong Cheng, Yu Tan, Yanzhen Xu, Li-Jun Lang
Materials Science
Physics-Informed Neural Networks for Sparse Strain-Field Reconstruction in 4D-STEM
Roberto dos Reis, Gabriel T. dos Santos, Yukun Liu et al. (+2 more)
Quantitative strain mapping using four-dimensional scanning transmission electron microscopy (4D-STEM) typically requires densely sampled scans that can damage beam-sensitive specimens. We develop a physics-informed neural network (PINN) for sparse 4D-STEM strain reconstruction that embeds elastic
equilibrium and Saint-Venant compatibility in the training loss through automatic differentiation. The architecture combines a coordinate-based implicit representation, sine activations with stable second derivatives, frozen residual-scale normalization, an exponential physics-weight ramp, and residual-based adaptive collocation. We apply a sine-activated residual network to an experimental $180\times400$-pixel strain map of domain-structured PbGeSnSe$_{1.5}$Te$_{1.5}$. Across $1$-$75%$ sampling ($720$-$54{,}000$ probe positions), $R^2$ for $\varepsilon_{xx}$ reaches $0.80$ at $10%$ sampling and saturates near $0.86$ by $25%$; the chevron strain-band morphology is recovered from $10%$ of probe positions. At $10%$ sampling, the PINN reduces mean absolute error by approximately $26%$ relative to compressed sensing and $22%$ relative to Gaussian-process regression. An ablation against an equal-capacity data-only SIREN shows that the PDE prior improves accuracy at extreme sparsity and consistently improves physical self-consistency, but biases the reconstruction when data are abundant. Monte Carlo dropout and mean-field variational inference provide per-pixel epistemic uncertainty maps correlated with reconstruction error. With an appropriate constitutive model, the framework is adaptable to strain mapping across diverse material systems.
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All authors Roberto dos Reis, Gabriel T. dos Santos, Yukun Liu, Xiaobing Hu, Vinayak P. Dravid
Mesoscale and Nanoscale Physics · Cross-listed from math-ph
Beyond $K$-Theory: Geometry and Holomorphy in Hyperbolic Band Theory
Steven Rayan
Topological $K$-theory supplies the decisive stable classification principle for gapped free-
fermion phases in Euclidean
crystals once
symmetry and stabilization are fixed. In
hyperbolic band theory, by contrast, it is less decisive for the full band problem: generalized momentum sectors vary through
moduli spaces, but passing to ordinary $K$-classes collapses their
geometric and holomorphic variation. We distinguish kinematical holomorphy, in which complex geometry organizes the sector spaces, from dynamical holomorphy, in which that geometry informs a
Hamiltonian or projector, and formulate the resulting loss as an observable-factorization problem. For a compact
hyperbolic surface $X$, we prove nonfactorization in three settings: fibrewise $K^0(X)$, occupied-state $K^0(B)$, and operator-algebraic $K$-theory. The affected quantities include spectra and
Higgs spectral curves, the Berry holonomy and the
quantum metric, the partially filled
Hall response, and the
Fermi surface and nodal geometries. We also identify the quantized pairings and local charges retained by
topology. Up to an explicit area factor, the Kotani–Sunada bottom-band Hessian is the Hodge inner product on $H^1(X;\mathbb R)$. Together with the integral intersection form, it recovers the homology-marked principally polarized Jacobian and hence, by Torelli and uniformization, the underlying complex and
hyperbolic surface, though not a full Teichmüller marking. We also separate finite-rank sectors from the thermodynamic bulk. Locally faithful covers reproduce
polynomial traces exactly and control continuous spectral observables. In arithmetic congruence towers, analytic observables converge as $O(|G_n|^{-\eta})$ for some $\eta>0$, and $C^s$ observables as $O((\log |G_n|)^{-s})$, while established coherent large-rank limits recover bulk density-of-states moments.
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Statistical Mechanics
LieStoNet: Learning Lie Symmetries from Spatiotemporal Data for Stochastic Dynamical Systems
Shida Liu, Abhishek Gupta, Sumit Sinha et al. (+1 more)
Symmetry is central to modern machine learning and physics: invariances and equivariances improve sample efficiency, robustness, and out-of-distribution generalization, while
symmetry principles guide scientific modeling. Yet for
stochastic dynamical systems the relevant continuous
symmetries are rarely known, and
symmetry discovery for SDEs has remained essentially unexplored. We introduce LieStoNet, an end-to-end, template-free framework for discovering Lie-point
symmetries of SDEs directly from spatiotemporal trajectories, without prespecifying
symmetry groups, templates, or canonical coordinates. Building on the seminal SDE Lie-
symmetry theory of Gaeta and Quintero (1999), which formalizes Lie-point SDE
symmetries and their relation to Fokker-Planck
symmetries, LieStoNet learns neural surrogates for drift and
diffusion from increments, then learns projectable generators by enforcing the SDE determining equations, separately regularizing for closure under Lie brackets, adherence to the Lie
algebra axioms (bilinearity, antisymmetry, Jacobi), and a non-redundant independent basis. The surrogate also defines an associated Fokker-Planck equation, enabling optional discovery of its Lie-point
symmetries in parallel. Across multiple canonical SDEs with known analytic
symmetries, LieStoNet recovers generators consistent with the ground-truth
symmetry algebra, providing interpretable
symmetry discovery for noisy dynamics. Code is available at \href{https://github.com/sumit-sinha-seas/LieStoNet_Final.git}{this link}.
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All authors Shida Liu, Abhishek Gupta, Sumit Sinha, L. Mahadevan
Mesoscale and Nanoscale Physics
Layer-Hybridized Wigner Crystals in MoSe2/WS2 Moiré Superlattice
Tianyi Ouyang, Yuze Meng, Li Yan et al. (+11 more)
Transition metal dichalcogenide moiré heterobilayers with type-II band
alignment provide a versatile platform for layer-polarized generalized Wigner
crystals, in which strong Coulomb interactions drive charge ordering at fractional
lattice fillings. With a finite interlayer band offset, an out-of-plane electric field can tune layer-resolved moiré bands through resonance and enable controllable interlayer hybridization. Although hybridized Mott
insulators have been previously demonstrated, whether fractional charge-ordered states can survive such hybridization remains elusive. Here we drive an H-stacked MoSe2/WS2 moiré heterobilayer through a type-I-to-type-II band-
alignment transition and realize layer-hybridized Mott
insulator and generalized Wigner
crystals. For fillings below one electron per moiré
cell, tunneling delocalizes electrons and modifies Wigner crystallization. However, above one electron per
cell, Coulomb repulsion overcomes tunneling and favors layer-separated occupation, stabilizing stronger charge-ordered states. These results establish electrically tunable hybridized moiré heterobilayers as a powerful platform for engineering correlated charge order and exploring fractional Chern phases and emergent magnetism.
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All authors Tianyi Ouyang, Yuze Meng, Li Yan, Yuxuan Chen, Shuai Zhang, Xinyue Chen, Melike Erdi, Takashi Taniguchi, Kenji Watanabe, Seth Ariel Tongay, Benjamin Hunt, Ming Xie, Yong-Tao Cui, Su-Fei Shi