Soft Condensed Matter · Cross-listed from physics.flu-dyn
A Solid-Based Approach for Modeling Simple Yield-Stress Fluids: Rheological Transitions, Overshoot and Relaxation
Jehyeok Choi, Ju Min Kim and Kwang Soo Cho
Yield-stress fluids are ubiquitous and encountered in diverse fields ranging from natural muddy flows to industrial applications such as secondary battery electrode slurries and direct ink writing. Despite the proposal of various constitutive equations, few models have been shown to successfully predict both steady and transient rheological behaviors in yield-stress fluids. In this study, a constitutive equation is hereby proposed, offering a comprehensive description of the rheological characteristics observed in simple yield-stress fluids, excluding thixotropy, such as the Carbopol dispersion. The constitutive equation is derived from a Zener-type viscoelastic solid element combined with an additional linear dashpot connected in parallel, together with a nonlinear viscosity model, a flow rule, an
evolution equation for the back stress, and the Kroner-Lee decomposition. This combination satisfies the principle of material frame invariance. The proposed model successfully reproduces the rheological characteristics qualitatively in a manner consistent with experimental observations conducted during start-up shear, creep, and stress relaxation tests. In particular, the present viscoelastic solid-based constitutive equation is shown to accurately predict stress overshoot during start-up shear. Importantly, the overshoot is found to originate from a homogeneous mechanism in which normal stress difference enhances the stress invariant and thereby accelerates the plastic response, rather than from isotropic hardening or spatially heterogeneous microstructural
evolution. This study is expected to facilitate a deeper understanding of the intricate dynamics governing the flow of yield-stress fluids.
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Statistical Mechanics · Cross-listed from physics.chem-ph
Electron dynamics mediate the water-carbon {\pi} bond
N. LeMessurier, E. Katz, R. Pant et al. (+5 more)
The intermolecular interaction between a water molecule and the electrons in aromatic {\pi} systems–the water-{\pi} bond–lies at the heart of many chemical processes, yet its properties remain challenging to measure experimentally and model computationally. Infrared spectroscopy of pyrene anions hydrated by a single water molecule reveals vibrational and electronic motions that are often hidden in condensed phase measurements. Results from new machine-learning approaches to potentials and dipole moments show that the electron dynamics of the aromatic {\pi} cloud quench signals from some of water's vibrations and amplify others. The observed interplay between electronic and vibrational motions has general implications for modeling intermolecular interactions between water and aromatic systems in clusters, solutions, and at interfaces.
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All authors N. LeMessurier, E. Katz, R. Pant, S. Ganley, H. Salzmann, L. M. McCaslin, J. M. Weber, J. D. Eaves
Materials Science
Microwave-to-optical transduction using magnon-exciton coupling in a layered antiferromagnet
Pratap Chandra Adak, Iris McDaniel, Suvodeep Paul et al. (+12 more)
Coherent interfaces between microwave-frequency
quantum systems and low-loss optical links are essential for
quantum networks. However, existing microwave-optical transducers often trade conversion efficiency against added noise, bandwidth, and device integrability. Here, we demonstrate coherent microwave-to-optical transduction based on
magnon-
exciton coupling in the layered antiferromagnet CrSBr. Driving the
antiferromagnetic resonance with microwave signals imprints coherent modulation on a reflected optical probe, generating optical sidebands that are resonantly enhanced near excitonic transitions. While prior
magnon-based approaches to microwave-to-optical transduction have typically relied on intrinsically weak off-resonant magneto-optical effects (e.g., Faraday rotation), our scheme exploits strong light-matter interactions at
exciton resonances. Even in a bulk
crystal without cavity enhancement, we observe coherent conversion over an intrinsically broadband window of ~ 300 MHz. We further show that multiple
exciton-polariton resonances inherit the
magnon-coupled response, suggesting a route to broaden the usable optical detuning range and to mitigate optical dissipation. Our results establish
magnon-coupled
excitons in layered magnets as a scalable platform for broadband microwave-optical interfaces, with pathways to higher cooperativity via reduced
magnetic volume and cavity integration.
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All authors Pratap Chandra Adak, Iris McDaniel, Suvodeep Paul, Caleb Heuvel-Horwitz, Bikash Das, Vitali Kozlov, Kseniia Mosina, Arun Ramanathan, Xavier Roy, Zdeněk Sofer, Tian Zhong, Akashdeep Kamra, Arno Thielens, Andrea Alù, Vinod M. Menon
Soft Condensed Matter
Shear Banding in Simulations of Polymer Melts
Lucas L. Nelson, Gary S. Grest and Peter D. Olmsted
Results from numerical simulations of
polymers under shear flow are compared with predictions for shear banding based on a model coupling Rolie-Poly-like tube dynamics to the
entanglement dynamics mediated by Convected Constraint Release (CCR). CCR is controlled by a parameter $\beta$, whose dependence on the bending stiffness $k_{\theta}$ is calculated from the simulations. The model predicts shear banding for
polymers whose
equilibrium entanglement number $Z$ exceeds a critical value $Z_{c}$ that depends on $\beta$. The simulations are in semi-quantitative agreement with the model, with deviations that are attributed to approximations inherent in the model, and the inadequacy of tube models to describe partially-disentangled
liquids in strong flow. These results may help determine which physical
polymers could undergo shear banding.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph
Universal Scaling and Many-Body Resurrection of Polaritonic Double-Quantum Coherences
Maxim Sukharev
The ultrafast nonlinear optical response of molecular ensembles is fundamentally altered under strong light-matter coupling. To rigorously isolate the genuine many-body contributions, an exact time-domain field-subtraction protocol is developed within a fully non-perturbative Maxwell-Liouville framework explicitly incorporating the two-
exciton manifold in real space and time. This approach reveals that while collective cavity delocalization drives the macroscopic nonlinear signal toward a severe harmonic cancellation (an effect termed "spectral starvation"), intrinsic many-body molecular interactions robustly resurrect genuine polaritonic double-
quantum coherences (DQCs). This many-body resurrection is governed by a universal two-
photon matching rule, $\Delta_B + 4J = \Omega_R$, linking molecular anharmonicity ($\Delta_B$) to the macroscopic Rabi splitting ($\Omega_R$) and excitonic coupling ($J$). Crucially, this resonance exploits the spatial mismatch between macroscopic polaritons and localized two-
exciton pairs to break harmonic cancellation. For J-aggregates ($J < 0$), this condition uniquely isolates the resonant many-body state below the dense
manifold of localized dark states, protecting the macroscopic coherence from spatial fragmentation. This predictive framework establishes a direct phase diagram to engineer and protect optical nonlinearities across diverse strongly coupled platforms.
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Soft Condensed Matter
Anatomy of a Complex Crystallization Pathway
Charlotte Shiqi Zhao, Domagoj Fijan and Sharon C. Glotzer
Using molecular dynamics simulations, we investigate the crystallization pathways of two exemplary systems that form the same complex
crystal structure but differ fundamentally in the nature of their particle interactions. One system is composed of point particles interacting via an isotropic pair potential characteristic of metallic compounds, while the other system contains hard polyhedra whose interactions arise from emergent entropic forces. Despite the stark difference in the origins of the particle interactions, we find that both systems are polymorphic and share the same
crystal polymorphs. Moreover, the two systems follow the same multistep crystallization pathways, and by examining the complex crystallization pathways on the single particle level, we find that the local structure
evolution of the two systems is also similar. By mapping the hard particle system's interaction to an effective pairwise potential, we find that such resemblance arises from the particle interactions being effectively similar.
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Soft Condensed Matter · Cross-listed from cs.CE
A Differentiable Framework for Gradient Enhanced Damage with Physics-Augmented Neural Networks in JAX-FEM
Mark Wilkinson, Amirhossein Amiri-Hezaveh and Adrian Buganza Tepole
Soft materials such as rubbers, hydrogels, and biological tissues undergo damage in the form of stiffness degradation without apparent changes in their stress-free geometry. Accurate simulation of this behavior is critical in applications ranging from soft robotics to the design of medical devices, yet two persistent challenges are the difficulty of constructing flexible, thermodynamically consistent constitutive models, and the mesh dependence of finite element solutions caused by strain softening. Here we address both challenges simultaneously by combining physics-augmented neural network constitutive models with a gradient-enhanced damage formulation implemented within the differentiable finite element framework JAX-FEM. The elastic strain energy and the damage yield function are each parameterized by input-convex neural networks (ICNNs), which enforce polyconvexity and satisfaction of the Clausius–Duhem inequality by design. The gradient-enhanced formulation introduces a non-local damage field governed by an additional partial differential equation, regularizing the spatial distribution of damage and eliminating mesh dependence. The implementation is validated through local stress-strain fits, single-element parametric studies, a mesh and solution strategy study for a uniform deformation case, and a notched plate simulation. The results demonstrate that the proposed framework enables flexible, data-driven, mesh-independent damage simulation for a broad class of soft materials. We anticipate that the open-source implementation will lower the barrier to adopting physics-augmented neural network constitutive models.
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Superconductivity
Enhanced Kadowaki-Woods Ratio and Weak-Coupling Superconductivity in Noncentrosymmetric YPt$_2$Si$_2$ Single Crystals
Gustavo Gomes Vasques, Shyam Sundar, Deisy Aristizábal-Giraldo et al. (+6 more)
Superconductivity in noncentrosymmetric RPt2Si2 (R = rare earth) compounds exhibit a rich playground to explore the competition between different ground states, such as unconventional superconductivity, antiferromagnetism and charge density wave. Here, we report the successful single
crystal synthesis of noncentrosymmetric YPt2Si2
superconductor, with a transition temperature Tc = 1.67 K, via Sn flux method. The high quality of the prepared single
crystals was confirmed using powder and Laue XRD measurements. The superconducting and normal state properties are investigated using electrical transport and heat capacity measurements down to 0.5 K. In the normal state, unlike LaPt2Si2, no charge density wave transition is observed in YPt2Si2, as evidenced by electrical transport and specific heat measurements. A relatively large Kadowaki-Woods ratio and a linear temperature variation of the electrical resistivity in an extended temperature range of 50-300 K suggest an unconventional normal-state in YPt2Si2. The estimated superconducting parameters indicate that YPt2Si2 is a type-II
superconductor with weak electron-
phonon coupling. The temperature dependence of specific heat in the superconducting state can be explained reasonably well using an isotropic two-gap model. A positive
curvature near Tc in the temperature variation of upper critical field also supports the two-gap superconductivity. First-principles DFT calculations suggest a BCS-like superconducting state driven primarily by d-electron contributions. The calculated electron-
phonon coupling constant identifies the material as a weak-coupling
superconductor, with the McMillan-Allen-Dynes formula yielding a Tc of 1.8 K. Additionally, we provide a comparative analysis of the superconducting and normal-state properties of YPt2Si2 and compositionally similar LaPt2Si2.
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All authors Gustavo Gomes Vasques, Shyam Sundar, Deisy Aristizábal-Giraldo, Juan F. Castello-Arango, Rafael Sá de Freitas, Adriano Reinaldo Viçoto Benvenho, Takahiro Onimaru, Jorge M. Osorio-Guillén, Marcos A. Avila
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
V. Srinivasa
We present an approach for entangling
spin qubits via capacitive coupling mediated by an ac electric field-driven multielectron mediator
quantum dot. To illustrate this method, we consider the case of a driven two-electron dot that mediates
entanglement between resonant exchange
qubits defined in three-electron triple
quantum dots, which enable direct capacitive coupling and interaction with microwave fields via intrinsic
spin-charge mixing. The method can also be applied to other types of
spin qubits that can be coupled capacitively. We show that this approach leads to rapid, single-pulse universal entangling gates for resonant exchange
qubits that are activated via the drive on the mediator dot. Unlike conventional tunneling-based two-
qubit gates between exchange-only
qubits, the capacitive interaction-based gates we describe do not require an extensive sequence of pulses to mitigate leakage. We describe how this drive-activated local entangling approach can be integrated with the driven sideband-based long-range approach for cavity-mediated entangling gates developed in our previous work in order to enable modularity for
spin-based
quantum information processing.
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Statistical Mechanics
Non-reciprocal Ising gauge theory
Nilotpal Chakraborty, Anton Souslov and Claudio Castelnovo
Non-reciprocity and
geometric frustration enable many-body systems to avoid crystalline order and instead exhibit complex,
liquid-like behavior. Here we show that their interplay is richer than the sum of its parts, leading to surprising structural and dynamical phenomena. In our minimal model, two copies of Ising gauge theory are non-reciprocally coupled in a way that crucially preserves a local $\mathbb{Z}_2$
symmetry. We discover that the combined Wilson loop observable of the two copies exhibits linear asymptotic scaling, with a quasiparticle-pair confinement length tuned by the strength of the non-reciprocal coupling. Key dynamical features are revealed in the behavior of individual deconfined excitations due to strong interactions induced by the non-reciprocity, leading to motion on a critical percolation cluster that follows a self-avoiding trail. Mapping from this quasiparticle dynamics onto the
magnetic noise spectrum, we discover that non-reciprocity tunes topological logarithmic contributions and causes long-lived metastable states due to quasiparticle trapping. Our work opens the way for broader investigations of geometrically frustrated non-reciprocity.
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Statistical Mechanics · Cross-listed from quant-ph
Belief Propagation and Tensor Network Expansions for Many-Body Quantum Systems: Rigorous Results and Fundamental Limits
Siddhant Midha, Grace M. Sommers, Joseph Tindall et al. (+1 more)
Belief propagation (BP) provides a scalable heuristic for contracting tensor networks on loopy graphs, but its success in
quantum many-body settings has largely rested on empirical evidence. Developing upon a recently introduced cluster-expansion framework for tensor networks, we rigorously study the applicability of BP to many-body
quantum systems. For a state represented as a PEPS satisfying a “loop-decay" condition, we prove that BP supplemented by cluster corrections approximates local observables with exponentially small relative error, and we give explicit formulas expressing local expectation values as BP predictions dressed by connected clusters intersecting the observable region. This representation establishes a direct link between cluster corrections and physical correlation functions. As a result, we show that “loop-decay" necessarily implies exponential decay of connected correlations, yielding sharp, rigorous criteria for when BP can and cannot succeed, and ruling out its validity at critical points. Numerical simulations of the two- and three-dimensional transverse field Ising model at zero and finite temperature confirm our analytical predictions, demonstrating quantitative accuracy deep in gapped phases and systematic failure near criticality.
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All authors Siddhant Midha, Grace M. Sommers, Joseph Tindall, Dmitry A. Abanin
Mesoscale and Nanoscale Physics
Vibrationally-mediated Dzyaloshinskii-Moriya interaction as the origin of Chirality-Induced Spin Selectivity in donor-acceptor molecules
Alessandro Chiesa, D. K. Andrea Phan Huu, Arianna Cantarella et al. (+4 more)
Chirality-induced
spin selectivity (CISS) was recently observed in photo-excited donor-
chiral bridge-acceptor molecules, but a predictive theory able to explain available experiments is still lacking. Here we show that low-energy torsional modes modulating hopping and
spin-orbit coupling give rise to a Dzyaloshinskii-Moriya interaction between the transferred electron and the one sitting on the donor, producing high
spin polarization for perfectly realistic parameters. Our model introduces a low energy scale in the
spin dynamics which explains the
magnetic field dependence observed in EPR measurements and predicts a non-trivial temperature dependence, as demonstrated by numerical simulations. The present theory lays the foundations for future test-bed experiments and for the design of applications in spintronics and
quantum technologies.
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All authors Alessandro Chiesa, D. K. Andrea Phan Huu, Arianna Cantarella, Leonardo Celada, Michael R. Wasielewski, Paolo Santini, Stefano Carretta
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Bifurcations in Stokes Flow Sedimentation
Elias Huseby, Pierre Mathier, Meera Das et al. (+5 more)
Particles whose shapes couple translation to rotation display a rich array of behaviors as they sediment at low Reynolds number. We introduce a unifying perspective in which the possible dynamical regimes and bifurcations between them can be understood. We use experimental measurements of helical ribbons, with controlled center of mass offsets, to identify the key bifurcation from complex dynamics to a single attracting state as the magnitude of the offset increases. The sedimentation dynamics are very sensitive to small center of mass offsets, with the bifurcation occurring for offsets less than one percent of the particle length. Using mobility tensors obtained from immersed boundary method simulations, we simulate helical particle sedimentation and identify an
alignment bifurcation surface, defined in the three dimensional space of center of mass offsets, that separates simple from complex sedimentation dynamics. Inside this surface we find limit cycles which emerge through
Hopf and homoclinic bifurcations. Cocentered particles with coincident centers of force and mobility provide a reference case at the center of the bifurcation surface. We show how the
geometric and dynamical
symmetries of sedimenting cocentered particles are broken as the center of force offset moves away from the cocentered case. Three parity time-reversal (PT)
symmetries exist for all cocentered particles under reflections normal to the eigenvectors of its translation-rotation coupling tensor. When a center of force offset preserves at least one of these PT
symmetries, then there are closed orbits for particles inside the
alignment bifurcation surface.
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All authors Elias Huseby, Pierre Mathier, Meera Das, Arjun Menezes, Theo Witkamp, Ziqi Wang, Bernhard Mehlig, Greg A. Voth
Other Condensed Matter · Cross-listed from cs.NE
Biologically Realistic Dynamics for Nonlinear Classification in CMOS+X Neurons
Steven Louis, Hannah Bradley, Artem Litvinenko et al. (+3 more)
Spiking neural networks encode information in spike timing and offer a pathway toward energy efficient artificial intelligence. However, a key challenge in spiking neural networks is realizing nonlinear and expressive computation in compact, energy-efficient hardware without relying on additional
circuit complexity. In this work, we examine nonlinear computation in a CMOS+X spiking
neuron implemented with a
magnetic tunnel junction connected in series with an NMOS transistor.
Circuit simulations of a multilayer network solving the XOR classification problem show that three intrinsic neuronal properties enable nonlinear behavior: threshold activation, response latency, and absolute refraction. Threshold activation determines which
neurons participate in computation, response latency shifts spike timing, and absolute refraction suppresses subsequent spikes. These results show that magnetization dynamics of MTJ devices can support nonlinear computation in compact neuromorphic hardware.
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All authors Steven Louis, Hannah Bradley, Artem Litvinenko, Cody Trevillian, Darrin Hanna, Vasyl Tyberkevych
Materials Science
Observation of anomalous thermal Hall effect in altermagnets
Wenbo Wan, Xu Zhang, Yixuan Luo et al. (+2 more)
Altermagnets, recently proposed as a third category of collinear magnets, combine the features of zero net magnetization in antiferromagnets and the
spin splitting in ferromagnets. While abundant spectroscopic evidence for altermagnetism has been reported, experimental observation of the anomalous
Hall effect, a hallmark of ferromagnetism, remains scarce. Here, we shift the paradigm from charge to heat carriers and report the systematic study of the thermal
Hall effect in two representative altermagnet candidates, MnTe and CrSb. In both materials, we observe a pronounced anomalous
phonon thermal
Hall signal, with no electrical counterpart observed, attributed to the coupling of this distinctive
magnetic structure with
phonons. Our findings establish the anomalous
phonon thermal
Hall effect as an intrinsic feature of altermagnets, and provide a sensitive probe to identify this new kind of
quantum magnets. The anomalous
phonon thermal
Hall effect in altermagnets directly links the Néel vector to
lattice vibrations, opening prospects for low-loss phononic devices and thermally readable
memories.
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All authors Wenbo Wan, Xu Zhang, Yixuan Luo, Yanfeng Guo, Shiyan Li
Quantum Gases
Determination of the ground state polarizability of $^{162}$Dy near 530 nm
Alexandre Journeaux, Maxime Lecomte, Julie Veschambre et al. (+3 more)
Open-shell lanthanide atoms, and dysprosium in particular, combine a large ground-state angular momentum with dense electronic spectra, making their dynamical polarizability strongly dependent on wavelength and internal state, and therefore challenging to calculate and characterize experimentally. This issue has become especially relevant with the recent development of single-atom trapping of dysprosium in optical-tweezer arrays, where precise knowledge of the polarizability is needed to design optimized trapping architectures. Here, we exploit the strong
spin-dependent light shift near the $J'=J-1$ intercombination line at 530.306 nm to determine the background scalar and vector polarizabilities of $^{162}$Dy in its ground state near this wavelength. Our measurements quantitatively agree with atomic-structure calculations and provide new insight into the contributions of nearby transitions in a spectral region relevant to emerging dysprosium tweezer platforms.
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All authors Alexandre Journeaux, Maxime Lecomte, Julie Veschambre, Maxence Lepers, Jean Dalibard, Raphael Lopes
Strongly Correlated Electrons · Cross-listed from physics.optics
Localized Photon Absorption in a Single-Crystalline Material
Daniel Kazenwadel, Jacob Holder, Livio Ciorciaro et al. (+6 more)
The absorption of light is one of the most fundamental processes in condensed-matter physics and optics. Here we investigate under which conditions
laser light is absorbed by a crystalline material as an electromagnetic wave with delocalized properties or rather as
photons that cause discrete, localized, nanometer-sized consequences. We excite the first-order phase transition of vanadium dioxide with
laser pulses of sufficient frequency to overcome the band gap but with insufficient pulse energy to overcome the latent heat. According to Maxwell's equations and Bloch theory, no transition should occur, because nowhere in the material is enough energy. Nevertheless, we observe with ultrafast electron diffraction a disordered
crystal geometry with nanometer-sized spots of switched material that grow and diminish with time. The amount of localized spots matches approximately to the number of
photons in the absorbed
laser wave. Two optical experiments substantiate this phenomenon, and simulations reproduce all measurements results. We discuss whether
crystals defects, temperature, or a genuine wavefunction collapse can explain the discovered phenomenon. Practically, the reported absorption mechanism enables local consequences at substantially higher energy than average and provides insight into
symmetry breaks and non-thermal fluctuations within complex materials.
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All authors Daniel Kazenwadel, Jacob Holder, Livio Ciorciaro, Noel Neathery, Raphael Schwenzer, Leon Oleschko, Jannik Hertkorn, Margaretha Sandor, Peter Baum
Statistical Mechanics
Testing the Role of Diagonal Interactions in High-Order Hopfield Models via Dynamical Mean-Field Theory
Yuto Sumikawa and Yoshiyuki Kabashima
High-order extensions of the Hopfield model are known to exhibit dramatically enhanced storage capacity at
equilibrium, while their dynamical
retrieval properties remain less well understood. In our previous work, we carried out a dynamical mean-field theory (DMFT) analysis of the Krotov–Hopfield-type dense associative
memory and found that the transition between successful and failed
retrieval is accompanied by pronounced slow dynamics. As a consequence, the effective basin of attraction observed in numerical simulations extends well beyond that predicted by
equilibrium statistical mechanics. A natural hypothesis is that this discrepancy originates from diagonal (self-interaction) contributions in the Krotov–Hopfield model, which generate a large number of lower-order interaction terms and may induce glassy relaxation near the
retrieval boundary. To test this hypothesis, we analyze an alternative high-order associative
memory model, namely the Abbott–Arian-type $p$-body Hopfield model, in which such diagonal contributions are absent by construction. Using dynamical mean-field theory, we derive an effective single-site process together with closed macroscopic equations governing the
retrieval dynamics. Our analysis reveals that both slow dynamics and a substantial enlargement of the apparent basin of attraction persist even in this model. These results indicate that the dynamical slowdown near the
retrieval boundary cannot be attributed primarily to diagonal self-interaction effects, but instead originates from intrinsic properties of high-order interactions.
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Strongly Correlated Electrons
Proximate quantum spin liquids and Majorana continua in magnetically ordered Kitaev magnets
Peng Rao, Roderich Moessner and Johannes Knolle
We study the
spin excitation spectra in magnetically ordered phases proximate to the Kitaev
quantum spin liquid (KQSL). Although the low-energy universal features should be governed by the
magnetic orders, the $\textit{non-universal}$ high-energy features of the KQSL and adjacent phases can be remarkably similar. Therefore, we study the extended Kitaev model within a Stoner-like theory using Majorana partons, and compute the inelastic
neutron scattering (INS) intensities in the random phase approximation. First, we
benchmark against the
antiferromagnetic (AFM) Heisenberg model and recover the AFM order with linear Goldstone modes. We then explore the phase diagram which agrees qualitatively with previous numerical results. In particular, the Majorana parton theory accurately captures Order-by-Disorder effects in the Kitaev-Heisenberg limit. We also find large INS intensities near the associated high-
symmetry Brillouin zone (BZ) points of the
magnetic orders. At intermediate and high energies, broad multi-spinon continua emerge across the BZ, providing a distinct mechanism for
magnon decay and spectral broadening beyond the conventional multi-
magnon decay scenario. Finally, we study the model
Hamiltonian of candidate Kitaev material $\alpha$-RuCl$_3$. The zigzag ground state agrees qualitatively with experiments, its stability under external
magnetic field also exhibits strong anisotropy in the field directions, and broad scattering continua are recovered similar to those observed experimentally.
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Disordered Systems and Neural Networks
Escape dynamics and implicit bias of one-pass SGD in overparameterized quadratic networks
Dario Bocchi, Theotime Regimbeau, Carlo Lucibello et al. (+2 more)
We analyze the one-pass
stochastic gradient descent dynamics of a two-layer neural network with quadratic activations in a teacher–student framework. In the high-dimensional regime, where the input dimension $N$ and the number of samples $M$ diverge at fixed ratio $\alpha = M/N$, and for finite hidden widths $(p,p^*)$ of the student and teacher, respectively, we study the low-dimensional ordinary differential equations that govern the
evolution of the student–teacher and student–student overlap
matrices. We show that overparameterization ($p>p^*$) only modestly accelerates escape from a plateau of poor generalization by modifying the prefactor of the exponential decay of the loss. We then examine how unconstrained weight norms introduce a continuous rotational
symmetry that results in a nontrivial
manifold of zero-loss solutions for $p>1$. From this
manifold the dynamics consistently selects the closest solution to the random initialization, as enforced by a conserved quantity in the ODEs governing the
evolution of the overlaps. Finally, a Hessian analysis of the population-loss landscape confirms that the plateau and the solution
manifold correspond to saddles with at least one negative
eigenvalue and to marginal minima in the population-loss geometry, respectively.
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All authors Dario Bocchi, Theotime Regimbeau, Carlo Lucibello, Luca Saglietti, Chiara Cammarota
Strongly Correlated Electrons
Hilbert space fragmentation in quantum Ising systems induced by side coupling
E. S. Ma and Z. Song
We study
Hilbert space fragmentation and
quantum scars in
quantum spin systems with Ising interactions. The system consists of two sets of
quantum spins, A and B. As the parent system, set A is an Ising model on arbitrary
lattices with a transverse field, while set B comprises free
spins that are coupled to set A. We show that the
Hilbert space is fragmented into exponentially many decoupled sectors when the transverse field and the side coupling strength are at resonance. As examples, several typical systems with
quantum scars are studied analytically. Numerical simulations of probability distribution of
entanglement entropy for finite-size chains, square and triangular
lattices are performed using the Monte Carlo method. The results show that
Hilbert space fragmentation and the corresponding
quantum scars become pronounced when the system approaches resonance.
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Materials Science
Maximizing the magnetic anisotropy of Dy complexes by fine tuning organic ligands: A systematic multireference high-throughput exploration of over 30k molecules
Lion Frangoulis, Lorenzo A. Mariano. Vu Ha Anh Nguyen, Zahra Khatibi et al. (+1 more)
The design of the coordination environment of
magnetic ions is key to achieving properties such as large
magnetic anisotropy and slow
magnetic relaxation, but a systematic exploration of the relevant chemical space for these compounds is missing. Here, we automatically extract all entries of mononuclear Dy coordination complexes from crystallographic databases and use multireference ab initio methods to compute their
magnetic anisotropy. In addition, we generate and simulate
magnetic anisotropy for 25k new molecules with the general formula [Dy(H$_2$O)$_5$L$_2$]$^{n-}$ and pentagonal bipyramidal coordination geometry, a motif selected as very promising. While no molecule with record
magnetic anisotropy is serendipitously identified in crystallography databases, molecules with
crystal field splittings over 1600 cm$^{-1}$ are identified by systematically exploring new organic ligands. This corresponds to a ~100% increase of
magnetic anisotropy over the reference compound, ~30% over any known pentagonal bipyramidal Dy complex, and approaching record values of pseudo bi-coordinated Dy ions. This study demonstrates that the fine-tuning of Dy's second coordination sphere by organic ligands design can significantly improve
magnetic anisotropy and that automated computational screening is key to accelerating this chemically non-intuitive process.
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All authors Lion Frangoulis, Lorenzo A. Mariano. Vu Ha Anh Nguyen, Zahra Khatibi, Alessandro Lunghi
Materials Science · Cross-listed from physics.chem-ph
Regio-Connectivity and Torsional Angle Effects on Singlet Fission and SOCT-ISC in Aza-BODIPY Dimers
Sophiya Goyal and S. Rajagopala Reddy
Aza-BODIPY dimers represent promising molecular systems for efficient triplet-state generation through either intramolecular-singlet fission (iSF) or
spin-orbit charge transfer intersystem crossing (SOCT-ISC). In this work, we investigate the role of molecular geometry in governing these mechanisms across four regioisomeric aza-BODIPY dimers (D[1,1], D[1,3], D[3,3], and D[2,2]) using multireference
quantum-chemical calculations. Ground- and excited-state properties were analyzed at the MP2 and SA-XMCQDPT levels of theory, while diabatic couplings and
spin-orbit
matrix elements were evaluated to estimate iSF and SOCT-ISC rate constants, respectively. Our results reveal that triplet formation is strongly governed by the torsional angle ({\Phi}) between monomer units, with regio-connectivity exerting a secondary influence. Dimers D[1,1] and D[1,3] exhibit favorable iSF energetics and coupling magnitudes, whereas D[2,2] displays low iSF rate constant (kSF ) but enhanced SOCT-ISC activity. The D[3,3] dimer shows exothermic multiexciton formation but reduced iSF efficiency due to destructive coupling interactions. The dominant ISC channel proceeds through the S1-T3 transition with large
spin-orbit coupling and a small energy gap. These findings provide critical mechanistic insights into geometry-dependent triplet generation in aza-BODIPY dimers.
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Materials Science
Spatially inhomogeneous delithiation in LiNiO2 positive electrode: the effect of X-rays dose
Francesco La Porta, Laurent Barthe, Anthony Beauvois et al. (+4 more)
Operando synchrotron X-ray techniques have become essential tools for investigating rechargeable batteries as they provide real-time insights into electrochemical processes. However, the high brilliance of synchrotron radiation can alter the electrochemical mechanisms within the battery, thereby compromising the reliability and reproducibility of operando measurements. In this study, we introduce a novel methodology that directly correlates the local X-ray dose with the Ni4+/Ni3+ redox activity in a LiNiO2 positive electrode. Full-field transmission X-ray absorption spectroscopy imaging (FFI-XAS) is employed to probe the charge-compensation mechanism during lithium extraction at the micrometre scale, using two beam configurations with different focal distances (far-focus and near-focus). While the spatially averaged XAS spectra exhibit sluggish reaction, regions exposed to lower dose rates exhibit the expected electrochemical
evolution. This contrast enables the identification of a dose threshold for reliable operando measurements. This approach establishes a practical dose limit and provides spatially resolved insight into beam-induced effects, offering both a diagnostic framework and a pathway toward more reliable operando experiments.
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All authors Francesco La Porta, Laurent Barthe, Anthony Beauvois, Gilles Wittmann, Valérie Briois, Antonella Iadecola, Stéphanie Belin
Mesoscale and Nanoscale Physics
Nanomechanical detection of vortices in an electron fluid
Andrey A. Shevyrin, Askhat K. Bakarov and Arthur G. Pogosov
Electron
vortices are the quintessential signature of a viscous electron fluid. For decades, their detection relied on indirect transport measurements with persistently debated interpretations. Recently, scanning magnetometry enabled direct visualization, yet these techniques demand considerable sophistication. Here we introduce a conceptually different and inherently simpler paradigm based on nanomechanics. By integrating a circular cavity into a suspended resonator, we create a
vortex whose circulating current generates a
magnetic moment. In an in-plane
magnetic field, this moment experiences a torque, driving vibrations that directly reveal the
vortex's presence and nature. We detect ballistic and hydrodynamic
vortices and trace their temperature-driven crossover. Our work establishes nanomechanics as a platform for electron hydrodynamics, showing that viscosity - subtle in transport - is one of the dominant factors shaping nanoelectromechanical response.
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Mesoscale and Nanoscale Physics
Hamiltonian learning for spin-spiral moiré magnets from electronic magnetotransport
Fedor Nigmatulin, Greta Lupi, Jose L. Lado et al. (+1 more)
Two-dimensional noncollinear
magnetic states, such as
spin-spiral magnets, offer an excellent platform for investigating fundamental phenomena, with potential for advancing stray-field-free spintronics. However, detection and characterization of noncollinear
magnetic states in two-dimensional systems remain challenging, motivating the development of alternative probing methods. Here, we present a methodology for extracting the
spin-spiral $\mathbf{q}$ vector from lateral electronic transport measurements. Our approach leverages the
magnetic field and bias dependence of the conductance to train a supervised machine learning
algorithm, which enables us to extract the $\mathbf{q}$ vectors of arbitrary
spin-spiral magnets. We demonstrate that this methodology is robust to the presence of
impurities in the system and noise in the conductance data. Our findings show that the conductance pattern reveals a complex dependence on the $\mathbf{q}$ vector of the
spin spiral, providing a new strategy to learn
magnetic structures directly from transport experiments.
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All authors Fedor Nigmatulin, Greta Lupi, Jose L. Lado, Zhipei Sun
Materials Science
Engineering Electrochromism in Ni-Deficient NiO through Defect, Dopant, and Strain Coupling
Katarina Jakovljević, Ana S. Dobrota, Igor A. Pašti et al. (+1 more)
The electrochromic response of Ni-deficient NiO is governed by vacancy-mediated electronic processes that can be strongly influenced by dopant chemistry and
lattice deformation. Using density functional theory, we systematically investigated Cu-, Sn-, and V-doped Ni-deficient NiO(001) surfaces and examined alkali-ion insertion at surface Ni vacancies. Li insertion proceeds as nearly complete ionic electron donation (~+0.9 e), but the fate of the injected electron depends on dopant identity. V-doping preserves framework-dominated charge compensation and leads to conventional bleaching through filling of vacancy-associated hole states. In contrast, Sn actively traps the injected charge, generating dopant-assisted optical transitions and reversing the electrochromic response, while Cu produces an intermediate spectral redistribution without significant dopant reduction. Substitution of Li by Na or K in the V-doped system does not alter the switching mechanism, confirming that vacancy-state filling governs the optical behavior. Biaxial tensile strain enhances the energetics of Li insertion but reduces optical contrast by altering the defect electronic structure. These results establish dopant activity, vacancy stabilization, and
lattice strain as key parameters controlling electrochromism in NiO-based materials.
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All authors Katarina Jakovljević, Ana S. Dobrota, Igor A. Pašti, Natalia V. Skorodumova
Statistical Mechanics
Resetting dynamics in a system with quenched disorder
Riya Verma, Binayak Banerjee, Shamik Gupta et al. (+1 more)
Although resetting has widespread applicability, applying it to the dynamics in the presence of spatial quenched disorder, which is essential in many physical problems, is challenging. In this study, we consider a well-known one-dimensional model of particle hopping on a
lattice with quenched disorder in the form of site-dependent hopping probabilities, drawn from a power-law distribution, and apply the resetting formalism. As a physical example, we recast the growth dynamics of microtubules with sudden catastrophic disassembly events as a resetting dynamics. We consider two distinct regimes for growth dynamics: a strongly biased case and a less biased case. Motivated by experimental results, we take a Gamma distribution for the resetting time. Our results show that occasional disassembly events are crucial for the experimentally observed distribution of reset (or catastrophe) lengths. We also analyze steady-state distributions under different resetting protocols-resetting to the initial position versus a random site. We also investigate the distribution of first-passage times to a fixed distance following reset. Finally, by considering other resetting probability distributions, we identify a regime where the mean displacement grows as slowly as $\log^2 t$. We also elucidate the role of disorder in the system properties under the resetting dynamics. Our study paves the way to treat the dynamics of complex physical systems using resetting.
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All authors Riya Verma, Binayak Banerjee, Shamik Gupta, Saroj Kumar Nandi
Strongly Correlated Electrons · Cross-listed from math.QA
Classification of Extended Abelian Chern-Simons Theories
Daniel Galviz
We classify extended Abelian Chern-Simons theories with gauge group $U(1)^n$ as extended $(2+1)$-dimensional topological
quantum field theories. For an even integral nondegenerate
lattice $(\Lambda,K)$, let $(G_K,q_K)$ denote its discriminant quadratic module. We prove that the associated theory is determined, up to symmetric monoidal natural isomorphism, by this finite quadratic module, and that every finite quadratic module is realized as the discriminant quadratic module of an even integral nondegenerate
lattice. It follows that finite quadratic modules classify extended Abelian Chern-Simons theories, pointed Abelian Reshetikhin-Turaev TQFTs, and pointed modular tensor categories.
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Strongly Correlated Electrons
Mott-Derived Local Moments and Kondo Hybridization in a d-electron Kagome lattice
Xing Zhang, Xintong Li, Boqin Song et al. (+25 more)
Unlike canonical Kondo
lattices in f-electron systems, where localized f orbitalsnaturally provide local moments, d-electron Kondo
lattices require a distinct mechanism for local-moment formation. However, the study of d-electron Kondo
lattices in bulk materials remains far from settled, particularly with regard to the microscopic origin of the local moments. Here, we report a microscopic mechanism for this process in the
bilayer kagome metal CsCr6Sb6, where strong correlations drive a Mott splitting of the kagome flat band to supply the requisite local moments. By combining STM/STS and ARPES, we resolve a spectroscopic hierarchy between high-energy correlation effects and low temperature hybridization. Low-temperature STS reveals a robust asymmetric suppression of the density of states near EF that is well captured phenomenologically by a Fano-type lineshape, while ARPES detects a sharp quasiparticlepeak near EF. These low-energy signatures evolveon the same temperature scale and disappear upon warming, consistent with the onset of Kondo hybridization. At the same time, STS resolves symmetric humps at approximately +-50 mV and ARPES identifies a weakly dispersive feature around 50 meV below EF; unlike the near-EF hybridization signatures, these features persist to substantially higher temperatures. This separation of energy and temperature scales supports a two-stage picture in which a kagome flat band first undergoes correlation-driven splitting into lower and upper Hubbard bands, and the occupied lower Hubbard band supplies the local moments that later hybridize with itinerant electrons at lower temperature. Our results therefore move beyond the phenomenology of a kagome Kondo
lattice candidate and instead provide a microscopic spectroscopic picture linking Mottness to Kondo hybridization in a frustrated d-electron system.
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All authors Xing Zhang, Xintong Li, Boqin Song, Yuyang Xie, Qinghong Wang, Taimin Miao, Shusen Ye, Junhao Liu, Bo Liang, Neng Cai, Hao Chen, Wenpei Zhu, Mingkai Xu, Wei-Jian Li, Shun-Li Yu, Shenjin Zhang, Fengfeng Zhang, Feng Yang, Zhimin Wang, Qinjun Peng, Hanqing Mao, Zhihai Zhu, Guodong Liu, Zuyan Xu, Yi-feng Yang, Tianping Ying, Lin Zhao, X. J. Zhou