Soft Condensed Matter
Is gelation a singularity or a flow induced instability?
Manuel Dedola and Ludovico Cademartiri
Gelation in the Smoluchowski coagulation equation is commonly interpreted as a finite-time singularity marked by mass loss or moment divergence. We instead characterize gelation as a loss of dynamical stability of the Smoluchowski flow, quantified through the time-dependent spectrum of the Jacobian along the evolving aggregation dynamics. Studying homogeneous kernels $K(i,j)=(ij)^{\alpha}$ together with the classical Smoluchowski, we show that gelation is consistently preceded by the appearance of positive real
eigenvalues, indicating a loss of local dynamical stability. While non-gelling kernels exhibit only transient finite-size effects, gelling kernels display persistent spectral destabilization associated with macroscopic gel formation. Our results identify gelation as a genuine dynamical instability of the Smoluchowski flow.
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Soft Condensed Matter
Strain-transport superposition in shear-thinning dense non-Brownian suspensions
Rishabh V. More
Shear thinning in dense non-Brownian suspensions is often attributed to shear-induced microstructural
evolution, including changes in
alignment, anisotropy, and near-contact statistics, yet how these changes influence particle-scale dynamics remains unclear. Using particle-resolved simulations of dense suspensions that shear thin through diverse microscopic mechanisms, including short-range attraction, repulsion, and load-dependent friction, we show that the magnitude of nonaffine particle velocities is controlled solely by the imposed shear rate, independent of coordination number, structural anisotropy, and interaction details. In contrast, macroscopic stress and viscosity remain strongly sensitive to the underlying interactions. When mean-squared displacements transverse to the flow are rescaled by accumulated strain and the nonaffine velocity variance, all data collapse onto a single master curve, revealing strain-controlled transport with a robust ballistic-to-diffusive crossover. These results demonstrate a fundamental decoupling between particle-scale kinematics and macroscopic rheology and identify nonaffine velocity fluctuations as the emergent dynamical scale governing shear-driven transport.
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Materials Science · Cross-listed from cs.LG
Machine learning model for predicting surface wettability in laser-textured metal alloys
Mohammad Mohammadzadeh Sanandaji, Danial Ebrahimzadeh, Mohammad Ikram Haider et al. (+3 more)
Surface wettability, governed by both topography and chemistry, plays a critical role in applications such as heat transfer, lubrication, microfluidics, and surface coatings. In this study, we present a machine learning (ML) framework capable of accurately predicting the wettability of
laser-textured metal
alloys using experimentally derived morphological and chemical features. Superhydrophilic and superhydrophobic surfaces were fabricated on AA6061 and AISI 4130
alloys via nanosecond
laser texturing followed by chemical immersion treatments. Surface morphology was quantified using the Laws texture energy method and profilometry, while surface chemistry was characterized through X-ray photoelectron spectroscopy (XPS), extracting features such as functional group polarity, molecular volume, and peak area fraction. These features were used to train an ensemble neural network model incorporating residual connections, batch normalization, and dropout regularization. The model achieved high predictive accuracy (R2 = 0.942, RMSE = 13.896), outperforming previous approaches. Feature importance analysis revealed that surface chemistry had the strongest influence on contact angle prediction, with topographical features also contributing significantly. This work demonstrates the potential of artificial intelligence to model and predict wetting behavior by capturing the complex interplay of surface characteristics, offering a data-driven pathway for designing tailored functional surfaces.
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All authors Mohammad Mohammadzadeh Sanandaji, Danial Ebrahimzadeh, Mohammad Ikram Haider, Yaser Mike Banad, Aleksandar Poleksic, Hongtao Ding
Superconductivity
Superconductivity from the Slater mode: Application to KTaO3 heterostructures
M. R. Norman
Superconductivity has been observed for the 2D electron gas (2DEG) at the interface of KTaO3 with other
oxides, with a transition temperature about an order of magnitude higher than its 3d cousin SrTiO3. The superconducting transition temperature is strongly dependent on the orientation of the interface. Motivated by this observation, we study pairing due to exchange of the soft transverse optic
phonon mode characteristic of
quantum paraelectrics and use the resulting theory to comment on the nature of superconductivity of this 2DEG. We find (1) an orientation dependence consistent with experiment along with an anisotropic gap function, but (2) a BCS coupling constant that is smaller than needed and so must be augmented by contributions from other
phonons to be consistent with the observed values of Tc.
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Mesoscale and Nanoscale Physics
Optical probing of magnons and phonons in Ni80Fe20 nanodot arrays
A. Adhikari, P. Graczyk, A. K. Chaurasiya et al. (+3 more)
Control of collective
spin excitations by static or dynamic strain is an emerging phenomenon that requires in-depth understanding for design of future
spin-wave-regulated devices. Here, we explore mutually interacting
spin waves and acoustic wave modes in addition to few non-interactive modes through all optical excitation in ordered arrays of Ni80Fe20 nanomagnets. The acoustic wave originated from elastic deformation resonantly couple to the
spin wave via magnetoelastic effect at their overlapping frequency. We demonstrate that the choice of the
lattice type in which the
magnetic nanodots are arranged is crucial for the observation of the magnetoelastic interaction. Therefore, the study shows that the simultaneous existence of elastic wave and
spin wave offer ingeneously advantageous features to pave the way of energy-efficient magnetoacoustic devices.
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All authors A. Adhikari, P. Graczyk, A. K. Chaurasiya, S. Mondal, J. W. Klos, A. Barman
Mesoscale and Nanoscale Physics
Combining laser ablation and Sol-Gel techniques for the synthesis of nanostructured organic-inorganic matrices
E. Haro-Poniatowski, C. A. Guarín, L. G. Mendoza-Luna et al. (+11 more)
In this work we report a new and simple method that combines the pulsed
laser ablation in
liquids (PLAL) and the Sol-Gel techniques to obtain nanocomposite glasses and gelatins. Gold nanoparticles (Au-NPs) are generated by PLAL using the corresponding target. The target is submerged in a transparent
liquid solution made previously with tetraetylorthosilicate (TEOS) adding diluted hydrochloric acid as catalyzer. In the case of gelatins commercial gelatin and tap water are used. The
laser source is a Nd:YAG
laser emitting at 1064 nm, with an energy of 100 mJ and 8 ns pulse duration at 10 Hz repetition rate focused on the target in a 2 mm diameter
laser spot. The ablation time is 10 min for the glasses and gelatins. The Au-NPs are uniformly dispersed in the solution. After the ablation process the gels are sealed and stored at room temperature for several days. The samples are characterized by UV-Vis spectroscopy, HRTEM, ellipsometry and AFM microscopy, these measurements reveal optical transparency and a refractive index near 1.45 for the pure glass, whereas a colorful aspect, a refractive index of 1.42, and a small surface roughness of 1.92 nm for the glass containing Au-NPs. In the case of gelatins self-sustained flexible films are obtained.
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All authors E. Haro-Poniatowski, C. A. Guarín, L. G. Mendoza-Luna, L. Escobar-Alarcón, J. L. Hernández-Pozos, L. I. Vera-Robles, P. Castillo, F. Cabello, J. Toudert, F. Chacón-Sánchez, M. García-Pardo, R. Serna, J. Gonzalo, J. Solís
Other Condensed Matter
Hopfions in screw chiral magnets
Sandra C Shaju, Maria Azhar and Karin Everschor-Sitte
Three-dimensional topological
spin textures have attracted growing interest due to their rich geometry and potential for functional
magnetic phenomena. In this work, we propose the concept of
symmetry-transforming
magnetic models as a novel route to generate and stabilize complex three-dimensional textures in an arbitrary
magnetic background. Using this framework, we predict a screw
chiral magnet model that stabilizes
magnetic Hopfions and other three-dimensional
magnetic textures within a
ferromagnetic background. We show that the resulting
solitons display distinctive physical properties, including unconventional Goldstone modes. Our results establish continuous
symmetry transformations as a general strategy for uncovering new classes of
magnetic solitons with unique dynamical signatures.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Geometrical optical activity induced by a continuous distribution of screw dislocations
Humberto Belich and Edilberto O. Silva
We study light propagation in a medium with uniform torsion, modeled as a continuum of screw dislocations within the
geometric theory of defects. By solving Maxwell's equations in covariant form, we show that torsion induces intrinsic chirality and circular birefringence: right- and left-circular polarizations acquire different wavenumbers, leading to a purely
geometric optical activity. The polarization plane of a linearly polarized beam rotates according to the simple law $\Delta\theta = \Omega\rho L$, linear in the dislocation density $\Omega$, propagation length $L$, and transverse coordinate $\rho$. This can be recast as an effective birefringence $\Delta n = 2c\Omega\rho/\omega$, providing
geometric design rules for torsion-induced rotatory power. Using parameters from dislocated
semiconductors, we obtain millidegree rotations over millimetre-scale paths, within reach of modern polarimetric techniques and amenable to enhancement in metamaterial platforms. We also show that the same spiral geometry implements a broadband
geometric phase gate for polarization
qubits and has an electronic analogue on the surface of cylindrical topological
insulators, where torsion shears the Dirac cone, establishing a unified
geometric link between torsion, optical activity, and topological electronic responses.
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Superconductivity
Widefield NV Magnetic Field Reconstruction for Probing the Meissner Effect and Critical Current Density under Pressure
Kin On Ho, Cassandra Dailledouze, Martin Schmidt et al. (+3 more)
The spatial distribution of a
magnetic field can be determined with micrometer resolution using widefield nitrogen vacancy (NV) center
magnetic imaging. Nevertheless, reconstructing the
magnetic field from the raw data can be challenging due to the degeneracy of the four possible NV axes and the tremendous amount of data. While a qualitative approach is sufficient for most analyses, a quantitative analysis offers deeper insight into the physical system. Here, we apply NV widefield
magnetic imaging to a HgBa$_{2}$Ca$_{2}$Cu$_{3}$O$_{8+\delta}$ (Hg-1223) superconducting microcrystal at a pressure of 4 GPa. We fit the results with solutions from the
Hamiltonian describing the NV center ground state and take into account the relative intensities of the resonances to determine the local
magnetic field magnitude and angle. Thus, we reconstruct the temperature-dependent expulsion of the
magnetic field due to the Meissner effect around the
superconductor. By comparing the resulting parameters to Brandt's model, which describes the
magnetic behavior of a type-II
superconductor, we extract the critical current density $j_c$. Overall, this work showcases the first widefield quantitative reconstruction of the Meissner effect under pressure and an optical method to study critical current density. Thus, it provides new insights into the application of NV magnetometry to superconductivity research at high pressures.
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All authors Kin On Ho, Cassandra Dailledouze, Martin Schmidt, Loïc Toraille, Marie-Pierre Adam, Jean-François Roch
Materials Science · Cross-listed from physics.app-ph
Supercritical Snapping and Controlled Launching via Dual Latch Gels
Xiaona M. Xu, Nolan A. Miller, Gregory M. Grason et al. (+1 more)
Natural organisms have evolved integrated Latch-Mediated Spring Actuation systems (LaMSA) that consist of multiple latches and springs to enhance power output and adapt to diverse environmental conditions. Similar designs are appealing yet largely unexplored in engineered materials due to the complexity of integrating multiple components into a single material platform. Here, we report a dual-latched magneto-elastic shell device capable of selectively activating the latches to regulate snapping pathways and energy output based on specific actuation requirements. Differential deswelling across the thickness acts as the motor to load the elastic energy into the shell, which is then released via the snap-through instability once the loading reaches the critical threshold, constituting an intrinsic mechanical latch. Activation of the external
magnetic latch delays snapping onset beyond the threshold of the intrinsic latch, leading to a power-amplified supercritical snap-through instability as well as a bifurcation instability. The combined function of both latches allows for flexible control over energy storage and release. Additionally, this integrated LaMSA system possesses an untethered anchoring mechanism, enabling the device to launch in arbitrary directions from the substrate, driven by the energy released during snapping. We envision that the design principles of dual-latched LaMSA systems will create opportunities for power-dense actuation in engineered materials and robotic devices.
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All authors Xiaona M. Xu, Nolan A. Miller, Gregory M. Grason, Alfred J. Crosby
Strongly Correlated Electrons · Cross-listed from physics.chem-ph
Chemically decisive benchmarks on the path to quantum utility
Srivathsan Poyyapakkam Sundar, Vibin Abraham, Bo Peng et al. (+1 more)
Progress towards
quantum utility in chemistry requires not only algorithmic advances, but also the identification of chemically meaningful problems whose electronic structure fundamentally challenges classical methods. Here, we introduce a curated hierarchy of chemically decisive
benchmark systems designed to probe distinct regimes of electronic correlation relevant to molecular, bioinorganic, and heavy-element chemistry. Moving beyond minimal toy models, our
benchmark set spans multireference bond breaking (N$_2$), high-
spin transition-metal chemistry (FeS), biologically relevant iron-sulfur clusters ([2Fe-2S]), and actinide-actinide bonding (U$_2$), which exhibits extreme sensitivity to active-space choice, relativistic treatment, and correlation hierarchy even within advanced multireference frameworks. As a concrete realization, we
benchmark a recently developed automated and adaptive
quantum algorithm based on generator-coordinate-inspired subspace expansion,ADAPT-GCIM, using a black-box workflow that integrates
entropy-based active-space selection via the ActiveSpaceFinder tool. Across this chemically diverse problem set, ADAPT-GCIM achieves high accuracy in challenging correlation regimes. Equally importantly, these
benchmarks expose general failure modes and design constraints-independent of any specific
algorithm-highlighting the necessity of problem-aware and correlation-specific strategies for treating strongly correlated chemistry on
quantum computers. To support systematic benchmarking and reproducible comparisons, the
Hamiltonians for all systems studied are made openly available.
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All authors Srivathsan Poyyapakkam Sundar, Vibin Abraham, Bo Peng, Ayush Asthana
Materials Science · Cross-listed from physics.ins-det
Charge-Carrier Mobility in Diamond: Review, Data Compilation, and Modelling for Detector Simulations
Faiz Rahman Ishaqzai, Muhammed Deniz, Kevin Kröninger et al. (+1 more)
Reported electron and hole mobilities and saturation velocities in diamond vary widely across the literature. We provide a consolidated review of first-principles predicted and experimentally measured mobility and saturation-velocity values in diamond, alongside a focused assessment of the semi-empirical mobility models used to extract low-field mobilities and high-field saturation velocities. We attribute the dispersion primarily to (i) the electric-field window probed in TCT measurements, (ii) the choice of mobility model, and (iii) the excitation source ($\alpha$,
laser, or electron). Using an aggregated literature
dataset, we
benchmark the Trofimenkoff and Caughey–Thomas parameterizations together with a new piecewise model for both conduction- and valence-band transport. For electrons, the piecewise model provides the best global description over a broad electric-field range. It can be interpreted as the room-temperature limit of a more general superposition framework that explicitly incorporates intervalley repopulation in the conduction band. For holes, the Caughey–Thomas model remains the statistically preferred description, consistent with the absence of a repopulation signature in the accessible data. Furthermore, we demonstrate a systematic source dependence ($\alpha$ versus
laser) and quantify its impact on fitted mobility and saturation-velocity values. We provide temperature scalings over narrow intervals around room temperature to support Jacoboni–Canali-type parameterization for diamond. Together, these results reconcile much of the apparent inconsistency in the literature and offer guidance for model selection, experimental design, and device-level simulation of charge transport in intrinsic diamond.
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All authors Faiz Rahman Ishaqzai, Muhammed Deniz, Kevin Kröninger, Jens Weingarten
Statistical Mechanics · Cross-listed from quant-ph
Parent Hamiltonians for stabilizer quantum many-body scars
Shane Dooley
Quantum many-body scars (QMBS) have attracted considerable interest due to their role in weak ergodicity breaking in many-body systems. We present a general construction that embeds stabilizer states as QMBS of local
Hamiltonians. The method relies on a notion of factorizability of Pauli strings on a
lattice, which is used to convert stabilizer elements into local, few-body operators that annihilate the stabilizer state. This enables the systematic construction of parent
Hamiltonians with zero-energy stabilizer QMBS typically near the middle of the spectrum. The method reproduces several known results in a unified framework, including recent examples of volume-law entangled QMBS, such as the “rainbow” QMBS and the entangled antipodal Bell pair state. We also apply the framework to construct examples of stabilizer QMBS with a more complex
entanglement structure, such as the cluster state, the toric code state, and a volume-law entangled state we dub the antipodal toric code (ATC) state. Exact diagonalization confirms our results and reveal the stabilizer states as exact eigenstates of their parent
Hamiltonian.
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Statistical Mechanics · Cross-listed from quant-ph
Critical non-equilibrium phases from noisy topological memories
Amir-Reza Negari, Subhayan Sahu, Jan Behrends et al. (+2 more)
We demonstrate the existence of an extended non-
equilibrium critical phase, characterized by sub-exponential decay of conditional mutual information (CMI), in the surface code subject to heralded random Pauli measurement channels. By mapping the resulting mixed state to the ensemble of completely packed loops on a square
lattice, we relate the extended phase to the Goldstone phase of the loop model. In particular, CMI is controlled by the characteristic length scale of loops, and we use analytic results of the latter to establish polylogarithmic decay of CMI in the critical phase. We find that the critical phase retains partial logical information that can be recovered by a global decoder, but not by any quasi-local decoder. To demonstrate this, we introduce a diagnostic called punctured coherent information which provides a necessary condition for quasi-local decoding.
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All authors Amir-Reza Negari, Subhayan Sahu, Jan Behrends, Benjamin Béri, Timothy H. Hsieh
Statistical Mechanics · Cross-listed from quant-ph
Exponential gain in clock precision using quantum correlated ticks
Florian Meier, Yuri Minoguchi, Gianmichele Blasi et al. (+2 more)
Creating precise timing devices at ultra-short time scales is not just an important technological challenge, but confronts us with foundational questions about timekeeping's ultimate precision limits. Research on clocks has either focused on long-term stability using an oscillator stabilized by a level transition, limiting precision at short timescales, or on making individual
stochastic ticks as precise as possible. Here, we prove the viability of a conceptually different avenue: the autonomous self-correction of consecutive ticks by
quantum correlations. This provides a new paradigm that integrates the advantages and insights from
quantum transport theory to operate clocks at ultra-short timescales. We fully solve a model of coupled
quantum systems and show how the emergent Pauli exclusion principle correlates the clock at the
quantum level yielding an exponential advantage in precision. We furthermore demonstrate through simulations with realistic imperfections that this remarkable gain in precision remains stable providing a roadmap for implementation with contemporary
quantum technologies.
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All authors Florian Meier, Yuri Minoguchi, Gianmichele Blasi, Géraldine Haack, Marcus Huber
Strongly Correlated Electrons
In search of diabolical critical points
Naren Manjunath and Dominic V. Else
A phase transition is an example of a “topological defect” in the space of parameters of a
quantum or classical many-body systems. In this paper, we consider phase diagram topological defects of higher codimension. These have the property that
equilibrium states undergo some kind of non-trivial winding as one moves around the defect. We show that such topological defects exist even in classical statistical mechanical systems, and describe their general structure in this context. We then introduce the term “diabolical critical point” (DCP), which is a higher-codimension analog of a continuous phase transition, with the proximate phases of matter replaced by the non-trivial winding of the proximate
equilibrium states. We propose conditions under which a system can have a stable DCP. We also discuss some examples of stable DCPs in (1+1)-dimensional
quantum systems.
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Statistical Mechanics
Exact and Approximate Constants of Motion in Stochastic Contact Processes
Damián H. Zanette and Eric A. Rozán
We study a variety of
stochastic contact processes – directly related to models of rumor and disease spreading – from the viewpoint of their constants of motion, either exact or approximated. Much as in deterministic systems, constants of motion in
stochastic dynamics make it possible to reduce the number of relevant variables, confining the set of accessible states, and thus facilitating their analytical treatment. For processes of rumor propagation based on the Maki-Thompson model, we show how to construct exact constants of motion as linear combinations of conserved quantities in each elementary contact event, and how they relate to the constants of motion of the corresponding mean-field equations, which are obtained as the continuous-time, large-size limit of the
stochastic process. For SIR epidemic models, both in homogeneous systems and on heterogeneous networks, we find that a similar procedure produces approximate constants of motion, whose average value is preserved along the
evolution. We also give examples of exact and approximate constants of motion built as nonlinear combinations of the relevant variables, whose expressions are suggested by their mean-field counterparts.
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Mesoscale and Nanoscale Physics
Lambert W Function Framework for Graphene Nanoribbon Quantum Sensing: Theory, Verification, and Multi-Modal Applications
F. A. Chishtie, K. Roberts, N. Jisrawi et al. (+3 more)
We establish a rigorous mathematical framework connecting
graphene nanoribbon
quantum sensing to the Lambert W function through the finite square well (FSW) analogy. The Lambert W function, defined as the inverse of $f(W)=We^W$, provides exact analytical solutions to transcendental equations governing
quantum confinement. Operating near the branch point singularity at $z=-1/e$ yields sensitivity enhancement factors scaling as $(z-z_c)^{-1/2}$, achieving 35-fold enhancement when the operating point lies within $\delta=0.001$ of the branch point. Comprehensive numerical verification confirms: (i) all seven bound states for strength parameter $R=10$ satisfy the constraint $u^2+v^2=R^2$ to machine precision; (ii) the theoretical band gap formula $E_g=2\pi\hbar v_F/(3W)$ is analytically equivalent to the independently determined empirical relation $E_g=1.38/W$~eV$\cdot$nm, establishing the validity of the FSW-GNR analogy; (iii) a universal sensitivity factorization $S_X = \mathcal{G}_k \cdot \eta_{\rm enh} \cdot \mathcal{P}_X$ applies across biomedical (SARS-CoV-2, inflammatory markers, cancer biomarkers), environmental (CO$_2$, CH$_4$, NO$_2$, N$_2$O, H$_2$O), and physical (strain,
magnetic field, temperature) sensing modalities. This unified framework provides analytically predictable design principles for next-generation
graphene quantum sensors. The framework is analytic and predictive rather than microscopic or experimental: band-structure and adsorption parameters are taken as inputs from tight-binding, first-principles, and experimental sources, and the framework returns closed-form sensitivity and design relations built upon them. Reported detection limits are labelled throughout as either literature-demonstrated device values or values predicted by the present framework.
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All authors F. A. Chishtie, K. Roberts, N. Jisrawi, S. R. Valluri, A. Soni, P. C. Deshmukh
Strongly Correlated Electrons
Emergence and transition of incompressible phases in decorated Landau levels
Bo Peng, Yuzhu Wang and Bo Yang
A single Landau level (LL) dressed with periodic electrostatic potentials can realize a plethora of interacting topological phases where the
Hall conductivity generally does not equal to the LL filling factor. Their physics can be captured by a new family of flat topological bands: decorated Landau levels (dLL) from imposing an electrostatic delta potential
lattice within a single LL. With $p/q$
magnetic fluxes per unit
cell, there are $q$ dispersive bands and $p-q$ zero energy bands forming the dLL. When the electrostatic potential strength dominates the electron-electron interaction, band mixing is suppressed and the dispersion bands consist of “localized states" with vanishing total Chern number. Nevertheless these dispersive bands can have highly nontrivial Berry
curvature distribution, and even non-zero Chern numbers when $q>1$. Interestingly even in the limit of large short range interaction, band mixing between dLL and dispersion bands can be strongly suppressed at low filling factor, leading to robust topological phases within the dLL stabilized by the one-body potential. The dLL and the associated dispersive bands can serve as minimal theoretical models for correlated physics in
lattice or moiré systems; they are also highly tunable experimental platforms for realizing rich phase diagrams of exotic 2D
quantum fluids.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Scalable Spin Squeezing in Power-Law Interacting XXZ Models with Disorder
Samuel E. Begg, Bishal K. Ghosh, Chong Zu et al. (+2 more)
While
spin squeezing has been traditionally considered in all-to-all interacting models, recent works have shown that it can also occur in systems with power-law interactions, enabling direct tests in Rydberg atoms, trapped ions, ultracold atoms, and nitrogen-vacancy (NV) centers in diamond. For the latter, Wu et al. Nature 646 (2025) demonstrated that
spin squeezing is heavily affected by positional disorder, reducing any capacity for a practical squeezing advantage, which requires scalability with the system size. In this Letter we explore the robustness of
spin squeezing in two-dimensional
lattices with a fraction of unoccupied
lattice sites. Using semiclassical modeling, we demonstrate the existence of scalable squeezing in power-law interacting XXZ models up to a disorder threshold, above which squeezing is not scalable. We produce a phase diagram for scalable squeezing, and explain its absence in the aforementioned NV experiment. Our work illustrates the maximum disorder allowed for realizing scalable
spin squeezing in a host of
quantum simulators, highlights a regime with substantial tolerance to disorder, and identifies controlled defect creation as a promising route for scalable squeezing in solid-state systems.
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All authors Samuel E. Begg, Bishal K. Ghosh, Chong Zu, Chuanwei Zhang, Michael Kolodrubetz
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Madelung hydrodynamics of spin-orbit coupling: action principles, currents, and correlations
Cesare Tronci
We exploit the variational and
Hamiltonian structures of
quantum hydrodynamics with
spin to unfold the correlation and torque mechanisms accompanying
spin-orbit coupling (SOC) in electronic motion. Using Hamilton's action principle for the Pauli equation, we isolate SOC-induced
quantum forces that act on the orbital Madelung–Bohm trajectories and complement the usual force terms known to appear in
quantum hydrodynamics with
spin. While the latter
spin-hydrodynamic forces relate to the
quantum geometric tensor (QGT), SOC-induced orbital forces originate from a particular current operator that contributes prominently to the
spin current. This distinction between force terms reveals two fundamentally different mechanisms generating
quantum spin-orbit correlations. Leveraging the
Hamiltonian structure of the hydrodynamic system, we also elucidate
spin transport features such as the correlation-induced
quantum torques and the current shift in the
spin Hall effect. This
Hall shift leads to a new definition of the transport
spin current thereby addressing an open question in spintronics. Finally, we illustrate the framework via the Madelung–Rashba equations for planar SOC configurations and propose a particle closure for possible numerical implementations.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.flu-dyn
Quantum geometry of the rotating shallow water model
Sriram Ganeshan and Alan T. Dorsey
The rotating shallow water equations (RSWE) are a mainstay of atmospheric and oceanic modeling, and their wave dynamics has close analogues in settings ranging from two-dimensional electron gases to active-matter fluids. While recent work has emphasized the topological character of RSWE wave bands, here we develop a complementary
quantum-
geometric description by computing the full
quantum geometric tensor (QGT) for the linearized RSWE on an $f$-plane. The QGT unifies two pieces of band geometry: its real part defines a metric that quantifies how rapidly wave polarization changes with parameters, while its imaginary part is the Berry
curvature that controls
geometric phases and topological invariants. We obtain compact,
symmetry-guided expressions for all three bands, highlighting the transverse structure of the metric and the monopole-like Berry
curvature that yields Chern numbers for the Poincaré bands. Finally, we describe a feasible route to probing this geometry in rotating-tank experiments via weak, time-periodic parametric driving.
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Superconductivity
Finite-momentum Cooper plasmons in superconducting terahertz microcavities
Alex M. Potts, Marios H. Michael, Gunda Kipp et al. (+12 more)
The phase mode of a
superconductor's order parameter encodes fundamental information about pairing and dissipation, but is typically inaccessible at low frequencies due to the Anderson-
Higgs mechanism. Superconducting samples thinner than the London penetration depth, however, support a gapless phase mode whose dispersion can be reshaped by a proximal screening layer. Here, we theoretically and experimentally show that this screened phase mode in a superconducting thin film integrated into on-chip terahertz circuitry naturally forms a superconducting microcavity that hosts resonant finite-momentum standing waves of supercurrent density, which we term Cooper plasmons. We measure two Cooper plasmons in a superconducting NbN microcavity and demonstrate that their resonance frequencies and linewidths independently report the density of participating carriers and plasmon's dissipation at finite momenta. Our results reveal an emergent collective mode of an integrated
superconductor-
circuit system and establish design principles for engineering or suppressing Cooper plasmons in superconducting terahertz devices and
circuits.
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All authors Alex M. Potts, Marios H. Michael, Gunda Kipp, Sara M. Langner, Hope M. Bretscher, Jonathan Stensberg, Kelson Kaj, Toru Matsuyama, Matthew W. Day, Felix Sturm, Abhay K. Nayak, Liam A. Cohen, Xiaoyang Zhu, Andrea Young, James McIver
Disordered Systems and Neural Networks · Cross-listed from cs.LG
On the origin of neural scaling laws: from random graphs to natural language
Maissam Barkeshli, Alberto Alfarano and Andrey Gromov
Scaling laws have played a major role in the modern AI revolution, providing practitioners predictive power over how the model performance will improve with increasing data, compute, and number of model parameters. This has spurred an intense interest in the origin of neural scaling laws, with a common suggestion being that they arise from power law structure already present in the data. In this paper we study scaling laws for
transformers trained to predict random walks (bigrams) on graphs with tunable complexity. We demonstrate that this simplified setting already gives rise to neural scaling laws even in the absence of power law structure in the data correlations. We further consider dialing down the complexity of natural
language systematically, by training on sequences sampled from increasingly simplified generative
language models, from 4,2,1-layer
transformer language models down to
language bigrams, revealing a monotonic
evolution of the scaling exponents. Our results also include scaling laws obtained from training on random walks on random graphs drawn from Erdös-Renyi and scale-free Barabási-Albert ensembles. Finally, we revisit conventional scaling laws for
language modeling, demonstrating that several essential results can be reproduced using 2 layer
transformers with context length of 50, provide a critical analysis of various fits used in prior literature, demonstrate an alternative method for obtaining compute optimal curves as compared with current practice in published literature, and provide preliminary evidence that maximal update parameterization may be more parameter efficient than standard parameterization.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Optimal universal bounds for waves with varied coherence based on supremum and infimum coherence spectra
Shiyu Li and Cheng Guo
We establish a majorization-based theory for bounding observables of waves with varied coherence. For any measurement, exact bounds are attained by the maximal and minimal elements in the set of input coherence spectra. The set's supremum and infimum, which may lie outside the set, provide optimal universal bounds: any alternative spectrum yielding universal bounds produces weaker constraints. We present an
algorithm to compute the supremum and infimum, and prove that they lie either at singular boundary points or strictly outside the set of coherence spectra.
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Statistical Mechanics
Synchronization with Annealed Disorder and Higher-Harmonic Interactions in Arbitrary Dimensions: When Two Dimensions Are Special
Rupak Majumder and Shamik Gupta
The impact of disorder on collective phenomena depends crucially on whether it is quenched or annealed. In synchronization problems, quenched disorder in higher dimensional Kuramoto models is known to produce unconventional dimensional effects, including a striking odd even dichotomy: synchronization transitions are continuous in even dimensions and discontinuous in odd dimensions. By contrast, the impact of annealed disorder has received comparatively little
attention. Here we study a D dimensional Kuramoto model with both fundamental and higher-harmonic interactions under annealed disorder, and develop an arbitrary dimensional center-
manifold framework to analyze the nonlinear dynamics near the onset of collective behavior. We show that annealed disorder fundamentally alters the role of dimensionality. With fundamental coupling alone, it completely removes the odd even dichotomy, yielding continuous synchronization transitions with universal mean-field scaling in all dimensions. Higher-harmonic interactions preserve this universality while rendering the synchronization transition tunable between continuous and discontinuous. At the same time, they give rise to a novel, correlation-driven transition between a
symmetry-protected incoherent phase and a
symmetry broken state lacking global synchronization, which is therefore invisible to the conventional Kuramoto order parameter. This transition is continuous in two dimensions but discontinuous in higher dimensions, revealing an emergent and previously-unrecognized special role of two dimensions.
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Mesoscale and Nanoscale Physics
Emergent electric field induced by dissipative sliding dynamics of domain walls in a Weyl magnet
Rinsuke Yamada, Daichi Kurebayashi, Yukako Fujishiro et al. (+10 more)
The dynamic motion of topological defects in magnets induces an emergent electric field, as exemplified by the continuous flow of skyrmion
vortices. However, the electrodynamics underlying this emergent field remains poorly understood. In this context,
magnetic domain walls - one dimensional topological defects with two collective modes, sliding and
spin tilt - offer a promising platform for exploration. Here, we demonstrate that the dissipative motion of domain walls under oscillatory current excitation generates an emergent electric field. We image domain patterns and quantify domain wall length under applied
magnetic fields in mesoscopic devices based on the
magnetic Weyl semimetal NdAlSi. These devices exhibit exceptionally strong domain wall scattering and a pronounced emergent electric field, observed in the imaginary component of the complex impedance.
Spin dynamics simulations reveal that domain wall sliding dominates over
spin tilting, where the phase delay of the domain wall motion with respect to the driving force impacts the emergent electric field. Our findings establish domain-wall dynamics as a platform for studying emergent electromagnetic fields and motivate further investigations on the coupled motion of
magnetic solitons and conduction electrons.
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All authors Rinsuke Yamada, Daichi Kurebayashi, Yukako Fujishiro, Shun Okumura, Daisuke Nakamura, Fehmi S. Yasin, Taro Nakajima, Tomoyuki Yokouchi, Akiko Kikkawa, Yasujiro Taguchi, Yoshinori Tokura, Oleg A. Tretiakov, Max Hirschberger
Mesoscale and Nanoscale Physics
Molecularly Thin Polyaramid Nanomechanical Resonators
Hagen Gress, Cody L. Ritt, Inal Shomakhov et al. (+8 more)
Two-dimensional polyaramids exhibit strong hydrogen bonding to create molecularly thin nanosheets analogous to
graphene. Here, we report the first nanomechanical resonators made out of a two-dimensional polyaramid, 2DPA-1, with thicknesses as small as 8 nm. To fabricate these molecular-scale resonators, we transferred nanofilms of 2DPA-1 onto chips with previously etched arrays of circular microwells. We then characterized the thermal resonances of these resonators under different conditions. When there is no residual gas inside the 2DPA-1-covered microwells, the eigenfrequencies are well-described by a tensioned plate theory, providing the Young's modulus and tension of the 2DPA-1 nanofilms. With gas present, the nanofilms bulge up and mechanical resonances are modified due to the adhesion, bulging and slack present in the system. The fabrication and mechanical characterization of these first 2DPA-1 nanomechanical resonators represent a convincing path toward molecular-scale polymeric NEMS with high mechanical strength, low density, and synthetic processability.
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All authors Hagen Gress, Cody L. Ritt, Inal Shomakhov, Kaan Altmisdort, Michelle Quien, Zitang Wei, John R. Lawall, Narasimha Boddeti, Michael S. Strano, J. Scott Bunch, Kamil L. Ekinci
Disordered Systems and Neural Networks · Cross-listed from stat.ML
Parametric RDT approach to computational gap of symmetric binary perceptron
Mihailo Stojnic
We study potential presence of statistical-computational gaps (SCG) in symmetric binary perceptrons (SBP) via a parametric utilization of fully lifted random duality theory (fl-RDT) [96]. A structural change from decreasingly to arbitrarily ordered $c$-sequence (a key fl-RDT parametric component) is observed on the second lifting level and associated with satisfiability ($\alpha_c$) – algorithmic ($\alpha_a$) constraints density threshold change thereby suggesting a potential existence of a nonzero computational gap $SCG=\alpha_c-\alpha_a$. The second level estimate is shown to match the theoretical $\alpha_c$ whereas the $r\rightarrow \infty$ level one is proposed to correspond to $\alpha_a$. For example, for the canonical SBP ($\kappa=1$ margin) we obtain $\alpha_c\approx 1.8159$ on the second and $\alpha_a\approx 1.6021$ (with converging tendency towards $\sim 1.59$ range) on the seventh level. Our propositions remarkably well concur with recent literature: (i) in [20] local
entropy replica approach predicts $\alpha_{LE}\approx 1.58$ as the onset of clustering defragmentation (presumed driving force behind locally improving
algorithms failures); (ii) in $\alpha\rightarrow 0$ regime we obtain on the third lifting level $\kappa\approx 1.2385\sqrt{\frac{\alpha_a}{-\log\left ( \alpha_a \right ) }}$ which qualitatively matches overlap gap property (OGP) based predictions of [43] and identically matches local
entropy based predictions of [24]; (iii) $c$-sequence ordering change phenomenology mirrors the one observed in asymmetric binary perceptron (ABP) in [98] and the negative Hopfield model in [100]; and (iv) as in [98,100], we here design a CLuP based
algorithm whose practical performance closely matches proposed theoretical predictions.
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