Superconductivity
Tailoring the properties of YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ thin films by 30 keV He$^+$ irradiation: An enabling route to superconducting device nanopatterning
Bernd Aichner, Simon Koch, Philipp A. Korner et al. (+8 more)
Focused helium ion beam (He-FIB) irradiation with 30 keV ions is a key tool for nanoscale patterning and defect engineering in high transition temperature (Tc) cuprate superconducting devices, yet its usable fluence window is constrained by the competing requirements of reliable superconductivity suppression and minimal structural degradation. In this work, we provide a comprehensive
dataset on the effects of large-area 30 keV He+ ion exposure on the electric transport and superconducting properties of epitaxial YBa2Cu3O7 (YBCO) thin films. X-ray diffraction shows a fluence-driven loss of crystalline order accompanied by an out-of-plane
lattice expansion and an orthorhombic-to-tetragonal transition, culminating at predominant amorphization at the highest fluence of 1 x 10^16 cm^-2. Raman spectra exhibit increasing disorder while lacking signatures of oxygen depletion, indicating that irradiation mainly generates oxygen-related Frenkel defects rather than changing the carrier concentration. Consistently, with increasing fluence, the normal-state resistivity \rho_N(T) at temperature T above Tc increases strongly, while d \rho_N/d T remains nearly unchanged at moderate fluence. The suppression of Tc is accurately described by Abrikosov-Gor'kov pair breaking and reaches complete quenching of superconductivity at 4.5 x 10^15 cm^-2. The anisotropic upper critical fields decrease approximately exponentially with increasing fluence, the
vortex activation energy is reduced, and the anisotropy drops, in contrast to oxygen-depleted YBCO.
Hall-angle analysis confirms a nearly constant carrier density but a systematic increase in defect scattering and reduced mobility, consistent with a crossover toward the dirty limit at high fluence. These results establish quantitative fluence thresholds and a practical operational window for He-FIB nanopatterning of YBCO
quantum circuits.
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All authors Bernd Aichner, Simon Koch, Philipp A. Korner, Max Karrer, Katja Wurster, Christoph Schmid, Ulrich Kentsch, Reinhold Kleiner, Edward Goldobin, Dieter Koelle, Wolfgang Lang
Soft Condensed Matter · Cross-listed from physics.flu-dyn
Wave turbulence theory of odd fluids and solids: kinetic equations and solutions
Xander M. de Wit, Léo Touzo, Sébastien Galtier et al. (+3 more)
The theory of wave
turbulence describes the properties of physical systems composed of a set of weak-amplitude random waves interacting nonlinearly. Here, we study odd wave
turbulence, which arises in
chiral media subjected to non-reciprocal stresses, notably odd viscosity and odd elasticity. In both cases, we consider simple models for which we can derive and solve analytically the kinetic equations describing the long-term statistical behavior of spectral quantities such as energy or wave action. For odd viscosity, we consider a three-dimensional model that exhibits wave
turbulence involving three-wave interactions, which gives rise to a direct energy cascade characterized by an anisotropic Kolmogorov-Zakharov (KZ) spectrum. For odd elasticity, we consider a quasi-one-dimensional overdamped model that exhibits much slower dynamics involving six-wave interactions. In that case, the KZ spectrum corresponding to a forward cascade of a conserved quantity we call odd energy, is nonlocal and therefore does not constitute a physical solution. However, the other KZ solution, which describes an inverse cascade of wave action, is only marginally non-local and is therefore valid up to a logarithmic correction. These two analytical theories provide a rigorous interpretation of direct numerical simulations, where the KZ spectrum is observed both in the case of odd viscosity (forward cascade) and of odd elasticity (inverse cascade).
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All authors Xander M. de Wit, Léo Touzo, Sébastien Galtier, Michel Fruchart, Federico Toschi, Vincenzo Vitelli
Quantum Gases · Cross-listed from physics.atom-ph
Trap-Quenched Matter-Wave Optics in Space
Gabriel Müller, Timothé Estrampes, Claudia Puertas González et al. (+12 more)
Dual-species atomic sources in space promise to be the testbed for a multitude of searches in
quantum gas physics such as a precise test of the Universality of Free Fall (UFF), few-body physics, cold molecules and
quantum bubbles. These experiments demand exquisite control over the expansion energies of both condensed ensembles as well as over their differential center-of-mass dynamics. We propose a trap-quenched collimation technique featuring in-trap excitations of collective modes compatible with state-of-the-art atom-chip setups. Using NASA's Cold Atom Laboratory aboard the International Space Station, we demonstrate it on a single-species $^{87}$Rb condensate. By controlling the center-of-mass release dynamics, we observe free expansion times up to 700 ms and measure a two-dimensional expansion energy of $k_B \cdot 78\pm 9 \;\mathrm{pK}$ in the imaging plane. A detailed model of the magnetically-induced dynamics indicates that this corresponds to a two-dimensional expansion energy of about $k_B \cdot 15^{+12}_{-5}\; \mathrm{pK}$ along two of the condensate's eigenaxes. Finally, we theoretically study this trap-quenched collimation scheme for a $^{41}$K-$^{87}$Rb mixture, predicting a simultaneous collimation that meets the expansion energy requirements for a state-of-the-art UFF test at the $10^{-15}$ accuracy level.
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All authors Gabriel Müller, Timothé Estrampes, Claudia Puertas González, Jannik Ströhle, David B. Reinhardt, Dana Codruta Marinica, Ethan R. Elliott, Jason R. Williams, Nathan Lundblad, Eric Charron, Ernst M. Rasel, Matthias Meister, Wolfgang P. Schleich, Naceur Gaaloul, Nicholas P. Bigelow
Soft Condensed Matter
On the physical meaning of latent track boundaries in swift heavy ion irradiated polymers
Adil Tuleushev, Fiona Harrison and Maxim Zdorovets
A large body of experimental studies of swift heavy ion latent tracks in dielectric materials has produced a wide range of estimates of track size. We investigate the physical meaning of these estimates by examining the different criteria of track boundary probed by various experimental techniques, including SAXS, XRD, chemical etching and conductometry. We show that different methods probe different physical aspects of ion induced modification, such as electron density redistribution, molecular ordering, chemical reactivity and charge separation, resulting in different determinations of effective track boundaries. Particular
attention is paid to
polymer films with electret-like properties, where post irradiation redistribution of weakly bound electrons may play an important role in the
evolution of latent track structure.
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Materials Science
First-principles calculations of internal conversion processes in spin defects
Stefano Paolo Villani, Yu Jin and Giulia Galli
Optically active
spin defects are foundational for
quantum technologies, yet common approximations underestimate their internal conversion (IC) rates by orders of magnitude. We propose a broad, predictive framework to compute IC rates that incorporates multi-configurational effects via many-body wavefunctions in TDDFT, and includes all-
phonon-mode contributions via analytical non-adiabatic couplings. Our approach resolves discrepancies with experiment, achieving quantitative agreement for the NV$^-$ center in diamond, and identifying a previously overlooked non-radiative channel in the divacancy triplet lifetime in SiC.
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Soft Condensed Matter
Bacterial adhesion to curved surfaces in fluid flow
Edwina F. Yeo, Benjamin J. Walker, Philip Pearce et al. (+1 more)
Minimising bacterial surface adhesion and subsequent biofilm formation in industrial and medical settings requires understanding how bacteria are transported and adhere to complex surface geometries in the presence of non-uniform flow. In this paper, we consider the transport of a dilute suspension of motile bacteria through a corrugated two-dimensional channel with perfectly adhesive walls. We asymptotically analyse the diffusive boundary layer that forms in high velocity flows using a curvilinear coordinate system based on the fluid streamfunction, presenting a similarity solution to the diffusivity-varying
diffusion-type equation that arises. From this solution, we derive an analytical expression for the bacterial adhesion rate as a function of surface arclength and the spatially varying wall shear rate. Our model predicts that bacterial adhesion becomes localised on curved surfaces, with bacteria showing preferential adhesion to wall `peaks' at lower shear rates and preferential adhesion to wall `valleys' at higher shear rates. More broadly, our results highlight how spatially varying flows generated by complex geometries can lead to localised bacterial adhesion, with potential implications for both enhancing and minimising biofilm formation.
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All authors Edwina F. Yeo, Benjamin J. Walker, Philip Pearce, Mohit P. Dalwadi
Statistical Mechanics
Boltzmann-Like Occupation of Nonequilibrium Steady States on Dense Networks
Jacob Calvert
A central problem in statistical physics is to extend the Boltzmann distribution to nonequilibrium steady states (NESS). We prove that NESS on large dense networks have Boltzmann-like occupation despite extensive
entropy production. We further show that the active-matter heuristic of "low rattling" is asymptotically exact. Intuitively, these NESS spend a greater fraction of their time in states they leave more slowly. This explanation extends to the broader class of "equiaccessible" steady states, which play a role in our analysis akin to that of
equilibrium in linear response.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Dissipation-induced superradiance in matter coupled to a self-interacting cavity
Sebastian Schmid, Matteo Soriente, Oded Zilberberg et al. (+1 more)
Light-matter interactions are often modeled via the Dicke model, namely, by two-level systems coupled to a cavity mode. Alas, the threshold for superradiance is often experimentally inaccessible or hindered by light's diamagnetic term. Here, within the Dicke setting, we consider self-interacting light in a cavity, modeled by a photonic Kerr nonlinearity. We show that negative Kerr nonlinearity gives rise to a low-threshold superradiant phase with
spin inversion. While unstable in a closed system, cavity dissipation stabilizes this lit phase, opening avenues for lasing and bath-engineered phases.
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All authors Sebastian Schmid, Matteo Soriente, Oded Zilberberg, Javier del Pino
Statistical Mechanics
Extending Covariant Fluctuation Theorems into Quantum Regime through Quasiprobability Approach
Ji-Hui Pei, Tingzhang Shi, Jin-Fu Chen et al. (+1 more)
The covariant formulation of
stochastic thermodynamics requires treating the
stochastic work as a 4-vector, posing significant challenges for
quantum systems due to the non-commutativity. We introduce a new quasiprobability distribution for the work 4-vector, which combines the Wigner and Margenau-Hill quasiprobabilities. This extends the covariant fluctuation
theorems from classical to
quantum regime. We illustrate our findings with a scalar field driven by classical particles with a generalized version of trace formula. Our work establishes a quasiprobability approach to studying relativistic
quantum thermodynamics in a covariant way.
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All authors Ji-Hui Pei, Tingzhang Shi, Jin-Fu Chen, H. T. Quan
Mesoscale and Nanoscale Physics
Spin-orbit coupling by design in quantum state engineering of atomically defined quantum dots
Hermann Osterhage, Julian H. Strik, Ivan Ado et al. (+4 more)
Tuning
spin-orbit coupling is essential in controlling both
spin and charge in confined
semiconductor nanostructures, yet it is rarely a truly controllable parameter. Here, we show control over the
spin-orbit
Hamiltonian in
quantum dots and the resulting
quantum states by tailoring the confinement potential with atomic-scale precision. Using scanning tunnelling microscopy and spectroscopy, we pattern individual Cs ions into designer
quantum dot structures on the surface of indium antimonide, in which electrons from a two-dimensional electron gas are confined with chosen in-plane electric-field gradients. We then quantify the atomic level structure, both spatially resolving the orbital character of the electronic states and their
magnetic-field
evolution. We demonstrate that the level structure, including the induced zero-field splitting, can be tailored by the designed geometry of the local electric fields. These effects can be described using a
Hamiltonian that allows consistent treatment of the confinement-induced
spin-orbit coupling beyond the conventional Bychkov-Rashba description. This
Hamiltonian is derived from a multiband k.p model and takes the energy dependence of the relevant physical parameters into account. Such precise control of
spin-orbit coupling in
semiconductor quantum dots is relevant to
quantum and spintronic technologies.
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All authors Hermann Osterhage, Julian H. Strik, Ivan Ado, Anna M. H. Krieg, Daniel Wegner, Mikhail Titov, Alexander A. Khajetoorians
Statistical Mechanics
Generic nonlocal statistics of the stationary measure in conserved active systems
Filippo De Luca, Michael E. Cates and Cesare Nardini
The stationary measure of
equilibrium systems with detailed balance follows a Boltzmann distribution, so that for short-ranged interactions the measure is local, meaning that distant spatial domains are statistically independent. In contrast, active systems break detailed balance, and can have nonlocal stationary measure even for fully local dynamics. Here, by expanding in nonlinearity about a Gaussian-model limit, we construct the measure perturbatively deep in the disordered phase for a class of models that includes Active Model A, Active Model B+, Model AB, the Nonreciprocal Cahn–Hilliard model, and the Toner–Tu model. In this regime, nonlocality is linked to a dynamical conservation law. Our results generically preclude construction of a Landau–Ginzburg expansion of the stationary measure (as opposed to the dynamical equations) for conserved active field theories.
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Mesoscale and Nanoscale Physics
On-chip superconducting GHz RF reflectometry of the capacitance response in bilayer graphene
Sung Jin An, Minseo Cho, Minjun Park et al. (+12 more)
In dual-gated
bilayer graphene, a perpendicular displacement field opens a band gap that modifies both the channel conductance and the electronic compressibility, motivating measurements that resolve resistive and capacitive responses on the same device. We integrate an hBN-encapsulated
bilayer graphene heterostructure with an on-chip superconducting Nb lumped-element LC resonator and carry out RF reflectometry near 4.25 GHz. DC transport and finite-bias spectroscopy on the same device provide a transport reference. Top and bottom gates independently set the carrier density and displacement field. The DC and RF gate maps share the same gate-dependent features, with finite-bias measurements revealing a region of suppressed conductance whose bias extent grows with the displacement field, consistent with a field-induced gap. The gate-dependent resonance-frequency shift is converted to the effective capacitance seen by the resonator using an equivalent-
circuit model. The capacitance shows a minimum near the conductance-suppressed region, consistent with reduced electronic compressibility in the gapped
bilayer graphene, and exhibits an electron-hole asymmetry. The on-chip configuration probes the gate-dependent admittance of a dual-gated van der Waals
heterostructure, providing capacitance-sensitive information that complements DC transport within a single device.
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All authors Sung Jin An, Minseo Cho, Minjun Park, Dohun Kim, HyeonJeong An, Seung-Bo Shim, Hakseong Kim, Sunghun Lee, Myoung-Jae Lee, Kenji Watanabe, Takashi Taniguchi, Jungpil Seo, Myunglae Jo, Youngwook Kim, Minkyung Jung
Strongly Correlated Electrons
SmoQyElPhQMC.jl: An open-source Julia package for efficient and scalable quantum Monte Carlo simulations of electron-phonon coupled models
Benjamin Cohen-Stead, James Neuhaus, Kipton Barros et al. (+2 more)
We introduce version 1.0 of the SmoQyElPhQMC.jl package, an open-source Julia code for performing scalable
quantum Monte Carlo simulations of electron-
phonon coupled model
Hamiltonians. SmoQyElPhQMC.jl is built upon the SmoQyDQMC.jl codebase and implements improved versions of the
algorithms presented in [B. Cohen-Stead et al., Phys. Rev. E 105, 065302 (2022)] to enable (near-linear) scalable simulations of a broad class of uncorrelated $e$-ph models both in system size and inverse temperature. By extending the functionality of the flexible scripting interface introduced in SmoQyDQMC.jl, the SmoQyElPhQMC.jl package continues to allow users to adapt it to different workflows and interface with other software packages in the Julia ecosystem. The code for this package can be downloaded from our GitHub repository at https://github.com/SmoQySuite/SmoQyElPhQMC.jl or installed using the Julia package manager. The online documentation, including examples, can be obtained from our documentation page at https://smoqysuite.github.io/SmoQyElPhQMC.jl/stable/.
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All authors Benjamin Cohen-Stead, James Neuhaus, Kipton Barros, Thomas A. Maier, Steven Johnston
Mesoscale and Nanoscale Physics
Strain- and doping-tunable optical resonance in Kekulé-Y graphene
Yawar Mohammadi
We investigate the optical response of Kekulé-Y
graphene under uniaxial strain and carrier doping. Using a low-energy effective
Hamiltonian, we show that strain reshapes the low-energy electronic structure of the Kekulé-Y phase and induces Van Hove singularities at energies well below those of pristine
graphene. Within the Kubo formalism, we calculate the optical conductivity and identify multiple anisotropic interband features, with a pronounced resonance arising from strain-induced Van Hove singularities. The pronounced resonance is strongly anisotropic and robust against moderate thermal broadening and disorder, providing a clear optical signature of Kekulé-Y ordering. We further derive analytical expressions for the low-energy optical conductivity and the Drude weight, providing a detailed characterization of the strain- and doping-dependent optical response. Our results establish strain engineering as an effective route for controlling valley-dependent optical properties in Kekulé-Y
graphene, originating from the Kekulé-induced coupling of the Dirac valleys, and suggest feasible optical probes for the experimental identification of the Kekulé-Y phase.
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Materials Science
Modifying Electrochemical Doping in Light-Emitting Electrochemical Cells with Gold Nanoparticles
Ajay K. Poonia, Anton Kirch, Joan Ràfols-Ribé et al. (+8 more)
Electrochemical doping offers dynamic control of the electronic properties of organic
semiconductors, and it is the enabling feature of a range of technologies, including electrochemical transistors, energy-storage devices, light-emitting electrochemical
cells (LECs), and bioelectronics. Electrochemical doping is commonly controlled by the selection of the constituents in the active material of the device or the applied voltage bias, but herein we report that the incorporation of Au nanoparticles (Au-NPs) at an electrode interface can constitute an alternative control parameter. The LEC features balanced p- and n-type electrochemical doping that forms a p-n junction doping structure in its active material, and we find that it is possible to reshape this doping profile by incorporating Au-NPs at an electrode interface. Specifically, we establish that the inclusion of neat non-capped Au-NPs at the anodic interface shifts the p-n junction (i.e., the emission zone) away from the anode. In contrast, the inclusion of Au-NPs capped with sodium citrate is found to reverse this behavior, so that the emission zone is instead moved towards the anode. We utilize this control parameter to shift the emission zone towards a position of constructive (destructive) interference, as manifested in a strong increase (decrease) of the LEC emission efficiency. Our findings establish an interfacial strategy for modulating the spatial profile of electrochemical doping and tuning device performance without altering the chemistry of the active material, relying instead on the surface modification of one electrode. This approach is important because it provides a versatile and minimally invasive route to optimize electrochemical devices while preserving the intrinsic properties and formulation of the active material.
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All authors Ajay K. Poonia, Anton Kirch, Joan Ràfols-Ribé, Lucrezia Catanzaro, Anish Rao, Karol Kołątaj, Vittorio Scardaci, Giuseppe Compagnini, Guillermo P. Acuna, Ludvig Edman, Nicolò Maccaferri
Disordered Systems and Neural Networks
Local Coverage Governs Memorization in Diffusion Models
Claudia Merger and Sebastian Goldt
Memorization in
diffusion models is often treated as a global property of the model or
dataset. In practice, however, a single
diffusion model can simultaneously generate both memorized and novel samples. Which training samples are most likely to be memorized? In this work, we show that memorization is governed by local data coverage. Leveraging the connection between
diffusion models and kernel density estimation (KDE), we derive a theoretical criterion that predicts whether a point is memorized based on the density of training data in its neighborhood and the size of the training
dataset. In the high-dimensional limit, this leads to a sharp, local transition: regions of low coverage are dominated by isolated training samples, which are memorized, while dense regions support interpolation and generalization. We validate these predictions empirically, showing that memorization increases with local sparsity and that
diffusion models exhibit a coexistence of memorized and novel samples within the same model. Extending this framework to multi-class settings, we further show that classes with higher intra-class sparsity (and thus lower local coverage) are more strongly memorized. Our results provide a local view of memorization in
diffusion models, explaining when and where memorization occurs in terms of data geometry.
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Materials Science
The Future of Computing for Materials Science Challenges
Phalgun Lolur, Richard P. Padbury, George H. Booth et al. (+10 more)
Materials discovery increasingly relies on the coordinated use of theory, computation, experiment, data-driven methods, and emerging
quantum technologies, yet the full potential of these tools is realised only when they operate within workflows that reflect the complexity of real systems. This perspective summarises current capabilities, limitations, and opportunities across these domains, drawing on contributions from academia, industry, and national laboratories to identify the scientific and structural requirements for more reliable and efficient discovery. Classical simulations provide broad coverage across design spaces, while experimental measurements reveal degradation, heterogeneity, and kinetic processes that determine performance under realistic conditions. Machine learning accelerates exploration when supported by well-curated
datasets with clear provenance and uncertainty quantification, and
quantum computing offers promising routes into correlated electronic behaviour when aligned with properties that influence engineering decisions. Collectively, these insights highlight the need for reproducible workflows, shared data standards, realistic
benchmarks, and a research culture that prepares scientists to work across paradigms. By integrating these methodological and organisational elements, the community can move toward discovery processes that deliver robust predictions, support confident decision making, and shorten the path from conceptual design to deployable materials.
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All authors Phalgun Lolur, Richard P. Padbury, George H. Booth, Katherine Inzani, Nicole Holzmann, Thomas W. Keal, Joseph Montaya, Daniel F. Urban, Thomas Eckl, Emanuele Marsili, Wibe A. de Jong, Jonathan R. Owens, Julian van Velzen
Materials Science
Multistate Manipulation of Charge-Spin Conversion in Two-Dimensional Ferroelectric Bilayers
Weiyi Pan, Xinyuan Jiang and Jaroslav Fabian
Achieving nonvolatile and multistate manipulation of charge-
spin conversion, including the Edelstein effect (EE) and
spin Hall effect (SHE), is crucial for high-density spintronic
memory. Here, we propose a mechanism to simultaneously control both EE and SHE in two-dimensional ferroelectric
bilayers, where interlayer-parallel and interlayer-antiparallel polarization configurations can coexist.
Symmetry analysis shows that in the interlayer-parallel states, reversal of the total polarization switches the sign of the EE, whereas changing to an interlayer-antiparallel configuration suppresses the EE to zero, enabling electrically switchable current-induced
spin accumulation among three distinct states, which could be used for ternary logic operations. Meanwhile, the magnitude of the SHE can be tuned by switching between two different classes of polarization configurations, namely interlayer-parallel and interlayer-antiparallel configurations. Using first-principles calculations, we demonstrate this mechanism in
bilayer metallic ferroelectric PtBi2, where both interlayer-parallel and interlayer-antiparallel polarization configurations are energetically stable. The EE coefficient in interlayer-parallel states, which can be reversed by polarization switching, arises from competing electron- and hole-pocket contributions near the
Fermi surface. The intrinsic SHE coefficients originate from
spin Berry
curvature that can be reshaped by polarization configuration variation and
Fermi-level tuning. Our results establish ferroelectric
bilayers as an all-in-one platform for electrically programmable charge-
spin conversion.
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Strongly Correlated Electrons
Bond-operator analytical approach for the $t$-$J$ model
A. V. Syromyatnikov
We present a bond-operator theory (BOT) for analytical consideration of the $t$-$J$ model and its extensions with longer-rage hopping terms. This technique is based on previously suggested representation of electron operators via localized
spins 1/2 and spinless
Fermi-operators of mobile holons which requires no constraint between them. We introduce a representation of operators of
spins, holons, and electrons in (extended) unit
cell containing several
lattice sites via a zoo of Bose- and
Fermi-operators acting in the
Hilbert space of all
quantum states of the whole unit
cell. BOT provides a regular expansion of physical quantities in powers of $1/n$ using conventional diagrammatic technique, where $n\ge1$ is the maximum number of introduced quasiparticles (
bosons and
fermions) which can occupy a unit
cell. The suggested representation reproduces commutation
algebra of all operators at any $n>0$ and allows to consider both magnetically ordered and disordered phases. Some elementary excitations described in the BOT by separate
bosons or
fermions appear in common approaches as bound states of conventional quasiparticles. In particular, there are two-hole bound states (Cooper pairs of two holes) which are described within the BOT by separate
bosons. We discuss in detail properties of the $t$-$J$ model on the square
lattice with no more than two holes (polarons). Although the expansion parameter $1/n$ is not small in the physically meaningful case of $n=1$, we obtain a good quantitative agreement with previous numerical findings at $n=1$ even in the first order in $1/n$ after taking into account a few simple diagrams. Self-consistent calculations in the first order in $1/n$ bring our results to a very good quantitative agreement with previous numerical findings of the ground state energy, staggered magnetization, and spectra of
magnons, polarons, and lowest-energy two-hole bound states.
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Soft Condensed Matter
Spherical metadensity functional learning for inhomogeneous classical fluids
Stefanie M. Kampa, Matthias Schmidt and Florian Sammüller
We develop classical density functional learning to address fluids with truncated pairwise interparticle interactions in three-dimensional spherical geometry. Simulation data for systems with randomized repulsive pair potentials provide the basis for supervised training of a neural metadensity functional, thereby making efficient use of results for radial distribution functions in the bulk fluid via the test particle route. Specifically, we develop spherical local learning in order to represent the one-body direct correlation functional in terms of a neural network, which captures spatial
curvature effects as well as the metadensity functional dependence on the thermally scaled pair potential. The framework yields efficient access to inhomogeneous structuring and related physical phenomena that occur in fluids and general solvents when adsorbed against curved solutes and confined inside of spherical and planar cavities. Test particle setups facilitate accurate prediction of the bulk fluid pair structure and verification of thermodynamic test particle sum rules via functional line integration. Applying the metadensity functional for Henderson inversion allows one to infer accurately the pair potential from the bulk radial distribution function. We address implications of the geometrical setup for two-body quantities and obtain the two-body direct correlation functional from automatic differentiation. For the hard sphere fluid, we confirm metadensity functional predictions against results from a standard neural density functional with fixed pair potential as well as to an analytic functional as given by fundamental measure theory. Simulation results provide further reference and corroborate reliable results of the spherical neural metadensity functional across a broad range of applications.
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Quantum Gases
Modeling light-matter coupled systems with neural quantum states
Noe Salmeron, Marin Bukov and Markus Schmitt
Recent advances in cold atom manipulation enable the study of many-body systems where short-range interactions between neighboring atoms coexist with long-range interactions mediated by
photons. Such a combination of interactions makes a theoretical approach challenging beyond mean-field methods. In this work, we develop a neural
quantum state based approach to study these systems numerically. We introduce a neural-network architecture capable of handling hybrid
Hilbert spaces with large local bosonic dimensions in strongly interacting
spin-
photon systems. We
benchmark this approach on a model of a two-dimensional
lattice of Rydberg atoms coupled to a
photon mode. The superradiant ground states found in the large
spin-
photon coupling regime allow us to demonstrate the efficiency of the method in the presence of high
photon occupation. Furthermore, the ability to capture
spin-
spin and
spin-
photon correlations leads us to observe quantitative deviations in the ground state phase boundaries with respect to mean-field theory. The method extends to other systems with a similar hybrid
Hilbert space structure, such as
spin-
phonon systems, and provides a scalable framework for investigating their ground state properties.
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Statistical Mechanics · Cross-listed from physics.soc-ph
Detecting Historical Turning Points in Italian Media: A Complex Systems Approach to a Diachronic News Corpus
Dario Zarcone, Salvatore Miccichè and David Sanchez
The increasing availability of large-scale textual corpora has opened new possibilities for data-driven, quantitative approaches to historical analysis using Natural
Language Processing (NLP). However, diachronic corpora with historical relevance from the pre-digital era remain scarce and often incomplete. We present a quantitative approach to historical analysis based on the reconstruction and exploration of a diachronic corpus of around 600,000 articles from the Italian newspaper "La Repubblica", covering all the articles published from the 1st of January 1985 to the 31st of December 2000 - a period of major political, social, and geopolitical change in Italy and globally. Using NLP techniques, we analyze the text at both lexical and semantic levels; we then apply tools from complex systems and statistical physics to trace shifts in media discourse over time. This allows us to detect key transition periods, such as the transition from the First Republic to the Second Republic in Italy, or major international conflicts like the Gulf War or the Kosovo War, without relying on prior labeling. The results show how combining computational linguistics with ideas from complex systems can offer new quantitative insight into historical changes, opening up new paths for studying the dynamics of media and society through large-scale textual data.
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Quantum Gases
Mass-imbalanced two-dimensional Bose-Fermi mixtures with boson-fermion pairing
Cristiano Luigi Kosman Chiarappa, Pietro Bovini and Pierbiagio Pieri
We analyze a two-dimensional Bose-
Fermi mixture at zero temperature in the presence of a tunable Bose-
Fermi attraction. We adopt a diagrammatic T-
matrix approach and study the behavior of several thermodynamic quantities for the two species as functions of density, mass ratio, and coupling strength. These include the chemical potentials, the
boson momentum distribution function, the condensate density, and Tan's contact parameter. We analytically demonstrate that the present T-
matrix formalism recovers the correct second-order perturbative expansion of the chemical potentials in the weak-coupling regime, and test it numerically. The near-universal behavior of the condensate fraction already found in prior work for the mass-balanced case is confirmed for different masses and becomes even more accurate when the
boson mass is large. The mass imbalance emerges as an additional control parameter that qualitatively affects the bosonic momentum distribution. In particular, we found that it can be used to allow for the experimental observation of a peculiar peak in the
boson momentum distribution at finite momentum.
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Statistical Mechanics · Cross-listed from physics.soc-ph
Wealth Inequality and Planetary Boundaries in a Stylized Agent-Based Model
Thomas Valade, Michael Benzaquen, Matthieu Cristelli et al. (+2 more)
At the intersection of rising wealth inequality and intensifying environmental pressures, we investigate a reverse causal relationship that has received comparatively little
attention: wealth inequality may not only be a consequence of environmental crises, but also act as a structural obstacle to the ecological transition itself. We develop a stylized
agent-based model in which heterogeneous
agents, whose initial wealth follows a Pareto distribution, allocate their income between either a Brown or a Green sector through a utility function. The function is designed to capture the trade-off between short-term returns and exposure to long-term systemic risks. A central ingredient is that wealthier
agents perceive themselves as less vulnerable to environmental shocks, thereby reducing the amount of resources available for the transition. We show that, beyond inequality thresholds compatible with those observed in most developed countries, the economy remains locked in a Brown regime, even when a substantial share of
agents is sensitive to externalities. We then assess a set of stylized fiscal policies (basic income, carbon taxation, Green incentives, and a combined scheme) and find that their effectiveness depends strongly on the inequality regime and on the regressivity embedded in the fiscal mechanism, revealing multidimensional trade-offs between transition speed, cumulative environmental destruction, growth, and fiscal pressure.
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All authors Thomas Valade, Michael Benzaquen, Matthieu Cristelli, Stanislao Gualdi, Pierre Lenders
Statistical Mechanics
Thermodynamic Bounds from Otto–Villani Functional Inequalities
Andrea Auconi
The dissipation in the relaxation of an ensemble of conservative
stochastic systems towards the
equilibrium steady state is quantified by the free energy difference. Functional inequalities within the framework of [F. Otto and C. Villani, J. Funct. Anal. 173, 361 (2000)] are here revisited which connect the free energy dynamics and optimal transport, offering a
geometric perspective on the instantaneous speed of relaxation in the presence of potential barriers. These are illustrated with numerical relaxation experiments on Landau-Ginzburg potentials. The same inequalities hold for relaxation toward nonequilibrium steady states once the potential is replaced by the pseudo-potential defined by the stationary density.
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Soft Condensed Matter
Thinning-by-spinning: shear rheology of dense chiral fluids
Lucio Mauro Carenza, Giuseppe Gonnella, Demian Levis et al. (+1 more)
We investigate the linear and nonlinear rheology of dense
chiral fluids composed of self-spinning particles under external shear. Using particle-based simulations of a two-dimensional Lennard-Jones model with transverse interactions, we show that chirality acts as an intrinsic source of fluctuations and shear. In the solid regime, spinning fluidizes the system, weakening hexatic order. In the
liquid regime, the viscosity is quantitatively described by a Green-Kubo relation upon replacing the temperature by a chirality-dependent effective temperature. Beyond linear response, flow curves collapse when expressed in terms of the ratio between imposed shear and spinning rates, revealing a thinning-by-spinning mechanism. At large forcing, this correspondence breaks down and a pronounced handedness asymmetry emerges: when transverse interactions oppose the imposed shear, stresses relax through the formation of string-like flow channels. Our results identify chirality as a generic mechanism for fluidization and provide a unified framework for understanding the rheology of dense
chiral suspensions.
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All authors Lucio Mauro Carenza, Giuseppe Gonnella, Demian Levis, Giuseppe Negro
Statistical Mechanics
Thermodynamic Framework for $q$-Affinity
Dani Rodríguez-Castellanos and Petr Jizba
We develop a thermodynamic framework for non-
equilibrium affinities based on generalized
entropies. In particular, we extend the classical concept of De Donder by introducing $q$-affinities associated with Rényi and Tsallis
entropies. This in turn allows us to generalize thermodynamic driving forces to systems with long-range interactions and/or strong correlations. For Rényi
entropy, we build on a thermodynamic interpretation due to Baez, where the
entropy is expressed through finite differences of the Helmholtz free energy at two temperatures. This leads to a generalized thermodynamic potential whose derivative with respect to a reaction coordinate defines the Rényi $q$-affinity. The resulting expression admits a representation in terms of exponential work averages, establishing a connection to Jarzynski-type fluctuation relations. For Tsallis
entropy, we consider Markov jump processes using a master-equation-based approach. We derive a $q$-deformed
entropy balance law and obtain an explicit expression for the Tsallis
entropy production rate, proving its non-negativity and thus recovering a generalized second-law structure. This allows to identify a local
stochastic $q$-affinity with the generalized thermodynamic force entering the
entropy production rate.
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Materials Science
Pronounced in-plane anomalous Hall effect with vanishing out-of-plane response in Cr1.2Te2
Wenzhi Peng, Zheng Liu, ShaSha Wang et al. (+8 more)
We report an unconventional anomalous
Hall regime in the van der Waals ferromagnet Cr1.2Te2, in which the anomalous
Hall effect (AHE) is present for in-plane magnetization but absent for out-of-plane magnetization. In this purely in-plane regime, the anomalous
Hall signal exhibits a threefold angular dependence during both in-plane and out-of-plane rotations of the magnetization, which cannot be accounted for by the conventional dipolar contribution but instead requires an octupolar contribution. Although the octupolar term qualitatively captures the observed behavior, the experimentally extracted octupole differs quantitatively from first-principles calculations based solely on the intrinsic Berry-
curvature mechanism, indicating an essential role for extrinsic scattering processes.
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All authors Wenzhi Peng, Zheng Liu, ShaSha Wang, Haolin Pan, Changlong Wang, Xiangbiao Shi, Jiahao Han, Qian Niu, Yang Gao, Bin Xiang, Dazhi Hou
Materials Science
$p$-wave magnet and hedgehog-type Berry curvature in helimagnetic MnAu$_2$
Hogyun Jeong, Sangyun Lee, Junhee Shin et al. (+4 more)
Recently discovered altermagnetism in collinear compensated magnets shows even-parity
spin texture in momentum space. Beyond the collinear
spin ordering, unique odd-parity
spin textures emerge in noncollinear compensated magnets. The noncollinear candidates, however, remain unexplored toward a room-temperature metallic altermagnet. Here, we demonstrate that MnAu2 exhibits metallic p-wave magnetism and large
spin splitting induced by helical
spin ordering. By adapting the band-unfolding scheme based on the translation operators combined with
spin rotations, first-principles calculations reveal an unconventional
Fermi surface around the $\tilde{M}$-point composed of a single electron pocket with $p$-wave
spin texture. Moreover, the
spin twist in the helimagnet triggers topologically non-trivial hedgehog Berry
curvature, which links to the nonlinear
Hall effect and
spin Hall effect. Considering the experimental T$_C$ = 335 to 370 K, MnAu$_2$ could establish itself as an ideal candidate for a room-temperature metallic $p$-wave magnet, promising for versatile spintronic applications.
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All authors Hogyun Jeong, Sangyun Lee, Junhee Shin, Jung-Woo Yoo, Changhee Sohn, Yoon Seok Oh, Hosub Jin
Quantum Gases
Spin mixing induced dynamics of spinor solitons in $F=1$ Bose Einstein condensates
T. Panagos, A. Romero-Ros, G.C. Katsimiga et al. (+2 more)
We explore
soliton interactions in a homogeneous spinor $F=1$ Bose Einstein Condensate (BEC) in the presence of a
magnetic field, focusing on dark bright dark and bright dark bright configurations. We investigate how these interactions depend on the phase differences among bright
solitons and their influence during the dynamics. Our findings align with prior non spinor results, i.e., repulsion among in phase bright
solitons and attraction among out of phase pairs in self repulsive atomic BECs. The potential bright
soliton attraction, added to the short range repulsion of dark dark
soliton interactions, can lead to bound states. However, we find that these bound states break in the presence of spinor interactions due to the particle exchange dynamics between the hyperfine states of the components. Additonally, we develop an effective classical model to describe the
soliton dynamics, using a Lagrangian approach. The accuracy of the model is tested by comparing it against numerical simulations. Our results suggest that the proposed model captures the essential features of
soliton behavior in the presence of
spin interactions, and provides congruent
soliton trajectories and interspecies particle exchange dynamics in most of the cases.
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All authors T. Panagos, A. Romero-Ros, G.C. Katsimiga, P. Schmelcher, P.G. Kevrekidis