Materials Science
Epitaxial Growth and Electronic Properties of QuasiFreeStanding Rhombohedral WSe2 Bilayers on Cubic W110
Niels Chapuis, Meryem Bouaziz, Eva Desgue et al. (+6 more)
Rhombohedral-stacked transition metal dichalcogenides (TMDs) break inversion
symmetry between adjacent layers, giving rise to an intrinsic out-of-plane ferroelectric polarization.Controlling the formation of this stacking polytype is therefore essential for harnessing ferroelectric effects in two-dimensional materials. In this work, we demonstrate the epitaxial growth of rhombohedral
bilayer tungsten diselenide (3R-WSe2) on a cubic W(110) single
crystal by molecular beam epitaxy. We show that selenium passivation of the substrate is key to enable a quasi van der Waals epitaxy effectively suppressing strong interfacial bonding and promoting the growth of quasi free standing
bilayer films. The 3R stacking order is confirmed through a combination of Raman spectroscopy and high-resolution angle-resolved photoemission spectroscopy (ARPES), supported by density functional theory (DFT) calculations. ARPES and DFT reveal an indirect-gap electronic structure with the valence-band maximum at the Gamma point, as well as a pronounced
spin orbit driven splitting of 520 +- 20 meV at the K point. Analysis of the measured dispersions yields hole effective masses of 0.46 +- 0.04 me and 0.75 +- 0.06 me for the upper and lower valence bands at K point, respectively. These results establish a robust route for synthesizing quasi free standing 3R-WSe2 and provide a platform for exploring the electronic, optical, and ferroelectric functionalities that emerge from inversion
symmetry breaking in layered TMDs. Our findings further highlight the potential of cubic substrates for deterministic fabrication of rhombohedral TMD
heterostructures and ferroelectric devices at the nanoscale.
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All authors Niels Chapuis, Meryem Bouaziz, Eva Desgue, Iann Gerber, François Bertarn, Pierre Legagneux, Fabrice Oehler, Julien Chaste, Abdelkarim Ouerghi
Quantum Gases · Cross-listed from math.NA
An efficient and accurate numerical method for computing the ground states of three-dimensional rotating dipolar Bose-Einstein condensates under strongly anisotropic trap
Qinglin Tang, Hanquan Wang, Shaobo Zhang et al. (+1 more)
In this article, we propose an efficient and spectrally accurate numerical method to compute the ground states of three-dimensional (3D) rotating dipolar Bose-Einstein condensates (BEC) under strongly anisotropic trapping potentials.The kernel singularity, convolution non-locality and density anisotropy together complicate the dipolar potential evaluation. The fast rotation mechanism not only induces a complicated energy landscape with many local minima, but also creates a large number of
vortices in the condensates. Such factors collectively make the ground state computation challenging in terms of convergence, accuracy and efficiency, especially for 3D anisotropic systems. Coupled with
Fourier spectral discretization, we proposed a preconditioned conjugate gradient method (PCG) by integrating the anisotropic truncated kernel method (ATKM) for the dipolar potential evaluation. An adaptive step size control strategy is designed and ATKM allows for a spectral accuracy without introducing any extra anisotropy-dependent
memory requirement or computational time. Our
algorithm is spectrally accurate, highly efficient and
memory-economic. Extensive numerical results are presented to confirm the accuracy and efficiency, together with applications to study impacts of the model parameters on critical rotational frequency, energies and chemical potential. Furthermore, these simulations reveal additional novel ground state patterns, such as bent
vortices.
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All authors Qinglin Tang, Hanquan Wang, Shaobo Zhang, Yong Zhang
Materials Science · Cross-listed from physics.chem-ph
Escaping the Hydrolysis Trap: An Agentic Workflow for Inverse Design of Durable Photocatalytic Covalent Organic Frameworks
Iman Peivaste, Nicolas D. Boscher, Ahmed Makradi et al. (+1 more)
Covalent organic frameworks (COFs) are promising photocatalysts for
solar hydrogen production, yet the most electronically favorable linkages, imines, hydrolyze rapidly in water, creating a stability–activity trade-off that limits practical deployment. Navigating the combinatorial design space of nodes, linkers, linkages, and functional groups to identify candidates that are simultaneously active and durable remains a formidable challenge. Here we introduce Ara, a large-
language-model (LLM)
agent that leverages pretrained chemical knowledge, donor–acceptor theory, conjugation effects, and linkage stability hierarchies, to guide the search for photocatalytic COFs satisfying joint band-gap, band-edge, and hydrolytic-stability criteria. Evaluated against random search and
Bayesian optimization (BO) over a space consisting of candidates with various nodes, linkers, linkages, and r-groups, screened with a GFN1-xTB fragment pipeline, Ara achieves a 52.7% hit rate (11.5$\times$ random, p = 0.006), finds its first hit at iteration 12 versus 25 for random search, and significantly outperforms BO (p = 0.006). Inspection of the
agent's
reasoning traces reveals interpretable chemical logic: early convergence on vinylene and beta-ketoenamine linkages for stability, node selection informed by electron-withdrawing character, and systematic R-group optimization to center the band gap at 2.0 eV. Exhaustive evaluation of the full search space uncovers a complementary exploitation–exploration trade-off between the
agent and BO, suggesting that hybrid strategies may combine the strengths of both approaches. These results demonstrate that LLM chemical priors can substantially accelerate multi-criteria materials discovery.
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All authors Iman Peivaste, Nicolas D. Boscher, Ahmed Makradi, Salim Belouettar
Quantum Gases · Cross-listed from nucl-th
Emergence of the geometric contribution to the superfluid density in the inner crust of neutron stars
Giorgio Almirante
The
geometric contribution to the superfluid density has been found to be of great importance in the inner crust of
neutron stars. In this work we clarify how this contribution arises in the context of a band theory for
neutrons. Specifically, we derive the dependence of the superfluid density on the magnitude of the pairing gap when the system has many bands cutting the
Fermi energy, as it is the case for the
neutrons in the inner crust. Also, in the perturbation theory framework, we find that it is essential to account for the corrections to the (Bogoliubov) quasi-particle states in order to get the
geometric contribution. Accounting only for the corrections to the (Hartree-Fock) single-particle states leads to the conventional contribution only.
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Superconductivity
Thin amorphous molybdenum silicide superconducting shells around individual nanowires deposited via magnetron co-sputtering
Luize Dipane, Martins Zubkins, Gunta Kunakova et al. (+4 more)
Employing amorphous
superconductors, such as Type-II molybdenum silicide (MoSi), instead of crystalline materials significantly simplifies the material deposition and scalable nanoscale prototyping, beneficial for
quantum electronic and photonic device fabrication. In this work, deposition of amorphous superconductive MoSi thin films on flat and nanowire (NW) substrates was demonstrated via pulsed direct-current magnetron co-sputtering from molybdenum and silicon targets in an argon atmosphere. MoSi films were deposited on oxidized silicon wafers and Ga2O3 NWs with 6 nm Al2O3 insulating shell, grown around the NWs using atomic layer deposition, and studied using scanning and transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Four-point Cr/Au electrical contacts were defined on the thin films and on individual Ga2O3-Al2O3-MoSi core-shell NWs using lithography for low-temperature electrical measurements. By controlling the sputtering power of the targets and thus adjusting the molybdenum-to-silicon ratio in the MoSi films, their properties were optimized to achieve critical temperature Tc of 7.25 K. Such superconducting shell NWs could provide new avenues for fundamental studies and interfacing with other materials for
quantum device applications.
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All authors Luize Dipane, Martins Zubkins, Gunta Kunakova, Eriks Dipans, Tom Yager, Boris Polyakov, Edgars Butanovs
Statistical Mechanics
Waiting-time based entropy estimators in continuous space without Markovian events
Jonas H. Fritz and Udo Seifert
Estimating
entropy production in continuous systems that can only be observed with a limited resolution remains an open problem in
stochastic thermodynamics. Existing
estimators based on the measurement of waiting-time distributions require either the detection of Markovian events, which uniquely determine the state of the system, or assume a discrete underlying dynamics. We present a novel
estimator that relies solely on the detection of a single particle leaving or entering regions, or crossing
manifolds, in continuous space. This
estimator is based on the frequency and the duration of transitions between such events. We derive this bound by introducing two kinds of discretization of space. Finally, we compare our novel bound to the thermodynamic uncertainty relation improved by correlations using simulations of a Brownian
vortex and discuss its relation to other lower bounds to
entropy production.
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Disordered Systems and Neural Networks
Machine Learning the Strong Disorder Renormalization Group Method for Disordered Quantum Spin Chains
A. Ustyuzhanin, J. Vahedi and S. Kettemann
We train machine learning
algorithms to infer the
entanglement structure of disordered long-range interacting
quantum spin chains by learning from the strong disorder renormalisation group (SDRG) method. The system consists of $S=1/2$-
quantum spins coupled by
antiferromagnetic power-law interactions with decay exponent $\alpha$ at random positions on a one-dimensional chain. Using SDRG as a physics-informed teacher, we compare a Random Forest classifier as a classical baseline with a graph neural network (GNN) that operates directly on the interaction graph and learns a bond-ranking rule mirroring the SDRG decimation policy. The GNN achieves a disorder-averaged pairing accuracy close to one and reproduces the
entanglement entropy $S(\ell)$ in excellent quantitative agreement with SDRG across all subsystem sizes and interaction exponents. RG flow heat maps confirm that the GNN learns the sequential decimation hierarchy rather than merely fitting final-state observables. Finite-temperature
entanglement properties are incorporated via the SDRGX framework through a two-stage strategy, using the zero-temperature GNN to generate the RG flow and sampling thermal occupations from the canonical ensemble, yielding results in agreement with both numerical SDRGX and analytical predictions without retraining.
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Materials Science
A Geometry-Adaptive Deep Variational Framework for Phase Discovery in the Landau-Brazovskii Model
Yuchen Xie, Jianyuan Yin and Lei Zhang
The discovery of ordered structures in pattern-forming systems, such as the Landau-Brazovskii (LB) model, is often limited by the sensitivity of numerical solvers to the prescribed computational domain size. Incompatible domains induce artificial stress, frequently trapping the system in high-energy metastable configurations. To resolve this issue, we propose a Geometry-Adaptive Deep Variational Framework (GeoDVF) that jointly optimizes the infinite-dimensional order parameter, which is parameterized by a neural network, and the finite-dimensional
geometric parameters of the computational domain. By explicitly treating the domain size as trainable variables within the variational formulation, GeoDVF naturally eliminates artificial stress during training. To escape the attraction basin of the disordered phase under small initializations, we introduce a warmup penalty mechanism, which effectively destabilizes the disordered phase, enabling the spontaneous nucleation of complex three-dimensional ordered phases from random initializations. Furthermore, we design a guided initialization protocol to resolve topologically intricate phases associated with narrow basins of attraction. Extensive numerical experiments show that GeoDVF provides a robust and geometry-consistent variational solver capable of identifying both stable and metastable states without prior knowledge.
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Strongly Correlated Electrons · Cross-listed from hep-th
Simulating Lattice Gauge Theories with Virtual Rishons
David Rogerson, João Barata, Robert M. Konik et al. (+2 more)
Classical tensor network and hybrid
quantum-classical
algorithms are promising candidates for the investigation of real-time properties of
lattice gauge theories. We develop here a novel framework which enforces gauge
symmetry via a
quantum-link virtual rishon representation applied at intermediate steps. Crucially, the gauge and matter degrees of freedom are dynamical variables encoded in terms of
qubits, enabling analysis of gauge theories in $d+1$ spacetime dimensions. We
benchmark this framework in a U(1) gauge theory with and without matter fields. For $d = 1$, the multi-
flavor Schwinger model with $1\leq N_f\leq3$
flavors is analyzed for arbitrary boundary conditions and nonzero topological angle, capturing signatures of the underlying Wess-Zumino-Witten conformal field theory. For $d = 2$, we extract the confining string tension in close agreement with continuum expectations. These results establish the virtual rishon framework as a scalable and robust approach for the simulation of
lattice gauge theories using both classical tensor networks as well as near-term
quantum hardware.
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All authors David Rogerson, João Barata, Robert M. Konik, Raju Venugopalan, Ananda Roy
Materials Science
Inverse-design of two-dimensional magnonic crystals via topology optimization with frequency-domain micromagnetics
Ryunosuke Nagaoka, Takahiro Yamazaki, Chiharu Mitsumata et al. (+2 more)
Magnonic
crystals (MCs) are emerging spintronic metamaterials capable of manipulating transmission properties of
magnons, the quanta of
spin waves. Due to the complex relationship between
lattice geometry and magnonic band dispersion, it remains challenging to establish general design strategies for optimizing targeted properties in MCs. In this study, we demonstrated an inverse-design framework for two-dimensional MCs to explore unconventional
lattice structures with large magnonic band gaps. We employed genetic
algorithms to enable global exploration of structures with a complete band gap as the objective property, and used frequency-domain micromagnetic simulations for computationally efficient band gap evaluation. Our established inverse-design method successfully discovered several previously unreported designs of MCs, whose performance was validated using time-domain micromagnetic simulations. Furthermore, we observed that the design landscape becomes increasingly non-convex at high-order bands, suggesting the existence of multiple design solutions. The overall inverse-design framework is expected to be broadly applicable to experimentally accessible material systems and device dimensions, facilitating the formulation of design rules for MCs.
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All authors Ryunosuke Nagaoka, Takahiro Yamazaki, Chiharu Mitsumata, Yuma Iwasaki, Masato Kotsugi
Strongly Correlated Electrons
Crystal growth and magnetic properties of spin-$1/2$ distorted triangular lattice antiferromagnet CuLa$_2$Ge$_2$O$_8$
S. Thamban, C. Aguilar-Maldonado, S. Chillal et al. (+7 more)
CuLa$_2$Ge$_2$O$_8$ forms a distorted triangular
lattice of
quantum spin-1/2 Cu$^{2+}$ ions. A
crystal growth method was developed using the traveling-solvent floating zone technique resulting in the synthesis of a large single
crystal (4 mm$\times$4 mm$\times$10 mm). The
crystal was characterized with regard to phase purity and crystallinity using powder X-ray diffraction, energy dispersive X-ray analysis and Laue diffraction, and found to be of excellent quality. The
magnetic properties were characterized using dc-susceptibility, magnetization, and heat capacity measurements which revealed weak
magnetic frustration with long-range
magnetic order occurring below $T_N=1.14(1)$~K. The
magnetic structure determined using
neutron powder diffraction is a commensurate, noncollinear
antiferromagnetic, different from the 120$^{\circ}$ order of an equilateral triangular antiferromagnet. The ordered moments lie in the bc-plane, with components $m_b=0.50(3)$~$\mu_{B}$ and $m_c= 0.73(5)$~$\mu_{B}$ along the b- and c-axes respectively, giving a total ordered moment of $M_{total}$= 0.89(6)$\mu_{B}/$Cu$^{2+}$ at 20~mK.
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All authors S. Thamban, C. Aguilar-Maldonado, S. Chillal, R. Feyerherm, K. Prokeš, A. J. Studer, D. Abou-Ras, K. Karmakar, A. T. M. N. Islam, B. Lake
Superconductivity
First-principles calculation of coherence length and penetration depth based on density functional theory for superconductors
Mitsuaki Kawamura, Takuya Nomoto, Niklas Witt et al. (+1 more)
We develop a first-principles framework for evaluating the fundamental length scales of superconductivity, namely the coherence length $\xi_0$ and the
magnetic penetration depth $\lambda_\mathrm{L}$, within superconducting density functional theory (SCDFT). By incorporating finite-momentum Cooper pairs, we formulate a microscopic scheme that enables a consistent and parameter-free determination of $\xi_0$, $\lambda_\mathrm{L}$, and the superconducting transition temperature $T_\mathrm{c}$ on the same theoretical footing. Applying the method to representative elemental
superconductors, the A15 compound V$_3$Si, and H$_3$S under high pressure, we obtain results in good agreement with available experimental and reproduce the type-I/type-II classification across all materials studied. The unified access to $\xi_0$ and $\lambda_\mathrm{L}$ further allows us to construct the Uemura plot entirely from first principles, showing that higher-$T_\mathrm{c}$ systems are characterized by the simultaneous realization of strong pairing and large phase stiffness. Our results establish a predictive first-principles route to superconducting length scales and provide a microscopic interpretation of empirical correlations in superconductivity.
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All authors Mitsuaki Kawamura, Takuya Nomoto, Niklas Witt, Ryotaro Arita
Materials Science
Altermagnetic Metal-Organic Frameworks
Diego López-Alcalá, Andrei Shumilin and José J. Baldoví
Altermagnetism has recently emerged as a new class of
spin compensated
magnetic materials that exhibit momentum dependent
spin splitting despite having zero net magnetization. The origin of these electronic signatures lies in
symmetry operations that connect opposite
spin sublattices while allowing
spin splitting in momentum space. While most candidate materials identified so far belong to inorganic
crystals with fixed
lattice symmetries, the realization of altermagnetism ultimately requires platforms in which
magnetic symmetry can be deliberately engineered. In this Perspective, we discuss how metal-organic frameworks (MOFs) provide a unique chemical platform to address this challenge. We first place altermagnetism in the broader context of
magnetic and electronically active metal-organic networks, highlighting how reticular chemistry enables precise control over
lattice geometry, dimensionality and electronic structure. We then discuss how these features position framework materials as promising candidates for realizing altermagnetism and highlight the key challenges that must be addressed to translate theoretical proposals into experimentally accessible systems. Finally, we critically assess current experimental challenges and outline emerging directions for realizing and controlling altermagnetism in coordination framework materials, which emerge as a versatile and powerful platform for exploring new paradigms in spintronics.
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Statistical Mechanics
Sampling the Liquid-Gas Critical Point with Boltzmann Generators
Luigi de Santis, John Russo and Andrea Ninarello
Generative models based on invertible transformations provide a physics-aware route to sample
equilibrium configurations directly from the Boltzmann distribution, enabling efficient exploration of complex thermodynamic landscapes. Here, we evaluate their applicability in regions where conventional simulations suffer from severe dynamical bottlenecks, focusing on the
liquid-gas critical point of a Lennard-Jones fluid. We show that Boltzmann Generators capture essential signatures of critical behavior, retain reliable performance when trained at or near criticality, and extrapolate across neighboring states of the phase diagram. An intriguing observation is that the model's efficiency metric closely traces the underlying phase boundaries, hinting at a connection between generative performance and thermodynamics. However, the approach remains limited by the small system sizes currently accessible, which suppress the large fluctuations that characterize critical phenomena. Our results delineate the current capabilities and boundaries of Boltzmann Generators in challenging regions of phase space, while pointing toward future applications in problems dominated by slow dynamics, such as glass formation and nucleation.
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Materials Science
Domain-Direct Band Gaps: Classification and Material Realization
Yalan Wei, Hairui Ding, Shifang Li et al. (+4 more)
The conventional classification of direct band-gap
semiconductors relies on point-like extrema in momentum space. Here, we introduce the concept of domain-direct band gaps, where the conduction-band minimum (CBM) and valence-band maximum (VBM) form extended
manifolds in the Brillouin zone. We demonstrate this concept through the material realization of an extreme two-dimensional-two-dimensional (2D-2D) domain-direct band gap in twisted diamond. First-principles calculations show that both the CBM and VBM exhibit nearly flat 2D
manifolds in the kx-ky plane with minimal energy variation (a few meV), yielding a direct band gap of 3.264 eV. In contrast, strong dispersion along the out-of-plane kz direction induces anisotropic carrier dynamics, with strongly suppressed in-plane
Fermi velocities (down to about 10$^1$-10$^3$ m/s in certain directions) and much larger out-of-plane velocities (about 10$^6$ m/s). The nearly flat CBM and VBM
manifolds enhance the joint density of states, leading to a pronounced optical absorption peak at the band gap onset. This new type of domain-direct gap, coupled with strong directional anisotropy, opens up opportunities for anisotropic optoelectronic applications. Our results establish domain-direct band gaps as a new class of
semiconductors, demonstrating their feasibility in real materials.
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All authors Yalan Wei, Hairui Ding, Shifang Li, Yuke Song, Chi Ren, Xiao Dong, Chaoyu He
Soft Condensed Matter
The effect of fluorine or chlorine substitution on mesomorphic properties of ferroelectric nematic liquid crystals
Martin Cigl, Natalia Podoliak, Dalibor Repček et al. (+3 more)
Ferroelectric nematic phase (NF) represents an attractive and foremost field of
liquid crystals, combining fluidity with ferroelectricity. NF materials exhibit large polarization values and remarkable non-linear optical properties. We have designed an original molecular structure with halogen substituents in the position of an electron donating group. In a prolonged molecular core, such a modification led to the presence of the ferroelectric nematic phase (NF) below the nematic one. Besides, an application of Cl atom in the molecular core of one of the presented materials has been utilized for the first time for ferroelectric nematogens. We have examined mesogenic behaviour and ferroelectric characteristics of the NF phase. In the NF phase for the
cell with antiparallel rubbing, we have detected a textural transformation, which evidences strong polar character of anchoring at the surfaces. The presented results provide valuable insight into the design of ferroelectric nematic
liquid crystalline compounds.
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All authors Martin Cigl, Natalia Podoliak, Dalibor Repček, Pavlo Golub, Marta Lavrič, Vladimíra Novotná
Mesoscale and Nanoscale Physics
Christian Spånslätt, Jinhong Park and Alexander D. Mirlin
Edge transport serves as a powerful probe of remarkable low-energy properties of fractional
quantum Hall states, including the anyonic character of their excitations. Here, we develop a theory of fractional
quantum Hall edges driven out of
equilibrium, which is based on the Keldysh action for the bosonized
chiral Luttinger
liquid. With this non-
equilibrium FQH bosonization framework, we first consider a single-mode Laughlin edge and analyze the full counting statistics of charge, the quasiparticle Green's functions, and tunneling transport properties through a
quantum point contact, allowing for generic edge excitations. We then extend the formalism to multi-mode edges with inter-mode interactions, and explore, with focus on the $\nu=4/3$ and $\nu=2/3$ edges as paradigmatic examples, how interaction-induced fractionalization of anyons modifies the edge dynamics and the associated transport observables. While the full counting statistics probes the fractionalized charge of the excitations, the Green's functions and tunneling transport are governed by mutual braiding phases of fractionalized excitations and tunneling quasiparticles. We emphasize in particular the effect of interaction-induced fractionalization on the Fano factor $F$ and the differential Fano factor $F_d$, observables that can be measured experimentally. Our formalism, which provides a unified framework for non-
equilibrium transport in FQH edges and Luttinger
liquids, permits extracting anyonic braiding information from non-
equilibrium edge-transport experiments, and paves the way to various extensions, including more involved experimental geometries and edge structures.
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Materials Science
Large-scale Integration of Experimental and Computational Data for 2D Materials
Mohammad A. Akhound, Tara M. Boland, Mikkel O. Sauer et al. (+19 more)
The past decade has seen rapid growth in the number of experimentally realized two-dimensional (2D) materials with diverse chemical and physical properties. However, information on their
crystal structure, synthesis routes, and measured or predicted properties, remains scattered across thousands of publications. Here we consolidate this fragmented knowledge by establishing X2DB - an open infrastructure that integrates experimental and computational data on 2D materials. Using extensive literature mining and direct community uploads, we identify 370 unique 2D materials that have been realized in monolayer or few-layer form, and link them to their digital counterparts in computational databases, enabling consistent ab initio characterization of their properties across monolayer,
bilayer and bulk forms. We describe the structure and content of the database highlighting its support for community uploads, illustrate how it can be used to generate new scientific insight and introduce a hierarchical classification of the known set of 2D materials. Our work provides a foundation for the integration and cross-fertilization of experimental and theoretical knowledge, opening new avenues for data-driven, predictive synthesis of novel 2D materials.
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All authors Mohammad A. Akhound, Tara M. Boland, Mikkel O. Sauer, Matthias Batzill, Moses A. Bokinala, Stela Canulescu, Yury Gogotsi, Philip Hofmann, Andras Kis, Jiong Lu, Thomas Michely, Søren Raza, Wencai Ren, Joshua A. Robinson, Zdenek Sofer, Jing H. Teng, Søren Ulstrup, Meng Zhao, Xiaoxu Zhao, Jens J. Mortensen, Thomas Olsen, Kristian S. Thygesen
Soft Condensed Matter · Cross-listed from physics.chem-ph
Viscosity as a Smoking Gun for Complex Formation in Solution: Fe$^{2+}$ and Mg$^{2+}$ Chlorides as Examples
Amrita Goswami, Samuel Blazquez, Lucía Fernández-Sedano et al. (+4 more)
Electrolyte solutions at high concentration are indispensable and yet poorly understood. In particular, the extent of speciation – the formation of complexes composed of multiple species – in concentrated ionic solutions is very challenging to obtain theoretically and experimentally, but can have a strong effect on solution properties. The literature is rife with contradictory estimates of speciation from experiments. We find that speciation affects transport properties, and is therefore, a prerequisite to accurately model concentrated solutions. We turn this to our advantage by showing that the viscosity can be used to determine the extent of complexation in concentrated aqueous solutions. Results of simulations as well as experimental measurements are presented. The atomistic Madrid-2019 force-field is extended to model FeCl$_2$. Solutions of FeCl$_2$ and MgCl$_2$ are compared and the observed difference in viscosity explained by more complexation in the former, a conclusion supported by recently reported X-ray absorption and
neutron scattering experiments.
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All authors Amrita Goswami, Samuel Blazquez, Lucía Fernández-Sedano, Eva González Noya, Hannes Jónsson, Jacobo Troncoso, Carlos Vega
Statistical Mechanics
Fokker-Planck description of an active Brownian particle with rotational inertia
Lingyi Wang, Ziluo Zhang, Zhongqiang Xiong et al. (+3 more)
We develop a perturbative framework to calculate the mean-squared displacement (MSD) of active Brownian particles (ABPs) with a finite moment of inertia. Starting from the corresponding Fokker-Planck equation, we employ a
Fourier transform for the spatial coordinates and Hermite
polynomials as eigenfunctions for the angular velocity, which enables a systematic perturbative expansion of the MSD order by order. By resumming the resulting series in Laplace space and performing the inverse transform, we obtain an explicit expression for the MSD as a function of the moment of inertia. The analytical results are further validated by comparison with numerical simulations.
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All authors Lingyi Wang, Ziluo Zhang, Zhongqiang Xiong, Zhanglin Hou, Linli He, Shigeyuki Komura
Statistical Mechanics · Cross-listed from hep-lat
Constrained Symplectic Quantization: Disclosing the Deterministic Framework Behind Quantum Mechanics
Martina Giachello, Francesco Scardino and Giacomo Gradenigo
Symplectic quantization is a functional approach to
quantum field theory that allows sampling of
quantum fluctuations directly in Minkowski space time by means of a generalized
Hamiltonian dynamics in an extra time variable $\tau$ which, at large times, samples a microcanonical ensemble. In a previous work we showed that, for an interacting scalar theory in 1+1 dimensions, this framework captures genuine real time features that are inaccessible to Euclidean simulations. That original formulation suffers from two structural limitations, an ill defined non interacting limit and the lack of a direct correspondence between its correlation functions and those generated by the Feynman path integral. To solve these problems we introduced constrained
symplectic quantization, a holomorphic reformulation in which fields and action are analytically continued and constraints are imposed on the intrinsic time
Hamiltonian flow. The constraints select stable deterministic trajectories and they define convergent holomorphic integration cycles for the corresponding microcanonical measure. In the continuum limit we establish exact equivalence with the Feynman path integral at the level of the generating functional, thus providing a direct link between intrinsic time correlators and real time Green functions. In this contribution, we apply the method to the
quantum harmonic oscillator on a real-time 1-dimensional
lattice. Testing various observables, we find agreement between numerical and exact results for one- and two-point functions, and we reconstruct characteristic real-time features such as an oscillatory propagator, the discrete energy-gap spectrum, and the
evolution of eigenstate probability densities. These tests provide numerical evidence that constrained
symplectic quantization can sample real-time
quantum observables and offers a practical route beyond Euclidean-time importance sampling.
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Materials Science
Ab initio quasi-harmonic thermoelasticity, piezoelectricity, and thermoelectricity of polar solids at finite temperature and pressure: Application to wurtzite ZnO
Xuejun Gong and Andrea Dal Corso
We generalize a previously established ab initio approach-originally developed for hexagonal close-packed (hcp) metals-to accommodate solids with both internal and external degrees of freedom. This extension enables the thermodynamic and thermoelastic characterization of
insulators, including those with non-vanishing piezoelectric and pyroelectric tensors. Utilizing Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) within the quasi-harmonic approximation, we derive the pressure and temperature dependence of these properties. Specifically, we investigate internal degrees of freedom using two distinct frameworks: the Zero Static Internal Stress Approximation (ZSISA) and Full Free Energy Minimization (FFEM). We then compare these approximations by computing internal and external thermal expansions, as well as temperature-dependent piezoelectric and pyroelectric tensors. Finally, we demonstrate the generalized formalism by calculating the thermodynamic properties of wurtzite ZnO across a broad range of pressures and temperatures.
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Mesoscale and Nanoscale Physics
Fabry-Pérot interferometry with stochastic anyonic sources
Sarthak Girdhar, Edvin G. Idrisov and Thomas L. Schmidt
We investigate the interference of Laughlin quasiparticles (QPs) in the fractional
quantum Hall regime that are stochastically injected into a Fabry–Pérot interferometer. We find that the effective Aharonov–Bohm (AB) phase accumulated along the interferometer loop acquires an additional contribution of $\sin(2\pi\lambda)/2$ per QP present on it, where $\pi\lambda$ is the QP exchange phase. This contribution originates from time-domain braiding processes associated with injected QPs passing the interferometer
quantum point contacts. In the limit of symmetric QP injection, the tunneling current noise exhibits AB oscillations as a function of the total injected current, providing access to the exchange phase $\pi\lambda$. In the regime of large total injection, we identify a universal Fano factor that displays power-law scaling and a characteristic phase shift reflecting time-domain QP braiding at the interferometer QPCs. These results are relevant for accessing anyonic exchange statistics in mesoscopic interferometers.
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Materials Science · Cross-listed from physics.optics
Real-Space Plasmon Imaging Reveals Modified Electronic Structure of Gold at the Monolayer Limit
Andrei Bylinkin, Philippe Roelli, Naveen Shetty et al. (+8 more)
Atomically thin materials exhibit electronic and optical properties distinct from their three-dimensional counterparts. For metals, particularly gold, monolayer studies remain largely unexplored due to fabrication and characterisation challenges. Here we report the first optical study of a stable quasi-freestanding gold monolayer formed by Au intercalation between
graphene and SiC. Mid-infrared nanoimaging reveals plasmon-polaritons with wavelengths nearly an order of magnitude shorter than free-space light. Analysis of their dispersion using a Drude model yields a relaxation time of $\tau = 18\,$fs, comparable to bulk gold, and a Drude weight of $D = 1.3\,$mS$\cdot$eV, nearly twice the bulk expectation. These results establish monolayer gold as a two-dimensional metal, opening opportunities for nanoscale photonics, plasmonics and ultra-thin electronics.
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All authors Andrei Bylinkin, Philippe Roelli, Naveen Shetty, Rositsa Yakimova, Ulrich Starke, Camilla Coletti, Stiven Forti, Alexei Zakharov, Vyacheslav M. Silkin, Samuel Lara-Avila, Rainer Hillenbrand
Mesoscale and Nanoscale Physics
Topological Surface Charge Detection via Active Capacitive Compensation: A Pathway to the 4D Quantum Hall Effect
Yuanze Li, Renfei Wang, Yifan Zhang et al. (+6 more)
The topological magnetoelectric effect (TME) in three-dimensional topological
insulators (TIs), described by $\Delta P = \frac{e^2}{2h} N_{\rm Ch}^{(2)} \Delta B$, serves as a condensed-matter realization of the four-dimensional
quantum Hall effect (4D QHE). In dual-gate
axion-
insulator devices, the TME-induced polarization yields a current $I_{\rm TME} \propto (C_{\rm total}/C_{\rm S})\,Q_{\rm 4D\mathrm{-}QHE}$, where the signal is suppressed by the capacitance ratio $C_{\rm total}/C_{\rm S}$. Here we propose an active compensation scheme that introduces a tunable negative capacitance $C_{\rm comp} \approx -C_{\rm gate}$ into the gate line, effectively canceling the gate dielectric capacitance and driving $C_{\rm total}/C_{\rm S} \to 1$. We validate the method using a
quantum anomalous
Hall (QAH) device, which shares the same surface-state physics as the
axion insulator but permits direct charge measurement via a single gate, recovering over $95\%$ of the quantized charge signal from an initially half-attenuated state. This compensation method provides a robust means of resolving minute TME signals, offering a promising pathway toward direct measurements of the 4D QHE.
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All authors Yuanze Li, Renfei Wang, Yifan Zhang, Jiahao Chen, Yingdong Deng, Jin Xie, Xufeng Kou, Yang Liu, Tian Liang
Statistical Mechanics
Fluctuation-induced quadrupole order in magneto-electric materials
Finja Tietjen and R. Matthias Geilhufe
Phases that go beyond dipolar ordering and into multipolar ordering have recently been observed in magneto-electric materials. The resulting phase diagram is commonly explained using the concept of competing orders and exact microscopic interactions. In contrast, we propose an approach based on composite order emerging from a parent phase to explain quadrupoling above
magnetic or electric dipolar orders. We include thermal fluctuations and
symmetry and show their influence on the emergence of quadrupolar order. We find an analytical expression for the quadrupolar transition temperature, the critical anisotropy and explain the coupling of the quadrupolar order to mechanical strain, in agreement with experiments. The shift in perspective on quadrupolar ordering from competing to composite order is universal and can be extended to other types of multipolar ordering. This offers the possibility of understanding tunability and material-specific predictions of the related phase transitions without explicit knowledge of the microscopic mechanisms.
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Mesoscale and Nanoscale Physics
Systematic study of superconductivity in few-layer $T_d$-MoTe$_2$
Taro Wakamura, Masayuki Hashisaka, Yusuke Nomura et al. (+7 more)
We present a systematic investigation of superconductivity in a topological
superconductor candidate $T_{\rm d}$-MoTe$_2$ in the few-layer limit. By examining multiple mechanically exfoliated samples with different thicknesses, substrates and
crystal qualities, we quantitatively correlate superconducting temperature ($T_c$) with disorder, carrier density, carrier type and mobility. By integrating these experimental findings with first-principles calculations, we reveal the relationship between the band structure and superconductivity in this material. Notably, in 2 L samples we access a highly hole-doped regime that has not been systematically explored in previous experiments, providing a complementary perspective to earlier studies. In this regime, we demonstrate that superconductivity can be realized in a manner consistent with a conventional
phonon-mediated $s_{(++)}$-wave pairing.
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All authors Taro Wakamura, Masayuki Hashisaka, Yusuke Nomura, Matthieu Bard, Shota Okazaki, Takao Sasagawa, Takashi Taniguchi, Kenji Watanabe, Koji Muraki, Norio Kumada
Soft Condensed Matter
Extended dynamical density functional theory for nonisothermal binary systems including momentum density
Michael te Vrugt, Hartmut Löwen, Helmut R. Brand et al. (+1 more)
In order to describe the nonisothermal dynamics of two-phase flows or binary mixtures such as colloidal suspensions consisting of colloidal particles and solvent on a microscopic level, we derive a new extended dynamical density functional theory (EDDFT) that includes the total mass density, the local concentration of one species, the total momentum density, and the energy density as variables using the Mori-Zwanzig-Forster projection operator technique. Through the incorporation of the momentum density into EDDFT, not only the diffusive but also the convective dynamics is taken into account. We derive an exact
entropy and free-energy functional for the case of hard spheres. The hydrodynamic limit of our new EDDFT and its relation to the mode-coupling theory of the glass transition are discussed. It is shown that EDDFT allows to obtain the correct value for the speed of sound.
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All authors Michael te Vrugt, Hartmut Löwen, Helmut R. Brand, Raphael Wittkowski
Superconductivity
Spin-polarized Andreev molecules and anomalous nonlocal Josephson effects in altermagnetic junctions
Sayan Mondal and Jorge Cayao
Altermagnetism has emerged as a promising ingredient for realizing nontrivial Josephson phases, but so far explored in single Josephson junctions. In this work, we consider the coherent coupling of two Josephson junctions with
spin-singlet $s$-wave superconductivity and demonstrate that $d$-wave altermagnetism gives rise to
spin-polarized Andreev molecules due to the hybridization of Andreev bound states of each junction when the coupling is weak. Interestingly, these
spin-polarized Andreev molecules induce an anomalous nonlocal Josephson effect, where the current flow across one Josephson junction due to phase changes across the other junction develops $0-\pi$ and $\phi_{0}$ transitions originating from altermagnetism. Furthermore, the nonlocal Josephson current carried by
spin-polarized Andreev molecules exhibits nonreciprocal critical currents, enabling a nonlocal Josephson diode effect whose polarity is tunable by the altermagnetic strength and right phase. Our findings put forward altermagnetism as a promising arena for designing nonlocal
spin Josephson phenomena.
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Materials Science · Cross-listed from physics.app-ph
Modular memristor model with synaptic-like plasticity and volatile memory
Daniel Habart, Stephen H. Foulger, Kristyna Kovacova et al. (+5 more)
Compact models of memristors are essential for simulating large-scale neuromorphic systems, yet they often do not include description of complex dynamics like volatile relaxation and synaptic plasticity. We introduce a modular, computationally efficient memristor model that bridges this gap by integrating principles from physics and computational neuroscience. The model defines a framework consisting of a standard formulation of memristive device dynamics, a functional rule mapping state variables to cumulative conductance, a
volatility module inspired by the theory of linear viscoelasticity and a saturation module implementing a linear-nonlinear technique. Additionally, we develop a formulation of synaptic-like plasticity inspired by a biological spike-timing-dependent plasticity (STDP) rule, which is compatible with the general framework for memristive devices. Finally, we propose a Laplace transform-based technique to derive the precise form of the mapping from state variables to cumulative conductance, replacing ad hoc voltage-current relationships with principled construction. We quantitatively validate the complete model against a rich set of experimental data from polymeric memristors exhibiting potentiation, synaptic-like plasticity and volatile decay. Our work presents a new paradigm for memristor modeling that is both practical for large-scale simulation and rich in explanatory power, providing a principled tool for the design of next-generation neuromorphic hardware.
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All authors Daniel Habart, Stephen H. Foulger, Kristyna Kovacova, Ambika Pandey, Yadu R. Panthi, Jiri Pfleger, Jarmila Vilcakova, Lubomir Kostal