Statistical Mechanics
Optimal feedback control under stepwise equilibration and partial observation
Francesco Mottes and Michael P. Brenner
Many microscopic machines rely on noisy signals to direct nonequilibrium transformations and operate in a timescale-separated regime. We consider feedback protocols in which a system equilibrates between rapid, measurement-conditioned changes of its energy landscape. In this limit, the partially observable control problem reduces exactly to a finite-horizon Bellman recursion over
Hamiltonian updates. For a harmonic trap translated to a prescribed target under noisy position measurements, we solve this recursion analytically. The optimal protocol balances its response to the estimated fluctuation against progress toward the target, exploiting information early while enforcing the endpoint near the deadline. The minimum work decomposes into a positive thermodynamic-length transport cost and a negative information-enabled extraction term set by the fraction of
equilibrium fluctuations resolved by the measurement. When a fixed intervention cost exceeds the asymptotic extraction per cycle, it selects a finite optimal number of cycles. We show that, in this translated harmonic case, the minimum thermodynamic cost of creating and resetting the measurement record always exceeds this threshold, making the optimal cycle count finite and the net work non-negative for any measurement channel.
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Superconductivity
Supercurrent effect in a charge density wave intertwined superconductor
Zhen Zhu, Wei Cheng, Dang Liu et al. (+15 more)
The energy-momentum (E-k) dispersion of quasiparticles constitutes a fundamental concept in condensed matter systems. The ability to modify the E-k dispersion, exemplified by supercurrent-induced Doppler shifts of Bogoliubov quasiparticle spectra in
superconductors, enables manipulation of various emergent
quantum properties. However, investigations into the supercurrent effect on
superconductors intertwined with charge orders remain scarce. Here, we report that the Meissner current, generated by the diamagnetic response to an applied in-plane
magnetic field, can tailor Bogoliubov quasiparticle excitations at the precursor charge density wave (CDW) vectors. Our scanning tunneling spectroscopic imaging reveals a field-driven
symmetry breaking of CDW modulations, specifically a C3v-to-Cs transition, in superconducting NbSe2. Model calculations suggest that the observed anisotropy originates from a selective Doppler-shift-induced E-k dispersion reconstruction. Furthermore, altering the field direction enables on-demand tuning of anisotropic CDW modulations and visualization of their momentum-space distribution. These results highlight a novel mechanism for controlling emergent electronic phases through momentum-space engineering.
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All authors Zhen Zhu, Wei Cheng, Dang Liu, Pengyu Hu, Yi Yang, Qiaoyan Yu, Shasha Xue, Ruijun Xi, Xingsen Chen, Jice Sun, Dandan Guan, Yaoyi Li, Shiyong Wang, Canhua Liu, Zhuan Xu, Xin Liu, Hao Zheng, Jinfeng Jia
Soft Condensed Matter
A statistical-physics framework for translocation elastometry of deformable particles
Pierre Ronceray
A soft particle driven through a pore narrower than itself must deform to pass, and how quickly it does so is set by how hard it is to squeeze. We propose a mathematical framework for turning rate measurements of this driven,
stochastic passage into quantitative mechanical measurements. Treating the entry of the particle as one-dimensional Brownian dynamics across an elastic barrier, we solve the transport problem exactly and identify two dynamical regimes: at low drive the passage is thermally activated and limited by the energy needed to deform the particle, and at high drive it is friction-limited. We propose a framework to extract the particle's deformation energy and relevant geometrical information by combining measurements in these two regimes. This method could be used in the context of nanopore sensing, where the drive is an applied voltage: the framework then provides a self-calibrating route—translocation elastometry—from a current-voltage measurement to the elasticity and shape of individual soft nanoparticles.
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Quantum Gases · Cross-listed from quant-ph
Flow of local sensitivity in a spin chain coupled to a bosonic bath
Marcin Płodzień
We study how local sensitivity to an encoded parameter, captured by the
quantum Fisher information, flows between a
spin chain, a coupled bosonic bath, and their
quantum correlations, where we treat the bath as a full many-body
quantum system beyond the Lindbladian approximation. We analyze how the coupling
symmetry determines the destination of the departed sensitivity directly at the level of the
Hamiltonian. We consider an excitation-exchanging Jaynes–Cummings coupling, which preserves the total number of excitations, and a
spin-excitation-conserving Holstein coupling. We find that the Holstein coupling leaves the bath with no first-order information about the phase and stores the lost sensitivity entirely in
spin–bath correlations, whereas the Jaynes–Cummings coupling passes this sensitivity to the bath, in full for a single excitation. The bath spectrum then governs whether the sensitivity ever returns to the
spins. It revives fully and periodically when the coupled-system frequencies share a common period, but when those frequencies disperse the departed share dephases across the bath modes and never returns. We note that a transported metrological register loses more sensitivity than its arrival fidelity implies.
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Strongly Correlated Electrons
Strong correlations and local self-energies from on-site ensembles
Alberto Carta, Hugo U. R. Strand, Michael Schüler et al. (+1 more)
Addressing the many-body electronic-structure problem is a central goal of modern condensed-matter physics. Paramagnetic Mott
insulators, in particular, have long represented a challenge for standard approaches, such as density-functional theory. Historically, these systems have been tackled either by considering many-body dynamics, as in the case of dynamical mean-field theory (DMFT), or, more recently, by invoking a polymorphous description consisting of large supercells populated with static
symmetry-broken motifs whose spatial average restores the paramagnetic state. Inspired by these viewpoints, we introduce the on-site dephased ensemble (DE) approximation, in which the local electronic-structure problem is described by a thermal ensemble of all accessible local static solutions; this gives rise to a strong frequency dependence of the local electronic self-energy, as seen in DMFT or in the coherent-potential approximation of disordered
alloys. We show that the DE successfully recovers defining hallmarks of strongly correlated Mott systems, both in terms of the self-energy as well as the persistence of local moments in time, in quantitative agreement with DMFT. By bypassing expensive
quantum Monte Carlo solvers or large supercell calculations, this approach offers efficient routes to treating paramagnetic Mott systems in a first-principles setting, and highlights a deeper connection between the physics of strong correlations and that of disorder.
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All authors Alberto Carta, Hugo U. R. Strand, Michael Schüler, Nicola Marzari
Mesoscale and Nanoscale Physics
An on-chip programmable mechano-quantum transducer
Xinrui Zhang, Wei Liu, Duanyu Ma et al. (+13 more)
Solid-state
spin defects encode local perturbations as measurable shifts in
spin-transition frequencies, but mechanical actuation and
quantum readout remain physically separated, resulting in a discrete measurement setup. Integrating these functions requires an on-site mechano-
quantum interface that programs the
lattice state of a defect host and quantitatively maps it onto the
spin Hamiltonian. Here we first report an on-chip programmable mechano-
quantum transducer (OCPMQT) that integrates voltage-defined micromechanical actuation with in situ
spin-frequency readout in a two-dimensional van der Waals
quantum-defect host. Mechanically programmed
lattice states are encoded as shifts in the axial zero-field splitting parameter and resolved by optically detected
magnetic resonance (ODMR) spectroscopy. Within a chip volume of 2.05*10^-2 cm^3, the transducer accesses ODMR-inferred strains as low as 0.0080% and delivers a volumetric force density of approximately 2.6*10^4 N*m^-3. A micromechanical-to-
spin-
Hamiltonian framework links on-chip electromechanics, interfacial strain transfer, and strain-
spin coupling, enabling the electrical control micromechanical input to be measured directly as
spin-frequency response.
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All authors Xinrui Zhang, Wei Liu, Duanyu Ma, Lin-Ke Xie, Nai-Jie Guo, Zhongtao Gou, Yifan Wang, Jianxin Xu, Xiaoguang Luo, Zhao Mu, Honglong Chang, Weizheng Yuan, Jian-Shun Tang, Chuan-Feng Li, Guangcan Guo, Tao Ye
Strongly Correlated Electrons
Pseudogap formation in the moderate correlated layered attractive Hubbard model
A. V. Belov, A. N. Rubtsov and B. Krippa
We consider the layered attractive Hubbard model with a moderate interaction strength at quarter filling. The Green's function, self-energy, and density of states are calculated for relatively large clusters using the fluctuating local field method within the approximation of vanishing effective interaction. The emergence of a pseudogap is demonstrated for the cluster system, and it is shown that integration over the fluctuating field is equivalent to the summation of zero-mode ladder diagrams above critical temperature. For the large layered system, a pseudogap in the density of states is obtained within a cluster scheme that treats the coupling between layers as a static $U(1)$
symmetry-breaking field.
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Strongly Correlated Electrons
Interlayer interactions reshape charge-density wave through electronic elasticity in 4H$_{\mathrm{b}}$-TaS$_2$
Carolina A. Marques, Martha Rösler, Berk Zengin et al. (+7 more)
Incommensurate charge-density waves (CDWs) in layered
quantum materials frequently exhibit widely varying ordering wave vectors, even among nominally identical samples, obscuring their intrinsic electronic properties. Here we identify an inherent origin of this variability through the electronic elasticity of an incommensurate CDW using the model
heterostructure 4H$_{\mathrm{b}}$-TaS$_2$, composed of alternating commensurate CDW on 1T and incommensurate CDW on 1H layers. Low-temperature scanning tunneling microscopy, combined with
Fourier and quasiparticle-interference analysis, exploits the
lattice-pinned 1T CDW as an internal reference to resolve discrete compressive ($-2.3\%$) and tensile ($+3.2\%$) elastic states of the neighboring 1H CDW selected by the interlayer registry of the adjacent layers. Corresponding few-meV shifts of a flat band demonstrate that weak interlayer interactions reshape the low-energy electronic structure through the intrinsic elasticity of the incommensurate CDW. These findings establish electronic elasticity as a mechanism by which subtle interlayer interactions control correlated electronic states in van der Waals
heterostructures.
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All authors Carolina A. Marques, Martha Rösler, Berk Zengin, Aleš Cahlík, Edoardo Martino, Konstantin Semeniuk, Helmuth Berger, László Forró, Ana Akrap, Fabian D. Natterer
Other Condensed Matter · Cross-listed from quant-ph
Rack-integrated quantum dot-based source of single and entangled photons at telecom C-band
Michal Vyvlecka, Raphael Joos, Benjamin Breiholz et al. (+8 more)
For
quantum light sources in everyday telecommunication networks,
quantum science needs to be fully transformed into
quantum technology. The first necessary step to move outside a well-controlled lab environment requires the use of
quantum light sources operating in the technologically relevant telecom O- and C-band. This can be provided using epitaxial
quantum dots as deterministic sources of
quantum light. Particularly intriguing is that emitters operating at telecom wavelengths are rapidly catching up with their short wavelength counterparts in terms of performances. Here, we make a decisive step forward in the development of
quantum communication networks: a state-of-the-art source of
quantum light, a
semiconductor quantum dot (QD), with record coincidence rate for entangled
photon emission in the telecom C-band, is operated inside an optimized rack-based setup. This setup includes a tunable pulsed
laser for the QD excitation (from quasi- to fully resonant excitation), all optics for the excitation filtering, and QD signal coupling into single-mode fibers. Overall, the setup allows for above $50\%$ transmission for both
exciton and biexciton
photons. These results show that
quantum dots-based telecom light sources can now be transported and integrated into existing fiber infrastructures, an important step to demonstrate the feasibility of the upcoming
quantum internet.
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All authors Michal Vyvlecka, Raphael Joos, Benjamin Breiholz, Emma Marmasse, Anna Friederike Köhler, Ponraj Vijayan, Tobias Huber-Loyola, Sven Höfling, Michael Jetter, Simone Luca Portalupi, Peter Michler
Strongly Correlated Electrons
Shiba duality and $\eta$-altermagnetism: Pairing and charge orders in bipartite attractive Hubbard models
Yu-Ping Lin
We show that Shiba duality maps the altermagnetic principle of momentum-dependent band splitting from
spin to $\eta$-pseudospin, defining $\eta$-altermagnetism ($\eta$-ALM) as a Bogoliubov-de Gennes (BdG) counterpart of ALM in pairing and charge orders. In half-filled pure Hubbard models on bipartite
lattices, the duality relates repulsion-driven antiferromagnetism (AFM) to attraction-driven $\eta$-AFM with uniform singlet pairing and staggered charge-density modulation. In the BdG bands, the Shiba-dual parity-time-reversal $\mathcal{\tilde{P}}\mathcal{\tilde{T}}$
symmetry protects a Kramers degeneracy of $\eta$-pseudospin. Anisotropic second-neighbor hopping breaks this degeneracy and generates $\eta$-ALM. Odd-parity $\eta$-ALM shows $\eta$-pseudospin splitting, whereas even-parity $\eta$-ALM has
spin-$\eta$-locked splitting. Hartree-Fock-Bogoliubov computations on checkerboard and honeycomb
lattices find $\eta$-ALMs with $p$-, $d$-, and $f$-wave splitting structures. Possible generalizations and experimental probes are discussed.
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Statistical Mechanics
Free-volume origin of diverging direct correlations in hard crystals: insights from an exact one-dimensional model
Alessandro Simon and Martin Oettel
Second order direct correlation functions in three-dimensional hard-sphere
crystals have much larger amplitudes (of the order of $1/n_{\mathrm{vac}}$ where $n_{\mathrm{vac}}$ is the vacancy concentration) and a more strongly structured spatial form of apparent shorter range than their
liquid-state counterparts. We separate the two underlying questions—why the correlations are large and why they have the form they do—using the exact one-dimensional Percus functional for hard rods. A periodic
crystal-like density is represented by Gaussian peaks with occupation probability $q=1-n_{\mathrm{vac}}$. The relevant thermodynamic quantity is the local insertion free volume $A(x)$. Its minimum can be written as $A_{\mathrm{min}} =\Delta_{\alpha a}+(1-\Delta_{\alpha a})n_{\mathrm{vac}}$, where $\Delta_{\alpha a}$ is the residual free volume at full occupation caused by finite localization (characterized by a width parameter $\alpha$) and
lattice spacing $a$. The first and second direct correlations therefore contain the singular dependences $c^{(1)}\sim\ln A_{\mathrm{min}} $ and $c^{(2)} \sim-1/A_{\mathrm{min}} $. The observed $1/n_{\mathrm{vac}}$ dependence is the vacancy-dominated limit $n_{\mathrm{vac}}\gg\Delta_{\alpha a}$, rather than the most general result. The spatial form of $c^{(2)}$ has a separate geometrical origin: the hard-rod weight functions select configurations in which exclusion intervals and their boundaries intersect regions of small free volume. This produces plateaus, edges, and localized ridges tied to the underlying periodic density. A numerical solution of the inhomogeneous Ornstein–Zernike equation shows how these singular direct correlations are redistributed in the total and pair correlations. The model provides a minimal free-volume explanation for both the magnitude and the
lattice-specific form of crystalline direct correlation functions.
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Soft Condensed Matter
Pressure and asymmetry govern the shape and stiffness of inflatables
Nathan Vani, Tom Joblin, Alejandro Ibarra et al. (+3 more)
Inflatables made of thin sheets constitute a lightweight, scalable alternative to conventional soft
robots. Since sheets are essentially inextensible while offering low resistance to bending, the shape of a straight tube should be trivially set by volume maximization. We show that networks of parallel tubes made from two sheets differing in stiffness defy this expectation as their global shape is governed by the binding angle at the junctions of adjacent tubes. Through this angle, the stiffness asymmetry induces a pressure-dependent curling and stiffening of the networks. Modeling a tube cross-section as two coupled rods, we quantitatively describe the geometry and mechanics of this new class of inflatables. Our model captures unexpected mechanical features such as a stiffness scaling as the square root of pressure and a contact-induced stiffening between neighboring tubes – challenging common assumptions on thin-sheet inflatables. Unlike prior work restricted to the high-pressure regime, the pressure-dependent description further enables multiprogrammable control over a continuous range of
curvatures. Discussing a variety of examples, we finally show that networks of asymmetric tubes are a versatile platform for functional shape-morphing objects.
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All authors Nathan Vani, Tom Joblin, Alejandro Ibarra, José Bico, Étienne Reyssat, Benoît Roman
Materials Science · Cross-listed from physics.chem-ph
Graph Neural Network Force Fields (GPTFF-mol) for Organic Molecules from Optimization Trajectories (OpenGEM26)
Yifan Huang, Fankai Xie, Jiangnan Zheng et al. (+3 more)
Density functional theory (DFT) serves as a reliable tool for atomistic molecular simulations, while machine learning potentials have become powerful complements to balance accuracy and efficiency. In this work, we release OpenGEM26 (Open Generated Ensemble of Molecules, 2026), a large-scale
dataset comprising 200,000 unique molecules and 4.4 million conformations composed of H, C, N, O, S and Cl with up to ten heavy atoms. All calculations are carried out at the {\omega}B97X-D/Def2-SVP and Def2-TZVP levels with dispersion corrections, and complete structural optimization trajectories and abundant non-
equilibrium structures are recorded. Statistical analyses confirm that this
dataset covers a broader conformational space than QM9 in terms of energy, bond lengths and bond angles. A graph neural network-based potential GPTFF-mol is trained using the new
dataset, achieving an energy mean absolute error of 16 meV/molecule, which is equivalent to 0.82meV/atom, and superior force prediction performance compared with ANI-2x. Validated by butane rotation and keto-enol tautomerization tests, the model accurately describes molecular dynamical behaviors and reaction barriers at distorted geometries. This work provides a high-quality resource and robust ML potential for efficient simulations of sulfur- and chlorine-containing organic molecules.
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All authors Yifan Huang, Fankai Xie, Jiangnan Zheng, Tenglong Lu, Sheng Meng, Miao Liu
Statistical Mechanics
Thermal pseudo-transitions in a frustrated spin-pseudospin sawtooth chain
Onofre Rojas and Jozef Strečka
We present an exact analysis of a
spin–pseudospin X sawtooth chain that incorporates three distinct valence states of copper ions and serves as a minimal model for one-dimensional cuprates composed of corner-sharing copper triangles. The model includes
magnetic exchange and electrostatic coupling constants both along the base sites and between base and apex sites capturing the competition between
spin and charge degrees of freedom. Using the transfer-
matrix method, we derive exact expressions for the free energy and obtain an analytical condition defining the pseudo-critical line associated with pronounced thermodynamic anomalies. The ground-state analysis reveals, besides an
antiferromagnetic phase, three frustrated phases characterized by distinct residual
entropies. At finite temperatures, these zero-temperature phase boundaries evolve into narrow
entropy ridges signaling pseudo-transitions between the corresponding quasi-phases. The specific heat and the avoided-crossing scale exhibit sharp but continuous peaks at the pseudo-critical temperature, whereas the physical correlation length may be controlled by a different subleading
eigenvalue. Local correlation functions uncover a cooperative rearrangement from charge-dominated to magnetically correlated regimes. Our results demonstrate that the sawtooth geometry promotes frustration and short-range coherence leading to pronounced pseudo-transition behavior.
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Soft Condensed Matter
A single length scale rules ballistic aggregation: travels of a droplet train
Nathan Vani, Stefan Kooij, Aritro Mukherjee et al. (+3 more)
Ballistic aggregation is a canonical non-
equilibrium process, relevant across scales from granular gases to planetary
accretion. Collisions are driven by differences in velocities, building up persistent correlations between neighbors. Here, we provide the first experimental realization of one-dimensional ballistic aggregation in a train of droplets formed by the breakup of a
liquid jet. Experiments and simulations confirm the analytically predicted scaling, with the global process shown to be governed by a single length scale. While air drag inverts the sign of neighbor velocity correlations, a 1D ordering constraint protects bulk characteristics of ballistic aggregation such as the scaling exponent and the shape of the large mass tail. More broadly, our results show that Smoluchowski-like mean-field descriptions fail when collisions carry directional
memory – as demonstrated here for jet-generated sprays.
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All authors Nathan Vani, Stefan Kooij, Aritro Mukherjee, Antoine Parrenin, Cees J.M. van Rijn, Daniel Bonn
Mesoscale and Nanoscale Physics
Visualization of Defect Electronic States in Layered Semiconductor CrSBr
Jonathan Brunette, Joost Aretz, Kiyoung Jo et al. (+5 more)
Chromium sulfur bromide (CrSBr) is a layered
magnetic semiconducting material combining a rich
magnetic phase diagram with axis-dependent electronic and optical properties. While defects in CrSBr have been shown to affect
magnetic order and excitonic responses, their microscopic nature, atomic structure, and electronic properties are not yet fully understood. In this work, we use scanning tunneling microscopy/spectroscopy (STM/STS) to explore the structure and electronic signatures of two prominent defects in bulk CrSBr. Their structure reflects the
symmetries of the underlying
lattice, with electronic features near the valence band edge. By comparing experimental data with ab initio simulated STM images, we infer that a common defect corresponds to a b-axis-aligned double sulfur vacancy, in line with findings from a recent growth analysis study. This result advances our understanding of the role of intrinsic defects in shaping the electronic structure of CrSBr.
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All authors Jonathan Brunette, Joost Aretz, Kiyoung Jo, Aljoscha Soll, Zdeněk Sofer, Malte Rösner, Nathan Guisinger, Adina Luican-Mayer
Materials Science
Lifetime effects and satellites in the photoelectron spectrum of platinum metal
Prajna Bhatt, José Julio Gutiérrez Moreno, Laura E. Ratcliff et al. (+9 more)
This work presents a comprehensive investigation of the electronic structure and many-body photoemission effects in metallic platinum using reflection high-energy electron energy-loss spec- troscopy (RHEELS), soft X-ray photoelectron spectroscopy (SXPS), and hard X-ray photoelectron spectroscopy (HAXPES), supported by ab initio calculations. Shallow and deep core state spectra enable the systematic characterisation of intrinsic line-shape asymmetries and satellite structures. Correlation of photoelectron satellites with RHEELS loss features allows the assignment of inter- band transitions, surface and bulk plasmons, plasmonic overtones, and semi-core ionisation losses across the Pt spectrum. Several previously unresolved satellite features and
spin-orbit splittings are identified and discussed. Comparison of experimental valence band spectra with orbital-projected densities of states calculated using ab initio density functional theory (DFT) and G0W0 approaches, with and without
spin-orbit coupling, demonstrates the critical role of relativistic effects in reproducing the Pt valence electronic structure. Together, these results establish a unified, internally consistent spectroscopic reference for metallic platinum, providing a robust framework for interpreting photoelectron spectra of Pt-containing catalysts, electronic materials, and related 5d transition metal systems.
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All authors Prajna Bhatt, José Julio Gutiérrez Moreno, Laura E. Ratcliff, Aysha A. Riaz, Charlotte. M. L. André, Ann S. Y. Lu, Robert G. Palgrave, Andrei Gloskovskii, Christoph Schlueter, Pardeep K. Thakur, Tien-Lin Lee, Anna Regoutz
Quantum Gases
Fluctuation-Induced Bistability in the Dissipative Dynamics of Generic Cavity-Matter Quantum Systems
Luisa Tolle, Simon B. Jäger, Ameneh Sheikhan et al. (+2 more)
We demonstrate that fluctuation-induced bistability is a robust and generic phenomenon in strongly interacting many-body systems with strong light-matter coupling. We identify a common microscopic mechanism based on resonances between photonic transitions and many-body energy scales, unifying the emergence of fluctuation-induced bistability across a broad class of models, including interacting
spins,
fermions, and
bosons coupled to cavity modes. We develop complementary methods to study both the steady-state properties of fluctuation-induced bistability and its dynamical formation at finite times. In particular, we introduce the dressed-state rate equation approach, which reveals rich metastable dynamics and enables the investigation of its system-size dependence. By comparing its predictions with numerically-exact tensor-network simulations, we identify signatures of fluctuation-induced bistability already in small systems on finite timescales. Our results establish fluctuation-induced bistability as a universal feature of dissipative cavity-coupled many-body systems and provide a general framework for the investigation of its non-
equilibrium dynamics across a wide range of hybrid
quantum platforms.
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All authors Luisa Tolle, Simon B. Jäger, Ameneh Sheikhan, Corinna Kollath, Catalin-Mihai Halati
Soft Condensed Matter
Two-Temperature Induced Phase Separation: Non-equilibrium Phase Behavior, Ordering, and Kinetics
Nayana Venkatareddy, Jaydeep Mandal, Jayeeta Chattopadhyay et al. (+1 more)
Two-temperature induced phase separation (2-TIPS) has emerged as a generic non-
equilibrium mechanism in scalar active systems with heterogeneous activity, where particles coupled to different thermal reservoirs spontaneously demix into dense cold and dilute hot phases. Unlike
equilibrium phase separation or motility-induced phase separation (MIPS), 2-TIPS is driven solely by unequal energy injection and the resulting heat flux between particle species. This review summarizes recent advances in 2-TIPS across diverse soft-matter systems, highlighting both its universal non-
equilibrium mechanisms and the emergent ordered phases arising from particle shape anisotropy, chirality, confinement, and
topology. We further discuss density-dependent phase-separation kinetics and coarse-grained descriptions linking microscopic dynamics to macroscopic behavior, and outline key directions for future research.
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All authors Nayana Venkatareddy, Jaydeep Mandal, Jayeeta Chattopadhyay, Prabal K. Maiti
Materials Science · Cross-listed from physics.chem-ph
Determination of fundamental properties of nitrogen from first principles. III. Temperature and frequency dependence of the molecular polarizability and magnetic susceptibility
Jakub Lang, Giovanni Garberoglio, Michał Przybytek et al. (+1 more)
This work is the third part of the series of papers that focus on the theoretical determination of the properties of nitrogen that are relevant in metrology. Here we present first-principles calculations of the temperature and frequency dependence of the molecular polarizability and
magnetic susceptibility of the nitrogen molecule (N$_2$). The purely electronic contributions to the static polarizability, Cauchy coefficients (up to sixth order), and isotropic
magnetic susceptibility are computed over a range of internuclear distances using a robust composite scheme combining several electronic structure methods. The temperature dependence, evaluated from $50$~K to $2000$~K, is determined using two independent methods: rovibrational averaging and path integral Monte Carlo (PIMC). The polarizabilities obtained from theory agree with the recent high-precision thermometry measurements, wherever the latter are available, but are significantly less accurate. However, the main usefulness of the theoretical data revolves around combining it with the available experimental results to generate semi-empirical estimates of various quantities that have never been measured thus far. As an example, we determine highly accurate semi-empirical estimates of the static polarizability at key reference temperatures, $\alpha_0(T)=11.735\,962$~a.u.\ at $T=303$~K and $\alpha_0(T)=11.735\,585$~a.u.\ at $T=273.16$~K. Furthermore, we report theoretical values for the
magnetic susceptibility, highlighting the importance of the paramagnetic contribution, and address a significant discrepancy with the experimental data for this quantity.
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All authors Jakub Lang, Giovanni Garberoglio, Michał Przybytek, Michał Lesiuk
Quantum Gases
Thermodynamic Signatures of Phase Separation in Mass Imbalanced Fermi Mixtures: Superfluid Density of States and Quasiparticle Specific Heat in the 163Dy 40K Atomic Mixture
Neda Ebrahimian
Mass imbalance changes not only pairing in a polarized
Fermi gas but also the thermodynamic condition under which normal and superfluid components can remain phase separated. The low-temperature properties of mass imbalanced two component
Fermi gases are investigated within the local density approximation on the BCS side of the BCS BEC crossover, with an unpolarized superfluid spatially separated from a partially polarized normal component. For each interaction strength and mass ratio, the pairing gap, average chemical potential, Hartree Fock potentials, and imbalance chemical potential are obtained self consistently, with the latter determined by the normal superfluid phase separation condition rather than varied independently. The results show that a larger mass ratio requires a larger imbalance chemical potential to maintain phase separation. For the 163Dy 40K mixture, an increase in the absolute value of the interaction strength raises the average and imbalance chemical potentials while reducing the pairing gap. The resulting changes modify the quasiparticle spectrum and the superfluid density of states and are reflected directly in the thermal response, with the quasiparticle specific heat decreasing at a fixed mass ratio. In contrast, increasing the mass ratio enhances the specific heat, which is associated with the larger density of available states near the
Fermi surface of the heavier majority component. The results thus connect the normal superfluid phase separation condition with the quasiparticle spectrum and superfluid density of states, and show that the specific heat provides a clear thermal signature of mass imbalance in the phase separated regime.
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Materials Science
Machine learning based prediction of optical properties in two-dimensional Mo-W-S-Se-Te transition-metal dichalcogenide alloys through physics-informed sampling
Vivek Chowdhury, Tarvir Anjum Aditto, Md. Samrat et al. (+2 more)
Two-dimensional transition-metal dichalcogenide (TMD)
alloys provide a compositionally tunable platform for controlling the optical and electronic properties. However, systematic prediction of their dielectric response across multicomponent
alloy spaces remains challenging owing to the combinatorial cost of first-principles calculations. In this work, we combined ab initio optical-property calculations with a tabular foundation-model regression to predict the real and imaginary components of the frequency-dependent dielectric function for Mo-W-S-Se-Te TMD
alloys. A
dataset of 99
alloy structures spanning binary, ternary, quaternary, and quinary compositions was generated using density functional theory (DFT). The resulting polarization-dependent dielectric spectra were used to train a tabular prior-fitted network (TabPFN) and evaluated against the conventional Extra Trees and XGBoost models. To accommodate the in-context capacity limit of TabPFN, we introduced a non-uniform, physics-informed energy subsampling strategy that concentrates sampling in the optically active region above the band gap, where interband absorption is strongest. Trained solely on quaternary
alloys, our TabPFN reconstructed the dielectric spectra of held-out quaternary compositions with an R2 > 0.98 and a mean absolute error below 0.10 for all four dielectric components, outperforming both baselines while requiring no gradient-based training or hyperparameter tuning. Our model further predicted derived optical quantities, including refractive index, extinction coefficient, and absorption coefficient. Additionally, our model generalized in a zero-shot manner to binary, ternary, and quinary
alloys absent from the training set, with quinary predictions achieving an R2 > 0.97.
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All authors Vivek Chowdhury, Tarvir Anjum Aditto, Md. Samrat, Hafiz Imtiaz, Ahmed Zubair
Mesoscale and Nanoscale Physics
Direct Measurement of Exciton Dispersion in the Long-Wavelength Limit
Peiyi He, Jiade Li, Jiakai Wang et al. (+15 more)
Exciton dispersion, which governs the propagation, scattering and radiative decay of electron-hole pairs, is essential to optoelectronics and
quantum materials. In two-dimensional systems, weakened dielectric screening and long-range electron-hole exchange are predicted to induce nonanalytic
exciton dispersion in the long-wavelength limit. However, direct quantitative characterization of its dimensional
evolution remains lacking, especially in the ultralow-q regime (q < 0.02 $\r{A}^{-1}$). Here we employ defocus-engineered momentum-resolved electron energy-loss spectroscopy in scanning transmission electron microscopy, achieving an ultrahigh momentum resolution of 0.0002 $\r{A}^{-1}$. Using freestanding hBN as a prototypical platform, we resolve layer-dependent
exciton dispersion and quantify its characteristic crossover momentum and group velocity in the long-wavelength limit. With increasing thickness, the nonanalytic linear-dispersion regime is progressively compressed, manifested by a reduction in characteristic crossover momentum q_c from $1.82 \times 10^{-1} \r{A}^{-1}$ in the monolayer to $3.0 \times 10^{-1} \r{A}^{-1}$ in 25 layers. Meanwhile, the low-q group velocity increases from $2.0 \times 10^{-3} c$ to $2.9 \times 10^{-2} c$, before the dispersion ultimately approaches the bulk-like
parabolic limit. We further examine how the
exciton band structure of monolayer hBN responds to its surrounding environment, including temperature, adjacent
graphene layers, and interlayer twist in BN/
graphene heterostructures. These findings uncover the fundamental physics of low-dimensional
excitons, deliver valuable guidance for modulating
exciton transport,
diffusion and quasiparticle coupling in layered
quantum materials, and establish a powerful experimental route to explore low-dimensional
exciton physics.
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All authors Peiyi He, Jiade Li, Jiakai Wang, Jiangxu Li, Jiahao Wang, Weiyu Sun, Yiwen Song, Xiaoyue Gao, Quanlin Guo, Bo Han, Ruochen Shi, Niklas Dellby, Tracy Lovejoy, Xing-Qiu Chen, Kaihui Liu, Yu Ye, Hailin Peng, Peng Gao
Disordered Systems and Neural Networks
Driven criticality links universal computation and optimal representations
Adrián Roig, Miguel A. Muñoz and Guillermo B. Morales
Near-critical dynamics are often linked to enhanced computation, but the underlying mechanism remains unclear. We address this question in reservoir computing, where a fixed recurrent network maps input sequences into high-dimensional states and only a simple readout is trained. We extend fixed-reservoir universality results to discrete-time input-driven reservoirs and connect their key
geometric condition, neighborhood separation, to dynamics. To this end, we introduce a finite-resolution neighborhood separability index and an input-conditioned maximal Lyapunov exponent. We find that neighborhood separability, chaotic time-series prediction, and smooth high-dimensional representation geometry are optimized in the same narrow window of marginal driven stability. In this regime, the covariance spectrum approaches the power-law scaling expected for near-optimal smooth representations. Our results link edge-of-instability computation, universality, readout performance, and optimal representation geometry within a common dynamical framework.
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Statistical Mechanics
Entanglement asymmetry and quantum Mpemba effect for Kramers-Wannier duality
Milo Vescovo, Pasquale Calabrese and Filiberto Ares
The Kramers-Wannier duality is the prototypical example of a non-invertible
symmetry, yet little is known about its fate away from criticality and out of
equilibrium. We introduce the Kramers-Wannier
entanglement asymmetry, a
quantum-information measure that quantifies the breaking of this non-invertible
symmetry in the transverse-field Ising chain. We first investigate its
equilibrium properties, showing that it exhibits a striking crossover between the ordered and disordered phases together with a pronounced dip at the critical point that becomes increasingly sharp with subsystem size. We then study
quantum quenches from both gapped phases to criticality and show that the Kramers-Wannier
entanglement asymmetry decays to zero, signaling the dynamical restoration of the non-invertible
symmetry. Remarkably, we uncover the emergence of a
quantum Mpemba effect: under suitable conditions, states initially farther from
equilibrium restore the Kramers-Wannier
symmetry faster than states prepared closer to it. We provide both analytical and numerical evidence for this phenomenon and identify the mechanism responsible for its occurrence. Our work establishes
entanglement asymmetry as a powerful probe of non-invertible
symmetries beyond
equilibrium and opens new perspectives on the dynamics of dualities in
quantum many-body systems.
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Mesoscale and Nanoscale Physics
Circular phonon dichroism in $d$-wave altermagnets
Ding Li, Tao Qin and Jianhui Zhou
Altermagnets, a new class of collinear antiferromagnets, exhibit momentum-dependent
spin splitting and offer compelling advantages for
antiferromagnetic spintronics. However, the
magnetic order is intrinsically difficult to read out, which hinders practical applications. We propose finite-momentum circular
phonon dichroism as a direct probe of Néel vector in two-dimensional $d$-wave altermagnets. Combining Onsager reciprocity with $C_{2z}$
lattice symmetry, we find that the dichroic signal reverses sign when the Néel vector is flipped for the in-plane
phonon wave vectors. Moreover, a channel-resolved decomposition identifies the circular
phonon dichroism originates from the interband coherent transitions. Representative finite-momentum cuts show pronounced dichroic asymmetric ratio, with $|\eta_{\mathrm{CPD}}|=37.3\%$. Our work reveals that the circular-ultrasound absorption acts as a direct probe of the Néel vector of $d$-wave altermagnets.
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Mesoscale and Nanoscale Physics
Emergent ferromagnetism in the NiI$_2$-NbSe$_2$ van der Waals heterostructure
Büşra Gamze Arslan, Mohammad Amini, Ziying Wang et al. (+6 more)
Multiferroicity arising from non-collinear
spin textures and strong
spin-orbit interactions offers a route to magnetoelectric functionality in the monolayer limit. Although theory predicts that the properties of monolayer multiferroics can be tuned by strain, gating, or proximity effects, experimental demonstrations of such control remain scarce. Here we show that the
magnetic ground state of monolayer NiI$_2$, a prototypical two-dimensional multiferroic, is altered by proximity to a superconducting NbSe$_2$ substrate. Using low-temperature scanning tunnelling microscopy (STM) and spectroscopy (STS), we show that the metallic substrate renormalizes the exchange interactions within NiI$_2$ and drives it into a
ferromagnetic ground state. This can be visualized by probing the Yu-Shiba-Rusinov (YSR) states within the superconducting gap of the NbSe$_2$ substrate. Our results establish YSR states as an in situ probe of two-dimensional magnetism and demonstrate substrate engineering as a means of controlling
magnetic order in atomically thin materials.
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All authors Büşra Gamze Arslan, Mohammad Amini, Ziying Wang, Alessandro Orsini, Aleš Cahlík, Jose L. Lado, Adolfo O. Fumega, Robert Drost, Peter Liljeroth
Strongly Correlated Electrons
Long-wavelength density response and momentum resolution in strange-metal charge spectroscopy
Ilmo Sung
Momentum-resolved electron energy-loss spectroscopy (EELS) on strange-metal Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (Bi-2212) observes a broad charge continuum that is nearly momentum independent over an extended finite-momentum regime, whereas optical spectroscopy determines a metallic local conductivity. We analyze the long-wavelength response function that connects these regimes: the proper homogeneous bulk charge-density polarization. For any homogeneous $U(1)$-conserving metal whose longitudinal matter conductivity remains finite in the $q\to0$ limit at fixed nonzero frequency, the Ward identity gives $\chi''_{\rho\rho}({\bf q},\omega)=q^2\operatorname{Re}\sigma_L({\bf q},\omega)/\omega$. We then prove that any nonnegative normalized momentum-resolution kernel with a self-similar $q$-scaled profile, uniformly bounded second moment, and tight second-moment tails preserves this $q^2$ asymptotic behavior, changing only the prefactor. Consequently, a nearly local finite-$q$ continuum in Bi-2212, if continuously connected to a regular metallic optical limit of the same proper bulk response, is naturally described by a crossover surface $q_\ast(\omega,T)$. The
theorem is a constraint on the proper bulk density response, or on a positive $q$-scaled convolution of it; screened loss functions and surface EELS observables require the corresponding electrodynamic conversion before the constraint is applied.
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Superconductivity
Puzzling superconductivity in strontium ruthenate: then and now
James F. Annett and Karol I. Wysokiński
Strontium ruthenate is a very interesting low temperature
superconductor with relatively simple normal state and very puzzling superconducting state properties. Despite over thirty years of intensive research, even the precise
symmetry of the order parameter is not known. In this paper we briefly review some of the key developments, focussing on some of the newer experiments, especially those which challenged the previous understanding that it is a
spin triplet odd parity
chiral p-wave
superconductor. Since Sr$_2$RuO$_4$ now appears most probably a
spin singlet
superconductor we have calculated the Kerr effect for one candidate $d$-wave pairing state. We find that for the
chiral $d$-wave $E_g$ pairing state the calculated
Hall conductance is non-zero and qualitatively similar to that found earlier under the assumption of a
chiral p-wave $E_u$ order parameter. We characterize the
Hall conductance in relation to two sum rules, one related to Berry
curvatures in the Bogoliubov quasiparticle states, and the other $f$-sum rule indicating the presence of inter-orbital pairing.
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Materials Science
Magneto-Caloric effect and Multiple magnetic phases in Al doped Ni2MnSn0.75Al0.25 Heusler Alloys
Satya Vijay Kumar, Simran, Madhusmita Jena et al. (+9 more)
Among Heusler compounds,Ni based
alloys have been extensively investigated because they exhibit desirable properties such as high Curie temperatures, which are advantageous for advanced
magnetic and spintronic devices.The effect of Al substitution on the
magnetic ground state of Ni2MnSn was investigated using the Ni2MnSn0.75Al0.25 Heusler
alloy.Temperature-dependent magnetisation measurements identify a second-order paramagnetic to
ferromagnetic transition at TC is 734K,followed by a first-order martensitic transformation near 263K,demonstrating strong magnetostructural coupling.Curie Weiss analysis yields a positive Weiss temperature theta CW is 746.4K and an effective
magnetic moment of 6.82muB,confirming the predominance of
ferromagnetic exchange interactions. The bifurcation between the ZFC and FCW magnetization curves,together with non saturating hysteretic M vs H loops, indicates the coexistence of competing
ferromagnetic and
antiferromagnetic interactions.Further
magnetic investigations establish the formation of an interacting reentrant cluster glass state accompanied by an exchange-bias effect.The observed
magnetic behavior is attributed to the modification of Mn Mn exchange interactions induced by Al substitution and the associated atomic disorder,resulting in a complex
magnetic ground state.
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All authors Satya Vijay Kumar, Simran, Madhusmita Jena, Mehroosh Fatema, Atul Gangwar, Srishti Dixit, Umashankar Rajput, Nisha Shahi, Chetna Gautam, Sanjay Singh, Anup K. Ghosh, Sandip Chatterjee