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Physics Condensed Matter

cond-mat Watch Condensed Matter

Sunday 26 July

Materials Science

Observation of correlation-driven topological transport and robust ferromagnetism in 2D CrS$_2$

Sk Md Obaidulla, M. Nur Hasan, Dayal Das et al. (+10 more)

The realization of correlated layered magnets hosting robust ferromagnetism with emergent topological transport remains a key challenge in quantum materials. Here we report the first catalyst-free chemical vapour deposition growth of layered 1T-CrS$_2$, establishing a highly stable vdWs ferromagnet with an out-of-plane easy-axis anisotropy and a Curie temperature above room temperature. Transport measurements reveal a semimetal–insulator crossover near 80 K and pronounced negative magnetoresistance up to 350 K. A topological Hall effect emerges below 30 K, a rare signature of correlated transport in layered transition-metal dichalcogenide ferromagnets. First-principles calculations show that spin–orbit coupling gaps Dirac-like crossings, while electronic correlations reconstruct the Fermi surface by suppressing electron pockets and reducing the carrier density, enhancing momentum-dependent out-of-plane spin polarization. Magnetic measurements, supported by Heisenberg exchange calculations, reveal strong nearest-neighbour ferromagnetic exchange that stabilizes long-range ferromagnetism. Our results establish 1T-CrS$_2$ as a rare correlated 3$d$ layered ferromagnet in which electronic correlations and spin–orbit coupling cooperatively drive emergent topological transport.
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All authors Sk Md Obaidulla, M. Nur Hasan, Dayal Das, Rafiqul Alam, Antonio Supina, Muhammad Awais Aslam, Sherif Kamal, Iva Šarić Jankovic, Aleksandar Matkovic, Christian Teichert, Atindra Nath Pal, Heike C. Herper, Marko Kralj

Disordered Systems and Neural Networks

Local micromechanics in a mean-field model of glasses reveal key properties of its non-equilibrium RSB phase

Makoto Suda, Edan Lerner and Eran Bouchbinder

A recently formulated mean-field model of glasses features an equilibrium, zero-temperature Replica-Symmetry-Breaking (RSB) transition in some parameter range. In this range, the model's solution in the Replica-Symmetric phase is expressed in terms of an effective, self-consistent random potential for uncoupled degree of freedoms, where the transition to the RSB phase is characterized by the emergence of spectral-edge localized modes and a pseudogapped quartic vibrational spectrum, resulting in a finite spin-glass susceptibility. These properties are preserved in numerical solutions of the model under non-equilibrium conditions, i.e., upon an instantaneous quench. Inspired by recent advances in computer glasses, we define a micromechanical response function — the linear response to local force monopoles — in the framework of the mean-field model. We establish exact relations between the force monopole stiffness and global susceptibilities, which suggest a close correspondence between the non-equilibrium RSB phase of the model and the above-mentioned effective random potential description. As such, the obtained micromechanical observables constitute a concrete realization of the collective degrees of freedom of the model, offering a bridge between a glassy mean-field model and finite-dimensional glasses. We show that the model's vibrational spectrum can be computed solely from the monopole response statistics and, by employing a marginal stability criterion, we extract a characteristic frequency/stiffness scale of soft glassy modes, which is related to the boson peak in finite-dimensional, laboratory glasses.
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Mesoscale and Nanoscale Physics

Spin-Hall devices: spin relaxation spatially separates current injection from Joule dissipation

Yanbo Qiao, Sariah Al Saati and Jean-Eric Wegrowe

The stationary state of a spin Hall bar connected to an external load circuit is investigated through a variational approach based on the principle of minimum power dissipation generalized to the two-spin-channel model. The self-consistent distributions of longitudinal and transverse current densities, alongside the corresponding spin and charge accumulations and dissipation power in the resistance, are derived. Surprisingly, it is shown that the Joule dissipation vanishes when the load resistance is placed at a sufficiently large distance compared with the spin-relaxation length. Such a highly non-trivial global stationary state appears as the most striking characteristic of the injection of pure spin current compared with more usual current injection.
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Quantum Gases

Permutationally Invariant Quantum State Tomography for Fermions

Shion Yamashika and Daisuke Yamamoto

Quantum state tomography provides complete information about a quantum state, but its measurement cost generally grows exponentially with system size. In many-particle quantum simulators, this challenge is further compounded by the limited accessibility of local measurements and controls. Here we develop a tomography protocol for permutation-invariant fermionic many-body states with U(1) particle-number symmetry. We show that any such state is completely determined by the distribution of the total particle number and the occupation of a single collective mode within each particle-number sector, both of which are accessible in current ultracold-atom experiments. The number of required observables scales only linearly with the system size. More generally, the protocol reconstructs the permutation-symmetrized component of arbitrary U(1)-symmetric fermionic states, which can still encode nontrivial many-body and state-level structure beyond conventional few-body observables. We demonstrate this protocol in interacting non-Gaussian states of the complex Sachdev-Ye-Kitaev model and in free-fermion chains across a Lifshitz transition. This framework opens a route toward information-theoretic characterization of strongly correlated itinerant quantum matter in experimentally realistic fermionic quantum simulators.
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Soft Condensed Matter

On the flash temperature in sliding rubber contacts

B.N.J. Persson

We present an analytical theory for the flash temperature for viscoelastic solids sliding on rigid and randomly rough surfaces. The theory takes into account the surface roughness on all relevant length scales.

Strongly Correlated Electrons

Observation of an emergent energy scale close to dimensional reduction in a quasi-two-dimensional quantum magnet

Anneke Reinold, Laur Peedu, Kirill Amelin et al. (+19 more)

By appropriately perturbing a critical transverse-field Ising chain away from its critical point, the system can develop a finite correlation length with a characteristic purely massive spectrum, whose ratios and correlations are precisely described by an integrable field theory and an infinite set of integrals of motion corresponding to the $E_8$ Lie algebra. In this work, we report on experimental observation of a characteristic massive spectrum close to transverse field-induced dimensional reduction in a quasi-two-dimensional quantum magnet Cu$_2$(OH)$_3$Br, providing evidence for an emergent $E_8$ symmetry and the corresponding excitations of bound states in the sublattice of its ferromagnetic chains. These results demonstrate the power of integrable field theory in describing emergent many-body quantum critical phenomena in condensed matter systems.
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All authors Anneke Reinold, Laur Peedu, Kirill Amelin, Urmas Nagel, Toomas Rõõm, Sven Luther, Hannes Kühne, Dirk Wulferding, Kingshuk Mukhuti, Maarten W. de Dreu, Peter C. M. Christianen, Dennis Kudlacik, Dmitri Yakovlev, Zhiying Zhao, Taro Nakajima, Yoshimitsu Kohama, Thomas Lorenz, Franco Lisandrini, Corinna Kollath, Marcin Raczkowski, Fakher F. Assaad, Zhe Wang

Quantum Gases

Dynamical control of particle jets from a driven condensate in a one-dimensional lattice with double-well potential

Z. Li and L. Q. Lai

We investigate the nonlinear dynamics of a Bose-Einstein condensate trapped in a double-well potential of a one-dimensional lattice, where the interatomic interactions are periodically modulated in time. In the typical case of a symmetric double-well, we observe collective particle emission under resonant driving, where the excitation regimes are explicitly constrained by the interplay between the drive strength and the hopping amplitude. By introducing a depth asymmetry between the wells, we find that moderate bias specifically enhances the emission rate, while large asymmetry suppresses it. The particle jets can be further controlled by modulating the hopping amplitudes, where the emission is weakened for finite hopping imbalances. These results outline the roles of asymmetry and external driving in precisely manipulating quantum many-body transport, and may offer insights into the design of atomtronic devices.
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Mesoscale and Nanoscale Physics

Current cross-correlations as probes for poor man's Majorana states

Saatwik Patnaik, Aditya Saran, Himadri S Dhar et al. (+3 more)

The minimal Kitaev chain that emulates a topological superconductor with three quantum dots offers a tunable platform for potentially hosting poor man's Majorana (PMM) modes. Asserting the need to go beyond differential conductance spectroscopy, we introduce current-current correlations as a viable framework for verifying their true non-locality. The robustness of the PMM modes, specifically with respect to delocalization as the system is tuned away from sweet spots, we show, is embedded in the relative magnitudes of the nonlocal transport processes. This aspect is adeptly captured by current cross-correlations, whose features show remarkable stability around the PMM sweet spot, specifically with respect to the detuning of an outer dot. We establish this as a prominent feature and a diagnostic for true PMMs even in the short chain limit. Our results accentuate the need for current cross-correlation measurements as a diagnostic framework for unambiguously verifying true non-locality of entangled states as well as topologically protected states.
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All authors Saatwik Patnaik, Aditya Saran, Himadri S Dhar, Pertti Hakonen, Thierry Martin, Bhaskaran Muralidharan

Strongly Correlated Electrons

Interplay of Spin Waves, Crystal-Field Excitations, and Phonons in Multiferroic Ba3HoRu2O9 revealed by Inelastic Neutron Scattering, Crystal-Field Analysis, and Machine-Learned Phonon Calculations

Ekta Kushwaha, Sayan Ghosh, Gourab Roy et al. (+6 more)

Understanding the microscopic origin of spin-dipole coupling and high-energy excitations in correlated 4d-4f multiferroic oxides is challenging because magnetic, crystal-field, and lattice excitations frequently overlap in energy. The hexagonal 6H perovskite Ba3HoRu2O9 provides an ideal platform to investigate this interplay owing to the coexistence of Ru2O9 molecular units and localized Ho3+ moments. To identify the contributions from these different excitations, we combine inelastic neutron scattering (INS) with linear spin-wave calculations, crystal-field analysis, Raman spectroscopy, and machine-learned force field (MLFF) phonon calculations. A dispersive magnetic excitation below 6.2 meV is accurately reproduced by linear spin-wave theory, establishing its origin as a collective spin-wave excitation of the coupled Ru-Ho magnetic network. At higher energies, broad excitations centered near 20, 39, 70, and 90 meV is observed that are present far above magnetic ordering temperature. Crystal-field calculations based on the Stevens formalism place the strongest Ho3+ transitions within the experimentally observed energy window, while Raman spectroscopy and MLFF phonon calculations identify optical phonons with comparable energies. Together, these complementary results show that the broad INS feature near 39 meV is consistent with overlapping contributions from Ho3+ crystal-field excitations, lattice vibrations, and previously reported Ru2O9 molecular magnetic excitations. These findings establish a microscopic framework for understanding the interplay between spin, crystal-field, and lattice degrees of freedom in this multiferroic 4d-4f compound.
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All authors Ekta Kushwaha, Sayan Ghosh, Gourab Roy, Mohit Kumar, Manh Duc Le, Jhuma Shannigrahi, Som Datta Kaushik, Devashibhai T. Adroja, Tathamay Basu

Materials Science

Universal temperature-dependent electrical resistivity in actinides

E.F. Talantsev

Temperature-dependent electrical resistivity $\rho(T)$ is one of the most common types of experimental data analyzed in condensed matter physics. For one group of pure metals, the actinides, experimental $\rho(T)$ curves differ radically from one another to the point that there is no unified theoretical approach to understanding and fitting $\rho(T)$ data in these elements. First-principles calculations result in $\rho(T)$ curves that differ from experimental data, even qualitatively. In an attempt to unravel this long-standing problem, here I propose a simple model that accurately fits the $\rho(T)$ data for nine phases of elemental actinides (from thorium (Th) to curium (Cm)) for which experimental data are publicly available to date. The model is based on the concept of two parallel conduction channels: one is described by the Bloch-Grüneisen equation, which is associated with the classical electron-phonon dissipation mechanism, and the other by the Arrhenius equation, which is associated with the nearest-neighbor hopping (NNH) conductivity. Debye temperatures $\Theta_D$ obtained by applying the model to the $\rho(T)$ data for nine elemental actinide phases are in good agreement with published values deduced from heat capacity measurements. For neptunium (Np) a maximum Arrhenius activation energy (among all actinides) of $E_a=15.9$ $meV$ was derived. The model was also successfully applied to $\rho(T)$ data measured on $\delta$-phase plutonium-based alloys Pu-Ce and Pu-Ce-Ga.
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Materials Science

Molecular dynamics with a first-principles-validated universal machine-learning potential reveals dynamic elementary processes of growth-related adspecies on GaN(0001)

Yoshito Takaesu, Akira Kusaba, Junko Ishii et al. (+2 more)

Atomic-scale understanding of the surface elementary processes in metalorganic vapor phase epitaxy (MOVPE) of GaN has so far relied on static density-functional-theory (DFT) energetics and on first-principles molecular dynamics (FPMD) limited to a few tens of picoseconds. Here we combine FPMD with a universal machine-learning interatomic potential (MLIP), UMA, to follow the dynamics of growth-related adspecies on GaN(0001) over time scales inaccessible to purely first-principles approaches. FPMD simulations of a GaNH admolecule coexisting with H adatoms reveal a hitherto unrecognized diffusion mode, in which the N atom lifts the Ga atom of the GaNH unit off the surface layer during migration, and show that the lifted Ga abstracts an H adatom from the surface, events invisible to static DFT. Single-point UMA calculations on FPMD snapshots reproduce the first-principles relative energies along the trajectory (RMSE of about 8.5 meV/atom) without any retraining. Long-time MLIP-based MD (150 ps) then reveals dynamics never observed within the FPMD window: site-to-site H-adatom hopping, which gates the migration paths of the growth unit, and reversible dissociation of the GaNH unit into independently migrating Ga and NH adspecies. This work constitutes, to our knowledge, the first application of an MLIP to the molecular dynamics of GaN MOVPE.
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All authors Yoshito Takaesu, Akira Kusaba, Junko Ishii, Shigenori Matsushima, Yoshihiro Kangawa

Materials Science

Fe-doping-induced band structure modification and cryogenic phase stability in Cs2AgBiBr6 single crystals

Yanan Li, Xuejiao Wu, Jidong Deng et al. (+1 more)

Despite its promise as a lead-free alternative, the practical application of Cs2AgBiBr6 in optoelectronics is limited by its wide band gap and detrimental intrinsic defects. To overcome these challenges, we synthesized Cs2AgBi0.5Fe0.5Br6 single crystals via a modified hydrothermal method. While both pristine and Fe-doped crystals undergo a structural phase transition near 125 K, Fe incorporation fundamentally alters its impact. The dopant simultaneously narrows the band gap in the high-temperature phase and suppresses the associated cryogenic structural instability. Our optical and X-ray structural studies establish Fe doping as a powerful strategy for tailoring the properties of Cs2AgBiBr6 , advancing its potential for high-performance, low-temperature optoelectronic and spintronic devices.
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All authors Yanan Li, Xuejiao Wu, Jidong Deng, Jinbao Zhang

Materials Science · Cross-listed from quant-ph

Multiconfigurational Mixed Quantum-Classical Approach for Correlated Many-Body Dynamics

Pritha Ghosh, Rajanya Sarkar and Arkajit Mandal

In this work, we introduce a multiconfigurational mixed quantum-classical many-body approach for simulating the finite-temperature correlated multi-exciton dynamics in the presence of phonon-induced static and dynamic disorder. In this mixed quantum-classical approach, the excitonic subsystem is described using a multiconfigurational wavefunction that extends beyond the mean-field limit, while the phonons are evolved quasi-classically. Using this approach, we simulate a multi-excitonic dissipative system and show how the interplay between phonon-induced dynamic disorder and exciton-exciton many-body interactions determines excitation-dependent excitonic transport and spatial correlations. Our results show that while the mean-field approach produces semi-quantitatively accurate diffusive dynamics, it does not capture the spatial correlations as expected. We find that a mean-field path approximation, where we generate pre-computed trajectories using our mean-field mixed quantum-classical approach and then perform multiconfigurational dynamics, can reproduce the spatial correlations to a good accuracy, positioning this approach as an efficient method for capturing spatial correlations in complex systems.
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Soft Condensed Matter

The Polymer Physics of Kinetoplast DNA as a Polymerised Membrane

Takahiro Sakaue and Davide Michieletto

We analyze the conformational and dynamical properties of the kinetoplast DNA (kDNA), a massive sheet-like structure made from thousands of circular DNA molecules, found in the mitochondrion of certain parasites. The connectivity between circular DNA molecules is achieved by topological linking, hence, the kDNA may be regarded as a naturally occurring two-dimensional version of Olympic gels, whose physical properties are yet to be understood. We propose that the basic aspects in the large scale behaviors of kDNA could be described by the physics of polymerized membrane. Our analysis indicates the relevance of the hydrodynamic interactions in the dynamics of kDNA in aqueous solution. We demonstrate that the predicted dynamical scaling scenario captures various experimental data recently obtained from in vitro imaging experiments in a unified manner. We also provide an estimate for the in-plane elastic modulus of kDNA, whose magnitude agrees well with recent measurements.
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Materials Science

Tailoring the Frequency-Dependent Optical Response of Hematite through Mono- and Co-Doping: A First-Principles Study

Abdul Ahad Mamun and Muhammad Anisuzzaman Talukder

Understanding the effects of doping on the crystal structure and optical properties of semiconductor materials is crucial for advancing next-generation semiconductor and photonic technologies. Although various studies have focused on doped hematite ($\alpha$-Fe$_2$O$_3$), the relationship between dynamical stability and optical properties remains insufficiently explored. This study presents a comprehensive first-principles investigation that simultaneously evaluates the phonon dispersion characteristics and frequency-dependent optical response of B-doped, Y-doped, and (B, Y)-co-doped $\alpha$-Fe$_2$O$_3$, providing deeper insights into the underlying mechanisms. We examined the finite-temperature vibrational properties, dielectric function, and optical characteristics to comprehend the lattice dynamics and light-matter interactions under electromagnetic radiation. Vibrational thermodynamics reveal that pristine and Y-doped hematite maintain dynamic stability, while B-doped hematite exhibits imaginary phonon modes indicating lattice instability due to distortions in the Fe–O framework. Notably, Y co-doping with B helps suppress these soft modes, restoring structural stability through lattice relaxation and improved interatomic forces. B doping enhances low-energy absorption by introducing additional states in the valence band, while Y doping alters orbital hybridization, leading to a broader dispersion. In the optical regime, doped hematite displays dominant interband transitions below $2$ eV and strong absorption between 1.80 eV and 4 eV. The (B, Y) co-doping combines the low-energy benefits with an improved optical response profile. In summary, doping significantly enhances lattice vibrations, light-matter interactions, and optical responses, providing an effective strategy for tailoring hematite for diverse applications in photoactive, optoelectronic, and photonic technologies.
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Soft Condensed Matter

Transient fluid removal at soft interfaces: Stationary squeeze-out and dynamic scraping in a block-on-flat contact

R. Xu, T. Tada, D. Ferré Sentis et al. (+1 more)

Fluid removal from rubber-substrate interfaces is crucial for maintaining friction during walking and vehicle braking on contaminated surfaces. We study the transient friction of rectangular rubber blocks sliding against tile and glass surfaces lubricated with water, glycerol, mud, or silicone grease. Two block configurations with different lengths in the sliding direction were tested after different stationary waiting times. For water, stationary squeeze-out is nearly complete before sliding begins. For glycerol, both stationary squeeze-out and sliding-induced fluid removal are important. For mud and grease, the steady-sliding state is reached after a sliding distance of the order of the block length, with little dependence on the preceding waiting time, showing that sliding-induced scraping dominates fluid removal for highly viscous substances. Dividing the contact into shorter blocks accelerates fluid removal by reducing the drainage distance and increasing the number of leading edges. Stationary squeeze-out calculations based on the measured surface roughness are in reasonably good agreement with the glycerol experiments. The results provide design guidelines for rubber tread blocks with multiscale drainage channels and sufficient compliance to promote transient fluid removal.
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All authors R. Xu, T. Tada, D. Ferré Sentis, B.N.J. Persson

Materials Science · Cross-listed from physics.plasm-ph

Comparative qualification of advanced plasma-facing materials for fusion pilot plants through public- and private-sector experiments in DIII-D

Florian Effenberg, Jonathan D. Coburn, Luca Cappelli et al. (+44 more)

A coordinated DIII-D campaign exposed and comparatively assessed 44 advanced plasma-facing materials from 12 institutions, including four public-private fusion partnerships, to support fusion pilot plant wall and divertor material down-selection. Samples were exposed using the Divertor Materials Evaluation System (DiMES) under Ohmic, L-mode, and H-mode conditions with edge-localized modes, at 0.2-2.5 MW m$^{-2}$ on flush geometries and 10-15 MW m$^{-2}$ on 10$^{\circ}$ angled geometries. Engineered tungsten architectures retained integrity; long-fiber Wf/W showed the clearest crack-arrest behavior. W-Re and K-doped W showed near-ITER-W-like responses, while additively manufactured W-Ta showed heat-flux-sensitive mass losses of 0.64 mg for the flat sample and 2.19-2.87 mg for angled samples. After irradiation to 0.3 dpa at 550$^{\circ}$C, neutron-irradiated ITER-grade W retained 2.8 times more deuterium than pristine W, while TiB$_2$ showed the lowest D$_2$ release in the Ohmic set. VTaHfMo was the most stable refractory multi-principal-element alloy. NbC and (Nb$_{0.5}$Ta$_{0.5}$)C retained integrity with 0.02-0.03 mg mass loss, whereas ZrC lost 7 mg. CVD SiC retained macroscopic integrity but exhibited an effective Si erosion yield of 0.5, about 5-10 times above prior DIII-D trends. Renewable boron pebble rods underwent controlled recession; 13% of released boron was ionized near the outer strike point and up to 50% was recovered locally. Initial in-situ chromium gross-erosion measurements yielded values of order $10^{-2}$. Together, these results provide cross-material benchmarks for fusion pilot plant down-selection and future AI/ML-assisted plasma-facing-material development.
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All authors Florian Effenberg, Jonathan D. Coburn, Luca Cappelli, Simon D. Corah, Amoolya Grandhi, Jerome Guterl, Charlie Hirst, Mike Jackson, Dylan A. Kohler, Rob Kolasinski, Erick Martinez-Loran, Ria Meston, Lauren Nuckols, Angelica Ottaviano, Zana Popovic, Sergey Tsurkan, Tessa Van Volkenburg, Daniel Velazquez, Aaliyah Zuniga, Arunodaya Bhattacharya, Jose Boedo, Kent Christian, Giacomo Dose, Eric Hollmann, Mykola Ialovega, Florian M. Laggner, Samara Levine, Xavier Navarro, Andrew Shone, Lance L. Snead, David Sprouster, Jason Trelewicz, Jayson Barr, Ryan Hood, Charlie Lasnier, Yan-Ru Lin, Vincent Mazon, Jun Ren, Gilson Ronchi, Dmitry Rudakov, Dinh Truong, Cedric Tsui, Shawn Zamperini, Weicheng Zhong, Tyler Abrams, Anthony W. Leonard, Roberto Maurizio

Saturday 25 July

Disordered Systems and Neural Networks · Cross-listed from hep-th

Learning the Emergent Bulk Geometry of the Three Dimensional Ising Model

Ritam Basu

We use Monte Carlo data for the three-dimensional Ising model at the critical temperature to predict an emergent radial geometry of the bulk using machine learning. Specifically, we employ a differentiable solver for a probe field on an asymptotically $\mathrm{AdS}_4$ background, trained to reproduce the measured momentum-space two-point functions of the boundary operators ($\sigma$ and $\epsilon$). We find that a single metric cannot simultaneously serve both operators. Fitting each channel separately improves its own residual by a factor of three to five, but degrades the other by up to two orders of magnitude. We quantify this tension between the two operators and show that it survives changes to the momentum window and the lattice size. Our results numerically demonstrate that the bulk geometry of a theory with an $\mathcal{O}(1)$ central charge, such as the 3D Ising model, is not captured by a single classical metric.
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Materials Science · Cross-listed from cs.AI

Harnessing agent memory to build lifelong AI partners for materials scientists

Siyu Liu, Bo Hu, Beilin Ye et al. (+3 more)

Materials research advances through accumulated experience - scripts that work, protocols that are trusted, warnings attached to failed calculations or experiments, and judgement that links a new question to an old result. This experience is essential for reproducibility and knowledge transfer, yet it is usually fragmented across notebooks, repositories, job logs and individual memory, and it is rarely portable across artificial-intelligence agents. Here we argue that a lifelong AI partner for materials science can be designed around persistent memory rather than around a particular agent implementation. We introduce a self-evolving memory framework that stores scientific experience as inspectable facts and executable skills, so that observations, failure boundaries, protocols and validation checks can be retrieved, revised and migrated across models. We evaluate the idea in three computational settings that expose different layers of materials-research competence. In 49 real-world materials-tool-use questions comprising 138 executable subtasks, memory nearly doubles GPT-5.2 task success without model-parameter updates. In elemental-solid equation-of-state calculations, memory converts a wavefunction-initialization failure into a pre-execution guardrail, improving outcomes from 22/1/4 to 25/2/0 Correct/Partial/Error and avoiding 92% of repeated errors. In 13 practical material simulation workflows, remembered skills and failure facts halve the aggregate trace burden (tokens) and reduce tool calls by over a factor of two by the third round, while preserving physically meaningful outputs in band-gap, phonon, vacancy and work-function analyses. These results show that agent memory can serve as a durable scientific asset; a portable, self-improving record of materials-research experience that outlives any single model or agent stack.
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All authors Siyu Liu, Bo Hu, Beilin Ye, He Cao, David J. Srolovitz, Tongqi Wen

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Wave-functional formulation of dissipative CSL models

Y.M.P. Gomes

We formulate minimal and dissipative Continuous Spontaneous Localization (CSL) dynamics in the functional Schrödinger representation for a non-relativistic bosonic field. In this framework, the Fock-space state is encoded in a wave functional, and fixed particle-number wave functions are obtained by sector projection. For the minimal CSL coupling to the smeared mass density, this projection gives the standard nonlinear stochastic dynamics in each \(N\)-particle sector, with the collapse operator acting on the total smeared density of the configuration. This makes the amplification mechanism transparent and allows us to discuss sector superpositions, local probability balance, and the status of Bohmian equivariance at the wave-function level. We then consider a dissipative extension in which the collapse operator includes a smeared current contribution. The one-particle sector reproduces the expected dissipative CSL energy balance, while fixed many-body sectors contain additional collective momentum shifts and pair-mixing terms that are not reducible, in general, to independent one-particle contributions. Within a leading compact closure, the collective pair friction produces a non-extensive stationary mean kinetic energy: in three dimensions and for weak dissipation, $T_N^{\rm comp}\simeq 2T_\beta/N$, whereas the corresponding dilute energy remains extensive.
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Strongly Correlated Electrons

Hyperdeterminant wavefunctions

Guan-Lin Lin, Di Xiao and Ying Ran

We systematically introduce hyperdeterminant wavefunctions as a variational-wavefunction-based theoretical framework for strongly correlated quantum states of matter, together with practical numerical simulation algorithms. This framework generalizes previously known fermionic parton constructions, yields reliable microscopics with intuitive physical pictures, and allows direct access to the fractionalized degrees of freedom together with associated microscopic effective field theories. We demonstrate the applications of this framework to fractional Chern insulators and quantum spin liquids. We comment that the hyperdeterminant states belong to a more general class of variational wavefunctions: the fused Gaussian states.
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Materials Science

Fermi-level mediated acceleration of flash sintering of oxide ceramics

Qin-Kun Li, Evgeni S. Penev and Boris I. Yakobson

The atomistic understanding of flash sintering (FS) remains speculative, despite its efficiency and versatility in materials processing. Employing first-principles calculations we demonstrate how charge compensation of a range of defects in the prototypical Y-stabilized cubic ZrO$_2$ (YSZ) shifts Fermi level E$_F$ up during FS, thereby accelerating cation migration for fast mass transport. The charge transition of Zr vacancy, V$_{Zr}^q$, reduces its bulk diffusion barrier in V$_{Zr}^{-4}$ during flash by 2 eV, relative to V$_{Zr}^0$ before flash, which is triggered by the charge equilibrium of nonstoichiometric defects. The substituent defect Y$_{Zr}$, released by annihilating O vacancy, V$_O$, in Y$_{Zr}$V$_O$Y$_{Zr}$ defect complex, acts as electron acceptor and favors V$_{Zr}^0$ before flash whereas excess V$_O$, as electron donor thermally generated at the FS onset, upshift E$_F$ and thus support V$_{Zr}^{-4}$. The proposed mechanism of Fermi-level mediated cation diffusion for YSZ is generalized to other flash-sintered ceramics and has considerable bearing on the general theory of FS techniques in oxide ceramics.
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Soft Condensed Matter

Shear-mode Direct Piezoelectric Response of Ferroelectric Nematic Liquid Crystals

Péter Salamon, Marcell Tibor Máthé, Hiroya Nishikawa et al. (+2 more)

Piezoelectricity (linear coupling between mechanical deformation and electric signal) was originally observed only in solid crystals. Recently, it was discovered that liquid ferroelectric nematic liquid crystals are also piezoelectric. However, so far only their converse piezoelectric signals (applied voltage-induced mechanical deformation) were measured quantitatively. In this work, we have carried out periodic shear-induced electric current and oscillatory rheology measurements on the two archetypic ferroelectric nematic compounds, RM734 and DIO. From temperature, frequency and strain dependent results of the first and second harmonic current signals together with the results from oscillatory rheometry, we were able to quantitatively determine the shear-mode direct piezoelectric coupling constants. These values are similar for both materials and are compared to results of previous converse piezoelectric measurements. We propose a physical mechanism in which the flow alignment of ferroelectric polarization leads to the direct piezoelectric response.
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All authors Péter Salamon, Marcell Tibor Máthé, Hiroya Nishikawa, Fumito Araoka, Antal Jákli

Superconductivity

Bipolar Thermoelectric Superconducting Quantum Devices

F. Antola, G. Marchegiani, A. Braggio et al. (+1 more)

Quantum technologies increasingly require accurate modeling of their hardware components and of the non-equilibrium regimes in which they operate, where managing heat and energy flow becomes a central challenge. Thermoelectric effects, the direct conversion of a thermal gradient into electrical signals, offer one such route to this control. In this review, we present an overview of the bipolar thermoelectric effect, a recent development for thermoelectric conversion in reciprocal systems, where linear effects are forbidden by symmetry. This symmetry yields a bipolar thermoelectric signal, in which the generated voltage can exhibit both polarities at a fixed temperature gradient. This represents a non-trivial novelty relative to conventional thermoelectric effects, in which carrier dominance determines the sign of the thermoelectric signal. We summarize the underlying physical principles, showing how thermoelectricity emerges as a strong violation of detailed balance. Concrete physical conditions for obtaining bipolar thermoelectricity are then outlined, of which a tunnel junction between two superconductors with unequal energy gaps and suppressed Josephson coupling is the paradigmatic example. Afterward, we discuss the experimental observation of the effect to date and related proposals for different applications, including volatile memories and radiation detection. Finally, we briefly survey recent developments and outlooks, ranging from extensions to new platforms to a proposal for a novel quantum thermoelectric effect.
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All authors F. Antola, G. Marchegiani, A. Braggio, F. Giazotto

Soft Condensed Matter

Microphase Separation in Quorum-Sensing Active Particles with Competing Interactions

Michele Antonioli, Nicoletta Gnan and Claudio Maggi

Standard quorum-sensing models in active matter exhibit collective phenomena such as motility-induced phase separation. Here, we show that incorporating competing sensing ranges– a minimal ingredient inspired by microbial communication –qualitatively changes this behavior, replacing macroscopic phase separation with self-organized microphases characterized by an emergent finite length scale. Starting from the microscopic dynamics, we derive a coarse-grained field theory whose coefficients are explicitly related to the moments of the microscopic sensing function. This mapping enables a direct comparison between particle-based simulations and continuum theory, allowing the characteristic modulation and correlation lengths to be predicted directly from the microscopic interaction parameters. Two-dimensional numerical simulations confirm these predictions and reveal a transition from macrophase separation to finite-wavelength density modulations as the competition between sensing scales increases. For stronger competing interactions, the system develops a peculiar cluster phase with an interstitial percolating network, which is captured by a higher-order gradient expansion. Our results identify competing quorum-sensing interactions as a simple microscopic mechanism for generating tunable active microphases.
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Mesoscale and Nanoscale Physics

Current- and field-driven domain wall dynamics and chirality switching in a planar helimagnet

Roman Teslia and Oleksiy Kolezhuk

We study the effect of electric current and magnetic field on the dynamics of chirality in a helimagnet with a strong easy-plane anisotropy. Using a continuum theory, derived for a quasi-one-dimensional frustrated ferromagnet close to the Lifshitz point, we show that a domain wall connecting domains with opposite chiralities can be driven by the current via the dissipative (non-adiabatic) component of the spin-transfer torque. Further, it is demonstrated that the adiabatic part of the torque in the presence of a magnetic field breaks the symmetry of the effective magnetic potential energy with respect to the chirality. We show that the leading symmetry-breaking term arises in the third order in the magnetization gradient, and derive the conditions of the chirality switching. Our conclusions are supported by numerical spin-lattice simulations.
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Soft Condensed Matter

Universal Sign Reversal of Magnetic Response in Transmembrane Ionic Transport

Tina Arabi and Ehsan Noruzifar

Weak magnetic fields have long been reported to either enhance or suppress transmembrane ionic currents, yet the physical origin of these apparently contradictory responses remains unresolved. Here, we develop a mesoscopic equilibrium framework showing that weak magnetic fields primarily modify the equilibrium occupation probabilities of metastable transport states, thereby altering the resulting nonequilibrium ionic current. Rather than acting directly on microscopic ionic trajectories, magnetic fields regulate transport through the statistical redistribution of conducting states. This mechanism naturally explains both magnetic enhancement and suppression within a unified theoretical framework and predicts a universal criterion for magnetic sign reversal governed by a single equilibrium covariance. The theory further identifies experimentally testable signatures, including characteristic magnetic-field dependence and state-dependent transport modulation, providing a quantitative framework for interpreting weak-field magnetic effects in biological ionic transport.
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Statistical Mechanics

Kinetic and Hydrodynamic Theories of Chiral Intruder Dynamics in Nonequilibrium Baths

Raphaël Maire and Ignacio Pagonabarraga

We study the chiral dynamics of an intruder immersed in a nonequilibrium bath in two complementary limits: the dilute kinetic regime and the dense hydrodynamic regime. In the dilute limit, starting from a Boltzmann-Lorentz description, we derive an effective Langevin equation whose coefficients are given explicitly by geometry-dependent boundary integrals. This formulation separates the effects of intruder-shape chirality from those of chiral intruder-bath interactions. We find that the chiral interactions generate an odd response and a torque, whereas the chirality of the intruder leads to a ratchet effect. We also show that fluctuation-dissipation-like relations exist and that certain symmetry-allowed couplings vanish in the dilute regime. In the dense regime, we argue that intruder dynamics are governed primarily by bath hydrodynamics and torque-density-driven edge currents not captured by the previous framework. These currents can generate both an antisymmetric drag and a curvature-induced torque, leading to an antisymmetric response when inertia is accounted for. Taken together, these results provide a step toward understanding the mechanisms governing the chiral dynamics of an intruder in a nonequilibrium bath across different scales.
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Statistical Mechanics

Chiral Dynamics of an Intruder across Dilute and Hydrodynamic Regimes

Raphaël Maire and Ignacio Pagonabarraga

We introduce and simulate an analytically tractable model for an intruder of arbitrary shape in a nonequilibrium bath, with chirality originating from the bath, the intruder, or their coupling. In the dilute regime, a Langevin description derived from a Boltzmann-Lorentz equation shows how intruder geometry governs ratchet effects and odd response. In the dense regime, the dynamics of the intruder are instead governed by the hydrodynamic modes of the bath and edge currents, which are described by a Stokes equation including a chiral torque density. Our results link shape to chiral transport and show that odd response arises from distinct mechanisms in the dilute and dense limits.
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Materials Science

Stoichiometric cluster learning for few-shot property prediction of multi-ionic integrated energetic materials

Ming-Yu Guo, Wei-Jia Zou, Yu Shang et al. (+1 more)

Multi-ionic materials pose a distinct representational challenge in machine learning-driven materials design. Different from single-molecule or composition-based materials, their properties arise from how charged building blocks aggregate into specific assemblies. Here, we show how pretrained machine-learned interatomic potentials (MLIPs) can bypass full crystal-structure prediction and support pre-synthesis screening from stoichiometric ionic clusters using multi-ionic integrated explosives (MIXs) as a synthesis-facing example. This strategy combines a stoichiometric ionic-cluster representation, which represents each candidate material by a non-periodic, stoichiometry-preserved formula-unit cluster, with multi-task fine-tuning (MT-FT), which adapts a pretrained atomistic backbone while retaining the energy–force objective as physical regularization for the sparse detonation-velocity labels. With the pretrained backbone regularized by MT-FT, this surrogate provides a cross-validated screen across only 25 structurally curated perovskite-type energetic materials (PEMs) with experimentally derived Kamlet–Jacobs (K–J) detonation velocities. Representation probes show that the learned descriptors implicitly retain site-aware ionic organization, density information, and coarse packing compatibility, implying why non-periodic clusters can remain predictive before full crystal structures are known. The surrogate extends known PEMs chemistry to three newly synthesized ABX$_4$ materials with both unseen ABX$_4$ stoichiometry and an unseen ethylenediammonium B-site cation, yielding three-point concordance with K–J reference velocities and a mean absolute error (MAE) of 92~m$\cdot$s$^{-1}$ without retraining. Together, these results establish stoichiometry-preserved cluster learning as a synthesis-facing screening strategy for data-scarce multi-ionic materials.
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All authors Ming-Yu Guo, Wei-Jia Zou, Yu Shang, Wei-Xiong Zhang