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Physics Condensed Matter

cond-mat Watch Condensed Matter

Saturday 10 January

Statistical Mechanics · Cross-listed from math-ph

Comminution as a Non-Hermitian Quantum Field Theory: Log-Size Jump Generators, Branching Embeddings, and the Airy Solvable Sector

Juan J. Segura

Pure-breakage population balance equations (PBEs) give the standard deterministic description of fragmentation and comminution. They predict mean particle size distributions, but they do not determine fluctuations, size-size correlations, or universality under coarse-graining. We develop a field-theoretic framework anchored in the PBE kernel inputs (selection rate and daughter distribution) and compatible with the stochastic Doi-Peliti approach. From homogeneous kernels we derive an exact Markov jump generator in log-size for a mass-weighted (tagged-mass) distribution, with a jump law that is a probability density fixed by the daughter distribution. The generator is generically non-self-adjoint, admits a Lindblad embedding, and has a second-quantized extension. The deterministic PBE appears as the one-body sector, while multi-point correlators encode finite-population fluctuations. We also give a binary-fragmentation embedding whose mean-field limit reproduces the PBE but whose higher correlators capture multiplicative cascade noise. For a linear Airy-type kernel, long-wavelength coarse-graining yields an effective Airy operator as a solvable quadratic sector about a stationary profile, producing explicit mode-sum formulas for equal-time connected two-point correlations. Overall, the framework separates what is fixed by kernel data from what requires additional stochastic modeling and links comminution kernels to universality classes.
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Superconductivity

Magnetic exchange coupled nonreciprocal devices for cryogenic memory

Josep Ingla-Aynés, Lina Johnsen Kamra, Franklin Dai et al. (+5 more)

As computing power demands continue to grow, superconducting electronics present an opportunity to reduce power consumption by increasing the energy efficiency of digital logic and memory. A key milestone for scaling this technology is the development of efficient superconducting memories. Such devices should be nonvolatile, scalable to high integration density and memory capacity, enable fast and low-power reading and writing operations, and be compatible with the digital logic. We present a versatile device platform to develop such nonvolatile memory devices consisting of an exchange-coupled ultra-thin superconductor encapsulated between two ferromagnetic insulators (FIs). The superconducting exchange coupling, which is tuneable by the relative alignment between the FI magnetizations, enables the switching of superconductivity on and off. We exploit this mechanism to create a superconducting nonvolatile memory where single-cell writing is realized using heat-assisted magnetic recording, and explain how it can become a contender for state-of-the-art superconducting memories. Furthermore, below their critical temperatures, the memory elements show a marked nonreciprocity, with zero magnetic field superconducting diode efficiencies exceeding $\pm$60%, showing the versatility of the proposed devices for superconducting computing.
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All authors Josep Ingla-Aynés, Lina Johnsen Kamra, Franklin Dai, Yasen Hou, Shouzhuo Yang, Peng Chen, Oleg A. Mukhanov, Jagadeesh S. Moodera

Soft Condensed Matter

Snapping and Switching of Elastic Arches with Patterned Preferred Curvature

Michał Zmyślony, Ammar Khan and John S. Biggins

An elastic arch is an archetypal bistable system. Here, we combine elastica theory and photo-mechanical experiments to elucidate the mechanics of an active arch with a spatio-temporally varying preferred curvature $\overline \kappa(s)$. Our shallow-arch theory completely describes any such system via the decomposition of its $\overline \kappa(s)$ into Euler-buckling modes. Intuitively, if $\overline \kappa(s)$ overlaps with the fundamental mode, it snaps the arch up/down. Conversely, non-overlapping $\overline \kappa(s)$ drives a second-order transition to a higher-order shape. Furthermore, the form of $\overline \kappa(s)$ enables control over the instability's character; we find the forms for snapping with maximum energy release and at the lowest stimulation (both binary patterns) and design forms for symmetric and asymmetric switching pathways. Analogous control can also be achieved in boundary-driven instabilities of passive arches by fabricating them with suitable $\overline \kappa(s)$. We thus anticipate our results will improve switchable/snapping elements in MEMS, robotics, and mechanical meta-materials.
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Materials Science

Influence of Surface Functionalization on the Colloidal Stability and Magnetic Properties of Ferrite Nanoparticles

Arif Iqbal Sheikh and Radha Srinivasan

Magnetite ferrite (Fe3O4) nanoparticles have attracted considerable interest due to their tunable physico-chemical properties and relevance in functional materials. In this work, uncoated Fe3O4 nanoparticles and surface-modified Fe3O4 nanoparticles coated with polyethylene glycol (PEG-6000) and citric acid (CA) were synthesized via a chemical co-precipitation method. The effect of surface functionalization on the structural, spectroscopic, magnetic, and colloidal properties of the nanoparticles was systematically investigated. X-ray diffraction analysis confirmed the formation of phase-pure Fe3O4 with an inverse spinel structure for all the samples. Fourier transform infrared and Raman spectroscopy verified successful surface modification while preserving the Fe-O framework of the magnetite core. Dynamic light scattering and zeta potential measurements indicated improved dispersion and colloidal stability for the surface-modified nanoparticles. Magnetization studies performed at room temperature revealed superparamagnetic behaviour for all samples, accompanied by a coating-dependent reduction in saturation magnetization. Overall, the results emphasize the critical role of surface chemistry in tailoring the physicochemical, magnetic, and colloidal behaviour of Fe3O4 nanoparticles. Keywords: Fe3O4 nanoparticles, PEG, Citric acid, Co-precipitation, Surface functionalization, Zeta potential, Colloidal stability, Magnetic properties
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Materials Science

A Rechargeable Chromium Battery

Apurva Anjan, Adwitiya Rao, Rohit M. Manoj et al. (+6 more)

Multivalent ions exchange multiple electrons during redox reactions, leading to the possibility of improved energy storage performance. A variety of multivalent ions, including zinc (Zn$^{2+}$), magnesium (Mg$^{2+}$), calcium (Ca$^{2+}$), aluminum (Al$^{3+}$), and indium (In$^{3+}$), have been deployed in rechargeable batteries with varying degrees of success \cite{1-9}. While chromium (Cr$^{3+}$) offers a superior volumetric capacity (approximately $11117\ \mathrm{mAh\ cm^{-3}}$) compared to the aforementioned cations, there is no report of a rechargeable chromium battery. This is because chromium metal spontaneously oxidizes to form a passivating oxide layer \cite{10} that blocks Cr$^{3+}$ ingress and egress. Here, we show that this fundamental limitation can be overcome by developing a chromium-rich high-entropy alloy. The alloy consists of five elements (Cr, bismuth (Bi), copper (Cu), tin (Sn), and nickel (Ni)), producing a multi-element native oxide rich in heterointerfaces. Some of these interfaces (such as Cr$_2$O$_3$/Bi$_2$O$_3$) exhibit a very low barrier for Cr$^{3+}$ diffusion, offering multiple pathways for efficient Cr$^{3+}$ insertion and extraction, while others (such as Cr$_2$O$_3$/CuO) block oxygen transport, thereby suppressing further oxidation. In a symmetric cell configuration, the chromium alloy supports approximately $10000$ hours (about $5000$ cycles) of reversible chromium insertion and extraction at an overpotential of only $20$ mV. The chromium-rich alloy anode was also successfully paired with a sulfur cathode to cycle reversibly in a full-cell configuration. These findings could stimulate fundamental studies on chromium-ion batteries and high-entropy alloy electrodes, opening new pathways for multivalent energy storage.
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All authors Apurva Anjan, Adwitiya Rao, Rohit M. Manoj, Vrindha Pongalat, Varad Mahajani, Sohail Shah, Mukesh Bacchav, Chandra Veer Singh, Nikhil Koratkar

Materials Science

Beyond Predicted ZT: Machine Learning Strategies for the Experimental Discovery of Thermoelectric Materials

Shoeb Athar and Philippe Jund

The discovery of high-performance thermoelectric (TE) materials for advancing green energy harvesting from waste heat is an urgent need in the context of looming energy crisis and climate change. The rapid advancement of machine learning (ML) has accelerated the design of thermoelectric (TE) materials, yet a persistent "gap" remains between high-accuracy computational predictions and their successful experimental validation. While ML models frequently report impressive test scores (R^2 values of 0.90-0.98) for complex TE properties (zT, power factor, and electrical/thermal conductivity), only a handful of these predictions have culminated in the experimental discovery of new high-zT materials. In this review, we identify and discuss that the primary obstacles are poor model generalizability-stemming from the "small-data" problem, sampling biases in cross-validation, and inadequate structural representation-alongside the critical challenge of thermodynamic phase stability. Moreover, we argue that standard randomized validation often overestimates model performance by ignoring "hidden hierarchies" and clustering within chemical families. Finally, to bridge this gap between ML-predictions and experimental realization, we advocate for advanced validation strategies like PCA-based sampling and a synergetic active learning loop that integrates ML "fast filters" for stability (e.g., GNoME) with high-throughput combinatorial thin-film synthesis to rapidly map stable, high-zT compositional spaces.
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Strongly Correlated Electrons

Gapped topological spin-orbital liquid on the honeycomb lattice

Masahiko G. Yamada

We perform large-scale density matrix renormalization group simulations of the $\mathrm{SU}(4)$ Heisenberg model on the honeycomb lattice to address the long-standing question of its ground state in an unbiased and quantitatively controlled manner. We find reliable numerical evidence that the ground state is a gapped spin-orbital liquid, presumably with a $Z_4$ topological order, characterized by a finite topological entanglement entropy close to $\ln(4)$, the absence of both $\mathrm{SU}(4)$ and lattice symmetry breaking, and a variationally optimized ground-state energy well below the previously proposed $\pi$-flux variational state. By exploiting full $\mathrm{SU}(4)$ symmetry and keeping up to 12,800 $\mathrm{SU}(4)$ multiplets, corresponding to more than one million $\mathrm{U}(1)$ states, we achieve unprecedented accuracy for two-dimensional $\mathrm{SU}(4)$ quantum magnets. Finite-size scaling of energies and entanglement entropies supports a robust gapped phase in the two-dimensional limit, while a gapless critical state on narrow cylinders is identified as a proximate remnant of a Dirac spin-orbital liquid. Our results find the $\mathrm{SU}(4)$ honeycomb Heisenberg model a realization of a gapped topological spin-orbital liquid and provide convincing numerical evidence for topological order in a highly symmetric two-dimensional quantum magnet.
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Materials Science

On unconstrained solidification of spherical metallic drops

Priti Ranjan Panda, Harish Singh Dhami and Koushik Viswanathan

The solidification of metallic droplets into powder particles involves a complex interplay between heat diffusion, surface tension, and geometric constraints. In confined, curved systems – such as those encountered in atomisation, abrasion, and micrometeorite formation – positive curvature and finite boundaries significantly modify classical solidification dynamics. In this study, we systematically investigate the solidification of metallic spheres, focusing on how curvature and confinement influence nucleation pathways, growth kinetics, and interfacial stability. Two competing growth modes – radial outward and circumferential – are analysed using Stefan-type models under a quasi-steady approximation. A generalisation of Mullins–Sekerka stability theory is developed to account for finite spherical domains, revealing that particle size and curvature introduce new destabilising parameters that govern microstructural length scales. Experimental observations of dendritic and cellular morphologies are interpreted through this framework, demonstrating that the interaction between growth fronts, undercooling, and curvature collectively determines the final particle structure. These findings underscore the need to re-evaluate classical solidification theories in the context of curved geometries, with implications for both engineered and naturally occurring metal powders.
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Strongly Correlated Electrons

Altermagnetism in exactly solvable model: the Ising-Kondo lattice model

Miaomiao Zhao, Wei-Wei Yang and Yin Zhong

Altermagnet (AM), a recently identified class of collinear magnet, has garnered significant attention due to its unique combination of zero net magnetization and spin-split energy bands, leading to a variety of novel physical phenomena. Using numerically exact lattice Monte Carlo simulations, we investigate AM-like phases within the Ising-Kondo lattice model which is commonly employed to describe heavy-fermion materials. By incorporating an alternating next-nearest-neighbor hopping (NNNH) term, which arises from the influence of non-magnetic atoms in altermagnetic candidate materials, our results reveal key signatures of AM-like states, including spin-splitting quasiparticle bands and spectral functions, and demonstrate that d-wave AM remains stable across a broad range of interaction strengths, doping levels, NNNH amplitudes and temperatures, highlighting its robustness. Furthermore, through an analysis of non-magnetic impurity effects, we further confirm the d-wave symmetry of the AM phase. These findings establish a solid theoretical foundation for exploring AM-like phases in f-electron compounds, paving the way for future investigations into their exotic magnetic and electronic properties.
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Materials Science

Effect of substrate mismatch, orientation, and flexibility on heterogeneous ice nucleation

Miguel Camarillo, Javier Oller-Iscar, María M. Conde et al. (+2 more)

Heterogeneous nucleation is the main path to ice formation on Earth. The ice nucleating ability of a certain substrate is mainly determined by both molecular interactions and the structural mismatch between the ice and the substrate lattices. We focus on the latter factor using molecular simulations of the mW model. Quantifying the effect of structural mismatch alone is challenging due to its coupling with molecular interactions. To disentangle both factors, we use a substrate composed of water molecules in such a way that any variation on the nucleation temperature can be exclusively ascribed to the structural mismatch. We find that a one per cent increase of structural mismatch leads to a decrease of approximately 4 K in the nucleation temperature. We also analyse the effect of the orientation of the substrate with respect to the liquid. The three main ice orientations (basal, primary prism and secondary prism) have a similar ice nucleating ability. We finally asses the effect of lattice flexibility by comparing substrates where molecules are immobile with others where a certain freedom to fluctuate around the lattice positions is allowed. Interestingly, we find that the latter type of substrate is more efficient in nucleating ice because it can adapt its structure to that of ice.
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All authors Miguel Camarillo, Javier Oller-Iscar, María M. Conde, Jorge Ramírez, Eduardo Sanz

Materials Science

ZnO/ZnS heterostructures as hole reservoir to boost Ni foam energy storage performance

Alessia Fischetti, Giacometta Mineo, Daniela Russo et al. (+8 more)

Low-cost and environmentally friendly electrochemical energy storage systems are crucial to address the increasing global energy demand. Nanomaterials can play a pivotal role in catalysing charge storage and/or exchange, still the underlying mechanism often remains poorly investigated, as for ZnO/ZnS nanostructures onto Ni foam. In this work, we investigate hydrothermally grown ZnO/ZnS nanostructures decorating Ni foam for energy storage application. Morphology, structure and composition are evaluated via electron microscopy-based methodologies. The electrochemical energy storage performance is evaluated by cyclic voltammetry (CV) measurements with the aim to highlight the energy storage mechanism. When nickel foam (NF) is used as substrate, the system shows a predominant pseudocapacitive behaviour. By contrast, a modest and capacitive performance is measured on graphene paper (GP). Mott-Schottky (M-S) and open circuit potential (OCP) measurements suggests a key role of hole reservoir in ZnS decoration which boosts NF performances.
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All authors Alessia Fischetti, Giacometta Mineo, Daniela Russo, Francesco Salutari, Claudio Lentini Campallegio, Elena Bruno, Jordi Arbiol, Giorgia Franzò, Salvatore Mirabella, Vincenzina Strano, M. Chiara Spadaro

Superconductivity

Superconductivity in epitaxial PtSb(0001) thin films

C. Müller, S. P. Bommanaboyena, A. Badura et al. (+12 more)

We report superconductivity in epitaxial PtSb(0001) thin films grown on SrF2(111). Electrical transport measurements reveal a superconducting transition at $T_{\mathrm c}=1.72$ K. The field-induced broadening of the transition and the presence of finite upper critical fields are consistent with type-II superconductivity. We determine the resistively defined upper critical fields for magnetic fields applied perpendicular and parallel to the film plane and parameterize their temperature dependence using an anisotropic Ginzburg-Landau approach. For the thickest film ($d=50$ nm), this yields coherence lengths of $\xi_{ab}\approx 55$ nm and $\xi_c\approx 14$ nm. Current-voltage characteristics show sizeable critical currents, with a critical current density reaching $J_{\mathrm c}\approx 6e4$ A/cm$^2$ at 0.5 K. These results establish epitaxial PtSb as a superconducting thin-film platform compatible with lattice-matched heterostructures in the NiAs-type materials family.
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All authors C. Müller, S. P. Bommanaboyena, A. Badura, T. Uchimura, F. Husstedt, B. V. Schwarze, S. Banerjee, M. Ledinský, J. Michalicka, M. Míšek, M. Šindler, T. Helm, S. Fukami, F. Krizek, D. Kriegner

Quantum Gases

Emission of time-ordered photon pairs from a coherently-driven Kerr microcavity

Ferdinand Claude, Yueguang Zhou, Sylvain Ravets et al. (+8 more)

Weakly-interacting many-body systems possess remarkable quantum properties that are essential components of quantum technologies, and constitute a topic of fundamental interest. Here we show that in a solid-state nonlinear microcavity embedding discrete modes of exciton-dressed photons, we can isolate a single eigenmode of quantum fluctuations from the much brighter coherent fraction of the field. In this regime, we perform frequency- and time-resolved correlations measurements between photons on the red and blue side of the fluctuations spectrum. When the average number of fluctuation quanta is smaller than one, we observe the formation of large pairwise time-ordered correlations: red photon first and blue photon second. We show that this peculiar time-ordering correlation emerges spontaneously from the interplay between frequency-resolved detection, and the non-trivial internal quantum structure of the elementary fluctuations.
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All authors Ferdinand Claude, Yueguang Zhou, Sylvain Ravets, Jacqueline Bloch, Martina Morassi, Aristide Lemaître, Alberto Bramati, Anna Minguzzi, Iacopo Carusotto, Irénée Frérot, Maxime Richard

Materials Science · Cross-listed from cs.LG

Physics-Informed Tree Search for High-Dimensional Computational Design

Suvo Banik, Troy D. Loeffler, Henry Chan et al. (+4 more)

High-dimensional design spaces underpin a wide range of physics-based modeling and computational design tasks in science and engineering. These problems are commonly formulated as constrained black-box searches over rugged objective landscapes, where function evaluations are expensive, and gradients are unavailable or unreliable. Conventional global search engines and optimizers struggle in such settings due to the exponential scaling of design spaces, the presence of multiple local basins, and the absence of physical guidance in sampling. We present a physics-informed Monte Carlo Tree Search (MCTS) framework that extends policy-driven tree-based reinforcement concepts to continuous, high-dimensional scientific optimization. Our method integrates population-level decision trees with surrogate-guided directional sampling, reward shaping, and hierarchical switching between global exploration and local exploitation. These ingredients allow efficient traversal of non-convex, multimodal landscapes where physically meaningful optima are sparse. We benchmark our approach against standard global optimization baselines on a suite of canonical test functions, demonstrating superior or comparable performance in terms of convergence, robustness, and generalization. Beyond synthetic tests, we demonstrate physics-consistent applicability to (i) crystal structure optimization from clusters to bulk, (ii) fitting of classical interatomic potentials, and (iii) constrained engineering design problems. Across all cases, the method converges with high fidelity and evaluation efficiency while preserving physical constraints. Overall, our work establishes physics-informed tree search as a scalable and interpretable paradigm for computational design and high-dimensional scientific optimization, bridging discrete decision-making frameworks with continuous search in scientific design workflows.
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All authors Suvo Banik, Troy D. Loeffler, Henry Chan, Sukriti Manna, Orcun Yildiz, Tom Peterka, Subramanian Sankaranarayanan

Strongly Correlated Electrons

Emergence of Kugel-Khomskii physics in quarter-filled bilayer correlated systems

Guijing Duan, Yunlong Wang, Zhiguang Liao et al. (+2 more)

We present a theoretical study of the low-energy physics of a quarter-hole-filled two-orbital bilayer Hubbard model motivated by transition-metal bilayer systems with strong orbital-selective interlayer hybridization. By explicitly treating the strong interlayer bonding of dz2 orbitals within a molecular orbital basis and projecting out high-energy electronic states, we derive a low-energy effective Kugel-Khomskii Hamiltonian describing the interplay between electron spin and emergent layer pseudospin degrees of freedom. We map out a rich ground state phase diagram featuring diverse spin and charge ordered states. These include conventional ferromagnetic and antiferromagnetic phases with layer staggered charge densities, a layer-coherent phase characterized by spontaneous interlayer quantum coherence, and a novel maximally spin-layer-entangled phase with a hidden composite spin-layer order. We show that this exotic hidden ordered phase arises from the spontaneous breaking of an emergent O(4) symmetry down to a O(3), manifesting a unique excitation spectrum with three entangled gapless Goldstone modes. Our results uncover a geometrically driven mechanism for realizing composite entanglement in strongly correlated bilayer systems and provide a concrete theoretical framework relevant to bilayer nickelate superconductors and other multi-component correlated materials.
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All authors Guijing Duan, Yunlong Wang, Zhiguang Liao, Changle Liu, Rong Yu

Materials Science

Weakly spin-dependent band structures of antiferromagnetic perovskite LaMO$_3$ (M = Cr, Mn, Fe)

Takuya Okugawa, Kaoru Ohno, Yusuke Noda et al. (+1 more)

We investigate spin-dependent electronic states of antiferromagnetic (AFM) lanthanum chromite (LaCrO$_3$), lanthanum manganite (LaMnO$_3$), and lanthanum ferrite (LaFeO$_3$) using spin-polarized first-principles density functional theory (DFT) with Hubbard U correction. The band structures are calculated for 15 types of their different AFM structures. It is verified for these structures that there is a very simple rule to identify which wave number k exhibits spin splitting or degeneracy in the band structure. This rule uses the symmetry operations that map the up-spin atoms onto the down-spin atoms. The resulting spin splitting is very small for the most stable spin configuration of the most stable experimental structure. We discuss a plausible benefit of this characteristic, i.e., the direction-independence of the spin current, in electrode applications.
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All authors Takuya Okugawa, Kaoru Ohno, Yusuke Noda, Shinichiro Nakamura

Materials Science

Reaction-Diffusion Driven Patterns in Immiscible Alloy Thin Films

Vivek C. Peddiraju, Shourya Dutta-Gupta and Subhradeep Chatterjee

Controlling the microstructure of thin films is of critical importance for various applications. We demonstrate a methodology for tuning the local microstructure through film-substrate interactions using Ag-Cu as a model system. Metastable single-phase Ag-Cu thin films are deposited on Si substrates pre-patterned by FIB milling. During post-deposition annealing, localized film-substrate reaction around the milled patterns produces a distinct microstructure termed as the 'halo'. It consists of copper silicide and almost pure Ag, while the far-field film forms a random mixture of Cu and Ag-rich domains through phase separation. We show that the extent of the halo can be controlled by varying the temperature and duration of annealing. We present a semi-analytical kinetic model of product and halo growth that incorporates species balance, diffusional transport and a modified Stefan condition. Predictions from the model reveal two distinct growth regimes of the product with power law indices of 1/2 and 2/7 and experimental data fall into the latter regime. These regimes originate from the dimensionality of growth (2d or 3d) compared to that of solute transport (2d), which in turn depend on film thickness and species diffusivity. Using an inverse optimization procedure, we also estimate the diffusivity, which suggests grain boundary diffusion to be the dominant transport mechanism. This study provides an avenue and framework for microstructural engineering of alloy thin films through interfacial reaction.
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Materials Science

Mechanisms of alkali ionic transport in amorphous oxyhalides solid state conductors

Luca Binci, KyuJung Jun, Bowen Deng et al. (+1 more)

Amorphous oxyhalides have attracted significant attention due to their relatively high ionic conductivity ($>$1 mS cm$^{-1}$), excellent chemical stability, mechanical softness, and facile synthesis routes via standard solid-state reactions. These materials exhibit an ionic conductivity that is almost independent of the underlying chemistry, in stark contrast to what occurs in crystalline conductors. In this work, we employ an accurately fine-tuned machine learning interatomic potential to construct large-scale molecular dynamics trajectories encompassing hundreds of nanoseconds to obtain statistically converged transport properties. We find that the amorphous state consists of chain fragments of metal-anion tetrahedra of various lenght. By analyzing the residence time of alkali cations migrating around tetrahedrally-coordinated trivalent metal ions, we find that oxygen anions on the metal-anion tetrahedra limit alkali diffusion. By computing the full Einstein expression of the ionic conductivity, we demonstrate that the alkali transference number of these materials is strongly influenced by distinct-particles correlations, while at the same time they are characterized by an alkali Haven ratio close to one, implying that ionic transport is largely dictated by uncorrelated self-diffusion. Finally, by extending this analysis to chemical compositions $AMX_{2.5}\textsf{O}_{0.75}$, spanning different alkaline ($A$ = Li, Na, K), metallic ($M$ = Al, Ga, In), and halogen ($X$ = Cl, Br, I) species, we clarify why the diffusion properties of these materials remain largely insensitive to variations in atomic chemistry.
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All authors Luca Binci, KyuJung Jun, Bowen Deng, Gerbrand Ceder

Materials Science

Dynamic nanoscale spatial heterogeneity in a perovskite to brownmillerite topotactic phase transformation

Nicolò D'Anna, Erik S. Lamb, Robin Glefke et al. (+5 more)

Phase transitions are omnipresent in modern condensed matter physics and its applications. In solids, first-order phase transformations typically occur by nucleation and growth under non-equilibrium conditions. Under constant external conditions, $\textit{e.g.}$, constant annealing temperature and pressure, the nucleation and growth dynamics are often thought of as spatially and temporally independent. Here, $\textit{in-situ}$ Bragg X-ray photon correlation spectroscopy (XPCS) reveals nanoscale spatial and dynamical heterogeneity in the perovskite-to-brownmillerite topotactic phase transformation in La$_{0.7}$Sr$_{0.3}$CoO$_3$ thin films annealed under constant reducing conditions over a time span of multiple hours. Specifically, a timescale associated with domain growth remains stable, with a corresponding domain wall speed of $v_d = 6 \pm 0.5 \times10^{-4}$~nm/s ($2 \pm 0.2$~nm/h), while a slower timescale, associated with temperature-driven de-pinning of domains, leads to accelerating dynamics with timescales following an aging power law with exponent -2.2$\pm$0.5. This experiment demonstrates that Bragg XPCS is a powerful tool to study nanoscale dynamics in structural phase transformations, with the ability to extract quantitative average values related to nano-domain motion $\textit{in-situ}$. The results are relevant for phase engineering of phase-change devices, as they show that nanoscale dynamics, linked to domain and domain-wall motion, can continuously evolve and speed up with time, even hours after the initiation of the phase transformation, with potential repercussions on electrical performance.
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All authors Nicolò D'Anna, Erik S. Lamb, Robin Glefke, Daseul Ham, Ishmam Nihal, Su Yong Lee, Yayoi Takamura, Oleg Shpyrko

Friday 9 January

Quantum Gases · Cross-listed from physics.atom-ph

Controlling Rydberg atom-polariton interactions: from exceptional points to fast readout

Tamara Šumarac, Emily H. Qiu, Shai Tsesses et al. (+8 more)

Rydberg atoms represent a platform underpinning many recent developments in quantum computation, simulation, sensing, and metrology. They further facilitate optical nonlinearity at the single-photon level when coupled to photons propagating in atomic clouds, which form collective atomic excitations called Rydberg polaritons, strongly interacting with each other. Here, we experimentally explore interactions between a Rydberg polariton in an atomic ensemble and a single, adjacent, Rydberg atom. We discover three different regimes of quantum dynamics corresponding to polariton blockade, coherent exchange, and probabilistic hopping, which are defined by their distinct transmission characteristics, with a transition through an exceptional point occurring between blockade and coherent exchange. We investigate the applications of such interactions for fast, non-destructive detection of Rydberg atoms and present proof-of-principle demonstrations for their potential application in nonlinear photonic networks.
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All authors Tamara Šumarac, Emily H. Qiu, Shai Tsesses, Peiran Niu, Adrian J. Menssen, Wenchao Xu, Valentin Walther, Uroš Delić, Soonwon Choi, Mikhail D. Lukin, Vladan Vuletić

Soft Condensed Matter

Local structure characterization in particle systems

Rachael S. Skye and Erin G. Teich

Many tools and techniques measure local structure in materials in contexts ranging from biology to geology. We provide a survey of those tools and metrics that are especially useful for analyzing particulate soft matter. The metrics we discuss can all be computed from the positions of particles, and are thus most useful when there is access to this information, either from simulation or experimental imaging. For each metric, we provide derivations, intuition regarding its implications, example uses, and references to software packages that compute the metric. Our survey encompasses characterization techniques ranging from the simplest to the most complex, and will be useful for students getting started in the structural characterization of particle systems.
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Superconductivity

Coexistence of superconductivity and charge density wave in a correlated regime

E. J. Calegari, L. C. Prauchner, A. C. Lausmann et al. (+1 more)

To investigate the coexistence of superconductivity and charge density wave (CDW) in a correlated regime, we employ the Green's functions formalism, as well as the Hubbard-I approximation, as a way to introduce the correlations into the problem, in the form of a repulsive Coulomb interaction $U$. In addition, we investigate the effects of second-nearest neighbor hopping $t_1$ on a pure CDW state. The analysis of the results show that, for small values of $t_1$, both CDW and superconducting gaps compete for the same region on the Fermi surface. The increase of $t_1$ decreases the competition and may lead the system to a coexistence regime. Effects of temperature in the coexistence regime, are also investigated.
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All authors E. J. Calegari, L. C. Prauchner, A. C. Lausmann, S. G. Magalhaes

Strongly Correlated Electrons · Cross-listed from quant-ph

Quantum algorithm for dephasing of coupled systems: decoupling and IQP duality

Sabrina Yue Wang and Raul A. Santos

Noise and decoherence are ubiquitous in the dynamics of quantum systems coupled to an external environment. In the regime where environmental correlations decay rapidly, the evolution of a subsytem is well described by a Lindblad quantum master equation. In this work, we introduce a quantum algorithm for simulating unital Lindbladian dynamics by sampling unitary quantum channels without extra ancillas. Using ancillary qubits we show that this algorithm allows approximating general Lindbladians as well. For interacting dephasing Lindbladians coupling two subsystems, we develop a decoupling scheme that reduces the circuit complexity of the simulation. This is achieved by sampling from a time-correlated probability distribution - determined by the evolution of one subsystem, which specifies the stochastic circuit implemented on the complementary subsystem. We demonstrate our approach by studying a model of bosons coupled to fermions via dephasing, which naturally arises from anharmonic effects in an electron-phonon system coupled to a bath. Our method enables tracing out the bosonic degrees of freedom, reducing part of the dynamics to sampling an IQP circuit. The sampled bitstrings then define a corresponding fermionic problem, which in the non-interacting case can be solved efficiently classically. We comment on the computational complexity of this class of dissipative problems, using the known fact that sampling from IQP circuits is believed to be difficult classically.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Building blocks of topological band theory for photonic crystals

Yoonseok Hwang, Vaibhav Gupta, Antonio Morales-Pérez et al. (+6 more)

We derive a framework for classifying topological bands in three-dimensional photonic band structures, where the zero frequency polarization singularity implied by Maxwell's equations complicates the direct application of existing symmetry-based approaches. Building on recent advances in the regularization of photonic bands, we use the recently introduced concept of stable real-space invariants (SRSIs) to show how photonic band structures can be unambiguously characterized in terms of equivalence classes of band representations. We classify topologically trivial photonic bands using SRSIs, treating them as the fundamental building blocks of 3D photonic band structures. This means that if certain bands cannot be constructed from these building blocks, they are necessarily topological. Furthermore, we distinguish between photonic and electronic band structures by analyzing which SRSI values are allowed in systems with and without polarization singularity. We also explore the impact of the polarization singularity on the behavior of Wilson loops, providing new insights into the topological classification of 3D photonic systems.
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All authors Yoonseok Hwang, Vaibhav Gupta, Antonio Morales-Pérez, Chiara Devescovi, Mikel García-Díez, Juan L. Mañes, Maia G. Vergniory, Aitzol García-Etxarri, Barry Bradlyn

Statistical Mechanics

Confinement-controlled chase-escape dynamics

R. G. Rossatto, H. Ariel Alvarez, C. Manuel Carlevaro et al. (+1 more)

We investigate a minimal chase-and-escape model on a two-dimensional square lattice with randomly distributed static obstacles, focusing on how geometric disorder controls collective pursuit dynamics. Chasers and escapers move according to short-range sensing rules, while the density of obstacles tunes the connectivity of the accessible space. Using a combination of geometric analysis, dynamical observables, survival statistics, and transport characterization, we establish a direct link between lattice connectivity and pursuit efficiency. A Breadth-First Search analysis reveals that obstacle-induced fragmentation leads to a progressive loss of accessibility before the percolation threshold, defining the effective initial conditions for the dynamics. The trapping time and capture cost exhibit a non-monotonic dependence on obstacle density, reflecting a competition between path elongation in connected environments and geometric confinement near the percolation threshold. Survival analysis shows that the decay of the escaper population follows a Weibull form, with characteristic time and shape parameters displaying clear crossovers as a function of obstacle density, signaling the coexistence of cooperative capture and confinement-dominated trapping. Transport properties, quantified through the mean-squared displacement exponent, further support this picture, revealing sub-diffusive dynamics and a convergence toward a geometry-controlled regime near percolation. Overall, our results demonstrate that chase–and–escape dynamics in disordered environments are governed by a geometry-driven crossover, where percolation and connectivity act as unifying control parameters for spatial, temporal, and collective behavior.
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All authors R. G. Rossatto, H. Ariel Alvarez, C. Manuel Carlevaro, José Rafael Bordin

Mesoscale and Nanoscale Physics

Spin Hall effect in van der Waals ferromagnet Fe$_{5}$GeTe$_{2}$

Tomoharu Ohta, Yuto Samukawa, Nan Jiang et al. (+5 more)

We investigate the spin Hall effect (SHE) in a van der Waals (vdW) ferromagnet Fe$_{5}$GeTe$_{2}$ (FGT) with a Curie temperature $T_{\rm C}$ of 310 K utilizing the spin-torque ferromagnetic resonance method. In synchronization with the emergence of the ferromagnetic phase resulting in the anomalous Hall effect (AHE), a noticeable enhancement in the SHE was observed below $T_{\rm C}$. On the other hand, the SHE shows a different temperature dependence from the AHE: the effective spin Hall conductivity is clearly enhanced with decreasing temperature unlike the anomalous Hall conductivity, reflecting the variation of band-structure accompanied by the complicated magnetic ordering of the FGT. The results provide a deep understanding of the SHE in magnetic materials to open a new route for novel functionalities in vdW materials-based spintronic devices.
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All authors Tomoharu Ohta, Yuto Samukawa, Nan Jiang, Yasuhiro Niimi, Kohei Yamagami, Yoshinori Okada, Yoshichika Otani, Kouta Kondou

Materials Science

Sizes of Ferroelectricity Appearance and Disappearence in Nanosized Hafnia-Zirconia:Landau-type Theory

Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin et al. (+1 more)

Nanosized hafnia-zirconia HfxZr1-xO2 in the form of thin films, multilayers and heterostructures are indispensable silicon-compatible ferroelectric materials for advanced electronic memories and logic devices. The distinctive feature of nanoscale hafnia-zirconia are the critical sizes of ferroelectricity appearance, whereas the critical sizes of ferroelectricity disappearance exist in other ferroelectrics. Using the Landau-Ginzburg-Devonshire free energy functional with higher powers, trilinear and biquadratic couplings of polar, nonpolar and antipolar order parameters, we calculated analytically the strain-dependent critical sizes of the ferroelectricity appearance and disappearance, analyzed how the size effect and mismatch strains influence the phase diagrams and polarization switching barrier in epitaxial HfO2 thin films and nano-islands with the out-of-plane spontaneous polarization. We have shown that the critical thickness/height of out-of-plane spontaneous polarization disappearance is determined by the size dependence of the depolarization field and correlation effects. The critical thickness/height of the ferroelectricity appearance is determined by the size dependence of the effective mismatch strain considering possible appearance of misfit dislocations and lateral relaxion of strains. Derived analytical expressions can be generalized for HfxZr1-xO2 solid solutions, providing that corresponding parameters of the free energy are known from the first principles calculations.
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All authors Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin, Maksym V. Strikha

Materials Science

An assessment of mechanism-based plasticity models for polycrystalline magnesium alloys

R. Vigneshwaran, Showren Datta, A. A. Benzerga et al. (+1 more)

The objective of this work is to assess computationally efficient coarse-grained plasticity models against high-fidelity crystal plasticity simulations for magnesium polycrystals over a wide range of textures and grain sizes. A basic requirement is that such models are able to capture evolving plastic anisotropy and tension-compression asymmetry. To this end, two-surface and three-surface plasticity models are considered. The two-surface constitutive formulation separately accounts for slip and twinning, while the three-surface model further apportions the contributions of basal and nonbasal slip. Model identification is based on stress-strain responses for loading along six orientations under both tension and compression. The evolution of overall plastic anisotropy, as well as microscale relative activities of slip and twin systems, is analyzed in detail. The prospects of using coarse-grained plasticity models in guiding the development of physically sound damage models for magnesium alloys are discussed.
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All authors R. Vigneshwaran, Showren Datta, A. A. Benzerga, Shailendra P. Joshi

Quantum Gases · Cross-listed from quant-ph

Universal Predictors for Mixing Time more than Liouvillian Gap

Yi-Neng Zhou

We analyze the mixing time of open quantum systems governed by the Lindblad master equation, showing that it is determined not only by the Liouvillian gap, but also by the trace-norm factor of each decaying Liouvillian eigenmode. By utilizing them as universal predictors of mixing time, we establish general conditions for the fast and rapid mixing, respectively. Specifically, we derive rapid mixing conditions for both the strong and weak dissipation regimes, formulated as sparsity constraints on the Hamiltonian and the local Lindblad operators. Our findings provide a general framework for calculating mixing time and offer a guide for designing dissipation to achieve desired mixing speeds, which has significant implications for efficient experimental state preparation.
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Mesoscale and Nanoscale Physics

Topological phonons in anomalous Hall crystals

Mark R. Hirsbrunner, Félix Desrochers, Joe Huxford et al. (+1 more)

Recent experiments on few-layer graphene structures have reported indirect signatures of anomalous Hall crystals (AHCs), but the need for a top gate to stabilize the phase precludes direct imaging of the emergent electronic lattice. This situation necessitates the investigation of alternative signatures of AHCs. The gapless phonons of the emergent electronic lattice provide a clear distinction from conventional quantum Hall states, but it may be difficult to disentangle these phonons from the plethora of other possible low-lying modes. Intriguingly, the quantum geometry of the underlying electronic ground state can imprint on the collective modes, possibly leading the phonons themselves to be topological. Were this the case, the resulting neutral chiral edge modes would provide a further signature of an AHC. Using time-dependent Hartree-Fock, we compute the spectra of collective modes of Wigner crystals (WCs) and AHCs arising in minimal models and study the topology of the phonons and low-lying excitons. Across the WC to AHC transition, we observe a series of band inversions among collective modes, producing topological phonons and excitons, and a sharp sign change in the phonon Chern number upon entering the AHC phase. We conclude by discussing the relevance of collective mode topology to experiments on candidate systems for AHCs.
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All authors Mark R. Hirsbrunner, Félix Desrochers, Joe Huxford, Yong Baek Kim