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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 3 March

Materials Science

Decoupling Intrinsic Molecular Efficacy from Platform Effects: An Interpretable Machine Learning Framework for Unbiased Perovskite Passivator Discovery

Jing Zhang, Ziyuan Li, Shan Gao et al. (+3 more)

Rational design of interface passivators for perovskite solar cells is hindered by the entanglement of intrinsic molecular efficacy with extrinsic platform-dependent performance - a confounding factor that obscures true chemical advances. Here, we present a generalizable, interpretable machine learning framework that decouples these effects via an asymptotic saturation model, enabling unbiased discovery of molecules with genuine intrinsic gains. Trained on a curated dataset of 240 experimental entries, our model identifies hydrogen bond acceptor strength and electrostatic potential difference as key descriptors. Guided by these insights, we screened >121 million PubChem compounds using a hierarchical strategy integrating diversity clustering and uncertainty quantification. Five dual-functional candidates (e.g., TDZ-S, TZC-F) are identified, exhibiting superior predicted efficacy (surpassing experimental benchmarks) and high confidence. First-principles calculations confirm strong chemisorption (Eads<-1.7 eV), net electron donation, and optimized interfacial energetics. Crucially, our closed-loop "data-interpretation-screening-verification" pipeline establishes a transferable paradigm for rational materials design, extendable to other optoelectronic interfaces beyond perovskites.
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All authors Jing Zhang, Ziyuan Li, Shan Gao, Zhen Zhu, Jing Wang, Xiangmei Duan

Materials Science

One-Dimensional Metallic Polymeric Nitrogen

Kewei Ding, Junyi Miao, Ying Liu et al. (+7 more)

The pressure-induced metallic states of light elements attract significant attention, because of potential applications as high-temperature superconductor and high-energy-density material, especially for hydrogen and nitrogen1-10. Several semiconducting polymeric nitrogen phases with three- or two-dimensional sp3-bonded networks were synthesized6-10, but its metallic form remains unobserved. Here, we report the synthesis of a metallic polymeric nitrogen with one-dimensional feature (1D-PN) at 130-140 GPa and above 3000 K. Synchrotron XRD and Raman spectroscopy, supported by DFT calculations, reveal that it adopts an infinite arm-chair like chain with sp2-hybridized pi-bonds. Simulations predict a superconducting transition at 21.19 K under 113 GPa, higher than that reported in high-pressure experiments for non-metallic elements. At ambient pressure, this phase acquiring an energy density of as high as 8.78 kJ/g is not only kinetically stable but also thermodynamically more stable than cubic gauche nitrogen. This multifunctional property profile positions 1D-PN as a disruptive candidate for both electronic and energetic applications.
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All authors Kewei Ding, Junyi Miao, Ying Liu, Anxin Yu, Cheng Lu, Wenrui Zhang, Yanchun Li, Haipeng Su, Zhongxue Ge, Xianlong Wang

Mesoscale and Nanoscale Physics

Designing XY and Dzyaloshinskii–Moriya couplings in Majorana Cooper pair boxes

Manato Teranishi, Shintaro Hoshino and Ai Yamakage

We theoretically study how to design spin couplings in networks of Majorana Cooper pair boxes (MCBs) connected by multiple normal-metal leads. The inter-box interaction is generated by the conduction-electron-mediated Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction. We show that the connectivity of Majoranas to the leads enables arbitrary types of couplings. As concrete examples, we show the realization of the XY exchange interaction and the Dzyaloshinskii–Moriya (DM) interaction, which are difficult to implement in previously proposed MCB-based schemes. The sign and magnitude of the couplings can be tuned continuously via gate-controlled tunneling amplitudes. These results establish MCBs as a versatile platform for engineered quantum spin systems.
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Strongly Correlated Electrons

Metal-insulator transition and thermal scales in $d$-wave altermagnet

Santhosh Kannan, Jainam Savla and Madhuparna Karmakar

We present the first finite-temperature study of a strongly correlated $d$-wave altermagnet across the Mott insulator-metal transition using a non-perturbative numerical approach. We map out the thermal phase diagram and provide quantitative estimates of the transition scales in an interacting altermagnet. We show that altermagnetism-induced geometric frustration stabilizes a finite-temperature correlated magnetic metal and enhances the magnetic transition scale across regimes of interaction. These results establish the finite-temperature landscape of correlated altermagnets and clarify the role of strong electronic interactions in this phase.
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Materials Science

Manipulating Charge Distribution in Moiré Superlattices by Light

Ruiping Guo, Haowei Chen, Wenhui Duan et al. (+2 more)

In ordinary solids, nonlinear optical responses are typically studied in terms of unit-cell averages due to the angström-scale lattice constants. In contrast, moiré superlattices, characterized by a large length scale, unlock an often-overlooked degree of freedom: intra-supercell spatial variations of local observables. Here, we formulate the second-order direct current (DC) charge response in a spatially resolved manner, showing that even uniform optical illumination can drive a static, spatially non-uniform charge redistribution within a supercell. This effect is ubiquitous and cannot be forbidden by any crystalline symmetries. Furthermore, we identify a dominant contribution arising from diverging analytical response coefficients, which leads to linear-in-time growth of the redistribution in the absence of relaxation. This growth is driven by the convergence or divergence of local DC photocurrents. Applying our theory to twisted bilayer MoTe$_2$, we demonstrate strong, highly tunable charge modulation controlled by light intensity and frequency, opening a route to in situ, all-optical control of moiré-periodic electrostatic potentials. Our work underscores the importance of intra-cell degrees of freedom, which enable a qualitatively richer class of nonlinear optical responses in moiré superlattices.
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All authors Ruiping Guo, Haowei Chen, Wenhui Duan, Yong Xu, Chong Wang

Superconductivity

Possible Enhancement of Superconductivity in Ambient-Pressure La$_3$Ni$_2$O$_7$ Thin Film

Yichen Hua, Wenxin He, Wei-Qiang Chen et al. (+2 more)

As an unconventional superconducting system capable of reaching 60 K under ambient pressure, the La$_3$Ni$_2$O$_7$ thin film superconductor has recently become a focal point in the field of superconductivity, calling for further theoretical exploration of its possible pairing mechanisms. In this work, we employ the fluctuation exchange (FLEX) approximation to systematically analyze the superconducting properties of a previously proposed two-site, two-orbital model for the La$_3$Ni$2$O$7$ thin film in the weakly correlated regime, with particular emphasis on its dependence on hole doping. Through a more detailed examination of the Fermi-surface topology, we find that when a $\delta$ pocket composed of the $d_{z^{2}}$ antibonding orbital emerges near the $\Gamma$ point, its nesting with the $\gamma$ pocket, together with the nesting between the $\alpha$ and $\beta$ pockets, leads to a mutual enhancement of $s{\pm}$-wave pairing at the corresponding wave vector. Furthermore, we propose that this nesting-driven enhancement of spin-fluctuation-induced pairing may provide a viable mechanism for enhancing superconductivity.
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All authors Yichen Hua, Wenxin He, Wei-Qiang Chen, Jian-jian Miao, Changming Yue

Materials Science

Unusual magnetic and charge transport properties in In-Substituted Half-Metallic Kagome Ferromagnet Co3Sn2S2

Karan Singh, Subhadip Pradhan, K. Mukherjee et al. (+3 more)

The kagome ferromagnet Co3Sn2S2 has been studied extensively for its unusual topology of electronic bands, origin of ferromagnetism and strong coupling between magnetism and charge transport. To understand the role of nonmagnetic element Sn, we have investigated magnetic, transport, and electronic structure of the isostructural compound Co3SnInS2, where all the Sn (divalent) atoms in the Co3Sn Kagome layer are replaced by In (trivalent) atoms. We find long-range ferromagnetic order is nearly quenched in Co3SnInS2. The system exhibits predominantly antiferromagnetic correlations with only a very small net magnetic moment and turns ferromagnetic in the presence of an external magnetic field. Transport measurements show a semiconducting behaviour at low temperatures. Magnetoresistance shows a nonmonotonic field dependence, changing from negative to positive with increasing magnetic field. An anomalous Hall effect is observed, but its magnitude is significantly reduced compared to Co3Sn2S2 where the topological character of the Fermi surface plays a dominant role. These results indicate that substitution of Sn by In in the Co3Sn plane not only suppresses the topological electronic features of the transport electrons but drives the system away from the ferromagnetic Half-metallicity to an almost nonmagnetic semiconducting state with unusual paramagnetic response. Electronic structure calculations are consistent with some of these observations.
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All authors Karan Singh, Subhadip Pradhan, K. Mukherjee, Ashis Kumar Nandy, Subhendra D. Mahanti, D. Topwal

Materials Science

Fragmenting Diffusion Pathways Confers Extraordinary Radiation Resistance in Refractory Multicomponent Alloys

Bin Xing, Bijun Xie, Wanjuan Zou et al. (+11 more)

The accumulation and growth of vacancy clusters under irradiation is a pivotal degradation mode for structural materials in extreme environments. Even tungsten undergoes rapid defect coarsening compromising its integrity. Here we show a tungsten multicomponent alloy that effectively fragments the vacancy diffusion network, kinetically trapping defects within localized domains. This effect originates from a broad spectrum of migration barriers and substantial vacancy-jump heterogeneity, which drives the interconnectivity of diffusion paths below the percolation threshold. Starving clusters of the necessary vacancy supply, irradiation experiments and atomic-scale defect characterizations confirm negligible defect growth as radiation doses increase by four orders of magnitude. These results provide a fundamental paradigm for percolation-engineered kinetics, offering a predictive pathway for tailoring defect diffusion and discovering inherently radiation-tolerant materials.
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All authors Bin Xing, Bijun Xie, Wanjuan Zou, Eric Lang, Evgeniy Boltynjuk, Hangman Chen, Michael P Short, George Tynan, Timothy J Rupert, Jason Trelewicz, Horst Hahn, Blas P Uberuaga, Khalid Hattar, Penghui Cao

Materials Science

A hierarchy of thermodynamics learning frameworks for inelastic constitutive modeling

Reese E. Jones and Jan N. Fuhg

Recent advances in physics-augmented neural networks have enabled thermodynamically consistent data-driven constitutive modeling of complex inelastic materials. Most existing approaches, however, implicitly adopt a specific thermodynamic framework and embed structural assumptions such as normality, dual dissipation potentials, or other structure from manually constructed models directly into the learning architecture. Consequently, differences in predictive performance may arise not only from data or network design, but also from the underlying theoretical assumptions. In this work, we present a unified comparison of several thermodynamically consistent inelastic modeling frameworks from a machine learning perspective. We consider internal-variable formulations with dissipation potential, generalized standard materials, and metriplectic structures, and we analyze their structural assumptions, admissible dependencies, convexity requirements, and implications for dissipation and evolution. Each framework is implemented within a common neural potential architecture based on invariant representations and neural ordinary differential equations. This unified setting ensures that performance differences can be attributed to thermodynamic structure rather than architectural variation. The models are trained and evaluated on three representative inelastic datasets generated from high-fidelity representative volume element simulations: an elastoplastic alloy, a viscoelastic composite, and a rate-dependent crystal plasticity polycrystal. By isolating the role of thermodynamic structure, we assess how restrictions such as duality, normality, operator-based evolution, and convexity influence learnability, expressiveness, stability, and generalization.
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Materials Science

First-principles insights into the atomic structure of carbon-nitrogen-oxygen complex color centers in silicon

Péter Udvarhelyi

Spin-active color centers are the basis of solid-state defect systems utilized in quantum technologies. Although silicon is an emerging host material for quantum defects, there is an urgent need to characterize color centers with a non-zero electron-spin ground state in this platform, in addition to the prominent T-center. In this work, we carry out first-principles calculations to identify the possible atomic structures originating the experimentally observed N-line series in silicon. We propose that the core structure of the N1 center consists of a neighboring carbon and nitrogen interstitial pair. Furthermore, we predict that more complex defects involving self-interstitial and interstitial oxygen atoms are feasible candidates for the further lines in the series. As all of these color centers are isoelectronic to the T-center, they provide a family of alternative spin qubits with emission near the low-energy telecommunication bands.
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Quantum Gases

Geometry-Driven Thermodynamics: Shape Effects and Anisotropy in Quantum-Confined Ideal Fermi and Bose Gases

Rivo Herivola Manjakamanana Ravelonjato, Ravo Tokiniaina Ranaivoson, Raoelina Andriambololona et al. (+3 more)

This study presents a unified description of the thermodynamics of ideal quantum gases under nanoscale confinement using a Quantum Phase Space (QPS) formalism. We show that the statistical momentum variances B_ll capture quantum degeneracy: for fermions, they incorporate the Fermi energy, and for bosons, the condensate energy scale. This bridges our formalism with established results and allows both Fermi-Dirac and Bose-Einstein statistics to be treated within a single framework. From this, we derive exact analytical expressions for key properties - internal energy, anisotropic pressure tensor, and heat capacity - seamlessly describing the transition from classical to quantum regimes. Our results reveal that nanoscale thermodynamics is intrinsically anisotropic: pressure becomes direction-dependent, with fractional anisotropy reaching unity under extreme confinement. Notably, pure shape effects, controlled via geometric parameters in B_ll, enable manipulation of phase transitions without altering system size, temperature, or density. Numerical simulations for confined electron and helium-4 gases show significant quantum effects at accessible temperatures (mK to K) for confinement scales of 5-50 nm. This work provides a theoretical toolkit for nanosystems, with direct implications for nanofluidic devices and quantum sensors.
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All authors Rivo Herivola Manjakamanana Ravelonjato, Ravo Tokiniaina Ranaivoson, Raoelina Andriambololona, Naivo Rabesiranana, Charles Oyverné Randriamaholisoa, Wilfrid Chrysante Solofoarisina

Statistical Mechanics

Singularity of information flow at the Hopf bifurcation point

Kenshin Matsumoto and Shin-ichi Sasa

We investigate the singular behavior of information flow near the Hopf bifurcation point by analyzing the learning rate as a specific measure of information flow. We study the Brusselator, a model system exhibiting the Hopf bifurcation. We first numerically compute the learning rate in the stationary regime and find that it remains finite even in the deterministic limit, suggesting that the learning rate can be quantified in deterministic dynamics through probabilistic descriptions. Linear analysis accurately reproduces the numerical results in the stationary regime but fails near the bifurcation point. To overcome this limitation, we employ the singular perturbation method, well known in deterministic bifurcation theory, and carry out the corresponding calculation explicitly for a stochastic system described by a Langevin equation. This allows us to evaluate the learning rate near the bifurcation point. We then theoretically derive its non-smooth behavior in the deterministic limit. Our results demonstrate that changes in dynamical behavior are reflected in the learning rate and provide a basis for analyzing information processing in biochemical oscillations.
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Soft Condensed Matter

Disorder induced melting and glass formation in a one-component Lennard-Jones system

Saumya Suvarna, Prabhat K. Jaiswal and Madhu Priya

Identifying the conditions under which glass formation occurs is crucial for a fundamental understanding of the glass transition mechanism. Pure liquids devoid of any frustration avoid glass transition and undergo crystallization. In this work, we investigate a one-component liquid interacting via the Lennard-Jones potential in two dimensions, where disorder is introduced through pinning, a protocol in which a fixed fraction of particles is immobilized at positions selected from an equilibrium configuration. By employing molecular dynamics simulation, we systematically study the influence of pinning concentration on both structural and dynamical properties. Structural properties quantified by radial distribution function and hexatic-order parameter display a systematic decrease with a rise in pinning concentration. However, the dynamical properties such as the fragility index and the late-time mean squared displacement exhibit a non-monotonic trend as the concentration of pinned particles increases. A moderate concentration of pinned particles helps prevent crystallization and facilitates particle motion. A further rise in the number of pinned particles suppresses particle mobility, leading to a reduction in the overall dynamics of the system. These simulation results are in good agreement with experimental observations on colloidal suspensions confined between glass coverslips, where particles are immobilized. Our findings demonstrate the pivotal role of pinning in controlling the phase behavior of simple liquids and validate the unique dynamical features of two-dimensional liquids with pinned particles.
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Soft Condensed Matter

Dynamic Instabilities and Pattern Formation in Chemotactic Active Matter

Hongbo Zhao, Qiwei Yu, Andrej Košmrlj et al. (+1 more)

Collectives of actively-moving particles can spontaneously segregate into dilute and dense phases through a process known as motility-induced phase separation (MIPS). This captivating phenomenon is well-studied for randomly-moving particles with no directional bias. However, many active systems perform collective chemotaxis – directed motion along a chemical gradient collectively generated by the particles themselves through consumption or production. Here, we use linear stability analysis, amplitude equations, and numerical simulations to study how MIPS is influenced by collective chemotaxis. We find that chemotaxis can either arrest or entirely suppress MIPS, or give rise to novel dynamic instabilities such as traveling waves and spirals. We predict the stability region of the stationary and oscillatory patterns and identify four types of bifurcation that can arise: pitchfork, saddle-node, infinite period, and supercritical Hopf. We also derive analytical expressions for the amplitude of the pattern and traveling wave velocity, yielding excellent quantitative agreement with simulations. Furthermore, we generalize our model to study particles that either consume or produce chemoattractant or chemorepellent, as well as mixtures of particles with different chemotactic behaviors. By establishing quantitative principles describing the competition between MIPS and chemotaxis, our study helps deepen understanding of the rich physics underlying chemically-responsive active matter systems.
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All authors Hongbo Zhao, Qiwei Yu, Andrej Košmrlj, Sujit S. Datta

Materials Science

Exploring stable long-lifetime plasmon excitations in the Lieb lattice

Andrii Iurov, Liubov Zhemchuzhna, Godfrey Gumbs et al. (+1 more)

The subject of the present paper is a thorough numerical investigation of plasmon expectations, their dispersions and damping within a Lieb lattice. The Lieb lattice is known for its unique low-energy band structure which consists of a bandgap as well as a flat band intersecting the conduction band at its lowest point. In contrast to previously studied dice lattice, the location of the current flat band exhibits reduced and broken symmetries, which give rise to interesting electronic and optical properties of this new material. In this work, we have investigated the conditions for observing a well-defined and stable plasmon mode within a wide frequency range. Specifically, we have considered a free-standing layer with various doping levels, as well as different types of monolayers of the Lieb lattice interacting with a surface-plasmon mode localized on top of a semi-infinite conductor. In particular, we have observed and described fully long-living plasmon modes with unusual energy dispersions. Additionally, we have carried out a detailed investigation on the static screening associated with the Lieb lattice. Our study has further revealed that these predicted features seem to be quite different from those of pseudospin-1 materials but resemble those of graphene instead.
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All authors Andrii Iurov, Liubov Zhemchuzhna, Godfrey Gumbs, Danhong Huang

Statistical Mechanics

Hyperuniformity of Weighted Particle Systems

Salvatore Torquato, Jaeuk Kim, Michael A. Klatt et al. (+2 more)

Hyperuniform particle arrangements are characterized by a local number variance that grows more slowly than the volume of the observation window. We generalize this concept to describe particle systems in which particles carry weights: internal degrees of freedom such as scalars, vectors, pseudovectors, directors, tensors, or extrinsic local attributes. Our generalization extends hyperuniformity from fluctuations in particle positions to fluctuations in the spatial distribution of weights. We derive generalized weighted pair correlation, autocovariance, and spectral functions, and show their relation to the local variance in weighted many-particle systems. Applying this formalism to bond-orientational ordered phases, dipolar liquid water, Voronoi-cell volumes, and certain ionic liquids, we demonstrate that hyperuniformity in the particle system does not necessarily translate to hyperuniformity of the weighted system. In fact, cases exist where a hyperuniform particle system becomes antihyperuniform when weighted, and others where nonhyperuniform or antihyperuniform particle systems yield hyperuniform weighted systems. This theoretical framework provides a road map for quantifying large-scale fluctuations in weighted many-particle systems, offering a powerful tool for identifying systems with novel physical properties.
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All authors Salvatore Torquato, Jaeuk Kim, Michael A. Klatt, Roberto Car, Paul J. Steinhardt

Materials Science

Room-temperature magnetic p-n junctions for charge-and-spin diodes

Yuzhang Jiao, Yutong Wang, Xiangning Du et al. (+11 more)

Non-magnetic p-n junctions have been fundamental components in the silicon era, serving as the backbone for nearly all Si-based semiconductor devices, including transistors. To tackle challenges such as scaling limitations, excessive latency, and high-power consumption in Si-based electronics, we develop magnetic p-n junctions composed of a p-type amorphous magnetic semiconductor (p-AMS) and n-type Si. These charge-and-spin junctions exhibit typical diode characteristics for charge current, along with distinctive spin diode features. By manipulating spin-polarized space charges, we observed a giant magnetic enhancement of approximately 24.36% at a breakdown current of 5 mA, and an impressive 29-fold increase in magnetic moments for p-AMS. The observed spin behavior is attributed to space charge effects or carrier depletion in the p-AMS with extended hole states.
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All authors Yuzhang Jiao, Yutong Wang, Xiangning Du, You Ba, Yingqi Zhang, Zhiwei Tang, Xiangrong Wang, Tiantian Chai, Xiaoke Mu, Cheng Song, Kefu Yao, Zhengjun Zhang, Yonggang Zhao, Na Chen

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

High-Stress Si3N4 Reflective Membranes Monolithically Integrated with Cavity Bragg Mirrors

Megha Khokhar, Lucas Norder, Paolo M. Sberna et al. (+1 more)

High-stress silicon nitride (Si3N4) membranes represent the state-of-the-art for cavity optomechanics, combining ultralow dissipation, optical transparency, and full compatibility with wafer-scale nanofabrication. Yet their integration into high-finesse optical cavities has remained difficult, typically requiring bonding or alignment-sensitive assembly that limits scalability and long-term stability. Here, we introduce a monolithic, wafer-level integration strategy that directly suspends high-stress Si3N4 photonic-crystal membranes above thermally compatible SiN/SiO2 distributed Bragg reflectors (DBRs) capable of withstanding the high temperatures required for stoichiometric Si3N4 growth. A defect-free amorphous-silicon sacrificial layer and stiction-free plasma undercut yield vertically coupled cavities with sub-micron spacing-forming self-aligned resonators within seconds of release. Owing to the intrinsic tensile stress, the suspended membranes exhibit atomic-scale sagging, ensuring near-ideal cavity parallelism and long-term stability. Optical reflectivity measurements reveal cavity finesse exceeding 800 with nanoscale gaps between mirrors. Mechanical ringdown measurements show Q > 10^5, indicating that DBR integration preserves the low-dissipation character of high-stress Si3N4. This demonstrates that the integration process preserves the material's exceptional dissipation dilution, supporting straightforward extension to high-Q nanomechanical architectures reported in the literature. The resulting Si3N4-DBR platform unites optical and mechanical coherence with high fabrication yield and design flexibility, enabling scalable optomechanical devices for precision sensing and quantum photonics.
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All authors Megha Khokhar, Lucas Norder, Paolo M. Sberna, Richard A. Norte

Monday 2 March

Soft Condensed Matter

PolyMon: A Unified Framework for Polymer Property Prediction

Gaopeng Ren, Yijie Yang, Jiajun Zhou et al. (+1 more)

Accurate prediction of polymer properties is essential for materials design, but remains challenging due to data scarcity, diverse polymer representations, and the lack of systematic evaluation across modelling choices. Here, we present PolyMon, a unified and accessible framework that integrates multiple polymer representations, machine learning methods, and training strategies within a single, accessible platform. PolyMon supports various descriptors and graph construction strategies for polymer representations, and includes a wide range of models, from tabular models to graph neural networks, along with flexible training strategies including multi-fidelity learning, {\Delta}-learning, active learning, and ensemble learning. Using five key polymer properties as benchmarks, we perform systematic evaluations to assess how representations and models affect predictive performance. These case studies further illustrate how different training strategies can be applied within a consistent workflow to leverage limited data and incorporate physical model derived information. Overall, PolyMon provides a comprehensive and extensible foundation for benchmarking and advancing machine learning-based polymer property prediction. The code is available at github.com/fate1997/polymon.
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All authors Gaopeng Ren, Yijie Yang, Jiajun Zhou, Kim E. Jelfs

Strongly Correlated Electrons

Symmetry-protected topology and deconfined solitons in a multi-link $\mathbb{Z}_2$ gauge theory

Enrico C. Domanti and Alejandro Bermudez

With the advent of quantum simulators, exploring exotic collective phenomena in lattice models with local symmetries and unconventional geometries is at reach of near-term experiments. Motivated by recent progress in this direction, we study a $\mathbb{Z}_2$ lattice gauge theory defined on a multi-graph with links that can be visualized as great circles of a spherical shell hosting the $\mathbb{Z}_2$ gauge fields. Elementary Wilson loops along pairs of these bonds allow to identify a dynamical gauge-invariant flux, responsible for Aharonov-Bohm-like interference effects in the tunneling dynamics of charged matter residing on the vertices. Focusing on an odd number of links, we show that this leads to state-dependent tunneling amplitudes underlying a phenomenon analogous to the Peierls instability. We find inhomogeneous phases in which an ordered pattern of the gauge fluxes spontaneously breaks translational invariance, and intertwines with a bond order wave for the gauge-invariant kinetic matter operators. Long-range order is shown to coexist with symmetry protected topological order, which survives the quantum fluctuations of the gauge flux induced by an external electric field. Doping the system above half filling leads to the formation of topological soliton/anti-soliton pairs interpolating between different inhomogeneous orderings of the gauge fluxes. By performining a detailed analysis based on matrix product states, we prove that charge deconfinement emerges as a consequence of charge-fractionalization. Quasiparticles carrying fractional charge and bound at the soliton centers can be arbitrarily separated without feeling a confining force, in spite of the long-range attractive interactions set by the small electric field on the individual integer charges.
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Materials Science

TritonDFT: Automating DFT with a Multi-Agent Framework

Zhengding Hu, Kuntal Talit, Zhen Wang et al. (+8 more)

Density Functional Theory (DFT) is a cornerstone of materials science, yet executing DFT in practice requires coordinating a complex, multi-step workflow. Existing tools and LLM-based solutions automate parts of the steps, but lack support for full workflow automation, diverse task adaptation, and accuracy-cost trade-off optimization in DFT configuration. To this end, we present TritonDFT, a multi-agent framework that enables efficient and accurate DFT execution through an expert-curated, extensible workflow design, Pareto-aware parameter inference, and multi-source knowledge augmentation. We further introduce DFTBench, a benchmark for evaluating the agent's multi-dimensional capabilities, spanning science expertise, trade0off optimization, HPC knowledge, and cost efficiency. TritonDFT provides an open user interface for real-world usage. Our website is at https://www.tritondft.com. Our source code and benchmark suite are available at https://github.com/Leo9660/TritonDFT.git.
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All authors Zhengding Hu, Kuntal Talit, Zhen Wang, Haseeb Ahmad, Yichen Lin, Prabhleen Kaur, Christopher Lane, Elizabeth A. Peterson, Zhiting Hu, Elizabeth A. Nowadnick, Yufei Ding

Materials Science

Precursor-Dependent Energetics as a Predictive Principle for Polymorph Selection in Thin Films

Hyeon Woo Kim, Han Uk Lee, Rohan Mishra et al. (+1 more)

Vapor deposition allows for the synthesis of metastable polymorphs with unique properties, yet polymorph selection remains largely empirical due to the lack of predictive guidelines bridging thermodynamics, kinetics, and synthesis conditions. Here, we show that precursor chemistry can control metastable polymorph selection by modulating the reaction driving force governing nucleation. By integrating first-principles reaction energetics and substrate interactions into classical nucleation theory, we establish a quantitative framework that connects precursor-dependent reaction energetics to polymorph accessibility during vapor deposition. Using Ga2O3 as a model system, we demonstrate that highly reactive precursors with large reaction driving forces kinetically stabilize the metastable {\alpha} phase, whereas low-driving-force precursors permit thermodynamic relaxation to the stable e̱ta} phase. Furthermore, precursor flow rates amplify supersaturation, expanding the kinetic window for stabilizing the elusive ąppa} phase. The predictive capability of this approach is further validated in the TiO2 system, where precursor-dependent reaction energetics correctly capture the competitive nucleation between rutile and anatase. These results establish precursor chemistry as a tunable chemical lever for controlling nucleation kinetics and provide a predictive design principle for metastable polymorph synthesis in vapor deposition.
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All authors Hyeon Woo Kim, Han Uk Lee, Rohan Mishra, Sung Beom Cho

Superconductivity

Electrically-controllable superconducting memory effect in UTe2

Zheyu Wu, Hanyi Chen, Mengmeng Long et al. (+13 more)

If a computer could be assembled from superconducting components, the energy efficiency would far surpass that of conventional electronics. Historic research efforts towards this goal yielded pivotal breakthroughs in the development and discovery of scanning tunnelling microscopy and high temperature superconductivity. Although recent strides have been taken in advancing superconducting diode and switching technologies, harnessing read/writeable memory functionality in superconducting platforms has remained challenging. Here we show that bulk single crystal specimens of the triplet superconductor candidate uranium ditelluride (UTe$_2$) possess such properties. Upon applying a magnetic field to access an intermediate regime straddling two distinct superconducting phases, we find that direct current pulses can push the material in and out of a metastable state possessing an enhanced critical current $J_c$. This switching is controllable by the strength and duration of the stimuli, with the system `remembering' whether it is in the high or low $J_c$ state for extended periods. We interpret this to be due to competition between two distinct vortex species, which can be perturbatively pushed into a non-equilibrium high-disorder configuration with stronger pinning forces and thus higher $J_c$. Rather than requiring proximate magnetic or semiconducting interfaces, this memory functionality appears to be an intrinsic property of UTe$_2$ rooted in the superconducting order itself. Our findings underscore the rich complexity of quantum vortex matter, and demonstrate the viability of engineering a new class of superconducting memory elements with ultralow-power switching.
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All authors Zheyu Wu, Hanyi Chen, Mengmeng Long, Daniel Shaffer, Dmitry V. Chichinadze, Andrej Cabala, Theodore I. Weinberger, Alexander J. Hickey, Jinxu Pu, Dave Graf, Vladimir Sechovsky, Michal Valiska, Gang Li, Rui Zhou, F. Malte Grosche, Alexander G. Eaton

Materials Science

Strain-induced structural transitions in (111)-oriented (LaMnO$_3$)$_{2n}|$(SrMnO$_3$)$_n$ superlattices

Imran Ahamed, Shivalika Sharma, Fabrizio Cossu et al. (+1 more)

By means of first-principles electronic structure calculations, we hereby investigate the structural transitions induced by epitaxial strain in (111)-oriented (LaMnO$_3$)$_{2n}|$(SrMnO$_3$)$_n$ superlattices, with $n=2,4,6$. All superlattices in the explored range of strain are shown to prefer a half-metallic ferromagnetic order where the local magnetic moments are coupled to volume-breathing distortions. More in detail, our results reveal that thickness plays a crucial role in the response to epitaxial strain, which is particularly evident in the resulting tilt pattern of the oxygen octahedra. The thinnest superlattice, for $n=2$, always adopts the $a^-a^-a^-$ tilt pattern and the competing $a^-a^-c^+$ tilt pattern can be stabilized as a metastable state only in presence of compressive strain. Instead, the superlattice with $n=4$ favours the $a^-a^-c^+$ tilt pattern at equilibrium conditions, but the in-phase rotations around the third pseudocubic axis are so fragile that the $a^-a^-a^-$ pattern is recovered under a tiny amount of either compressive or tensile strain. The superlattice with $n=6$ exhibits a more nuanced behaviour: compressive strain drives a transition from $a^-a^-c^+$ to $a^-a^-a^-$, whereas tensile strain preserves the $a^-a^-c^+$ tilt pattern and significantly accentuates the structural differences between the two inequivalent sublattices within this symmetry. In fact, the Jahn-Teller distortions are quenched in one of the sublattices, leading to enhanced volume-breathing distortions and corresponding enhanced charge and spin oscillations. This suggests that Hund's physics may be more relevant in this regime of tensile strain, maximizing the interplay between strong electronic correlations and structural effects.
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All authors Imran Ahamed, Shivalika Sharma, Fabrizio Cossu, Igor Di Marco

Materials Science

Thermal conductivity and tunable thermal anisotropy of magnetic CrSBr monolayer

Marta Loletti, Alejandro Molina-Sánchez, Juan Sebastián Reparaz et al. (+2 more)

We present first-principles calculations of the thermal conductivity, ${\bm \kappa}$, of monolayer CrSBr, a van der Waals magnetic 2D material. We find a considerable thermal anisotropy, with a ratio $\kappa_{xx}/\kappa_{yy}$ of around 1.8. The anisotropy stems from a combined effect of phonon velocities and lifetimes and can be tuned by controlling the flake size by suppressing long mean path phonons.
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All authors Marta Loletti, Alejandro Molina-Sánchez, Juan Sebastián Reparaz, Xavier Cartoixà, Riccardo Rurali

Materials Science

The contribution of nitrogen Frenkel-pair formation to the high-temperature heat capacity of uranium mononitride

Mohamed AbdulHameed and Benjamin Beeler

The high-temperature heat capacity of uranium mononitride (UN) remains uncertain due to conflicting measurements and models above ~1700 K. To assess whether intrinsic defect formation contributes to the observed superlinear behavior of $C_P(T)$, we perform large-scale molecular dynamics simulations using two interatomic potentials to quantify nitrogen diffusion and Frenkel-pair populations from 1800–2600 K. Both models show increasing anion mobility, but the Tseplyaev potential yields substantially larger Frenkel concentrations, producing a defect heat-capacity contribution of up to ~10 J/(mol-K). This defect-driven term is consistent with the curvature seen in historical correlations and recent ab initio results, suggesting that nitrogen sublattice disorder provides a plausible intrinsic mechanism for the high-temperature heat capacity of UN.
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Strongly Correlated Electrons

Quantitative Determination of Quantum Fluctuations in Clean Magnets I: Neutron Spin Echo

Fanjun Xu

Starting from the magnetic total-moment sum rule of neutron scattering, we derive an explicit connection between ordered-moment reduction and the long-time limit of the intermediate scattering function. We show that this time-domain formulation establishes a direct and experimentally accessible measure of quantum fluctuation strength through neutron spin-echo spectroscopy, with \[P(t\rightarrow\infty)=\frac{I(Q,t\rightarrow\infty)}{I(Q,t=0)}=\frac{\langle \mu \rangle^{2}}{\langle \mu^{2} \rangle}\] This identity links the long-time polarization to the ratio between ordered and total magnetic moments. Linear spin-wave calculations for square and triangular Heisenberg antiferromagnets demonstrate that both quantum spin reduction and geometric frustration suppress the plateau value in quantitative agreement with moment reduction. The resulting framework establishes a direct and model-independent measure of the level of quantum fluctuations in bulk quantum magnets, particularly for polycrystalline samples.
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Materials Science

Charge, Bonding, and Optical Properties of the B$_7$Ca$_2$ Cluster: An Alkaline-Earth Dimer Stabilized by a Single Boron Ring

Peter Ludwig Rodríguez-Kessler

The charge, bonding, and optical properties of the calcium-doped boron cluster B$_7$Ca$_2$ have been systematically investigated using density functional theory calculations. Extensive global basin-hopping searches identify a single-ring B$_7$ geometry stabilized by two calcium atoms symmetrically located on opposite sides of the boron ring as the global minimum. Electronic structure analysis reveals pronounced charge redistribution and strong Ca–B interactions that promote electron delocalization over the boron framework. Hirshfeld charge analysis indicates substantial electron donation from the electropositive calcium atoms to the electron-deficient B$_7$ ring, leading to effective electronic stabilization without the involvement of transition-metal $d$ orbitals. Optical absorption spectra further reflect the delocalized nature of the frontier electronic states. Real-space bonding analyses based on the electron localization function (ELF), Interaction Region Indicator (IRI), and the Laplacian of the electron density reveal a multicenter bonding pattern dominated by electron delocalization within the boron ring, with calcium acting primarily as an electrostatic and charge-donating stabilizer rather than forming localized two-center Ca–B bonds. These results establish B$_7$Ca$_2$ as a prototypical example of an alkaline-earth-metal-stabilized boron ring and highlight the ability of non-transition metals to stabilize aromatic boron clusters through charge transfer and multicenter bonding.
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Mesoscale and Nanoscale Physics

Modulating Surface Acoustic Wave Generation through Superconductivity

Andrew Christy, Yuzan Xiong, Rui Sun et al. (+11 more)

Surface acoustic waves (SAWs), with their five orders-of-magnitude slower propagation velocity, allow for considerably shorter wavelengths at the same frequency compared to electromagnetic waves. The short wavelengths allow for device miniaturization and on-chip integration. The generic design of these devices involve piezoelectric substrates with comblike arrays of Al or Au electrodes known as interdigitated transducers deposited on the surface. However, Al and Au both have shortcomings at the cryogenic temperatures required for quantum applications, namely the formation of two-level systems and the lack of superconductivity perpetuating Ohmic losses, respectively. In this work, SAWs are generated in the high-MHz to low-GHz range using niobium nitride (NbN) interdigitated transducers (IDTs) and Bragg reflectors. We demonstrate the fabrication of acoustic devices through photolithography and reactive ion etching (RIE). The sharp transition between superconducting and normal states and the corresponding change in SAW transmission allows for fine control of the 'on' (superconducting) and 'off' (normal) states of NbN, with a \Delta_T = K separating the transmission minimum and maximum. We demonstrate a 16x difference in transmission between the 'on' and 'off' states of the device. The SAW transmission behavior mirrors the change in resistance of NbN at its Tc. These findings open up new possibilities for the integration of NbN SAW resonators into existing quantum architectures based on NbN and a method for adjusting transmission properties independent of applied voltage.
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All authors Andrew Christy, Yuzan Xiong, Rui Sun, Yi Li, Kenneth O. Chua, Andrew H. Comstock, Junming Wu, Sidong Lei, Frank Tsui, Megan N. Jackson, Dali Sun, Valentine Novosad, James F. Cahoon, Wei Zhang

Soft Condensed Matter · Cross-listed from math.DS

Invariant Curves and the Variational Structure in Tubular Origami Dynamical Systems

Ryutaro Ichikawa and Mitsuru Shibayama

We present a theoretical and numerical dynamical-systems analysis of tubular origami tessellations by identifying the inverse module number, $N^{-1}$, as a perturbation parameter within the framework of Kolmogorov–Arnold–Moser (KAM) theory. In the large-module limit ($N \to \infty$), we show that the conservative dynamics formally converges to an integrable map with a variational structure, whose generating function corresponds to the total discrete mean curvature. From the viewpoint of KAM theory, nonresonant invariant curves of the integrable limit are expected to persist for sufficiently large $N$. Consistent with this expectation, numerical computations with increasing $N$ show that large regions of the phase space are filled with structures that appear to be invariant curves. By adjusting mountain-valley fold assignments and fold lengths, the system can be transformed into a nontwist map that exhibits multiple zero frequencies. The frequency profile in the integrable limit and the persistence of invariant curves allow us to control the number and arrangement of stable folding regions appearing as coexisting elliptic islands. These islands provide a phase-space interpretation of distinct folding modes, separated by invariant curves that act as geometric barriers to continuous deformation and obstruct transitions without self-intersection. Finally, we analyze the expanding and contracting dynamics of the origami structure within the framework of conformally symplectic systems. By introducing a virtual auxiliary fold as a drift control mechanism, we numerically confirm the existence of stable quasi-periodic attractors.
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