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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 14 January

Quantum Gases · Cross-listed from quant-ph

Scale Invariance Breaking and Discrete Phase Invariance in Few-Body Problems

Satoshi Ohya

Scale invariance in quantum mechanics can be broken in several ways. A well-known example is the breakdown of continuous scale invariance to discrete scale invariance, whose typical realization is the Efimov effect of three-body problems. Here we discuss yet another discrete symmetry to which continuous scale invariance can be broken: discrete phase invariance. We first revisit the one-body problem on the half line in the presence of an inverse-square potential – the simplest example of nontrivial scale-invariant quantum mechanics – and show that continuous scale invariance can be broken to discrete phase invariance in a small window of coupling constant. We also show that discrete phase invariance manifests itself as circularly distributed simple poles on Riemann sheets of the S-matrix. We then present three examples of few-body problems that exhibit discrete phase invariance. These examples are the one-body Aharonov-Bohm problem, a two-body problem of nonidentical particles in two dimensions, and a three-body problem of nonidentical particles in one dimension, all of which contain a codimension-two “magnetic” flux in configuration spaces.
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Strongly Correlated Electrons

Evolution from three-dimensional charge density wave to one-dimensional stripe order in CsV$_{3-x}$Ti$_x$Sb$_5$

Qian Xiao, Xiangqi Liu, Zihao Huang et al. (+6 more)

Understanding intertwined phases near quantum criticality is a central challenge in correlated electron systems. The kagome metal CsV$_{3-x}$Ti$_x$Sb$_5$ provides a fertile platform to investigate the interplay between charge-density-wave (CDW) and superconductivity. Here, combining x-ray diffraction (XRD) and scanning tunneling microscopy (STM), we uncover a dimensional evolution of the CDW upon Ti substitution. We find that even infinitesimal Ti doping (x = 0.009) completely suppresses the three-dimensional 2 $\times$ 2 $\times$ 4 CDW present in pristine CsV3Sb5, while reducing the remaining 2 $\times$ 2 $\times$ 2 CDW to a quasi-two-dimensional order. With further Ti substitution, although no CDW transition is discernible in resistivity measurements, our XRD and STM data reveal the emergence of a (quasi-)one-dimensional CDW with a short correlation length of $\sim$ 20 $\AA$ at x = 0.2. The stripelike CDW undergoes a continuous second-order phase transition, characterized by a gradual increase in intensity and correlation length below $\sim$ 56 K. Our results elucidate the dimensional evolution of CDW order in CsV$_{3-x}$Ti$_x$Sb$_5$ and provide new insight into understanding the unconventional CDWs and their role in kagome superconductors.
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All authors Qian Xiao, Xiangqi Liu, Zihao Huang, Xiquan Zheng, Shilong Zhang, Hui Chen, Hong-Jun Gao, Yanfeng Guo, Yingying Peng

Statistical Mechanics · Cross-listed from nlin.SI

Matrix product operator representations for the local conserved quantities of the spin-$1/2$ XYZ chain

Kohei Fukai and Kyoichi Yamada

We present explicit matrix product operator (MPO) representations for the local conserved quantities of the spin-$1/2$ XYZ chain. Through these MPO representations, we simplify the coefficients appearing in the local conserved quantities originally derived by one of the authors, and reveal their combinatorial meaning: the coefficients prove to be a polynomial generalization of the Catalan numbers, given by weighted sums over monotone lattice paths. We also prove that a single recurrence relation for the coefficients guarantees the conservation law. We further show that these MPO representations can also be recovered from a product of two eight-vertex transfer matrices built from Baxter's R-matrix, providing the first direct connection between the R-matrix formalism and closed-form expressions for all local conserved quantities. We also obtain a simple Lax operator for the XYZ chain that, unlike Baxter's R-matrix, involves no elliptic functions.
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Quantum Gases

Gap solitons of the Wannier and Bloch types in spin-orbit-coupled Bose-Einstein condensates with a moiré lattice

Jun-Tao He, Xue-Ping Cheng, Xin-Wei Jin et al. (+3 more)

Gap solitons (GSs) bifurcating from flat bands, which may be represented in terms of Wannier functions, have garnered significant interest due to their strong localization with extremely small norms. Moiré lattices (MLs), with multiple flat bands, offer an appropriate platform for creating such solitons. We explore the formation mechanism and stability of GSs in spin-1 Bose-Einstein condensates under the combined action of the Rashba spin-orbit coupling (SOC) and an ML potential. We identify five Wannier-type GS families bifurcating from the lowest five energy bands in the spectrum induced by the ML with sufficiently large period and depth. These fundamental GSs serve as basic elements for constructing more complex Wannier-type GS states. Reducing the lattice period and depth triggers a transition from the Wannier-type GSs to ones of the Bloch type, the latter exhibiting higher norm thresholds and pronounced spatial broadening near edges of the energy bands. In addition to tuning the lattice-potential parameters, adjusting the SOC strength can also modulate the flatness of energy bands and enhance the localization of gap solitons, enabling reversible transitions between the GSs of the Wannier and Bloch types. Distinctive properties of GSs in the quasiperiodic ML are uncovered too. Thus, we propose the theoretical foundation for the creation of and manipulations with strongly localized GSs.
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All authors Jun-Tao He, Xue-Ping Cheng, Xin-Wei Jin, Hui-Jun Li, Ji Lin, Boris A. Malomed

Strongly Correlated Electrons

Magneto-optical Kerr effect measurements under bipolar pulsed magnetic fields

Soichiro Yamane, Sota Nakamura, Atsutoshi Ikeda et al. (+3 more)

The magneto-optical Kerr effect (MOKE) is a powerful probe of magnetism. Its contact-free optical nature makes it potentially well suitable for measurements under pulsed magnetic fields if various difficulties are overcome. In this paper, we report the establishment of MOKE measurements under bipolar pulsed magnetic fields up to 13.1 T. The accuracy of the setup was demonstrated by the excellent agreement with static-field results on the (001) surface of a Fe3O4 single crystal. Furthermore, clear hysteresis loops of various commercial permanent magnets were successfully observed. The capability for rapid characterization of hysteretic properties highlights the versatility of our pulsed-field MOKE setup for both fundamental materials science and engineering applications.
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All authors Soichiro Yamane, Sota Nakamura, Atsutoshi Ikeda, Kosuke Noda, Akihiko Ikeda, Shingo Yonezawa

Soft Condensed Matter

Entropic Colloidal Crystal Prediction: A Quantum Density Functional Theory Inspired Approach

Kristi Pepa, Isaac R. Spivack, Trevor F.G. Teague et al. (+3 more)

In pursuit of a colloidal analogue to quantum density functional theory (DFT) predictions of atomic crystal structures, we report a new, classical DFT that predicts the relative thermodynamic stability of colloidal crystals of hard, convex particle shapes. In contrast to standard classical DFT approaches, our theory maps the hard particle system to an auxiliary system in which we treat the particles as fixed "nuclei" embedded in a fictitious, spatially varying density field that distributes throughout the auxiliary system. By minimizing the free energy of the auxiliary system, and through comparison with known equations of state and free energy calculations using thermodynamic integration, we show that the auxiliary system with the lowest free energy corresponds to the most probable crystal of hard shapes in the original system.
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All authors Kristi Pepa, Isaac R. Spivack, Trevor F.G. Teague, Ryn Y. Oliphant, Domagoj Fijan, Sharon C. Glotzer

Statistical Mechanics · Cross-listed from physics.chem-ph

IEPDYN: Integral-equation formalism of population dynamics

Kento Kasahara, Ryo Okabe, Chia-en A. Chang et al. (+2 more)

We propose the integral-equation formalism of population dynamics (IEPDYN) to describe the population dynamics of distinct configurational states. According to classical reaction dynamics theory, the probability density associated with a given state obeys the Liouville equation, including influx from and efflux to neighboring states. By introducing a Markov approximation for the crossing of boundaries separating the states, tractable integral equations governing the state populations are derived. Once the time-dependent quantities appearing in these equations are evaluated, the population dynamics on long timescales can be obtained. Because these quantities depend only on a few states in the local neighborhood of a given state, they can be computed using a set of short-timescale molecular dynamics (MD) simulations. The IEPDYN method is formulated in continuous time and therefore does not rely on a coarse-grained timescale (lag time). Consequently, kinetic quantities obtained from IEPDYN are free from lag-time dependence, which has been discussed as a limitation in other approaches. We apply the IEPDYN method to the binding and unbinding kinetics of CH$_4$/CH$_4$, Na$^+$/Cl$^-$, and 18-crown-6-ether (crown ether)/K$^+$ in water. For both kinetics, the time constants estimated from the IEPDYN method are almost comparable to those obtained from brute-force MD simulations. The required timescale of each MD trajectory in the IEPDYN method is approximately two orders of magnitude shorter than that in the brute-force MD approach in the crown ether/K$^+$ system. This reduction in the trajectory timescale enables applications to complex binding and unbinding systems whose characteristic timescales are far beyond those directly accessible by brute-force MD simulations.
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All authors Kento Kasahara, Ryo Okabe, Chia-en A. Chang, Toshifumi mori, Nobuyuki Matubayasi

Soft Condensed Matter

Active alignment-driven coarsening in confined near-critical fluids

Parameshwaran A and Bhaskar Sen Gupta

We investigate vapor-liquid phase separation of an active near critical Lennard-Jones fluid confined within a cylindrical pore using molecular dynamics simulations. Activity is introduced via Vicsek-type alignment interactions, enabling a systematic study of how self-propulsion modifies domain morphology and coarsening kinetics under quasi-one-dimensional confinement. In the passive limit, the system undergoes early-time spinodal decomposition (diffusive growth characterized by the Lifshitz-Slyozov exponent $\alpha = 1/3$), followed by the formation of periodically modulated, plug-like liquid domains along the pore axis. At late times, coarsening becomes kinetically arrested, and the system remains trapped in a metastable striped state. Introducing activity destabilizes this arrested morphology by enhancing collective domain transport, leading to frequent domain mergers and complete phase separation at sufficiently high activity. The late-stage coarsening then exhibits a crossover to faster, ballistic growth with an effective exponent $\alpha = 2/3$, consistent with a cluster-coalescence mechanism. Analysis of two-point correlation functions and structure factors confirms dynamic scaling across all activity regimes. Our results demonstrate that alignment-induced activity can overcome confinement-driven kinetic arrest, providing new insight into phase separation in confined active fluids. The relevant growth laws are analyzed and interpreted using appropriate theoretical frameworks.
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Mesoscale and Nanoscale Physics

Multiple three-magnon splittings in bismuth yttrium iron garnet nanostructures

Sali Salama, Joo-Von Kim, Maryam Massouras et al. (+3 more)

We experimentally demonstrate the generation of multiple three-magnon splitting processes in an in-plane magnetized submicron Bi-YIG disk using micro-focused Brillouin light scattering. The low magnetic damping and strong magneto-optical response of BiYIG enable the detection of nonlinear spin-wave interactions at low threshold powers. By tuning the in-plane static magnetic field, excitation frequency, and power, we observe the generation of three pairs of secondary modes symmetrically distributed around half the excitation frequency. Time-resolved BLS measurements present temporal dynamics and threshold behavior associated with the successive activation of three-magnon pairs.
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All authors Sali Salama, Joo-Von Kim, Maryam Massouras, Jamal Ben Youssef, Abdelmadjid Anane, Jean-Paul Adam

Superconductivity

Vanishing Phase Stiffness and Fluctuation-Dominated Superconductivity in UTe$_2$

Sahas Kamat, Jared Dans, Shanta Saha et al. (+3 more)

Superconductivity in three dimensions is almost universally governed by Ginzburg-Landau mean field theory, with critical fluctuations typically confined to within a few percent of the transition temperature ($T_{\rm c}$). We report that the heavy-Fermion superconductor UTe$_2$ exhibits superconducting fluctuations that extend over a temperature range as wide as $T_{\rm c}$ itself - the largest observed for any three-dimensional superconductor. Through ultrasound measurements of the elastic moduli and sound attenuation, we find that UTe$_2$ transitions from a mean-field-like state at ambient pressure to a fluctuation-dominated state at higher pressures. This regime is marked by elastic softening and an increase in sound attenuation that onsets well above $T_{\rm c}$, with the attenuation remaining anomalously high deep in the superconducting state. Our analysis suggests that these features stem from an extremely low superfluid phase stiffness. This results in a kinetic inductance as high as that of granular aluminum, but achieved in the clean limit. We propose a model where this exotic state is driven by dominant inter-band pairing mediated by ferromagnetic fluctuations, leading to `local' cooper pairs with a coherence length of only a few lattice constants.
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All authors Sahas Kamat, Jared Dans, Shanta Saha, Daniel F. Agterberg, Johnpierre Paglione, B. J. Ramshaw

Materials Science

Data-Driven Exploration and Insights into Temperature-Dependent Phonons in Inorganic Materials

Huiju Lee, Zhi Li, Jiangang he et al. (+1 more)

Phonons, quantized vibrations of the atomic lattice, are fundamental to understanding thermal transport, structural stability, and phase behavior in crystalline solids. Despite advances in computational materials science, most predictions of vibrational properties in large materials databases rely on the harmonic approximation and overlook crucial temperature-dependent anharmonic effects. Here, we present a scalable computational framework that combines machine learning interatomic potentials, anharmonic lattice dynamics, and high-throughput calculations to investigate temperature-dependent phonons across thousands of materials. By fine-tuning the universal M3GNet interatomic potential using high-quality phonon data, we improve phonon prediction accuracy by a factor of four while preserving computational efficiency. Integrating this refined model into a high-throughput implementation of the stochastic self-consistent harmonic approximation, we compute temperature-dependent phonons for 4,669 inorganic compounds. Our analysis identifies systematic elemental and structural trends governing anharmonic phonon renormalization, with particularly strong manifestations in alkali metals, perovskite-derived frameworks, and related systems. Machine learning models trained on this dataset identify key atomic-scale features driving strong anharmonicity, including weak bonding, large atomic radii, and specific coordination motifs. First-principles validation confirms that anharmonic effects can dramatically alter lattice thermal conductivity by factors of two to four in some materials. This work establishes a robust and efficient data-driven approach for predicting finite-temperature phonon behavior, offering new pathways for the design and discovery of materials with tailored thermal and vibrational properties.
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All authors Huiju Lee, Zhi Li, Jiangang he, Yi Xia

Materials Science

Unexpected type-II multiferroic phase in GdMnO3 under high magnetic fields

Ming Yang, Jun Chen, Junfeng Wang et al. (+6 more)

Perovskite manganites with small A-site ions, as the first and canonical branch of type-II multiferroics, are ideal systems to exhibit magnetism-induced ferroelectricity. Despite their established magnetoelectric phase diagrams under low magnetic fields, here an unidentified phase with a large magnetism-induced polarization (up to 1500 {\mu}C/m2) is revealed in GdMnO3 under high magnetic fields up to 60 T. Based on multiprobe experiments, a complete phase diagram is constructed with successive polar-nonpolar-polar-nonpolar transitions. Such a nonmonotonic evolution is well mimicked by model simulation, while the spin-lattice coupling is the key ingredient for the reentrant ferroelectric phase.
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All authors Ming Yang, Jun Chen, Junfeng Wang, Chao Dong, Chengliang Lu, Gang Xu, Jinguang Cheng, Jianshi Zhou, Shuai Dong

Materials Science

Electronic procrystalline state in moire structures

Hui Guo, Zihao Huang, Yixuan Gao et al. (+15 more)

Solid state materials can display varieties of atomic structural orders ranging from crystalline to amorphous, underlying their properties and diverse functionalities. Procrystal has emerged as a new category of solids, featuring a long-range ordered lattice framework tiled with disordered atomic or molecular structures on the lattice sites, arousing great interest due to its novel structural and physical properties. However, the electronic analogue of a procrystal, dubbed as an electronic procrystalline (EPC) state, has never been experimentally observed. Here, we report the observation of an EPC state in a moire superstructure formed between a monolayer metallic NiTe2 and a superconductor NbSe2 with incommensurate lattice wavevectors. The observed EPC state exhibits a long-range periodic charge modulation at the moire scale inlaid with short-range irregular orders within each moire cell. Strikingly, the short-range charge orders inside the moire unit cells have proximately root3*root3 quasi-period, which is absent in pristine NiTe2. Intriguingly, the EPC order is also observed in the superconducting state of the moire superstructure. Furthermore, the emergent EPC state and short-range charge order, coexisting with the proximity induced superconductivity, can be precisely modulated with the thickness of NiTe2. Our findings uncover the potential of moire platform for understanding and tuning novel correlated quantum phases with this exotic procrystalline order.
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All authors Hui Guo, Zihao Huang, Yixuan Gao, Haowei Chen, Hao Zhang, Qian Fang, Yuhan Ye, Xianghe Han, Zhongyi Cao, Jiayi Wang, Runnong Zhou, Zhilin Li, Chengmin Shen, Haitao Yang, Hui Chen, Wang Yao, Ziqiang Wang, Hong-Jun Gao

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

Mechanistic principles of exciton-polariton relaxation

Ian Haines, Arshath Manjalingal, Logan Blackham et al. (+2 more)

Exciton-polaritons are light-matter hybrid quasi-particles that have emerged as a flexible platform for developing quantum technologies and engineering material properties. However, the fundamental mechanistic principles that govern their dynamics and relaxation remain elusive. In this work, we provide the microscopic mechanistic understanding of the exciton-polariton relaxation process that follows from an excitation in the upper polariton. Using both mixed quantum-classical simulations and analytical analysis, we reveal that phonon-induced upper-to-lower polariton relaxation proceeds via two steps: the first step is a vertical inter-band transition from the upper to the lower polariton, which is followed by a second step that is a phonon-induced Fröhlich scattering within the lower polariton. We find that in materials of finite thickness (which include filled cavities), phonon-induced polaritonic intraband Fröhlich scattering is significantly suppressed. We show that the microscopic origin of this suppression is phonon-fluctuations synchronization (or self-averaging) due to the polaritonic spatial delocalization in the quantization direction. Finally, we show that the same phonon fluctuation-synchronization effect plays a central role across polaritonic relaxation pathways, and we derive simple analytical expressions that relate a material's finite thickness to the corresponding relaxation rate constants.
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All authors Ian Haines, Arshath Manjalingal, Logan Blackham, Saeed Rahamanian Koshkaki, Arkajit Mandal

Disordered Systems and Neural Networks

Vibrational inhomogeneity in amorphous solids and its geometric features

Cunyuan Jiang

The dynamical response of amorphous solids is expected to be inhomogeneous due to the absence of translational symmetry, unlike in crystals. In this work, we use Green's function method combined with the Hessian matrix from simulation data to characterize the vibrational inhomogeneity of a two-dimensional amorphous solid. We define an order parameter for vibrational inhomogeneity, the frequency-resolved participation ratio, which equals a constant value of one over all frequencies for a crystal, while being around \(\sim 0.7\) for almost the entire frequency range in an amorphous solid, thus indicating a similar level of vibrational inhomogeneity across most of the frequency range. The spatial distribution of vibrational inhomogeneity in the amorphous solid is presented in three ways: by frequency, at the particle level, and via percolation analysis, all showing that the vibrational inhomogeneity is fragmented and occurs at the particle scale. The results suggest that the Green's function method is a convenient tool for probing vibrational inhomogeneity, and provide an alternative perspective on the role of vibrational inhomogeneity in amorphous solids.
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Strongly Correlated Electrons

Coexistence of long-range magnetic order and dynamical magnetism in the V-based Kagome metals: A combined thermodynamic and $\mu$SR study

Sheetal Devi, Yishui Zhou, Thomas J. Hicken et al. (+5 more)

V-based Kagome metals exhibit a unique lattice geometry that can give rise to exotic electronic and magnetic phenomena, making them an ideal platform to study the interplay of topology and magnetism. We present a combined thermodynamic and muon spin relaxation ($\mu$SR) investigation of single-crystal RV$_{6}$Sn$_{6}$ (R = Tb, Dy, Ho, Er) compounds, focusing on their low-temperature magnetic behavior. Heat capacity and $\mu$SR measurements reveal distinct magnetic phase transitions below 4 K, confirming the emergence of long-range magnetic order in all compounds studied. The $\mu$SR results further indicate persistent spin fluctuations within the magnetically ordered state down to 50 mK, reflected in reduced ordered moments obtained from hyperfine analysis of the heat capacity measurements. These findings uncover the coexistence of static and dynamic magnetism in V-based Kagome metals and emphasizing the key role of 4$f$-electron anisotropy in shaping their magnetic ground states. Compared with the Mn-based RMn$_{6}$Sn$_{6}$ analogs, our results highlight the unique magnetism arising from the decoupled rare-earth sublattice and its interplay with the nonmagnetic V Kagome network.
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All authors Sheetal Devi, Yishui Zhou, Thomas J. Hicken, Zurab Guguchia, Hubertus Luetkens, Min-Kai Lee, Lieh-Jeng Chang, Yixi Su

Disordered Systems and Neural Networks · Cross-listed from cs.ET

Probabilistic Computers for MIMO Detection: From Sparsification to 2D Parallel Tempering

M Mahmudul Hasan Sajeeb, Kevin Callahan-Coray, Corentin Delacour et al. (+3 more)

Probabilistic computers built from p-bits offer a promising path for combinatorial optimization, but the dense connectivity required by real-world problems scales poorly in hardware. Here, we address this through graph sparsification with auxiliary copy variables and demonstrate two fully on-chip parallel tempering solvers on an FPGA. Targeting MIMO detection, a dense, NP-hard problem central to wireless communications, we first fit 11 temperature replicas of a 128-node sparsified system (1,408 p-bits) on-chip and achieve bit error rates significantly below conventional linear detectors on $64 \times 64$ BPSK MIMO. We report complete end-to-end solution times of 3~ms per instance, including all loading, sampling, readout, and verification overheads. ASIC projections in 7~nm technology indicate 103~MHz operation at 285.8~mW, suggesting that massive parallelism across multiple chips could approach the throughput demands of next-generation wireless systems. Sparsification, however, introduces a sharp sensitivity to the copy-constraint strength $P$ that requires manual tuning. To eliminate this bottleneck, we utilize Two-Dimensional Parallel Tempering (2D-PT), which exchanges replicas across both temperature ($\beta$) and constraint ($P$) dimensions. On Sherrington–Kirkpatrick spin glasses, 2D-PT converges roughly $250\times$ faster than optimally tuned 1D-PT, and on $128 \times 128$ MIMO it reaches zero bit errors at high SNR where 1D-PT exhibits an error floor. We further validate 2D-PT entirely on-chip with 54 replicas (1,728 p-bits) on a $16 \times 16$ MIMO instance, where it tracks the maximum-likelihood bound in just 50 Monte Carlo steps – $10\times$ fewer than 1D-PT – at projected 111~MHz and 124~mW in 7~nm. Together, these results establish an on-chip p-bit architecture and a scalable, tuning-free algorithmic framework for dense combinatorial optimization.
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All authors M Mahmudul Hasan Sajeeb, Kevin Callahan-Coray, Corentin Delacour, Sanjay Seshan, Tathagata Srimani, Kerem Y. Camsari

Tuesday 13 January

Statistical Mechanics

Exact solution of a two-dimensional (2D) Ising model with the next nearest interactions

Zhidong Zhang

The exact solution of a two-dimensional (2D) Ising model with the next nearest interactions at zero magnetic field is derived. At first, the transfer matrices are analyzed in three representations, i.e., Clifford algebraic representation, transfer tensor representation and schematic representation, to inspect nontrivial topological structures in this system. The system is equivalent to a triangular Ising model plus an interaction along the z axis, so that the approaches developed for the 3D Ising model are modified to be appropriable for solving the exact solution of the 2D Ising model with the next nearest interactions. The partition function and the spontaneous magnetization are obtained. The comparison with the exact solutions of other Ising lattices reveals that either the increase of the number of interactions in a unit cell or the presence/increase of topological contributions enhances the critical point of the Ising lattices. The results obtained in this work are helpful for understanding the physical properties of the 2D magnetic materials.
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Mesoscale and Nanoscale Physics

Strain-Driven "Sinusoidal" Valley Control of Hybridized $\Gamma -\mathrm{K}$ Excitons

Yingtong Zhu, Kang Lan, Shiling Li et al. (+3 more)

The photoluminescence (PL) of momentum-indirect $\rm \Gamma- K$ excitons in monolayer WS$_2$ under biaxial strain was recently observed by Blundo et al. [Phys. Rev. Lett. 129, 067402 (2022)], yet its microscopic origin remains elusive. Here we develop a unified framework that reproduces the measured PL and reveals its fundamental excitonic mechanism. We reveal that: (i) the PL originates from genuinely hybridized direct-indirect excitonic eigenstates, rather than nominally mixed species with fixed dominant character; (ii) the direct exciton converts into the indirect one via a previously unrecognized two-step pathway – exchange-interaction-driven exciton transfer followed by a spin flip; and (iii) a higher-energy indirect exciton, absent from prior studies, acts as a crucial intermediate mediating this conversion. Beyond explaining experiment, our theory predicts a striking strain-driven "sinusoidal” valley response, furnishing a continuously tunable valley dial that far exceeds binary control schemes. This unified picture of strain-engineered direct-indirect exciton dynamics introduces a new paradigm for manipulating long-lived valley degrees of freedom, opening a pathway toward programmable valley pseudospin engineering and next-generation valleytronic quantum technologies.
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All authors Yingtong Zhu, Kang Lan, Shiling Li, Ning Hao, Ping Zhang, Jiyong Fu

Materials Science

Agentic AI and Machine Learning for Accelerated Materials Discovery and Applications

Jihua Chen, Panagiotis Christakopoulos, Karuna D. Chen et al. (+2 more)

Artificial Intelligence (AI), especially AI agents, is increasingly being applied to chemistry, healthcare, and manufacturing to enhance productivity. In this review, we discuss the progress of AI and agentic AI in areas related to, and beyond polymer materials and discovery chemistry. More specifically, the focus is on the need for efficient discovery, core concepts, and large language models. Consequently, applications are showcased in scenarios such as (1) flow chemistry, (2) biosensors, and (3) batteries.
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All authors Jihua Chen, Panagiotis Christakopoulos, Karuna D. Chen, Ilia N. Ivanov, Rigoberto Advincula

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

Casimir effect with dielectric matter in salted water and implications at the cell scale

Larissa Inácio, Felipe S. S. Rosa, Astrid Lambrecht et al. (+2 more)

The Casimir interaction in salted water contains a universal contribution of electromagnetic fluctuations that makes it of a longer range than previously thought. The universal contribution dominates non universal ones at the distances relevant for actin fibers inside the cell. We discuss universal and non-universal contributions with a model mimicking biological matter. We also show that the universal Casimir effect should have important implications at the cell scale.
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All authors Larissa Inácio, Felipe S. S. Rosa, Astrid Lambrecht, Paulo A. Maia Neto, Serge Reynaud

Statistical Mechanics

Divergent Fluctuations from a 2D Infrared Catastrophe

Richard G. Hennig and Clotilde S. Cucinotta

Molecular simulations of interfacial polar media routinely employ periodic boundary conditions parallel to the interface. We show that this lateral periodicity introduces a spatially uniform in-plane mode ($q_{\parallel}=0$) that is unscreened because every lateral replica carries identical charge fluctuations. This 2D mode reduces the plane-averaged potential to a stochastic integral of the plane-averaged charge density along $z$, so that in a semi-infinite slab the variance of the potential grows linearly with depth. In a finite or periodic cell along $z$, with boundaries held at fixed potential, it follows a parabolic profile–a Brownian bridge–pinned to zero at both ends, with amplitude inversely proportional to the lateral cell area. These diverging fluctuations are a pure artifact of the imposed 2D lateral periodicity: they remain bounded in systems that are non-periodic or of finite lateral extent. We provide an analytic expression for their magnitude in dipolar media, yielding a practical criterion for the choice of lateral cell dimensions.
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Strongly Correlated Electrons

Electronic layer decoupling driven by density-wave order in La$_4$Ni$_3$O$_{10}$

Ziqiang Guan, Sophia F. R. TenHuisen, M. Tepie et al. (+14 more)

We probe the density-wave transition of the trilayer nickelate La$_4$Ni$_3$O$_{10}$ with polarization-resolved infrared spectroscopy. The low-energy electrodynamics is strongly anisotropic, with metallic in-plane and insulating out-of-plane character. In the ordered phase, the anisotropy grows more than an order of magnitude as the out-of-plane conductivity is sharply suppressed. We interpret this enhancement as an effective electronic decoupling of the Ni-O layers, driven by a spin-density-wave-induced redistribution of Ni-$d_{z^2}$ occupation within the trilayers. This electronic response is accompanied by clear shifts and splittings of the out-of-plane phonons, compatible with a density-wave instability of electronic origin.
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All authors Ziqiang Guan, Sophia F. R. TenHuisen, M. Tepie, Yifeng Zhao, Ezra Day-Roberts, Harrison LaBollita, Alexander M. Young, Xiaomeng Cui, Xinglong Chen, Filippo Glerean, Carl A. Guia, Mark P. M. Dean, Philip Kim, J. F. Mitchell, Antia S. Botana, Christopher C. Homes, Matteo Mitrano

Mesoscale and Nanoscale Physics

Two-Dimensional Twisted Ferromagnetic Domain Wall as a Spin-Wave Diffraction Grating

Ehsan Faridi, Se Kwon Kim and Giovanni Vignale

We present a theoretical study of spin-wave scattering by a twisted domain wall (DW) in a two-dimensional ferromagnet with easy-axis anisotropy. While the twisted DW generates an effective gauge field for spin waves, leading to a deflection of their trajectories, our main focus is on a distinct effect that arises when a hard-axis anisotropy is present in addition to the easy-axis anisotropy. In this case, the translational symmetry of the spin-wave Hamiltonian along the DW is broken, resulting in a periodic modulation of the Hamiltonian. This periodicity leads to the formation of multiple diffracted spin wave modes on both sides of the DW, engendering a DW-induced magnonic diffraction pattern. The interplay between the emergent gauge field and the anisotropy-induced periodicity reveals rich spin-wave dynamics and suggests potential applications for manipulating magnon flow in two-dimensional magnetic textures.
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Materials Science

Quantifying the Relationship Between Strain and Bandgap in Thin Ga$_2$Se$_2$

Lottie L. Murray, Eric Herrmann, Igor Evangelista et al. (+3 more)

We present a rigorous analysis that combines theory, simulation, and experimental measurements to quantify the relationship between strain and bandgap in two dimensional gallium selenide (Ga$_2$Se$_2$). Experimentally, we transfer thin Ga$_2$Se$_2$ flakes onto patterned substrates to deterministically induce multiaxial localized strain. We quantify the local strain using a combination of atomic force microscopy (AFM) measurements and COMSOL Multiphysics simulation. We then experimentally map the strain-induced bandgap shifts using high-resolution hyperspectral PL imaging to generate a robust and statistically significant dataset. We systematically fit this data to extract gauge factors that relate the bandgap shift to the local uniaxial and biaxial strain. We then compute the uniaxial and biaxial strain gauge factors via density functional theory (DFT) and find excellent agreement with the experimentally-determined values. Finally, we show that a simple model that computes bandgap shifts from the local uniaxial and biaxial strain predicts the observed multiaxial bandgap shift with less than 10% error. The combined results provide a framework for deterministic realization of tailored bandgap profiles induced by controlled strain applied to Ga$_2$Se$_2$, with implications for the future realization of localized quantum emitters for quantum photonic applications.
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All authors Lottie L. Murray, Eric Herrmann, Igor Evangelista, Anderson Janotti, Xi Wang, Matthew F. Doty

Materials Science

Charge Transport and Multiplication in Lateral Amorphous Selenium Devices Under Cryogenic Conditions

M. Rooks, S. Abbaszadeh, J. Asaadi et al. (+6 more)

Cryogenic photon sensing for high-energy physics motivates photosensor technologies that combine large-area scalability with internal gain and stable operation at low temperature. Amorphous selenium is a promising photoconductor, yet its field- and temperature-dependent transport and avalanche response in lateral geometries have not been systematically established. This work reports field-resolved photocurrent measurements of lateral a-Se devices from 93 K to 297 K under 401 nm excitation at fields up to 120 V/um. Below avalanche onset, the external quantum efficiency was described by the Onsager model, yielding effective post-thermalization separations that decrease with decreasing temperature. The field-assisted detrapping region was evaluated using several transport models, with the data favoring field-assisted hopping and thermally-assisted tunneling as the mechanisms that best capture the temperature evolution of the photocurrent. The boundaries between field-assisted detrapping, transport-limited conduction, and avalanche shift with temperature; at 93 K the response transitions directly from detrapping into avalanche. Avalanche multiplication was analyzed using the Lucky-drift model. These results provide the first systematic characterization of cryogenic avalanche behavior in lateral a-Se detectors and establish quantitative trends relevant to low-temperature, high-gain photodetector design.
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All authors M. Rooks, S. Abbaszadeh, J. Asaadi, V. A. Chirayath, M. Á. García-Peris, E. Gramellini, K. Hellier, B. Sudarsan, I. Tzoka

Materials Science

Machine Learning-Driven Creep Law Discovery Across Alloy Compositional Space

Hongshun Chen, Ryan Zhou, Rujing Zha et al. (+8 more)

Hihg-temperature creep characterization of structural alloys traditionally relies on serial uniaxial tests, which are highly inefficient for exploring the large search space of alloy compositions and for material discovery. Here, we introduce a machine-learning-assisted, high-throughput framework for creep law identification based on a dimple array bulge instrument (DABI) configuration, which enables parallel creep testing of 25 dimples, each fabricated from a different alloy, in a single experiment. Full-field surface displacements of dimples undergoing time-dependent creep-induced bulging under inert gas pressure are measured by 3D digital image correlation. We train a recurrent neural network (RNN) as a surrogate model, mapping creep parameters and loading conditions to the time-dependent deformation response of DABI. Coupling this surrogate with a particle swarm optimization scheme enables rapid and global inverse identification with sparsity regularization of creep parameters from experiment displacement-time histories. In addition, we propose a phenomenological creep law with a time-dependent stress exponent that captures the sigmoidal primary creep observed in wrought INCONEL 625 and extracts its temperature dependence from DABI test at multiple temperatures. Furthermore, we employ a general creep law combining several conventional forms together with regularized inversion to identify the creep laws for 47 additional Fe-, Ni-, and Co-rich alloys and to automatically select the dominant functional form for each alloy. This workflow combined with DABI experiment provides a quantitative, high-throughput creep characterization platform that is compatible with data mining, composition-property modeling, and nonlinear structural optimization with creep behavior across a large alloy design space.
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All authors Hongshun Chen, Ryan Zhou, Rujing Zha, Zihan Chen, Wenpan Li, Rowan Rolark, John Patrick Reidy, Jian Cao, Ping Guo, David C. Dunand, Horacio D. Espinosa

Soft Condensed Matter

Emergent Elasticity and Quasiconformal Flow in Active Solids

Nikolas H. Claussen, Fridtjof Brauns and Boris I. Shraiman

Elasticity theory rests on a constitutive relation between stress and strain relative to a reference state. Living matter, however, generates forces by motor molecule activity independent of strain, requiring a different approach to active tissue mechanics. We develop a theory of two-dimensional continuum mechanics in which the active force configuration, not a reference shape, is the fundamental input. Motivated by the cell-level Active Tension Network model for epithelia, we encode motor-driven intercellular forces in a Riemannian tension metric, whose mapping into physical space relates macroscopic stress to the microscopic tensions. Assuming force balance, we show that a stress-free reference state and an effective stress-strain relation emerge at the tissue scale, making the system an effectively elastic active solid. Extending from statics to dynamics, we show how such a solid can morph its shape through adiabatic evolution of active tensions. To capture plastic cell rearrangement, we introduce a second metric representing the cell adjacency graph in the continuum; topological rearrangement then appears as a continuous reparametrization of the tension manifold. The key fields characterizing the tissue's local mechanical state - tension anisotropy, macroscopic stress, and cell shape - arise from the discrepancies between the tension, adjacency, and physical metrics, represented mathematically by quasiconformal maps. Our theory explains how local contractility controls tissue shape and yields predictions distinct from existing models: tissues can remain rigid while "flowing", with a speed set by the rate of change of active forces rather than their magnitude, and shear flow can occur even under isotropic stress, since macroscopic stress is distinct from local tension anisotropy.
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Strongly Correlated Electrons

Frustrated Magnetism in FeGe$_3$O$_4$ with a Chiral Trillium Network

Matt Boswell, Mingyu Xu, Haozhe Wang et al. (+7 more)

The discovery of new magnetic ground states in geometrically frustrated lattices remains a central challenge in materials science. Here, we report the synthesis, structural characterization, and frustrated magnetic properties of FeGe$_3$O$_4$, a newly identified compound that crystallizes in the noncentrosymmetric cubic space group $P2_13$. In this structure, Fe atoms form an intricate double-trillium lattice with nearest-neighbor Fe–Fe distances of $\sim$4.2~Å, while Ge$^{2+}$ ions mediate magnetic interactions through Fe-Ge-Fe pathways. Field-dependent magnetization at 2~K shows a pronounced nonlinearity, reaching a maximum moment of 2.55(3)~$\mu_\mathrm{B}$/Fe$^{2+}$ at 70~kOe without evidence of saturation. Magnetic susceptibility, heat capacity, and neutron scattering collectively reveal the onset of short-range magnetic interactions near 5~K, with no long-range ordering detected down to 0.06~K. Specific heat measurements demonstrate strong frustration: only $\sim$34% of the expected magnetic entropy is recovered at 2.4~K. Taken together, these results establish FeGe$_3$O$_4$ as a rare example of a geometrically frustrated trillium-lattice magnet, offering a promising platform for exploring exotic quantum magnetic phenomena.
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All authors Matt Boswell, Mingyu Xu, Haozhe Wang, Mouyang Cheng, N. Li, X. F. Sun, Haidong Zhou, Huibo Cao, Mingda Li, Weiwei Xie

Materials Science

Effect of Niobium Doping on the Crystal Structure and Hydrogen Sorption Properties of TiFe: Combined Synchrotron X-ray Diffraction and Extended X-ray Absorption Fine Structure Study

Abhishek Banerjee, Stefano Deledda and Olena Zavorotynska

TiFe alloys are attractive compounds for solid-state stationary hydrogen storage. They can absorb hydrogen gas reversibly at near ambient temperatures and practical pressures with high volumetric capacities surpassing that of cryogenically liquified H2. The main drawback of TiFe-based storage systems is a costly activation procedure required due to the formation of oxide surface layer, which hinders hydrogen diffusion into the bulk. Doping the alloy with various additives is known to improve hydrogen diffusion softening the conditions of the activation procedure. Hydrogen sorption properties of the modified alloys have been the focus of most studies whereas less attention has been dedicated to the fundamental understanding of the effects of hydrogen sorption on the alloys' structure. The latter, however, is an important information in the knowledge-guided design of novel materials. In this work, we investigated effects of Nb-doping on crystallographic structure of TiFe metal-alloy compounds and their hydrogen sorption properties. TiFe samples with two different Nb stoichiometries were synthesized using arc-melting (AM) and characterised with synchrotron powder X-ray diffraction (SR-PXRD) and extended X-ray absorption fine structure (EXAFS) analysis. Overall, H2 absorption measurements (at 50 +/- 2 degrees C and 40 +/- 2 bar), have shown that doping of TiFe with Nb can improve matrix activation and kinetics of hydrogen sorption without compromising the overall storage capacities. Refinement of SR-PXRD and EXAFS data showed significant Nb occupancy in secondary Ti phases, which improved the hydrogenation properties of the alloys.
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