Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter

cond-mat Watch Condensed Matter (sign in to use)

Monday 16 March

Materials Science · Cross-listed from astro-ph.EP

Coupled Space Weathering: Nanophase Iron Formation by Micrometeoroid Impact and Solar Wind Sputtering

Understanding the interplay between micrometeoroid impacts and solar wind irradiation is crucial for interpreting lunar surface evolution. Using reactive molecular dynamics simulations and surface binding energy (SBE) analyses, this study investigates the coupled effects of these two dominant space weathering processes on lunar regolith composed of Fe$_2$SiO$_4$. Our simulations reveal that micrometeoroid impacts significantly modify the lunar surface, creating structurally heterogeneous zones with varying SBEs across microcrater morphologies. Specifically, microcrater floors exhibit enhanced surface cohesion due to high-density compaction, whereas microcrater walls and ejecta show weakened structures. Applying Sigmund's sputtering theory with these SBEs indicates differential sputtering yields for Fe, Si, and O suggesting preferential retention of heavier elements like Fe. This selective sputtering mechanism supports the formation and growth of nanophase metallic iron (npFe$^0$) clusters, influencing the optical and compositional maturation of the lunar surface. These findings advance our understanding of lunar space weathering processes.
Read the full abstract

Strongly Correlated Electrons

Study of the triangular-lattice Hubbard model with constrained-path quantum Monte Carlo

We benchmark constrained-path Monte Carlo (CPMC) on the triangular-lattice Hubbard model for several fillings and $U$ values and show that symmetry-adapted trial wave functions substantially improve quantitative accuracy. Away from half-filling, simple free-electron-based trials that preserve the ground state symmetry yield energy deviations $\lesssim 1\%$ from exact diagonalization and density matrix renormalization group results. At half-filling, strong frustration in the intermediate to large $U$ regimes necessitates symmetry-projected trials to reach comparable accuracy, where both free-electron and symmetry-broken Hartree-Fock trials incur substantial constraint bias. Since the computational cost of CPMC with symmetry projection scales polynomially with system size, our results motivate its use as a practical route for studying competing ground states in strongly correlated, frustrated systems.
Read the full abstract

Materials Science

Predicting electron-phonon coupling and electronic transport at the moiré scale in twisted bilayer graphene

First-principles calculations can accurately describe electron-phonon (e-ph) interactions and electronic transport in a wide range of materials, but are currently limited to unit cells with up to $\sim$100 atoms due to computational cost. Here, we develop an atomistic electronic potential with Holstein- and Peierls-like terms for modeling e-ph interactions and phonon-limited electronic transport that enables the study of moiré systems with thousands of atoms per unit cell. This method can accurately reproduce first-principles e-ph coupling and resistivity in graphene and large-angle twisted bilayer graphene (TBG). Using this approach, we study TBG over a range of twist angles down to 1.6$^\circ$ (5044-atom unit cell), and report the evolution of e-ph interactions and phonon-limited resistivity with twist angle. The predicted resistivity increases by two orders of magnitude between 13.2$^\circ$ and 1.6$^\circ$, driven by the progressive reduction of the electronic energy scale. Our calculations can predict key experimental trends in 2.0$^\circ$ and 1.6$^\circ$ TBG, including the resistivity and its dependence on temperature and band filling. Our work establishes a scalable approach for quantitative studies of e-ph interactions and transport in moiré materials and other systems with previously inaccessible length scales.
Read the full abstract

Mesoscale and Nanoscale Physics

Universal tuning of quantum electrodynamic interactions from power laws to exponential screening and logarithmic antiscreening

We introduce a material-agnostic platform for universal tuning of quantum electrodynamic interactions from power laws to exponential screening and logarithmic antiscreening, realized in a dielectric spacer bounded by two gate-tunable two-dimensional conductors. The structured electromagnetic environment is completely specified by the transverse-magnetic and transverse-electric reflection amplitudes \(r_{\mathrm{TM/TE}}(q_\perp,\omega)\) of the sheets. Starting from the QED action and a Green-function formulation, we resum the multiple-reflection series and show that the interactions are governed by a discrete set of transverse cavity harmonics. In the transparent limit \(r_{\rm TM}\to 0\), the interactions reduce to bulk power laws \(U(\rho)\propto \rho^{-\alpha}\). In the reflective limit \(|r_{\rm TM}|\to 1\), the phase/parity of \(r_{\rm TM}\) selects two qualitatively distinct branches: a Dirichlet/PEC (screening) branch \(r_{\rm TM}\to -1\) that removes the gapless transverse mode and yields an evanescent Bessel-\(K\) function \(U(\rho)\propto e^{-\pi\rho/d}/\sqrt{\rho/d}\) at \(\rho\gg d\), and an opposite Neumann/PMC-like (antiscreening) branch \(r_{\rm TM}\to +1\) that retains a gapless mode and can strongly enhance the long-range tail. Thus, the same heterostructure provides in situ electrical control over both the range and the strength of mediated interactions.
Read the full abstract

Strongly Correlated Electrons

Neural network backflow for ab-initio solid calculations

Accurately simulating extended periodic systems is a central challenge in condensed matter physics. Neural quantum states (NQS) offer expressive wavefunctions for this task but face issues with scalability. In this work, we successfully extend the neural network backflow (NNBF) approach to ab-initio solid-state materials. Building on our scalable optimization framework for molecules [Liu et al., PRB 112, 155162 (2025)], we introduce a two-stage pruning strategy to manage the massive configuration space expansions: by utilizing a computationally cheap, physics-informed importance proxy, we devote exact NNBF amplitude evaluations solely to the most relevant determinants, significantly improving optimization efficiency, energy estimation, and convergence. Our framework achieves state-of-the-art accuracy across diverse solid-state benchmarks. For 1D hydrogen chains, NNBF matches or surpasses DMRG and AFQMC, remains robust in strongly correlated bond-breaking regimes where coupled-cluster methods fail, and smoothly extrapolates to the thermodynamic limit. We further demonstrate its scalability by computing ground-state potential energy curves for 2D graphene and 3D silicon. Finally, ablation studies validate the computational savings of our pruning strategy and highlight the dependence of the NNBF energies on basis sets.
Read the full abstract

Materials Science

Interfacial exchange and magnetostatic coupling in a CoFeB/Thulium Iron Garnet heterostructure

We investigate the exchange coupling between a ferrimagnetic insulator (FI) thulium iron garnet (TmIG) deposited on a gadolinium gallium garnet (GGG) substrate, which shows perpendicular magnetic anisotropy and a ferromagnetic metal (FMM) stack with oxide capping that consists of CoFeB(x)/W(0.4 nm)/CoFeB(0.8 nm)/MgO(1 nm)/W(5 nm). Vibrating sample magnetometry, magneto-optical Kerr microscopy and first-order reversal curve studies coupled with micromagnetic simulations are used to analyze the coupling between these layers. Strong interlayer exchange coupling and magnetostatic coupling are observed in the samples where the relative strength between these interactions can be controlled by varying the thickness of the CoFeB layer. Films with CoFeB thickness x <=1 nm are strongly exchange coupled, whereas the magnetostatic coupling dominates when the thickness is increased to 3 nm or above. These findings have important implications towards realizing fast and energy efficient spintronic devices using a FI, as its coupling to the FMM layer can be used for effective electrical read out of the magnetic state of the FI.
Read the full abstract

All authors Walid Al Misba, Jenae E. Shoup, Miela J. Gross, Dhritiman Bhattacharya, Kai Liu, Caroline A. Ross, Daniel B. Gopman, Jayasimha Atulasimha

Materials Science

Synchrotron-radiation X-ray topography and reticulography of bulk $\beta$-Ga$_2$O$_3$ crystals grown by the cold crucible method

The structural properties of a $\beta$-Ga$_2$O$_3$ single crystal grown by the oxide crystal growth from cold crucible (OCCC) method were investigated using synchrotron radiation X-ray topography and X-ray reticulography. The region grown beneath the seed exhibits high crystalline quality with a rocking curve full width at half maximum of about 26 arcsec. During diameter enlargement, a twist-type lattice misorientation develops between the central and laterally expanded regions, originating near the shoulder and propagating along boundaries parallel to the $\langle010\rangle$ growth direction. Dislocation analysis reveals that $\langle010\rangle$-oriented screw dislocations dominate the defect structure with densities of ~$10^{5}$cm$^{-2}$, while higher densities (~$10^{6}$cm$^{-2}$) appear in the wing region. These results clarify defect formation in OCCC-grown $\beta$-Ga$_2$O$_3$ and provide insights for optimizing growth conditions.
Read the full abstract

All authors Yongzhao Yao, Koki Mizuno, Kazuki Ohnishi, Yukari Ishikawa, Masanori Kitahara, Taketoshi Tomida, Rikito Murakami, Vladimir Kochurikhin, Liudmila Gushchina, Kei Kamada, Koichi Kakimoto, Akira Yoshikawa

Materials Science

Decoupling structural and bonding effects on ferroelectric switching in ScAlN via molecular dynamics under an applied electric field

ScxAl1-xN has emerged as a promising wurtzite-type ferroelectric material, where increasing the Sc composition reduces both the coercive field (Ec) and remanent polarization (Pr). This composition-dependent behavior is physically attributed to two simultaneous changes: the increase in the internal structural parameter u (structural effect) and the weakening of bond strength (bonding effect). Because these factors are strongly coupled in experiments, their individual contributions to ferroelectric switching remain unclear. In this study, we systematically decoupled these effects using machine-learning force field-based molecular dynamics (MD) simulations under an applied electric field. By artificially tuning u via in-plane strain at a fixed composition, we demonstrated that Pr is determined exclusively by the structural effect, exhibiting a universal linear dependence regardless of the composition. In contrast, Ec deviated from this structural trend, implying an additional compositional contribution. To isolate this, we evaluated configurations with identical u but varying Sc compositions; Pr remained constant, whereas Ec systematically decreased due to bond weakening. Furthermore, static nudged elastic band (NEB) calculations revealed that the static switching barrier depends solely on u, failing to explicitly capture the bonding effect on Ec. These results establish that while Pr is governed strictly by the structural effect, Ec is determined by a superposition of structural and bonding effects. Our findings highlight the necessity of dynamic MD simulations for fully understanding ferroelectric switching in compositionally tunable materials.
Read the full abstract

Soft Condensed Matter

Molecular Origin of UV-Induced Irreversible Phase Changes in a Chromonic Liquid Crystal

Aqueous solutions of disodium cromoglycate (DSCG), a representative model system for chromonic liquid crystals, exhibit temperature- and concentration-dependent phase behaviors spanning isotropic, nematic, and columnar phases, as well as their coexistence regions. Nastishin et al. (2018) reported that UV irradiation can alter the phase diagram, transforming a nematic phase into a nematic-isotropic biphasic state due to weakened molecular attractions, accompanied by a slow post-irradiation relaxation. Here, we revisit this phenomenon and elucidate the molecular origin of this phase diagram shift: the UV-induced photodegradation of DSCG into specific photodegradation products, which we identify using liquid chromatography-mass spectrometry. Through an integrated approach combining in situ X-ray scattering and polarized optical microscopy, we demonstrate that these degradation products disrupt the self-assembly of DSCG aggregates, thereby expanding the isotropic and biphasic regions in the phase diagram. These findings demonstrate that chromonic assemblies and their phase behaviors are highly sensitive to minor chemical alterations, providing a potential route toward light-controlled self assembly of soft matter.
Read the full abstract

All authors Junghoon Lee, Seonghun Jeong, Jung-Min Kee, Joonwoo Jeong

Strongly Correlated Electrons

Non-Abelian fractional Chern insulators from an exactly solvable two-body model

We construct a class of lattice Hamiltonians whose single-particle spectrum consists of an arbitrary number of exactly degenerate flat bands that reproduce the analytic structure of the first $p$ Landau levels restricted to the lattice. When combined with local bosonic contact interactions, these models become exactly solvable frustration-free parent Hamiltonians for FCIs that realize both Abelian and non-Abelian parton quantum Hall states. Using exact diagonalization, we confirm the expected zero-mode counting for variants of the model stabilizing the bosonic Jain-21 state as well as the non-Abelian 22- and 33-states, which are expected to support Ising- and Fibonacci-type anyons, respectively. Our construction provides an exactly solvable lattice realization of multi Landau-level physics and offers a new framework for studying FCIs with Chern number $C > 1$. More broadly, it supplies a family of idealized lattice models that capture the analytic structure of continuum Landau levels while remaining compatible with exponentially local hopping.
Read the full abstract

Mesoscale and Nanoscale Physics

Spatiotemporal Magnonic Vortex Beams with Alternating Transverse Orbital Angular Momentum

Recent theoretical and experimental advances have demonstrated spatiotemporal photonic and acoustic vortex beams in free space. Such spatiotemporal vortex beams possess orbital angular momentum oriented perpendicular to the wave propagation direction. Herein, we report the discovery of spatiotemporal magnonic vortex beams in a confined ferromagnetic nanostrip geometry. The spatiotemporal magnonic vortex beam features stationary phase dislocations and exhibits wave propagation along a zigzag-like trajectory. Notably, the transverse orbital angular momentum carried by these phase dislocations displays spatial alternation. Our results differ distinctly from their photonic and acoustic counterparts, offering new insights into the fundamental research of spatiotemporal vortex beams.
Read the full abstract

All authors Muyang Xie, Chenchen Liu, Jian Huang, Zhenyu Wang, Xinwei Dong, Ruifang Wang

Mesoscale and Nanoscale Physics · Cross-listed from physics.bio-ph

Digital unzipping of DNA through a solid-state nanopore: A theoretical study for base-by-base ratcheting

Solid-state nanopore DNA sequencers present mechanical and chemical stability, reusability, and large-scale integrability. However, their development is hindered by the absence of a protein-free mechanism for controlling DNA translocation, which is accomplished by motor proteins in their biological counterparts. Here, we propose and theoretically analyze a protein-independent ratchet mechanism based on the unzipping of double-stranded DNA at the nanopore rim. When the transmembrane bias exceeds a certain threshold, the base pairs mechanically dissociate, allowing one strand to translocate while the other remains upstream. This unzipping process is known to slow DNA motion, suggesting that voltage pulses can trigger individual unzipping events at externally defined times, a concept referred to as digital unzipping. However, the intrinsic unzipping barrier is insufficient to provide the dwell times required for a reliable ionic-current readout; therefore, an additional mechanism is needed to hold the DNA in place between voltage pulses. To overcome this limitation, we introduce a reversible hold mechanism implemented via electrostatic attraction between DNA and a charged nanopore wall, which temporarily immobilizes the strand once the unzipping fork catches on the nanopore rim. Using a statistical-mechanical model, we track the evolution of the mean and variance of DNA position through each ratchet cycle. Analytical expressions for the corresponding error probabilities show that submicrosecond switching of the hold mechanism enables base-by-base stepping with an error rate <5%. These results theoretically demonstrate that digital unzipping combined with a reversible hold mechanism can yield deterministic single-base motion, thus opening a viable route toward all-solid-state nanopore sequencing.
Read the full abstract

Statistical Mechanics

Scaling Autoregressive Models for Lattice Thermodynamics

Predicting how materials behave under realistic conditions requires understanding the statistical distribution of atomic configurations on crystal lattices, a problem central to alloy design, catalysis, and the study of phase transitions. Traditional Markov-chain Monte Carlo sampling suffers from slow convergence and critical slowing down near phase transitions, motivating the use of generative models that directly learn the thermodynamic distribution. Existing autoregressive models (ARMs), however, generate configurations in a fixed sequential order and incur high memory and training costs, limiting their applicability to realistic systems. Here, we develop a framework combining any-order ARMs, which generate configurations flexibly by conditioning on any known subset of lattice sites, with marginalization models (MAMs), which approximate the probability of any partial configuration in a single forward pass and substantially reduce memory requirements. This combination enables models trained on smaller lattices to be reused for sampling larger systems, while supporting expressive Transformer architectures with lattice-aware positional encodings at manageable computational cost. We demonstrate that Transformer-based any-order MAMs achieve more accurate free energies than multilayer perceptron-based ARMs on both the two-dimensional Ising model and CuAu alloys, faithfully capturing phase transitions and critical behavior. Overall, our framework scales from $10 \times 10$ to $20 \times 20$ Ising systems and from $2 \times 2 \times 4$ to $4 \times 4 \times 8$ CuAu supercells at reduced computational cost compared to conventional sampling methods.
Read the full abstract

All authors Xiaochen Du, Juno Nam, Sulin Liu, Rafael Gómez-Bombarelli

Soft Condensed Matter · Cross-listed from physics.bio-ph

A Unified Variational Principle for Branching Transport Networks: Wave Impedance, Viscous Flow, and Tissue Metabolism

The branching geometry of biological transport networks is characterized by a diameter scaling exponent $\alpha$. Two structural attractors compete: impedance matching ($\alpha \sim 2$) for pulsatile flow and viscous-metabolic minimization ($\alpha = 3$) for steady flow. Neither predicts the empirically observed $\alpha_{\mathrm{exp}} = 2.70 \pm 0.20$ in mammalian arterial trees. Incorporating sub-linear vessel-wall scaling $h(r) \propto r^p$ ($p = 0.77$) into a three-term metabolic cost rigorously breaks Murray's cubic law – via Cauchy's functional equation – bounding the static optimum to $\alpha_t \in [2.90, 2.94]$. We formulate a unified network-level Lagrangian balancing wave-reflection penalties against transport-metabolic costs. Because the operational duty cycle $\eta$ is uncertain over developmental timescales, we cast the optimization as a zero-sum game between network architecture and environment. Von Neumann's minimax theorem – proved via strict monotonicity of the cost curves – yields a unique saddle point $(\alpha^, \eta^)$ satisfying an exact equal-cost condition. We further prove $N = 2$ uniquely maximizes the network stiffness ratio $\kappa_{\mathrm{eff}}(N)$, deriving binary branching as a structural consequence of the framework. For the porcine coronary tree ($G = 11$ generations), $\alpha^* = 2.72$, within $0.1\sigma$ of morphometric data. Sensitivity analysis confirms $|\Delta\alpha^*| < 0.01$ across physiological metabolic ranges; the prediction depends critically only on the histological exponent $p$ – a zero-parameter derivation from fundamental scaling principles that simultaneously recovers a cumulative wave dissipation of 6.3%, consistent with independent clinical estimates.
Read the full abstract

Statistical Mechanics

Observation-Time-Induced Crossover in Driven Anomalous Transport

We investigate how a weak constant force becomes detectable through fluctuations in anomalous transport in strongly heterogeneous media. Rather than focusing on the mean drift, we show that the key signature of the force appears in the variance of the particle displacement. As representative models, we study a biased continuous-time random walk (CTRW) with nearest-neighbor jumps and a biased quenched trap model (QTM) with a power-law waiting-time tail. By analysing the force dependence of the displacement variance, we quantify how fluctuations respond to weak driving. We find that for $\alpha<2$, the response exhibits an observation-time-induced crossover: at fixed bias, the variance initially follows its unbiased scaling and only at later times crosses over to a force-dominated nonequilibrium regime. Equivalently, at fixed observation time $t$, there exists a threshold bias $\varepsilon_c(t)$ separating an apparently equilibrium-like regime from a detectable nonequilibrium response. This threshold decreases with increasing $t$, implying that weaker forces become observable over longer measurement windows. Quenched disorder further lowers the detection threshold compared with CTRW, and the crossover reflects a competition between the finite observation time and the intrinsic relaxation time of the driven heterogeneous system.
Read the full abstract

Strongly Correlated Electrons

Giant anomalous Hall conductivity in frustrated magnet EuCo2Al9

The interaction between conduction electrons and localized magnetic moments profoundly influences the electrical and magnetic properties of materials, giving rise to a variety of fascinating physical phenomena and quantum effects. Here, we discover a giant anomalous Hall effect (AHE) in a frustrated Eu-based magnet, exhibiting a giant anomalous Hall conductivity (AHC) of 31000 {\Omega}-1cm-1 and a remarkable anomalous Hall angle (AHA, tan{\theta}H) of 12 %–surpassing conventional mechanisms (either intrinsic or extrinsic) by two orders of magnitude. Combining magnetotransport, quantum oscillations, neutron diffraction and ab initio calculations, we establish that the giant AHC originates from fluctuating spin chirality skew scattering, generated by indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions of Eu-4f moments. Simultaneously, Hund's coupling of itinerant electrons and localized Eu-4f spins triggers giant exchange splitting, evidenced by temperature-dependent Fermi surface reconstruction. This work establishes a frustrated magnetic platform for engineering the AHE and elucidates the governing role of exchange interactions and spin textures in quantum transport, while also providing a framework for designing unconventional spintronic systems that harness emergent spin-texture dynamics.
Read the full abstract

All authors Sheng Xu, Jian-Feng Zhang, Shu-Xiang Li, Junfa Lin, Xiaobai Ma, Wenyun Yang, Jun-Jian Mi, Zheng Li, Tian-Hao Li, Yue-Yang Wu, Jiang Ma, Qian Tao, Wen-He Jiao, Xiaofeng Xu, Zengwei Zhu, Yuanfeng Xu, Hanjie Guo, Tian-Long Xia, Zhu-An Xu

Mesoscale and Nanoscale Physics

Composite boson theory of Hall crystals and their transitions to Wigner crystals

We consider the crystallization of a two-dimensional electron system in a perpendicular magnetic field using composite boson theory. There are three possible states to consider: the Hall liquid, the Wigner crystal, and the Hall crystal (a state with both broken translation symmetry and a quantized Hall response). Within composite boson theory, these states map onto a superconductor, a Mott insulator, and a supersolid of composite bosons respectively. We show that when a $\nu = 1$ Hall liquid has a sufficiently soft roton, there is a first order transition to a triangular lattice Hall crystal. If we continue to decrease the roton mass, there is a continuous transition from the Hall crystal to a Wigner crystal. {When the Hall crystal exhibits the integer quantum Hall effect,} this transition {is} described by a free Dirac fermion and, at the critical point, the coupling to the phonons of the crystal is irrelevant, {in the {renormalization group} sense}. We extend this analysis to fractional $\nu = 1/m$ Hall liquids. There, due to kinetic frustration arising from flux attachment, honeycomb lattice Hall crystals are preferred over triangular ones at intermediate interaction strength.
Read the full abstract

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

Stochastic Collision Theory of Magnetism in Radical Fluids

How stochastic, microscopic events generate deterministic, macroscopic properties is a fundamental question in physics. We address this question by developing a quantum master equation model for concentrated radical solutions, where random molecular collisions govern the magnetic properties of the system. Our theory reveals a simple mechanism: the first-order exchange contribution averages to zero over collisions, while the second-order term survives as an effective ferromagnetic coupling that enhances magnetization. The model captures the experimentally observed trends in magnetic behavior that deviate from conventional theories. Because the mechanism arises from statistical averaging, it may apply to a broader class of soft matter phenomena, including liquid crystals.
Read the full abstract

Materials Science

Acrylamide Conformers: A Revision of Published Density Functional Theory Studies

Acrylamide, with PubChem identifier CID=6579 is broadcasted to have four stable conformers contrasting with several journal publications characterizing only two or three. In this revision summary the discrepancy is clarified. Through very high precision density functional theory (DFT) calculations, three stable conformers and the three transition state barriers existing between them are verified to exist and validated with our own DFT calculations The most stable conformer is a planar molecular structure termed "sys" or "trans" in the literature. Meanwhile, a less stable structure termed "skew" pertains to two 3-dimensional structures that are energy-degenerate, but differ in their structure for being mirrored images of each other. Vibrational spectra, partial atomic charges, Cartesian coordinates, and Intrinsic Reaction Coordinate paths are summarized and recalculated with DFT at the $\omega$B97XD/Def2TZVPP level for the three stable acrylamide isomers: the sys/trans lowest in energy structure, and the two skew mirrored structures.
Read the full abstract

Sunday 15 March

Statistical Mechanics

Survival probability of random networks

In this work we study in detail all phases of the time evolution of a delta-like excitation in Erdös-Renyi (ER) random networks by means of the survival probability (SP): The initial decay of the SP (both, the fast decay followed by the power-law decay), the correlation hole regime (the regime between the minimum value of the SP and its saturation value), and the saturation of the SP. Specifically, we found that (i) the power-law decay of the SP and the time-averaged SP are proportional to $t^{-D_{2}}$ and $t^{-\widetilde{D}_{2}}$, respectively (where $D_2$ and $\widetilde{D}_2$ are the correlation dimension of the eigenstates of the randomly weighted adjacency matrices of the ER random networks and the correlation dimension associated with the initial state, respectively) and (ii) the relative depth of the correlation hole of the SP scales with the average degree $\langle k\rangle\approx np$ (here, $n$ and $p$ are the size and the connection probability of the ER random networks). In addition, we show that the eigenstates of the randomly weighted adjacency matrices of ER networks display clear multifractal properties.
Read the full abstract

Materials Science

A phase field model with arbitrary misorientation dependence of grain boundary energy

Grain growth in polycrystals is often simulated using orientation-field models, which employ a field to represent the local orientation of the crystal lattice. These models can be challenging to represent a realistic misorientation dependence of grain boundary free energy. We prove that existing orientation-field models, in general, cannot reproduce a decrease in the grain boundary free energy with a increasing misorientation angle, demonstrating a significant limitation of previous models in applications to polycrystalline materials. To overcome this limitation, we propose a modification to the Kobayashi-Warren-Carter model for grain growth wherein the coefficients of the free-energy functional become functions of the misorientation between the grains, which is a non-local quantity. Due to this modification, an arbitrary dependence of the grain boundary free energy on the misorientation can be embedded in the model. We propose calculating the non-local misorientation by interpolating the orientation field at a fixed distance in both directions along the local grain boundary normal vector. The capabilities of the model are demonstrated by introduction of a sharp cusp to the misorientation dependent grain boundary free energy. Finally, we propose an extension of the model to three dimensions.
Read the full abstract

All authors Philip Staublin, Yuri Mishin, Peter W. Voorhees, James A. Warren

Materials Science

Role of Oxygen Vacancies in Stabilizing the Orthorhombic Phases of Hf0.5Zr0.5O2 Nanoparticles

In this work we study the stabilization of the orthorhombic phases in small Hf0.5Zr0.5O2 nanoparticles (average size ~ 7 nm) annealed under different oxygen partial pressures. Concentration of the oxygen vacancies, which is determined by annealing conditions, was estimated from the electron paramagnetic resonance spectra and X-ray photoelectron spectroscopy. The fraction of the orthorhombic phases, that is determined by the X-ray diffraction and nuclear magnetic resonance, depends on the concentration of oxygen vacancies. Phenomenological calculations based on Landau-Ginzburg-Devonshire theory considering trilinear coupling between nonpolar, antipolar and polar phonon modes, indicate that chemical strain induced by oxygen vacancies can stabilize the orthorhombic phase o-III with the ferroelectric long-range ordering in small Hf0.5Zr0.5O2 nanoparticles. The theory confirms the stability of ferroelectric polarization in the vacancy-enriched Hf0.5Zr0.5O2 nanoparticles. The increase in the intensity of the dielectric permittivity maximum, observed near 350 - 380 K in the PVDF matrix with the Hf0.5Zr0.5O2 nanoparticles annealed in the CO+CO2 atmosphere, is clearly associated with the increase in oxygen vacancies concentration. The vacancies lead to the defect-induced elastic dipole formation and to the increase in ionic conductivity, which decreases the depolarization field and may induce the ferroelectric-like phase transition in the vacancy-enriched Hf0.5Zr0.5O2 nanoparticles. Due to the interfacial effects the negative capacitance states may be realized in weakly screened and spatially isolated Hf0.5Zr0.5O2 nanoparticles embedded in the PVDF matrix.The present approach based on oxygen-vacancy-induced elastic and screening effects may provide a route for engineering ferroelectric-like states in other nanoscale ferroic oxides.
Read the full abstract

All authors Yuriy O. Zagorodniy, Eugene A. Eliseev, Valentin V. Laguta, Petr Jiricek, Jana Houdkova, Lesya D. Demchenko, Oksana V. Leshchenko, Victor N. Pavlikov, Lesya P. Yurchenko, Anna O. Diachenko, Michail D. Volnyanskii, Oleksandr S. Pylypchuk, Myroslav V. Karpets, Mikhail P. Trubitsyn, Dean R. Evans, Anna N. Morozovska

Mesoscale and Nanoscale Physics

Quantifying quasiparticle chirality in a chiral topological semimetal

Recently, the projection of the electron's spin on its crystal momentum has been proposed as a metric to quantify electronic chirality of Bloch states in crystals, which is expected to affect a wide range of physical properties, such as magnetoelectric and optical responses. However, a direct experimental quantification of this chirality metric over an entire iso-energy surface has remained elusive. Here, we have used spin- and angle-resolved photoemission spectroscopy to directly probe the electronic chirality by measuring the bulk spin texture of Kramers-Weyl and Weyl cones in RhSi, a chiral topological semimetal with strong spin-orbit coupling (SOC). After quantifying the SOC splitting of Weyl cones, we determine their spin direction along different azimuthal angles to extract energy dependent the deviations (up to ~40{\deg}) from perfect parallel spin-momentum locking. From these deviations we define an energy-dependent normalized electron chirality density (NECD), a directly accessible metric of bulk electronic chirality. In RhSi, the NECD decreases from 1 at the Kramers-Weyl point to ~0.8 at ~200 meV below it. Finally, we show that this experimentally grounded NECD provides predictive power for magneto-optical and transport responses of chiral materials, exemplified by the longitudinal Edelstein effect.
Read the full abstract

All authors Jiaju Wang, Jaime Sánchez-Barriga, Amit Kumar, Markel Pardo-Almanza, Jorge Cardenas-Gamboa, Iñigo Robredo, Chandra Shekhar, Daiyu Geng, Emily C. McFarlane, Martin Trautmann, Enrico Della Valle, Moritz Hoesch, Meng-Jie Huang, Jens Buck, Vladimir N. Strocov, Annika Johansson, Stuart S. P. Parkin, Claudia Felser, Maia G. Vergniory, Niels B. M. Schröter

Soft Condensed Matter

Dissipative self-assembly of colloidal suspensions

Suspensions of paramagnetic colloids exhibit kinetic arrest in strong magnetic fields. Through a dissipative process of toggling the field on and off, suspensions self-assemble into dense and dynamic steady-state phases. Based on the domain elongation, alpha- and contour-shapes, and degree of phase separation, we construct a phase diagram using a k-means clustering analysis. We identify six characteristic structural regimes: a structureless phase, an arrested structure, sheets, ribbons, a spiky phase, and a transient fluid-fluid regime. We further report the distribution and alignment of domains and the generality of the results. We model self-assembled domain shapes using an equilibrium mean-field magnetostatic energy calculation, which predicts the surprising emergence of highly-anisotropic structures driven by the sample's confinement.
Read the full abstract

Materials Science

Sequential Quenching to Predict Semiconductor Defect Concentrations from Formation & Migration Energies: The Case of CdTe:As Doping

Defect concentrations in semiconductors are strongly influenced by thermal history during growth and cooldown, yet most defect calculations assume either instantaneous quenching from high temperature or that full-equilibrium is maintained - two limiting cases rarely approached in reality. Here, we introduce sequential quenching (SQ) as a 3rd type of defect calculation utilizing defect formation and migration energies to model defect concentrations subject to diffusion-limited kinetics in samples cooled at finite rates. In SQ, the concentration of each defect is frozen at a characteristic temperature determined by its diffusion rate, distance to sources/sinks, and cooling rate. Because different charge-states interact through charge neutrality but freeze at different temperatures, the sequence of freeze-in events is non-commuting. Critically, not all room-temperature SQ solutions can be predicted from full equilibrium (EQ) or full-quenching (FQ) calculations - erroneous predictions are likely without SQ. We illustrate SQ using the example of As-doped CdTe, for which experimental data show differences in doping with cooling rate and between polycrystalline thin-films for photovoltaics and bulk crystals. SQ calculations reveal that fast-diffusing defects such as Cd-interstitials remain mobile to lower temperatures and freeze-in at larger characteristic distances, leading to strong compensation and n-type behavior in rapidly cooled or bulk samples. Slower cooling and reduced characteristic distances suppress donor freeze-in and enhance p-type activation. These results establish SQ as a physically transparent and computationally efficient framework for connecting cooling conditions, sample geometry, and defect kinetics to dopant activation in CdTe and related materials.
Read the full abstract

All authors Khandakar Aaditta Arnab, Intuon Chatratin, Anderson Janotti, Michael Scarpulla

Strongly Correlated Electrons

Ferroaxial and nematic transitions in the charge density wave phase of 1T-TiSe$_2$

Charge density waves (CDWs) with multi-component order parameters can break unexpected symmetries through the interplay of nearly degenerate instabilities. In the widely investigated material 1T-TiSe$_2$, a central question is whether the observed CDW has a chiral character, which would manifest as the spontaneous breaking of mirror and inversion symmetries. Previous experiments have reported conflicting results about the broken symmetries in the CDW phase of 1T-TiSe$_2$. Here, we resolve this controversy by identifying the bulk broken symmetry as ferroaxial, corresponding to the breaking of vertical mirrors while preserving inversion symmetry. Using symmetry-resolved elastoresistivity, we detect the spontaneous emergence of intrinsic off-diagonal elastoresistivity coefficients that satisfy an antisymmetric relation ($m_{xx-yy,xy} \approx -m_{xy,xx-yy}$), providing an unambiguous bulk transport signature of a macroscopic electric toroidal moment. Simultaneous elastocaloric measurements reveal that the onset of ferroaxial order occurs just below the CDW transition. As the temperature is lowered further, a diverging nematic susceptibility signals a distinct rotational symmetry-breaking instability inside the ferroaxial CDW state. Our findings demonstrate that the proposed “chiral” CDW in 1T-TiSe$_2$ is actually a centrosymmetric ferroaxial state, reconciling previous surface-sensitive observations with bulk symmetry constraints.
Read the full abstract

All authors Sarah Edwards, Elliott Rosenberg, Ilaria Maccari, Jiaqin Wen, Chaowei Hu, Xiaodong Xu, Jong-Woo Kim, Philip J. Ryan, Rafael M. Fernandes, Fernando de Juan, Maria N. Gastiasoro, Jiun-Haw Chu

Strongly Correlated Electrons

Evidence for ferroaxial order in 1T-TiSe$_2$ via elastoresistivity measurements

The study of spontaneous symmetry breaking and electronic order is fundamental in condensed matter physics. Hidden order, symmetry-breaking states that elude conventional probes, potentially plays a crucial role in understanding complex quantum phases in a wide range of materials. Ferroaxial order, a state characterized by broken mirror symmetries while maintaining time-reversal and inversion symmetries, is one of the hidden orders that have proven most challenging to detect experimentally. Here, we demonstrate a new approach for investigating both the ferroaxial order parameter and ferroaxial susceptibility using elastoresistivity measurements. We do this for 1T-TiSe$_{2}$, a material that exhibits charge density wave order that has eluded comprehensive understanding for a long time. These measurements reveal an anomalous off-diagonal linear elastoresistivity in the CDW state. We discuss why this provides a smoking gun for ferroaxial order. Furthermore, we construct an appropriate combination of the symmetry-breaking strains $\epsilon_{x^2-y^2}$ and $\epsilon_{xy}$ that acts as an effective conjugate field for the ferroaxial order, and demonstrate how sweeping this effective field in the CDW state results in a hysteretic behavior of the elastoresistivity, associated with the movement of ferroaxial domain walls. Finally, we reveal a divergence of certain nonlinear elastoresistivity coefficients above the critical temperature, and discuss how this is consistent with a divergence of the ferroaxial susceptibility near T$_{\rm{CDW}}$ $\sim$ 200K. Our study also includes detailed elastocaloric measurements, which reveal the presence of an additional phase transition several tens of Kelvin below T$_{\rm{CDW}}$. Our results provide new insight into the symmetry of the ordered state in 1T-TiSe$_2$ and establish elastoresistivity as a powerful probe of hidden order and its symmetry.
Read the full abstract

All authors Qianni Jiang, Ezra Day-Roberts, Benito Gonzalez, Awadhesh Das, Darius H. Torchinsky, Turan Birol, Rafael M. Fernandes, Ian R. Fisher

Soft Condensed Matter

Mechanical waveform memory in an athermal random medium

Using numerical simulations it is shown that a random, athermal pack of soft frictional grains will store an arbitrary waveform that is applied as a small time-dependent shear while the system is slowly compressed. When the system is decompressed at a later time, an approximation of the input waveform is recalled in time-reversed order as shear stresses on the system boundaries. It is shown that this effect depends on friction between the grains, and is independent of some aspects of the friction model. By systematically increasing the complexity of the stored waveform, it is found that a pack of $10^4$ grains can recall any one of 128 different waveforms with 100% classification accuracy and 512 different waveforms with over 90% classification accuracy, as measured by a neural net trained only on the inputs. This type of waveform memory might be observable in other types of athermal random media that form internal contacts when compressed such as crumpled sheets and nest-like fiber assemblies.
Read the full abstract

Materials Science

Cut-and-Project Density Functional Theory for Quasicrystals

Cut-and-project from a symmetric structure in a higher-dimensional space is a standard method for describing the structure of a large class of quasicrystals. By means of a novel localization procedure, we now show how local physical interactions within these quasicrystals are also accurately described by cut-and-project, from corresponding physical interactions in the higher-dimensional space. A density functional theory (DFT++) formulation allows the cut-and-project method to handle the Schroedinger equation for interactions in quasicrystals. The theory is both rigorous and computationally tractable. The resulting ab initio approach specifies quasicrystalline quantum states, in contrast to previous approaches which only worked with crystalline approximants of the quasi-periodic structures.
Read the full abstract

All authors Gavin N. Nop, Jonathan D. H. Smith, Thomas Koschny, Durga Paudyal

Materials Science

Radiation-induced segregation in dilute Fe-Cr: A rate-theory framework for the Cr enrichment-depletion transition at the grain boundary

Radiation-induced segregation (RIS) poses a significant challenge for ferritic Fe-Cr alloys under irradiation, as it can compromise mechanical integrity and increase susceptibility to intergranular corrosion. Yet, the mechanisms governing Cr segregation remain incompletely understood. In this study, We present a physics-based rate-theory model parameterized using self-consistent mean field theory-based Onsager transport coefficients to investigate RIS at the grain boundary (GB) in dilute Fe-(0.1 at.%) Cr. Under equal production rates of vacancies and self-interstitial atoms (SIA), and their equal absorption rates by bulk dislocations, the model simulates the experimentally observed transition from Cr enrichment at low temperatures to depletion at higher temperatures. Under these unbiased conditions, systematic investigation reveals that while temperature-dependent transport properties dictate the segregation direction, dose rate, grain size, and dislocation density only influence the magnitude and spatial extent of Cr segregation. However, under more realistic conditions of preferential vacancy production within damage cascade and/or preferential SIA absorption by bulk dislocations, the enrichment-to-depletion transition shifts to lower temperatures. Our findings demonstrate that RIS predictions based solely on transport coefficients are valid only under symmetric point defect flux conditions, and that biases in defect production and absorption must be considered for accurate predictions. This work provides a mechanistic framework for understanding RIS in ferritic alloys and informs alloy design for advanced nuclear systems.
Read the full abstract

All authors Russell Oplinger, Mukesh Bachhav, Karim Ahmed, Sourabh Bhagwan Kadambi