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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Thursday 27 August

Materials Science

Electronic Structure and Band-Edge Character of Ga-Substituted $\alpha$-Al$_2$O$_3$: A First-Principles Study

Z. S. Machavariani, R. Ya. Kezerashvili and T. Tchelidze

We present a first-principles density functional theory study of substitutional Ga incorporation in an $\alpha$-Al$_2$O$_3$-derived host, isolating chemical embedding effects without explicit geometric quantum confinement. Using a 30-atom $\alpha$-Al$_2$O$_3$ supercell with two substituted Ga atoms, we examine three nonequivalent Ga-pair configurations and combine configuration-dependent energetics, local structural analysis, Ga-centered distortion metrics, and electronic-structure calculations.% to establish the relationship between local coordination distortion and band-edge modification. The energetically preferred configuration is governed not solely by Ga–O bond expansion but by the ability of the host lattice to accommodate bond-length and angular distortions around substituted Ga centers. Ga incorporation narrows the band gap relative to pristine $\alpha$-Al$_2$O$_3$ without generating mid-gap states, primarily modifying the conduction-band manifold while preserving the oxygen-dominated valence edge. Band-edge charge densities and charge-density-difference maps show that the electronic response remains localized around the Ga-centered coordination environment. These results establish a chemically resolved baseline for understanding Ga incorporation in ultrawide-band-gap oxides and for future studies of confinement and interface effects in Ga-containing oxide nanostructures.
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Materials Science

Scalable conformal electronics based on roll-to-roll exfoliated van der Waals semiconductors

Yigit Sozen, Esteban Zamora-Amo, Juan J. Riquelme et al. (+1 more)

Integrating electronic devices onto surfaces with complex topography such as skin, textiles, and biological tissues requires fabrication strategies that combine mechanical conformability with high electronic performance and scalable manufacturing. While two-dimensional (2D) semiconductors are promising materials for such applications, their integration into conformal electronic systems remains challenging because scalable liquid-phase processing typically yields films with limited electronic performance, whereas high-quality CVD materials require complex synthesis and transfer processes. Here we establish a scalable route toward conformal electronics based on semiconducting van der Waals materials by combining high-throughput roll-to-roll mechanical exfoliation with commercially available temporary tattoo and waterslide decal transfer substrates. This approach enables the fabrication of ultrathin MoS2-based electronic devices that can be transferred onto rough and curved surfaces such as skin, synthetic leather, and plant leaves. The resulting devices operate reliably after transfer and exhibit strong electronic and optoelectronic performance, including photodetectors with responsivities up to approximately 3.5 A W$^{-1}$, thermistors with temperature coefficients of resistance from -2 to -3.5% per degree Celsius, and ionic-gel-gated field-effect transistors with mobilities reaching approximately 18 cm$^2$ V$^{-1}$ s$^{-1}$.
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All authors Yigit Sozen, Esteban Zamora-Amo, Juan J. Riquelme, Andres Castellanos-Gomez

Materials Science · Cross-listed from cs.LG

Packora: Systematic Design for Generative Molecular Crystal Structure Prediction

Nayoung Kim, Kiyoung Seong and Sungsoo Ahn

Molecular crystal structure prediction (CSP) is important in pharmaceuticals, agrochemicals, and organic electronics, where subtle differences in molecular conformation and packing can strongly affect material properties. We present Packora, a flow-based generative model for molecular CSP that jointly predicts atomic coordinates and the lattice from molecular graphs. Packora supports multi-component and organometallic crystals and can condition on any subset of molecular conformers, stereochemical labels, and space-group information within a single model. Inspired by the CCDC CSP blind test, we evaluate generation and ranking separately, using generation to isolate generator quality and ranking to measure end-to-end performance under a common relaxation and ranking pipeline. We also systematically study architecture, training, conditioning, inference, and scaling, identifying an effective design based on cacheable pairwise reasoning, training objective and numerical solver choices, conditioning dropout, and balanced scaling of pairwise and single representations. Packora outperforms the baselines on both structure generation and ranking benchmarks, achieving the best matched-budget coverage across all six generation benchmarks, as well as higher experimental-form recovery, lower experimental-form ranks, and faster convergence in ranking.
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Materials Science

Decoupled domain-texture switching from magnetic easy axis in kagome ferromagnet EuTi3Bi4

Yunhao Wang, Shiyu Zhu, Guohao Xi et al. (+13 more)

Magnetic anisotropy defines the easy axis of a magnetic material and governs the spatial arrangement of its domains. To date, anisotropy engineering has focused on reorienting the easy axis or tuning the anisotropy energy, both of which demand substantial energy input. Here, we demonstrate that magnetic domain textures can be switched without reorienting the easy axis, as observed in a kagome ferromagnet EuTi3Bi4 crystal. Using low-temperature magnetic force microscopy, we observe that the preferred orientation of magnetic domains switches from the a-axis to the b-axis upon temperature variation, and that this switching can also be triggered by an out-of-plane magnetic-field reset. Magnetization measurements and density functional theory calculations confirm a robust c-axis easy magnetization, ruling out a conventional spin-reorientation transition. Instead, the texture switching is governed by the temperature dependence of the in-plane variation of the Magnetic anisotropy energy landscape, which arises from two competing interactions with different decay rates: single-ion anisotropy favors a-oriented spin components, while nearest-neighbor anisotropic exchange favors b-oriented ones. Furthermore, the critical switching temperature is substantially elevated in a mechanically exfoliated EuTi3Bi4 flake. Our findings establish that macroscopic magnetic textures can be effectively manipulated by tuning the competition between in-plane anisotropic interactions, without the energy cost of reorienting the easy axis.
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All authors Yunhao Wang, Shiyu Zhu, Guohao Xi, Runnong Zhou, Ruwen Wang, Jianfeng Guo, Jiali Liu, Zichao Chen, Kailin Xu, Cong Wang, Chengmin Shen, Jiang Xiao, Haitao Yang, Xiaoli Dong, Wei Ji, Hong-Jun Gao

Materials Science

Four-phonon scattering and coherent heat transport in ultrawide-bandgap SrSnO3

Xuejie Li, Xiaoying Wang, Shengying Yue et al. (+4 more)

SrSnO3 is a promising ultrawide-bandgap perovskite oxide whose thermal transport is governed by structural distortions and anharmonic lattice dynamics. Here, we investigate the lattice thermal conductivity (kL) of orthorhombic and cubic SrSnO3 within a unified first-principles framework combining self-consistent phonon renormalization, three- and four-phonon scattering, and coherent heat transport. Bonding analysis reveals a rigid Sn-O octahedral framework embedded in a weakly bonded Sr sublattice, giving rise to low-frequency vibrational modes susceptible to strong anharmonic effects. Four-phonon scattering is identified as a key mechanism limiting particle-like heat conduction, reducing the Peierls thermal conductivity by 19.4% at 300 K in the orthorhombic phase and by 52.1% at 1300 K in the cubic phase, while the coherent contribution provides a finite channel that partially compensates this reduction. We further show that the apparent agreement between three-phonon calculations and experimental thermal conductivity at room temperature is not indicative of a complete physical description. Instead, it arises from a near cancellation between four-phonon suppression of the particle-like channel and the neglected coherent contribution. This cancellation breaks down when the full temperature dependence is considered, where only the combined treatment improves agreement with the experimentally observed scaling behavior. A physically consistent description of kL therefore requires phonon renormalization, four-phonon scattering, and coherent transport to be treated on equal footing rather than inferred from three-phonon agreement at a single temperature. These results provide microscopic insight into thermal transport in ultrawide-bandgap stannate perovskites and establish a benchmark for anharmonic transport in strongly distorted oxides.
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All authors Xuejie Li, Xiaoying Wang, Shengying Yue, Turab Lookman, Xiangdong Ding, Jun Sun, Zhibin Gao

Materials Science

Band offsets and electronic structure at ${\alpha}$/${\beta}$-Ga$_2$O$_3$ and ${\kappa}$/${\beta}$-Ga$_2$O$_3$ phase heterojunctions

D. Q. Fang

Ga$_2$O$_3$ phase heterojunction materials are emerging as promising candidates for deep-ultraviolet optoelectronics. Here, the band offsets at the ${\alpha}$/${\beta}$-Ga$_2$O$_3$ and ${\kappa}$/${\beta}$-Ga$_2$O$_3$ phase heterojunctions are investigated through hybrid functional calculations. Explicit, realistic slab models that satisfy electron counting rules are constructed for the heterojunctions. Our calculations demonstrate that a type-II staggered band alignment forms at the ${\alpha}$/${\beta}$-Ga$_2$O$_3$ and ${\kappa}$/${\beta}$-Ga$_2$O$_3$ phase heterojunctions, where both the valence and conduction band edges of ${\alpha}$-Ga$_2$O$_3$ and ${\kappa}$-Ga$_2$O$_3$ are higher than those of ${\beta}$-Ga$_2$O$_3$. Strain effects on the band alignment are also discussed. Spatially resolved local density of states maps are presented, clearly revealing the interfacial electronic structures. These results provide valuable insights into the physical properties of Ga$_2$O$_3$ phase heterojunctions, offering guidance for future device design efforts.
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Materials Science

A novel Grand-Potential Phase-Field Lattice-Boltzmann model for multi-phase solidification with convection

Chirantandip Mahanta, Sanjeev Kumar, Gandham Phanikumar et al. (+1 more)

Melt convection plays a critical role in microstructure evolution during alloy solidification, yet accurately capturing its interaction with moving solid-liquid interfaces remains a significant computational challenge, particularly in multi-phase, multi-component systems. In this work, we develop a computational framework that couples a Grand-Potential phase-field model with the Lattice Boltzmann method (LBM) to simulate convection-driven solidification within a unified and thermodynamically consistent formulation. The proposed approach rigorously enforces no-slip conditions at evolving solid-liquid interfaces, while fluid transport is solved using the standard single-relaxation-time Bhatnagar-Gross-Krook collision operator. The framework provides an efficient and robust methodology for resolving the coupled evolution of interfaces, solute transport, and fluid flow. The versatility of the proposed framework is demonstrated through simulations of dendritic and eutectic solidification under natural convection. The results show that convection significantly modifies solute segregation, destabilizes growth fronts, and induces oscillatory growth modes in both systems. These examples illustrate the capability of the proposed method to capture complex flow-induced morphological instabilities and provide new insights into the mechanisms governing convection-driven microstructure evolution in alloy solidification.
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All authors Chirantandip Mahanta, Sanjeev Kumar, Gandham Phanikumar, Abhik N. Choudhury

Materials Science

The Effect of Geometry on Thermodynamic Response

Bojana Bokic, Sébastien R. Mouchet, Biljana Stankov et al. (+9 more)

At the nano- and microscale, various patterns influence and shape thermal and optical response, making them essential for the survival of various biological species. In addition, controlling thermal radiation is vital for a broad range of applications, such as thermal management, spectroscopy, optoelectronics, and energy conversion technologies. For this reason, there is strong pressure to elucidate the physics of thermal radiation at the nanoscale. In this article, we provide evidence that complex nanoscale geometries affect thermal management, leading to an unusual thermal response in heat-capacity measurements as a function of temperature. Beyond identifying the structural constraints associated with this unusual thermodynamic response, the current study introduces the possibility of shaping the apparent heat-capacity response through geometry without necessarily altering the system's chemistry.
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All authors Bojana Bokic, Sébastien R. Mouchet, Biljana Stankov, Sanja Ostojic, Nicolas Roy, Darko Vasiljevic, Yin Chang, Marija Radmilovic-Radjenovic, Branislav Radjenovic, Thierry Verbiest, Mohamed Hatifi, Branko Kolaric

Materials Science

Repeated Growth and Hot Delamination of Single-Crystal Graphene: A Two-Kilometer Process-Design Assessment with hBN as a Separate Case

Rodney S. Ruoff

Large single crystals of graphene and hexagonal boron nitride (hBN) remain difficult to manufacture because batch growth and transfer limit area, throughput, and quality. This Perspective asks whether an atomically thin film could instead be grown, hot-delaminated, and regrown repeatedly on a long, reusable single-crystal metal surface. No integrated process is demonstrated. Once rapid full-area growth is available, hot film removal is likely to become the rate-limiting step, whereas usable single-crystal growth area sets the material produced per cycle. Two experiments determine whether the concept merits further development: rapid, damage-free delamination at or near the growth temperature, and acceptable film growth through repeated complete growth-dwell-peel-regrowth cycles. The analysis then examines the crystalline growth surface, layer control, interface and gas chemistries, product capture, quality criteria, energy, and scale. These provisional analyses expose known requirements, define early stop criteria, and guide experiments; they cannot anticipate every coupled constraint or failure mode. Graphene is the quantitative baseline. hBN requires its own M(111), product thickness, apparatus, and scaling strategy. Pilot-scale development is justified only if the two central experiments succeed and the remaining gates can then be refined experimentally.
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Materials Science · Cross-listed from cond-mat.mes-hall

Switchable giant room-temperature nonlinear Hall effect in Bilayer Graphene

Margherita Melegari, Ignacio Gutiérrez-Lezama, Justin C. W. Song et al. (+1 more)

Utilizing quantum second-order nonlinear transport for practical junction-free devices require materials with large and tunable nonlinearites at room temperature – a current materials platform challenge. Here, we report the nonlinear Hall effect (NLHE) in double-ionic gated bilayer graphene devices that enable unusually strong inversion breaking. We observe NLHE that are readily switchable (on, off, and sign reversed) with second order nonlinear susceptibilities $\chi^{(2)}_{yxx}$ that reaches giant room-temperature values of $3\,10^{-3}\,\mu\mathrm{m}\,\mathrm{S/V}$, comparable to values commonly observed at low temperature in WTe$_2$ or in graphene-based moiré superlattices, and three-to-four orders of magnitude larger than values reported in material systems recently employed in search of a room-temperature NLHE. Our devices produce corresponding THz voltage responsivities $\simeq 4\,10^{4}\,\mathrm{V/W}$, comparable to commercially available Schottky diodes. These are orders of magnitude better than for previously reported room-temperature NLHE devices rendering double-ionic gated bilayer graphene a choice platform for junction-free nonlinear technology.
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All authors Margherita Melegari, Ignacio Gutiérrez-Lezama, Justin C. W. Song, Alberto F. Morpurgo

Materials Science · Cross-listed from cond-mat.mes-hall

Observation of dodecagonal replica bands in 30$^{\circ}$-twisted bilayer WSe$_2$

Christian Valentiner-Branth Fokdal, Chakradhar Sahoo, Thomas S. Nielsen et al. (+6 more)

Twisted bilayers of two-dimensional (2D) transition metal dichalcogenides are promising systems for achieving tunable quasicrystalline orders with emergent properties. The underpinning electronic structure and scattering processes in 2D quasicrystals with multiorbital dodecagonal replica bands have so far not been determined. Here, we utilize angle-resolved photoemission spectroscopy (ARPES) with micrometer spatial resolution to directly observe replica bands in 30$^{\circ}$-twisted bilayer WSe$_2$. The symmetry and intensity distribution of the observed replicas are explained by interlayer Umklapp scattering from bottom to top WSe$_2$ layers. Our spectral function measurements are consistent with the presence of a van Hove singularity adjacent to the $\mathrm{K}$-valleys, which underlines the possibility of inducing electronic reconstructions in bilayers with a large interlayer twist angle.
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All authors Christian Valentiner-Branth Fokdal, Chakradhar Sahoo, Thomas S. Nielsen, Alfred J. H. Jones, Zhihao Jiang, Kenji Watanabe, Takashi Taniguchi, Marcin Mucha-Kruczyński, Søren Ulstrup

Materials Science

Self-selective growth of GaAs1-xBix on GaAs zinc blende/wurtzite nanowire heterostructures

Rohit Yadav, Sebastian Lehmann, Vidar Flodgren et al. (+5 more)

Site-selective nanostructure growth and material incorporation at the atomic scale offer a promising pathway for engineering quantum materials and nanodevices. Here, GaAs nanowires (NWs) with an axial heterostructure of alternating zinc blende (Zb) and wurtzite (Wz) crystal phases are employed as templates for site-selective Ga and Bi overgrowth. Using X-ray photoemission electron microscopy (XPEEM) with nanoscale spatial resolution, we map elemental distribution and local chemical bonding to reveal the incorporation behavior of Bi atoms in {110} Zb and {11-20} Wz facets. Bi incorporation proceeds through an anion-exchange process, where Bi atoms replace As, forming local Ga-Bi bonds and producing a thin GaAs1-xBix shell. We observe crystal-phase-dependent Bi incorporation, with higher Bi concentration in the Zb segments than in the neighboring Wz segments within the same NW. Furthermore, the Zb segment with higher Bi content exhibits reduced susceptibility to oxidation compared with the Wz segment, resulting in increased Ga-oxide in the Wz surfaces. This study highlights GaAs NW Zb/Wz heterostructures as a template for controlled growth of GaBi and GaAs1-xBix nanostructures with tailored functionalities for quantum applications
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All authors Rohit Yadav, Sebastian Lehmann, Vidar Flodgren, Evangelos Golias, Alexei Zakharov, Kimberly A. Dick, Anders Mikkelsen, Rainer Timm

Materials Science

A review of simulation, measurement techniques, and development in chip thermal design

Junnian Zhou, Feng Zhou and Shengying Yue

As integrated circuits advance toward higher power densities, three-dimensional integration, and heterogeneous packaging, chip thermal management has become a key bottleneck limiting device performance, reliability, and lifetime. This article systematically reviews numerical simulation methods and experimental measurement techniques for chip thermal design, with particular emphasis on the technical challenges associated with multiscale and multiphysics coupling, thermal boundary resistance measurement, and high-heat-flux cooling. We first introduce macro- and device-scale thermal simulation methods, including equivalent thermal-circuit models, the finite element method, and computational fluid dynamics, and discuss the application of phonon transport theory and molecular dynamics at microscopic scales. We then examine the advantages and limitations of infrared thermography, thermoreflectance, Raman thermometry, and embedded sensors. Current limitations include the enormous computational cost, inaccurate multiscale coupling, expensive experimental facilities, and the physical limits of conventional cooling technologies. Finally, we discuss emerging directions, including AI-accelerated thermal simulation, embedded microchannel liquid cooling, two-phase cooling, advanced high-thermal-conductivity materials, and multiphysics co-design, with the aim of advancing chip thermal management toward greater efficiency and intelligence.
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Materials Science · Cross-listed from cond-mat.str-el

Interlayer-engineering of Charge Order Wave Vector in Kagome Metals

Muntafa M. Mahi, Quazi D. M. Khosru, M. Zahid Hasan et al. (+2 more)

Charge orders in the kagome metals AV$_3$Sb$_5$ sit at the center of a rich phase diagram that also includes superconductivity, nematicity, and signatures of time-reversal-symmetry breaking. Yet even the basic question of which charge ordering wave vectors are intrinsic, and which are selected by dimensionality and lattice coupling, remains unsettled. Importantly, the microscopic origin of different charge orders and, in particular, the relationship between the robust bulk $2 \times 2$ charge order and the controversial $4 \times 1$ modulation, which is primarily resolved by surface probes, remains unresolved. Here, we use first-principles calculations to study the role of interlayer coupling in CsV$_3$Sb$_5$ by tuning the interlayer separation from the monolayer limit to the bulk limit. In the monolayer AV$_3$Sb$_5$ (A = Rb, Cs), the phonon spectrum exhibits no instability at the M point; instead, the dominant lattice instability occurs at q = (1/4, 0, 0), consistent with a $4 \times 1$ modulation. As interlayer coupling increases in CsV$_3$Sb$_5$, an M-point phonon progressively softens and becomes unstable already near c = 12.24 Å, evolving into the strong $2 \times 2$ instability characteristic of the bulk. These results identify interlayer coupling as a control parameter at a fixed stoichiometry that links competing $4 \times 1$ and $2 \times 2$ tendencies, providing a unified framework for understanding why multiple charge-order wave vectors coexist and compete in kagome metals.
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All authors Muntafa M. Mahi, Quazi D. M. Khosru, M. Zahid Hasan, Mahbub Alam, Md Shafayat Hossain

Materials Science

Instability of two-dimensional nonrelativistic altermagnets

Zhejunyu Jin and Peng Yan

Altermagnets (AMs) are collinear compensated magnets that exhibit momentum-dependent spin splitting without requiring a net magnetization. Since local magnetic moments and exchange-driven order do not rely on relativistic effects, altermagnetism can be naturally formulated in a nonrelativistic spin-group framework. This raises a basic question: can two-dimensional altermagnetic order be stabilized by purely exchange interactions in the absence of spin-orbit-induced anisotropy? We address this question by applying Bogoliubov's inequality to a minimal $d$-wave altermagnetic spin model. We show that the anisotropic exchange pattern responsible for altermagnetism still contributes only a quadratic long-wavelength term to the Bogoliubov denominator. Consequently, short-ranged exchange interactions alone cannot stabilize long-range altermagnetic order in two dimensions when continuous spin-rotation symmetry is preserved. In contrast, the corresponding three-dimensional system has a finite small-momentum contribution and is not ruled out by the Mermin-Wagner argument.
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Materials Science

A solid-solution approach for room-temperature bulk plasticity in KTa1-xNbxO3

Alexander Frisch, Jiawen Zhang, Martin Setvin et al. (+3 more)

Dislocations are being engineered into perovskite oxides to harvest versatile functional properties. One major bottleneck, however, persists: perovskite oxides that can be engineered with dislocations, particularly via mechanical deformation at room temperature in bulk scale, have so far been limited to only three materials: SrTiO3 (2001, Brunner et al.), KNbO3 (2016, Mark et al.), and KTaO3 (2024, Fang & Zhang et al.). Here, we propose a simple and effective approach by using solid solution to significantly extend the range of materials. We showcase KTa1-xNbxO3 (0<x<1) perovskite oxides for their bulk plasticity at room temperature by constructing a closed-loop validation workflow that includes crystal growth, Brinell indentation, bulk compression, and transmission electron microscopy characterization. Our findings are expected to unlock the materials toolbox for dislocation-tuned functionality of perovskite oxides.
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All authors Alexander Frisch, Jiawen Zhang, Martin Setvin, Xuping Wang, Wenjun Lu, Xufei Fang

Materials Science · Cross-listed from cond-mat.supr-con

Strain-driven orbital-selective reconstruction and bicollinear-to-stripe evolution in FeTe

Zhenfeng Ouyang, Yin Chen, Yi-Heng Tian et al. (+4 more)

FeTe, as a representative parent material among iron-based superconductors, provides an ideal platform for exploring the interplay among orbital-selective correlations, magnetism, and unconventional superconductivity. However, a unified picture of the correlated electronic structure and magnetism of FeTe under strain remains to be fully clarified. Here, combining density functional theory plus dynamical mean-field theory and Heisenberg model analysis, we uncover an orbital-selective reconstruction of the correlated electronic structure and reveal a strain-driven trajectory from bicollinear to stripe antiferromagnetism (AFM) via an intermediate competing staggered $n$-mer AFM regime in FeTe. Moderate strain gives rise to a regime where more coherent quasiparticles coexist with suppressed local moments. Further strain drives FeTe into an incoherent correlated regime with robust local moments and Fe-$3d_{z^2}$-dominated low-energy states. These results establish a strain-driven trajectory across distinct magnetic and correlated electronic states in FeTe.
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All authors Zhenfeng Ouyang, Yin Chen, Yi-Heng Tian, Jia-Ming Wang, Rong-Qiang He, Kai Liu, Zhong-Yi Lu

Materials Science · Cross-listed from cond-mat.str-el

Thermally quenched metastability in metal-insulator transitions via elemental substitution

Hiroshi Oike, Yasunori Takahashi, Keisuke Shibuya et al. (+5 more)

Thermal quenching inhibits equilibration toward the thermodynamic ground state during phase transitions, revealing metastable phases such as structural glasses and quenched alloys. Whether such thermally quenched metastability can be realized in metal-insulator transitions has remained an open question because these transformations are governed by collective electronic reorganization rather than atomic diffusion. We demonstrate that rapid cooling exceeding 10$^9$ K s$^{-1}$ kinetically avoids the metal-insulator transition, stabilizing a long-lived metastable metallic phase in tungsten-substituted VO$_2$. Temperature-dependent relaxation reveals nucleation-dominated kinetics with a thermal activation barrier introduced by tungsten substitution. Our results establish elemental substitution as a route to thermally quenched metastability in metal-insulator transitions, expanding metastable phase control to electronic phases.
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All authors Hiroshi Oike, Yasunori Takahashi, Keisuke Shibuya, Masaki Nakano, Tatsuki Hanada, Motoaki Hirayama, Hiroko Tokoro, Fumitaka Kagawa

Materials Science

Atomic investigations on the mechanical properties of CoCrNi medium-entropy alloy nanowires

Yang Yu

This work investigated the mechanical properties of CoCrNi medium-entropy alloy (MEA) nanowires under uniaxial tensile loading along three crystallographic orientations [100], [110] and [111]. The face-centered cubic (FCC) single-crystal CoCrNi nanowires exhibit pronounced anisotropy Molecular dynamics simulations were employed to provide atomic-level insights into the plastic deformation mechanism. The surface effect causes dislocations to nucleate at the free surface and slip inward. The temperature effect was also considered. Under identical geometric configurations, crystal orientations, and temperatures, interatomic interactions govern key mechanical properties such as Young's modulus and yield strength. Simulation results reveal a strong linear correlation between the average atomic force and mechanical performance across eight representative FCC metallic nanowires (Al, Au, Ag, Cu, Ni, Al19Mg alloy, FeCoCrCuNi high-entropy alloy (HEA), and CoCrNi MEA). This study delivers novel insights into the mechanical behavior of metallic nanowires and offers guidance for the rational design of alloy nanowires.
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Materials Science · Cross-listed from cond-mat.soft

Phase transitions and microphases in elastomers. II. Anisotropy-driven morphologies

Manu Mannattil, David Andelman and Haim Diamant

In swollen elastomers, elasticity can arrest macroscopic demixing between the polymer network and the solvent, producing stable domains of finite size. While previous theories have focused on isotropically swollen elastomers, anisotropy strongly influences the phase behavior of many related systems, such as gels and crosslinked polymer blends. Building on the approach developed in Part I of this two-part paper, we investigate the effects of two experimentally induced sources of anisotropy: uniaxial swelling and stiffness gradients. We show that uniaxial swelling can lead to the formation of stable lamellar microphases and modify phase behavior, while stiffness gradients can cause spatial variations in the characteristic microphase size.
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Materials Science

Beyond Allen-Heine-Cardona: non-perturbative electron-phonon interactions in the linewidths and lineshifts of diamond

Jean Paul Nery, Samuel Longo and Matthieu J. Verstraete

The temperature-dependent band gap of solids is usually computed from the perturbative Allen-Heine-Cardona (AHC) electron-phonon self-energy evaluated on-shell. Extending AHC to arbitrary frequency $\omega$ to determine the full spectral function via the Dyson equation is known to fail, misplacing satellites and yielding no broadening at band extrema, while non-perturbative supercell (SC) methods have focused on eigenvalue averages rather than lineshapes, and approaches based on special displacements cannot describe the full lineshape, or the lineshift at degenerate bands. Here we use a non-perturbative Green's function method (NPG), stochastically sampling distorted SC configurations, from which the spectral function, including lineshift, linewidth, and asymmetry, follows directly, and we recover finite spectral weight at the renormalized band extrema. We prove that the perturbative self-energy, computed to any order with the bare propagator and introduced into the Dyson equation, has an imaginary part that vanishes within the bare gap, giving incorrect spectral functions: self-consistency of the propagator is essential to broaden the band edges. NPG satisfies this property by construction, and contains all non-bubble diagrams. We also give a simple explanation of why SC methods converge with much smaller SCs than the corresponding $\mathbf{q}$-grids required by perturbation theory. For the band gap shift itself, the NPG and on-shell AHC results are found to be comparable, demonstrating that higher-order terms do not significantly alter the resulting renormalization in diamond. When it comes to the spectral function though, our results show that going beyond bare perturbation theory is not merely more accurate, but necessary, and NPG provides a robust framework to capture spectral broadening and higher-order effects from first principles.
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Wednesday 26 August

Materials Science · Cross-listed from cond-mat.soft

Beyond Crease Geometry: Multistability in Origami-Inspired Structures through Local Fold Architectures

Sagi Senderovich, Ezra Ben-Abu, Shai Elbaz et al. (+3 more)

Origami-inspired tubular structures provide a versatile platform for shape morphing, with multistability achieved predominantly through crease-network geometry. Expanding the range of morphing behaviors can therefore require increasingly intricate crease patterns that become more difficult to model and fabricate, ultimately constraining the realizable morphing landscape. Here, we expand the design space of origami-inspired structures beyond geometry by introducing localized instabilities within the crease network, thereby creating compliant multistable structures whose local fold architectures govern global deformation and stability through both constitutive mechanics and geometric constraints. To relate local fold architectures to global multistability, we develop and experimentally validate a modeling framework in which compliant folds are represented as continuous fields that capture spatially varying bistable mechanics. Force- and displacement-controlled design maps demonstrate that global deformation and stability can be programmed through the fold architecture's local parameters. Redistributing bistability within a fixed crease-network topology shifts the global response between compliant, spatially distributed deformation in semi-bistable architectures and discrete transitions within a hierarchically organized space of stable configurations in fully bistable architectures. These results establish a local-to-global design principle for programming both the stable configurations of a structure and the transition pathways connecting them, expanding the design space for multistable metamaterials, adaptive morphing structures, and soft robotic systems.
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All authors Sagi Senderovich, Ezra Ben-Abu, Shai Elbaz, Nadav Zemah, Anna Zigelman, Amir Daniel Gat

Materials Science

Nucleation and propagation of brittle fracture as a constrained energy minimization problem

Oscar Lopez-Pamies, Farhad Kamarei, Gilles A. Francfort et al. (+1 more)

This paper presents a macroscopic, or continuum, theory aimed at describing when, where, and why cracks nucleate and propagate in nominally elastic brittle materials under monotonic, quasi-static, but otherwise arbitrary mechanical loads. Motivated by recent insights, the proposed sharp theory posits that: cracks nucleate and propagate exclusively in regions where the strength surface of the material is exceeded, with their evolution dictated by the minimization of the sum of the potential — the elastic energy minus the work done by the externally applied forces — and surface energies. While the theory applies to materials with any elasticity (linear or nonlinear) and any material symmetry (isotropic or anisotropic), attention is restricted here to the most basic case of isotropic elastic brittle materials. For demonstration purposes, the theory is confronted with a set of nine tests that span the entire range of well-settled experimental knowledge on fracture nucleation and propagation — the so-called “Nine Circles of Elastic Brittle Fracture” — on both a hard material (a silicate glass) and a soft material (a synthetic rubber).
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All authors Oscar Lopez-Pamies, Farhad Kamarei, Gilles A. Francfort, Alessandro Giacomini

Materials Science

Magnetic permeability and zone-folded phonons in layered NiPS$_3$

André A. A. Silva, Eduardo D. Stefanato, Nicolas M. Kawahala et al. (+8 more)

Nickel phosphorus trisulfide (NiPS$_3$) stands out as a Mott insulator exhibiting XY-type antiferromagnetic order. In this work, we investigate the electrodynamic response of single-crystalline NiPS$_3$ using Terahertz Time-Domain Spectroscopy (THz-TDS) as a function of temperature. In cases where the magnetic permeability cannot be approximated to unity, conventional THz transmission analysis is often restricted to the complex refractive index, hindering the distinction between magnetic and dielectric contributions. To overcome this limitation, we demonstrate an extraction methodology capable of decoupling the magnetic permeability from the electric permittivity. Assuming that the dielectric contribution remains invariant below the N'eel temperature (TN), we used data from the paramagnetic phase to isolate the intrinsic magnetic component at 13 K. The angular and thermal dependence of the spectra revealed a magnon mode near 1 THz (for 0$^\circ$ orientation) and, distinctively, a zone-folded phonon activated by symmetry breaking (at 90$^\circ$). The isolated magnetic permeability was successfully modeled using Drude-Lorentz oscillators, enabling the extraction of fundamental spin dynamics parameters in this material.
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All authors André A. A. Silva, Eduardo D. Stefanato, Nicolas M. Kawahala, Flávio H. Feres, João Vítor T. P. Vital, Bernardo R. A. Neves, Jan Plutnar, Zdenek Sofer, Ana C. F. Brito, Felix G.G. Hernandez, Raul O. Freitas

Materials Science

Above Room-Temperature Phase Transition in Helicoidal 2D Halide Perovskite Enables Pyro-Phototronic Control

Zinnia Mallick, Rajashi Haldar, Sudip Naskar et al. (+4 more)

Bridging pyro-phototronic and ferroelectric properties in a single material not only gives rise to exotic physical phenomena but also provides strategy to build-up next-generation multi-functional energy harvesting devices. The layered halide perovskites are emerging class of synergetic 2D-materials of exceptional light-induced functionalities. Here, we report synthesis of a lead-free perovskite (3-fluorobenzylamine)2CuCl4 of partially fluorinated aromatic rings. Molecular chains are chiral in helicoids so to render flexibility, energy-transfer, and freedom to tailor tunable pyro-phototronics on light illumination. The fluorinated framework promotes ferroelectric-to-paraelectric transition point (TC), as high as \textasciitilde 412 K of wide range of workably. A giant pyro-photronic response is distinctly evident even upon UV-visible light-illuminations. A significantly high pyro-photronic current of 60 nA was achieved under an illumination of {\lambda}ex\textasciitilde 365 nm (27 mW) in a self-powered configuration. Consequently, an intricate coupling of the spontaneous polarization to the optical properties is visualized from the piezo response force microscopy (PFM) responses. In particular, the polar domains get diminished reversibly in on-off steps of the light irradiations. It indicates, the light provides another degree of the freedom to control the features for the applications of optoelectronic devices, optical memories, photo/thermo-chromic systems, and energy-harvesters.
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All authors Zinnia Mallick, Rajashi Haldar, Sudip Naskar, Bapan Jana, Maheswaran Shanmugam, Shanker Ram, Dipankar Mandal

Materials Science

Laser-Induced Rashba Spin-Orbit Torques in Multiferroic Semiconductor (Ge,Mn)Te

Zeynab Sadeghi, Tomas Ostatnicky, Eva Schmoranzerova et al. (+8 more)

The multiferroic semiconductor GeMnTe exhibits ferroelectricity, strong Rashba spin-orbit coupling, and carrier-mediated magnetic order, making it a unique platform for exploring the interplay among electronic, structural, and magnetic degrees of freedom. In this study, we investigate the ultrafast magnetization dynamics of Ge0.85Mn0.15Te using time-resolved magneto-optical spectroscopy. By separating magnetic and nonmagnetic contributions in the transient response, we identify two distinct laser-induced magnetic phenomena, both resulting from photoinduced effective spin-orbit torque. Coherent magnetization precession arises from a laser-induced increase in hole concentration, which modifies the occupation of Rashba-split spin-locked valence band states and alters the magnetic easy axis. The transient change in magnetic ordering, observed as variations in the coercive field, is attributed to laser-induced modifications of the ferroelectric sublattice displacement, which affect the ferroelectric polarization and the associated Rashba spin-orbit interaction. While the first type of optical spin-orbit torque has already been observed in the diluted magnetic semiconductor (Ga,Mn)As, the second effect is unique to the multiferroic Rashba semiconductor (Ge,Mn)Te, opening new opportunities for all-optical manipulation of magnetic order and spin-orbit torque generation in spin-orbitronic devices.
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All authors Zeynab Sadeghi, Tomas Ostatnicky, Eva Schmoranzerova, Jozef Kimak, Dominik Kriegner, Helena Reichlova, Lukas Nadvornik, Gunther Sprinhgholtz, J. Hugo Dil, Juraj Krempasky, Petr Nemec

Materials Science

Milled to order: toward predictive mechanochemistry of halide perovskites

Susan A. Rigter and Loreta A. Muscarella

Mechanochemical milling is regarded as a scalable, solvent-free method that makes halide perovskites that solution processing cannot. Its deeper promise, though, is that mechanical force could become a new axis of synthetic control to turn milling from an empirical method into a predictive science. Halide perovskites are the ideal platform to establish this: their soft lattices and low formation energies make them intrinsically responsive to mechanical activation. Realising this requires settling what milling actually makes, and how: can a milled phase genuinely be trapped outside equilibrium, or is it just a convenient way to the equilibrium phase, and by what atomistic pathway does it work? These questions are mostly answered by assumption, while the in-situ and computational tools that resolved them for other material classes already exist. Closing this gap will unlock two design capabilities: mechanical energy used as a synthetic variable to tune phase selection, and metastability made programmable, producing trapped phases, specific intermediates, and compositions that have no possible solution route. Finally, two tests decide whether that control reaches practice: the state engineered during milling must survive into a working device, and the method must prove genuinely greener across the full device life cycle, rather than just solvent-free.
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Materials Science

When chemical potential continuity fails: kinetic interface models for hydrogen isotope transport

Remi Delaporte-Mathurin and James Dark

Macroscopic hydrogen transport codes model material interfaces with local thermodynamic equilibrium (LTE), imposing continuity of chemical potential as a per-species constraint. Three assumptions hide in that condition: fast interfacial equilibration, a single exchange pathway between the two sides, and a carrier species known in advance on each side. The literature scrutinises the first, but the other two are the more consequential failures, and neither survives at a metal/molten-salt interface. We replace the constraint with reversible reaction channels at the interface that obey mass action, with detailed balance fixing each ratio of rate constants from the thermodynamic data that already parameterise LTE, and we implement the framework in festim. LTE is recovered as the fast-kinetics limit of a single channel, in both its Sieverts/Sieverts and its Sieverts/Henry form, so the framework generalises LTE and does not compete with it. A Damköhler number delimits validity within a channel, a branching ratio between channels. In a representative nickel/FLiBe system, hydrogen partitions kinetically between molecular and fluoride carriers. The apparent interfacial law then drifts between Sieverts and Henry with loading and salt redox state, and an LTE condition underestimates the steady permeating flux. The measured pressure exponent is set by the branching ratio, not by any fixed property of the salt; a redox sweep at fixed temperature should continuously shift it between 0.5 and 1. With two isotopes, two metal-side species feed five salt-side carriers, and a per-species LTE condition is ill-posed.
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Materials Science · Cross-listed from cs.AI

SwarmWorld: Stigmergic technological evolution in societies of language-model agents

Subhadeep Pal, Fiona Y. Wang and Markus J. Buehler

Collective intelligence can emerge when individuals coordinate through a shared environment, allowing local actions to accumulate into durable social organization. Language-model agents offer a new substrate for this process, yet most multi-agent systems rely on direct conversation, predefined roles, or centralized workflows. It remains unclear whether decentralized agents can build functional technologies and outperform independent search. Here, initially homogeneous LLM agents in SwarmWorld self-organize without assigned roles or recipes into evolving technological societies. Agents explore a spatial environment, process resources, test materials, construct persistent artifacts, and write executable controllers evaluated by a deterministic simulator under unseen disturbances after the agents are removed. SwarmWorld splits cognition from consequence: agents propose architectures and controllers within fixed action and material schemas, while the simulated world determines function. Shared societies develop broader, more resilient technological portfolios than a strong best-of-N isolated-search baseline, although isolated search remains competitive for the strongest artifact. Agents differentiate into exploration, construction, maintenance, and coordination behaviors, transitioning as the world matures. Technologies accumulate through collaborative construction, executable inheritance, and persistent agent-artifact networks, with most reuse beginning through physical observation rather than communication. Explicit cultural mechanisms amplify collaboration and organization, but functional benefits depend on outcome and timescale. Physical stigmergy alone supports capable societies, while interaction drives persistent technological ecologies rather than universally superior individual inventions.
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Materials Science · Cross-listed from physics.geo-ph

Lab earthquakes confirm the theory of frictional slip pulses

Alina Shafir, Tom Gabrieli, Yuval Tal et al. (+1 more)

Large natural earthquakes are typically mediated by frictional pulse-like rupture, which features a finite slipping zone. Recently, a comprehensive two-dimensional theory of frictional slip pulses has been developed. It predicts that pulses are categorically unstable rupture modes, whose evolution is intrinsically slow. Unsteady pulses satisfy an equation of motion expressed in terms of discrete observables, which is inherently related to their steady-state counterparts. The theory also predicts a transition from decaying to slowly growing pulses. Here, we perform extensive lab earthquake experiments to test the theory. The experiments confirm the theoretical predictions for pulse-like lab earthquakes over a range of prestress levels, rupture nucleation conditions and small-scale fault roughness amplitudes. Specifically, the predicted time-dependent dynamics are tested in a plane defined by the evolving pulse size and peak slip rate, along with measurements of the dimensionless growth rate of pulses, demonstrating their intrinsically slow unsteady nature. The predicted transition between decaying and growing pulses is also experimentally demonstrated. These results constitute major progress in understanding a dominant earthquake rupture mode.
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All authors Alina Shafir, Tom Gabrieli, Yuval Tal, Eran Bouchbinder