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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Friday 29 May

Materials Science

Direct Observation of Chemical Short-Range Order in CoCrNi Alloy Using Neutron Diffraction

Vinícius P. Bacurau, Camilo Salvador, Guilherme C. Stumpfa et al. (+8 more)

This study provides experimental evidence of chemical short-range order (CSRO) in the equiatomic CoCrNi alloy, identified through neutron diffraction. The phenomenon manifests as a distinct diffuse peak at Q = 1.85 A-1, the intensity increases under thermodynamically favorable conditions for CSRO development such as prolonged aging (100 h and 240 h) at 748 K or shorter aging (24 h) at slightly higher temperature (798 K). The degree of ordering was measured by integrating the diffuse scattering intensity, revealing that the gas-atomized sample, i.e. the sample with the least amount of CSRO, still displays approximately 70% of the CSRO level observed in the sample subsequently aged for 240 h at 748 K, i.e. the sample with the highest amount of CSRO produced in this study. Predictive atomistic simulations reproduced both the presence and position of the diffuse peak, while two-dimensional fast Fourier transform (FT-2D) analyses indicated that reflections at (1 1/2 0) within the <001> zone axis originate from some structural projections associated with like D022, Pt2Mo and D1a motifs. Complementary small-angle neutron scattering (SANS) measurements identified Ni-rich, disk-shaped domains with radii of approximately 11 A and thicknesses of about 1 A, consistent with nanoscale CSRO characteristic length scale. These findings demonstrate that CSRO is an intrinsic and energetically favorable feature of the CoCrNi system, remaining stable even under rapid solidification and further enhanced by low-temperature aging. Combined use of neutron diffraction and atomistic modeling provides a framework for probing local ordering phenomena in multi-principal element alloys (MPEAs).
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All authors Vinícius P. Bacurau, Camilo Salvador, Guilherme C. Stumpfa, Angelo F. Andreolli, Caroline B. Stocoa, Eric M. Mazzer, Lewis Owen, Yifan Cao, Rodrigo Freitas, Daniel Miracle, Francisco G. Coury

Materials Science

Co-optimization of spin coherence and valley splitting in Si/SiGe heterostructures

Peihong Zhang, Xuedong Hu, Saif Ullah et al. (+1 more)

Single electron spins can be used to encode and process information in semiconductor quantum devices. Progress has been hindered by materials challenges, such as the small energy splitting between low-lying valley states and hyperfine coupling to nuclear spins. Here we use density functional theory to optimize the valley splitting and spin dephasing time in realistic Si/SiGe heterostructures. Reductions in the Si quantum well width generally increase the valley splitting. However, in narrow quantum wells, a larger fraction of the electronic wavefunction resides in the SiGe buffer layers, which increases the hyperfine coupling with spinful $^{73}$Ge. Our work shows that Si/SiGe heterostructures with 3~–~4~nm wide quantum wells and $^{73}$Ge and $^{29}$Si concentrations of 50 ppm should support average valley splittings $E_{v}$~$>$~500~$\mu$eV and spin dephasing times $T_2^*$ exceeding 15~$\mu$s assuming an effective quantum dot area of 700 nm$^2$. In addition, sharper Si/SiGe interfaces in general result in larger valley splittings and longer spin dephasing times.
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All authors Peihong Zhang, Xuedong Hu, Saif Ullah, Jason R. Petta

Materials Science

A Practical Guide for Diagnosing Imaginary Phonon Modes in Metal–Organic Frameworks: The Case of MOF-5

Julia Santana-Andreo and Caterina Cocchi

Assessing the dynamical stability of computationally predicted metal–organic frameworks (MOFs) is essential to distinguish synthetically feasible structures from dynamically unstable ones. However, reliable first-principles phonon calculations on these systems remain challenging: their large, flexible unit cells and soft collective modes make the vibrational spectrum highly sensitive to the numerical settings. Using MOF-5 as a representative case study, we establish a finite-displacement workflow to identify and isolate the origins of imaginary phonon modes. We demonstrate how numerical force convergence thresholds, real-space grid resolutions, symmetry-standardization protocols, and alternative unit-cell representations can qualitatively and spuriously alter the predicted lattice stability. Once numerical noise is confidently excluded, the remaining imaginary modes can be analyzed through mode mapping, with stochastic Monte Carlo symmetry-breaking distortions outlined as a complementary strategy for more complex landscapes. This protocol provides a robust, transferable strategy for the reliable assessment of dynamical stability and lattice vibrations in flexible porous frameworks.
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Materials Science · Cross-listed from cond-mat.mes-hall

Valley-polarized Orbital and Spin Magnetism Induced by Femtosecond Optical Pulses in Two-Dimensional Semiconductors

M. S. Mrudul and Peter M. Oppeneer

We theoretically investigate the ultrafast generation of spin and orbital magnetism in a two-dimensional gapped Dirac system with spin-orbit coupling. This system is representative of two-dimensional hexagonal semiconductors, such as transition-metal dichalcogenides that exhibit valley-selective optical selection rules arising from the valley-contrasting magnetic texture of their band structure. Using a time-dependent density-matrix formalism, we demonstrate that circularly polarized laser pulses generate nonequilibrium magnetization under both resonant and multiphoton resonant conditions. We show that the induced spin and orbital magnetic moments can be distinctly controlled via the photon energy and polarization of the driving field. Furthermore, spin and orbital dynamics originate from fundamentally different light-matter coupling mechanisms, leading to qualitatively dissimilar temporal behaviors. The orbital magnetic moment couples directly to the external electric field, resulting in faster dynamics and pronounced Rabi-like oscillations, whereas the spin response develops gradually through spin-orbit coupling. Consequently, orbital dynamics is significantly more sensitive to electron-hole dephasing than the spin response. Our results highlight the importance of properly accounting for orbital contributions in future technologies that utilize femtosecond control of magnetism.
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Materials Science

Magnetic domains reconfiguration on the Fe3O4(110) surface across the Verwey transition by Spin-Polarized Low-Energy Electron Microscopy

C. Gutiérrez-Cuesta, A. Mandziak, J.E. Prieto et al. (+6 more)

We have studied the (110) surface of Fe$_3$O$_4$ single crystals by means of spin-polarized low-energy electron microscopy (SPLEEM). After preparation by sputtering and annealing a well defined reconstructed surface was achieved, composed of rows aligned in the [010] direction. By acquiring SPLEEM images along different spin directions the vector magnetization was mapped on the surface, both at room temperature and at a temperature well below the Verwey transition. At room temperature, domains were observed with their magnetization aligned along the two <111> bulk easy axes which are in the (110) surface plane. They presented 180$^\circ$, 71$^\circ$ and 109$^\circ$ Néel-type domain walls. Below the Verwey transition, the magnetization directions changed to regions where the magnetization was oriented along the in-plane [100] and [001] directions. Those observations can be interpreted as the presence of magnetized regions on the surface where the monoclinic $c$ axis is in-plane in the former, and regions where the $c$ is out-of-plane in an oblique direction in the latter. However, the magnetization was at all times within the surface plane, with no out-of-plane component detected.
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All authors C. Gutiérrez-Cuesta, A. Mandziak, J.E. Prieto, P. Nita, A. Mascaraque, U. Choudhry, J. Turner, A. Stibor, J. de la Figuera

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

Emergence of spin entanglement with the pseudogap onset in the Fermi-Hubbard model

Frederic Bippus, Thomas Chalopin, Gabriele Bellomia et al. (+6 more)

Despite decades of intense theoretical and experimental investigation, the two-dimensional Fermi-Hubbard model still resists a complete microscopic understanding. Conventional approaches typically probe global observables and locally resolved correlation functions. Here, we develop a complementary perspective based on the measurement of entanglement. Using both an ultracold-atom quantum simulator and numerical simulations based on the dynamical vertex approximation, we find that entanglement is closely tied to the onset of the enigmatic pseudogap regime: spin-singlet entanglement emerges only as the pseudogap sets in and, in contrast to classical correlations, remains confined to nearest-neighbour sites in this regime. Our results, therefore, disfavour purely classical-fluctuation theories of the pseudogap and constrain microscopic models to those that develop nearest-neighbour spin-singlet entanglement at the pseudogap onset.
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All authors Frederic Bippus, Thomas Chalopin, Gabriele Bellomia, Gergő Roósz, Titus Franz, Antoine Georges, Anna Kauch, Immanuel Bloch, Karsten Held

Materials Science

In-situ operation of amorphous circuits under heavy-ion irradiation

Xuanzhe Sha, Shun Liao, Xiaoxi Li et al. (+10 more)

Radiation-hardened electronics using semiconductors beyond silicon are essential for computation and control in extreme environments. Yet complex digital circuits based on such material platforms operating in situ under heavy-ion irradiation remain largely unexplored. Here, we show a timing circuit based on amorphous thin-film semiconductors at the 100-transistor scale, and demonstrate its robust operation through a functional "Hello World" ASCII output sequence. Beyond static device characterization, we evaluate the circuit under powered heavy-ion irradiation using tantalum ions, providing an operationally relevant assessment of radiation tolerance at the system level. Under a high particle flux of 2.5 x 10^3 ions cm^-2 s^-1, the circuit maintains stable operation during the irradiation test, achieving a total fluence of 1 x 10^6 ions cm^-2, establishing a milestone of prolonged powered digital operation under extreme conditions. Our work expands the design space of radiation-tolerant electronics, highlighting amorphous semiconductors as a promising foundation for digital circuits deployed in harsh environments.
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All authors Xuanzhe Sha, Shun Liao, Xiaoxi Li, Chengyuan Li, Jianli Liu, Yu Pan, Wenhai Wang, Yu Ye, Chengxin Zhao, Liyi Li, Hanwen Wang, Zheng Vitto Han, Jianming Lu

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

Rigorous extension of semilocal collinear functionals to noncollinear DFT using $SU(2)$ rotations

Konstantin Gaul

In the presence of spin-orbit coupling and in geometrically frustrated materials, a noncollinear treatment the magnetization density is essential. However, in density functional theory most exchange–correlation functional approximations were originally developed for locally collinear magnetization. Many practical approaches to noncollinear DFT have emerged over the past decade. However, a first-principles connection between widely used semilocal collinear functionals and their noncollinear generalizations remains lacking. In this work, a locally exact relation between collinear and noncollinear exchange–correlation functionals is derived at the level of gradient expansions within a $u(2)$ matrix representation of the energy functional. Within this framework, collinear semilocal variables naturally acquire distinct dependencies on transverse and longitudinal magnetization gradient components. The widely used Scalmani–Frisch scheme emerges as a first-order approximation. The transformation of collinear functional derivatives to noncollinear space is implemented through numerically robust $SU(2)$ rotations. A consistent description of local magnetic torques is demonstrated for the prototypical spin-frustrated Cr$_3$ cluster. The approach further extends to fully nonlocal functionals and provides a direct route towards numerically stable relativistic response calculations. The influence on magnetic properties in presence of spin-orbit coupling is illustrated through calculations of hyperfine couplings in the high-spin ground states of uranium and the uranium ion.
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Materials Science

Topological Interstitial-Electron Conductor

Tingli He, Xiaoming Zhang, Chaoxi Cui et al. (+5 more)

Electron transport in solids arises primarily from two mechanisms: freely moving bulk electrons in metals, and gapless boundary states in topological insulators. Here, we report a new mechanism discovered in electrides. The topological interstitial-electron conductors (TIECs) proposed here are insulating electrides, but host interstitial electrons (IEs) distributed within crystal voids that traverse the entire unit cell. Without being tightly bound to real ions, the IEs generally experience low periodic potential barrier along the void channels. As a consequence, by applying a weak electric field sufficient to overcome the IE barriers but far below the system's dielectric breakdown threshold, one can expect that the TIECs would generate a persistent current contributed by the IEs and propagating along the void channels. We identify a family of realistic altermagnetic electrides, $A_5X_3$ ($A$ = Ca, Sr, Ba, Yb; $X$ = As, Sb), as TIECs. Remarkably, for $A_5X_3$ materials, the periodic potential barrier of the IEs along the void channels are ultralow, ranging from 13.43 to 67.96 meV per formula unit. This renders our proposal readily accessible to experimental verification. We further demonstrate that when the IEs of $A_5X_3$ undergo periodic motion along the channels, topological surface states will emerge at the boundary perpendicular to the channel direction, and continuously move across the bulk band gap. This pumping-like behaviour not only corroborates the topological nature of TIECs, but also rationalizes the finite-electric-field induced electronic transport within the band theory. Our findings expand the classification of electronic conductors, uncover unexplored transport properties of electrides, and establish a new material platform for low-power electronic devices.
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All authors Tingli He, Xiaoming Zhang, Chaoxi Cui, Yilin Han, Yang Wang, Wei Jiang, Zhi-Ming Yu, Yugui Yao

Materials Science

A Self-Evolving Machine-Learning-Based Kinetic Monte Carlo Method for Modelling Thin-Film Growth

Jyri Kimari, Flyura Djurabekova and Kostas Sarakinos

We present a kinetic Monte Carlo (KMC) simulation framework parameterized by automatically sampling machine-learning (ML) for modeling thin-film growth atom by atom. Given an interatomic potential energy function, the KMC algorithm builds an ML-based regression model for rate parameters on runtime, being trained on the local atomic environments encountered during the system evolution. New environments are continuously added to the training set in a self-evolving manner at points where the ML model estimates high uncertainty. As the simulation progresses, the ML model gains confidence, and the quick estimation of rates increasingly overtakes the relatively-expensive nudged elastic band calculations, promoting computational efficiency while retaining high fidelity description of the atomic diffusion kinetics. As a test case, we simulate the sub-monolayer growth of Ag on Ag {111}, where we demonstrate adatom islands forming in shapes and densities in accordance with the underlying atomistic interaction model, the theoretical framework, and available experimental results related to thin-film nucleation and growth.
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Materials Science · Cross-listed from cond-mat.mes-hall

Interplay of Cl Substitution and He$^{+}$ Irradiation in CrSBr$_{1-x}$Cl$_{x}$

Satyam Sahu, Adeel Bukhari, Arijit Kayal et al. (+8 more)

Two-dimensional magnetic semiconductors provide a promising platform for exploring the interplay between disorder, lattice dynamics, and resonant light–matter interactions. Among them, CrSBr exhibits strong in-plane anisotropy and pronounced resonance-enhanced Raman scattering. Here, we investigate the effects of Cl substitution and He$^{+}$ irradiation on the vibrational response of CrSBr using polarization-resolved Raman spectroscopy. Cl substitution activates additional phonon modes associated with local symmetry breaking, while He$^{+}$ irradiation introduces distinct defect-related scattering channels and enhanced phonon broadening. The combined effects of alloy disorder and externally introduced defects lead to strong anisotropic reconstruction of the Raman spectra and modification of the nonlinear Raman response under near-resonant 1.96 eV excitation. Power-dependent measurements reveal robust superlinear scaling of both intrinsic and substitution-induced phonon modes, indicating persistent resonance-enhanced electron–phonon coupling even in defect-engineered samples.
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All authors Satyam Sahu, Adeel Bukhari, Arijit Kayal, Valerie Černá, Bing Wu, Aljoscha Söll, Gregor Hlawacek, Zdeněk Sofer, Martin Kalbáč, Matěj Velický, Otakar Frank

Materials Science

Clustering in atom probe tomography data: coordination number metric, percolation-based parameter scaling, and size effects

Mykola Lazarev and John Banhart

The ability to identify nanometer-scale nuclei of new phases in atom probe tomography (APT) is often limited by the sensitivity of clustering algorithms to user-defined control parameters. Conventional approaches typically rely on the Euclidean distance metric and consider only solute atoms, thereby discarding the solvent atoms that contain most of the spatial information. Here, we introduce a coordination-number metric based on the composition and apply it to higher-order clustering. Using various metrics, we investigate percolation in typical APT structures. By scaling clustering properties to the corresponding percolation thresholds, we define a self-similar variable that is almost invariant with respect to metrics, clustering parameters, and structural disorder. This variable provides a relevant description of clustering and enables the formal transfer of optimal parameters between clustering methods. We also study the characteristic clustering behavior in small precipitates and quantify how the precipitate-matrix interface alters the composition spectrum and broadens the clustering curve. Finally, using simulations that incorporate finite spatial resolution, detection efficiency, and other APT reconstruction artifacts, we show that the approach based on coordination numbers effectively compensates for heterogeneous dilations and outperforms solute-density-based methods in all tested scenarios.
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Materials Science

Spin-Spiral Enhancement of Ultrafast Light-Polarization-Robust Magnetization

Yirui Lu, Zeyu Jiang and Bing Huang

Ultrafast light-driven magnetization, a frontier in quantum magneto-optics, has traditionally relied on circularly polarized lasers to provide external angular momentum. While increasing efforts have aimed to achieve light-polarization-robust (LPR) magnetization that is insensitive to the form of external light excitation, the underlying mechanism remains largely unclear. Here, we establish the symmetry-constrained rule for LPR magnetization in antiferromagnetic systems. Through real-time time-dependent density functional theory calculations, we observe the strong LPR magnetization in spin-spiral magnets and its suppression in collinear antiferromagnets, confirming our theory. Strikingly, laser excitation induces real-space demagnetization, rotation, and oscillation of atomic spins in spin-spiral monolayer NiI$_2$, whereas rotation is largely suppressed in conventional collinear antiferromagnets. Our work reveals a novel microscopic pathway for ultrafast magnetization that is independent of light polarization, paving the way for advanced femtosecond spin control.
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Materials Science · Cross-listed from physics.acc-ph

Explicit Turn Resolution with Anisotropic Homogenisation for Efficient 3D Magneto-Thermal Finite-Element Simulation of Large-Scale No-Insulation HTS Magnets

Louis Denis, Erik Schnaubelt, Julien Dular et al. (+3 more)

No-insulation (NI) and metal-insulation (MI) high-temperature superconducting (HTS) magnets require three-dimensional (3D) models to describe the current distribution around critical current defects. In this work, we design and validate the EXTRA homogenisation method, standing for explicit turn resolution with anisotropic homogenisation method. It allows 3D magneto-thermal finite-element (FE) simulations of large-scale magnets to be performed with high accuracy at a reasonable computational cost. The method combines the anisotropic homogenisation of turn-to-turn contact layers (T2TCLs) and their neighbouring winding turns with the explicit resolution of specific T2TCLs. In particular, the inner- and outermost winding turns and adjacent contact layers are explicitly resolved to properly describe the current distribution near current leads. In addition, the method is able to simulate local $J_{\textrm{c}}$ defects for a broad range of turn-to-turn contact resistances, provided the winding turns and T2TCLs next to the defect are explicitly resolved. For efficiency, the resolved T2TCLs are modelled using the surface contact approximation. The consistency of the proposed method is first verified on a 50-turn single pancake benchmark. It is shown to reproduce AC losses and temperature distributions obtained with a turn-resolved FE reference model, for both nominal operation and during thermal runaway. The computational efficiency of the EXTRA method is demonstrated with the simulation of a stack of three 150-turn pancake coils, for which computation time is reduced by a factor of up to 13 with respect to a turn-resolved FE reference model. Finally, the results of a large-scale 3D FE simulation, currently out of reach of turn-resolved models, are provided for an insert HTS magnet with 10,000 turns. The EXTRA method is open-source and input files to reproduce all results are made available.
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All authors Louis Denis, Erik Schnaubelt, Julien Dular, Mariusz Wozniak, Benoît Vanderheyden, Christophe Geuzaine

Materials Science

Saturated and Anisotropic Magnetostriction in an Altermagnet

Zhiyuan Duan, Qiyun Xu, Peixin Qin et al. (+14 more)

Magnetostriction, a fundamental phenomenon bridging magnetism and mechanics, has enabled a broad spectrum of applications. For almost two centuries, it has been mainly investigated for ferromagnets. Regarding the magnetostriction of antiferromagnets (AFMs), limitedly known examples for both conventional collinear AFMs and noncollinear AFMs predominantly exhibit non-saturating magnetic-field dependence. Herein, we report an easily saturated magnetostriction effect in a prototypical altermagnet - MnTe, which is an emerging class of collinear AFMs with special crystal symmetries. For high-quality MnTe single crystals, the magnetostriction saturates under a moderate field of ~0.7 T with an intriguing two-fold-symmetry anisotropy. First-principles calculations reveal that the saturated and anisotropic magnetostriction originates from symmetry-allowed coupling between elastic strain and its Néel order parameter. These findings break the traditional wisdom on antiferromagnetic magnetostriction.
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All authors Zhiyuan Duan, Qiyun Xu, Peixin Qin, Li Liu, Guojian Zhao, Yuzhou He, Xiaoyang Tan, Sixu Jiang, Jingyu Li, Xiaoning Wang, Qinghua Zhang, Wenhui Duan, Yong Xu, Ziang Meng, Peizhe Tang, Chengbao Jiang, Zhiqi Liu

Materials Science

Crystal Dislocations as Atomic Scale Ratchets

Wu-Rong Jian, Yifan Wang and Wei Cai

The symmetry of a system's response to external stimuli is a fundamental concept in physics and materials science. At the microscopic scale, breaking this symmetry to achieve a rectified response is exceptionally difficult to engineer and remains rare in nature. Conventional micromechanics models of crystalline solids often assume a symmetric response to applied stress, where reversing the load simply inverts the direction of defect velocity without altering its magnitude. In this work, we report an atomic-scale, geometry-rooted mechanism that breaks this symmetry. Molecular dynamics simulations of face-centered cubic nickel reveal that dislocations containing atomic-scale jogs exhibit asymmetric mobility under opposite applied stresses: reversing the loading direction triggers significantly higher drag. This asymmetry arises from the coupling of two internal variables with different transformation parity: a non-affine displacement of an atom at the jog core, and a strain-like tensor associated with the advance of the dislocation. Because jogs are ubiquitous structures in plastic deformation, this discovery challenges classical descriptions of plastic deformation mechanisms, with direct implications for cyclic creep, and opens new pathways for defect engineering to enhance fatigue resistance.
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Materials Science

Defect-engineered scaling of lead-free ferroelectrics with ultralow-voltage switching

Reza Ghanbari, Jiayue Wang, Harikrishnan KP et al. (+9 more)

Scaling ferroelectrics to nanometer thicknesses remains a central challenge for low-power, nonvolatile electronics, as leakage currents increasingly dominate with reduced dimensions. Alkali-based, lead-free ferroelectrics offer an environmentally sustainable alternative to lead-based systems, yet their scaling is severely limited by leakage arising from volatile alkali constituents. Here, we show that this intrinsic limitation can be transformed into an advantageous degree of freedom through defect engineering. By precisely modulating alkali deficiency during thin-film synthesis, we engineer clustered defect complexes that function as deep trap states, strongly suppressing leakage and enabling robust ferroelectric operation in ultrathin films down to the sub-10 nm regime at voltages below 100 mV. Our results establish defect-enabled scaling as a viable pathway for advancing environmentally benign ferroelectrics toward ultra-low-power, non-volatile electronic technologies.
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All authors Reza Ghanbari, Jiayue Wang, Harikrishnan KP, Zixiao Shi, Aarushi Khandelwal, Konnor Koons, Eli Rodrigues, Tao Zhou, Martin Holt, David A. Muller, Harold Y. Hwang, Ruijuan Xu

Materials Science

A Padding Method for Enhanced Encoding of Inorganic Structures with Varying Chemical Compositions

Thang Dang, Haderbache Amir, Tzanakakis Alexandros et al. (+1 more)

Designing novel inorganic materials through generative models remains an important challenge for material science, driven by the complexity and diversity of inorganic structures across expansive chemical compositions and structural landscape. The vast combinatorial space of inorganic compounds demands innovative, AI-driven approaches to overcome limitations in generative accuracy and efficiency. To address this, we introduce a novel method that redefines the encoding and generation of inorganic materials by utilizing domain-specific symmetry-aware representation. Our approach not only refines the representation of intricate inorganic structures but also contributes to the field of material discovery by enhancing the precision and stability of generated candidates. Central to our methodology is a novel padding technique that exploits crystal symmetry information to enhance the encoding process. By integrating Wyckoff position length-aware padding into an encoder architecture, we achieve a more robust informed representation of inorganic materials. This symmetry-driven enhancement improves deep learning models to generate stable, previously unexplored inorganic structures with superior accuracy and computational efficiency. Furthermore, we introduce an end-to-end system that leverages the machine learning potential models to seamlessly generate novel, even those unseen in the training data, and stable inorganic materials from initial data to validated output. This pipeline integrates advanced generative models with stability analysis, marking a significant leap forward in the automated exploration and design of next-generation inorganic materials. Our method improved reconstruction accuracy 5.3% in proton conductor data, and generated 63.5% more novel stable inorganic material to baseline model on the perov-5 dataset.
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All authors Thang Dang, Haderbache Amir, Tzanakakis Alexandros, Yoshimoto Yuta

Materials Science

A Convenient Sealing Method Using Boron Nitride Capping for Reactive Reactions

Boqin Song and Tianping Ying

While quartz (SiO2) ampule sealing is commonly used in laboratories to prevent sample oxidation during synthesis, its application is limited for reactions involving highly reactive elements such as alkali, alkaline-earth, and rare-earth metals. These elements can react with SiO2 at elevated temperatures, causing compositional loss, tube failure, and experimental inconsistencies. Here, we introduce an inexpensive boron nitride (BN) cap sealing technique. This approach is readily adaptable to centrifugal separation and flux transport growth and yields superior sample quality. We demonstrate its efficacy by growing KFe2As2 and CsCr6Sb6 single crystals, the former exhibiting record-high quality, with a residual resistivity ratio (RRR) exceeding 2500, and the latter achieving significantly larger crystal dimensions than other methods. This accessible and economical method promises to accelerate the discovery of novel materials that contain reactive elements.
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Materials Science

Simulations of dislocation dynamics on an atomic lattice: the effect of collision rules

Tom Hudson, Akaraphon Jantaraphum and Patrick van Meurs

The stochastic dynamics of dislocations on a one-dimensional periodic lattice domain are considered. Two models are studied: one without a collision rule, and one which annihilates colliding dislocations if they have opposite orientation. The behaviour of both models is investigated by means of a series of numerical simulations exploring the asymptotic behaviour of these models as the number of dislocations increases. From these simulations, evidence is obtained that the discrete model with annihilation tends to a PDE for the dislocation density that accounts for annihilation. However, the discrete model without a collision rule does not appear to exhibit consistent convergence behaviour; instead, it appears that the expected PDE with conserved dislocation density appears in the limit for some parameters, but that for other parameters the density appears to follow to the evolution of the PDE with annihilation. These findings provide evidence that a careful treatment of dislocation collisions is important in discrete dislocation dynamics models.
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Thursday 28 May

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

Wetting as an emergent property of water: reformulating Young equation on molecular grounds

Nicolas Loubet and Gustavo Appignanesi

Young equation provides a remarkably successful macroscopic description of wetting, yet its molecular origin (particularly for water) has remained elusive for over two centuries. Here we make the molecular basis of aqueous wetting explicit by reformulating it in terms of a molecular wetting coefficient, omega m, which quantifies how an interface compensates the intrinsic energetic cost of hydrogen-bond defects relative to bulk water. Across a broad and continuous spectrum of hydrophilicities, spanning chemically diverse experimental and model surfaces, macroscopic contact angles collapse onto a single universal master curve when expressed through omega m. This molecular reformulation closes Young and Young-Dupre relations on energetic grounds, establishing a unified and predictive physical link between wetting, adhesion, cavitation, and nanoconfined filling. By anchoring interfacial behavior to waters intrinsic hydrogen-bond energetic scales, our results reveal wetting as an emergent property of water itself, rather than a surface-specific attribute and provide a transferable molecular framework that recalibrates energetic intuition and guides the rational design of aqueous interfaces. (This document is the unedited Author version of a Submitted Manuscript subsequently accepted for publication in J. Am. Chem. Soc. For the published version, which includes a more complete molecular-thermodynamics grounding of the method see the published version)
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Materials Science

Deterministic fabrication of large-area, high-crystallinity oxide moire superlattices

Reza Ghanbari, Eli Rodrigues, Young-Hoon Kim et al. (+10 more)

Oxide twistronics extends moire engineering beyond van der Waals materials, offering a promising platform for accessing emergent interfacial phenomena arising from the strong coupling of lattice, charge, and orbital degrees of freedom in complex oxides. However, deterministic fabrication of high-crystallinity oxide moire superlattices over large lateral dimensions remains challenging due to the three-dimensional bonding network of oxides. Here, we demonstrate a scalable, generalized fabrication strategy that enables the formation of high-crystallinity oxide moire superlattices with clean, chemically bonded interfaces and precisely controlled twist angles down to nominal values of 0.1 degree, achieving sub-degree twist-angle accuracy across large contiguous lateral dimensions approaching the millimeter scale. Using NaNbO3 as a model system, we show that the resulting interlayer coupling drives pronounced structural reconstruction that modifies both the phase structure and ferroelectric domain configuration. Synchrotron-based X-ray 3D reciprocal space mapping reveals the emergence of a single-phase state in twisted bilayers, in contrast to the mixed-phase structure observed in single-layer membranes prior to twist assembly. The structural signatures are further consistent with gradual lattice rotation distributed along the thickness direction that may accommodate interfacial shear strain, distinct from reconstruction observed in van der Waals moire systems, which primarily occurs through in-plane stacking rearrangement. This collective lattice response is correlated with twist-dependent nanoscale electromechanical modulations observed by piezoresponse force microscopy. These results establish a scalable materials platform for oxide twistronics and open new pathways towards integrating twist-engineered complex oxides into practical, macroscale device architectures.
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All authors Reza Ghanbari, Eli Rodrigues, Young-Hoon Kim, Konnor Koons, Yan Li, Kabelo Lebogang, Yiming Ding, Doug Barefoot, Yueyin Wang, Yin Liu, Hua Zhou, Miaofang Chi, Ruijuan Xu

Materials Science

Symmetry-Resolved Second Harmonic Generation in Quantum and Functional Materials

Xiaoyu Guo, Chang Jae Roh and Youngjun Ahn

Second harmonic generation (SHG) has evolved from a probe of noncentrosymmetric crystals into a symmetry-resolved optical method for identifying order parameters in quantum and functional materials. In particular, polarization-resolved rotational anisotropy (RA) measurements of SHG can connect nonlinear susceptibility tensors to the crystallographic and magnetic point groups of the underlying materials. This capability is especially powerful when the ordered state is weak, spatially confined, multipolar, magnetic, or hidden from conventional linear probe techniques. In this review article, we established a systematic symmetry-based framework for understanding RA-SHG and provide a comprehensive overview of RA-SHG studies across a broad range of condensed matter systems. We begin with basic theoretical background for the multipole origins of SHG radiation, the construction of nonlinear susceptibility tensors, and a group-theoretical framework connecting tensor components to order parameters. We then review the applications of RA-SHG to polar materials, magnetic orders, and other hidden electronic orders. Finally, we outline challenges and future research directions for using SHG to reveal, image, and control hidden, intertwined, and nonequilibrium phases in quantum and functional materials.
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Materials Science

Observation and Control of the Magnetic Photogalvanic Effect from Strongly Bound Excitons

Xianfan Nie, Tarun Patel, Hyunggeun Lee et al. (+11 more)

Photogalvanic effects arising from the quantum geometry of noncentrosymmetric materials are promising for next-generation light-harvesting devices that do not require a built-in electric field. Recent theories predict photogalvanic currents generated in magnetic systems with spin-dependent symmetry breaking as well as by bound exciton states, allowing for potential magnetic field control of the photoresponse and enhanced detection of deep sub-gap signals, respectively. We demonstrate the magnetic photogalvanic effect in a bilayer CrI3 tunnel junction with both magnetic field switching and electric field tuning of interlayer symmetry. By controlling for the polarization and energy of light illumination, we disentangle the shift and injection current contributions and find that the peak response occurs under resonant excitation of strongly bound excitons in CrI3. Our results can be captured within a many-body framework of the photogalvanic effect, while our devices function as tunable, multispectral helicity- and polarization-sensitive detectors that highlight the potential of 2D magnets for future optoelectronic applications.
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All authors Xianfan Nie, Tarun Patel, Hyunggeun Lee, Chuangtang Wang, Meixin Cheng, Mingrui Lai, Bowen Yang, Matteo Pennacchietti, Shiyu Liu, Hechang Lei, Liuyan Zhao, Michael E. Reimer, Su Ying Quek, Adam W. Tsen

Materials Science

A new Fermi kinetic phase transition model for metals including hysteresis effects

Ann E. Mattsson Wills, Daniel N. Blaschke, Michael B. Prime et al. (+3 more)

We present a new phenomenological model for phase transformation (PT) kinetics in metals, the "Fermi Kinetic Phase Transition (KPT) Model". It is designed such that it captures the main macroscopic features of our previously developed micro-structure dependent model, but at a fraction of the computational cost of the latter. Using four model parameters, the Fermi KPT model performs better than other phenomenological PT kinetics models in the literature, as shown by our present comparisons to experimental data for iron and tin.
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All authors Ann E. Mattsson Wills, Daniel N. Blaschke, Michael B. Prime, David R. Jones, Saryu Fensin, Abigail Hunter

Materials Science

Harnessing diamond surface features for dense and aligned NV ensembles

Eveline Postelnicu, Lillian B. Hughes Wyatt, Tri Nguyen et al. (+6 more)

Controlling nitrogen doping in diamond is key to advancing nitrogen-vacancy (NV) center devices. We harness the hillock, a typically undesirable surface feature, to incorporate high densities of grown-in, aligned NV-centers on a (001)-oriented substrate. Enhanced cathodoluminescence at hillock sidewalls is correlated via nanoSIMS to up to 1000x greater nitrogen incorporation compared to the planar film. We find that these hillocks are associated with stacking faults and edge-type dislocations, consistent with an origin in surface preparation rather than substrate screw dislocations. Yet, the growth is orderly enough that each of the four hillock sidewalls hosts a distinct NV orientation. A 1.7-2% grown-in NV/substitutional nitrogen (P1) ratio, 4x higher than typical (001)-oriented growth, is measured via NV decoherence analysis. By revealing that spontaneously formed hillocks act as natural laboratories for dense, aligned NV formation, this work motivates systematic investigation of facet-dependent nitrogen incorporation and preferential NV alignment in (001) diamond.
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All authors Eveline Postelnicu, Lillian B. Hughes Wyatt, Tri Nguyen, Simon A. Meynell, Christine Jilly, Paul Wallace, Andrew Barnum, Ania Bleszynski Jayich, Kunal Mukherjee

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

Spectroscopic evidence for a molecular orbital Kondo insulator

Ke-Jun Xu, Kuan H. Hsu, Nathan Giles-Donovan et al. (+13 more)

A Kondo insulator (KI) is a prototypical example of a highly entangled phase of matter, where many-body interactions between local moments and delocalized electrons engender the non-magnetic insulating ground state. Conventionally, the local moments arise from atomic multiplet states with a narrow bandwidth, limiting Kondo coherence to low temperatures. Here, we realize a new paradigm for constructing the KI state with hybridized molecular orbitals in FeSb2. Resonant inelastic X-ray scattering (RIXS) at the Fe L-edge reveals distinct signatures of band-like continuum states and localized states. Comparisons with first-principles calculations establish a mixed-configuration ground state with hybridized Fe d-Sb p molecular orbitals as basis states. By systematically investigating the RIXS momentum, temperature, and doping dependences, we find propagating collective modes commensurate with many-body charge and spin excitations. Our results pave the way for understanding the emerging class of unconventional d electron insulators and engineering high temperature Kondo many-body states.
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All authors Ke-Jun Xu, Kuan H. Hsu, Nathan Giles-Donovan, Christopher T. Parzyck, Gi-Hyeok Lee, Wanli Yang, Jun Okamoto, Hsiao-Yu Huang, Di-Jing Huang, Joshua J. Kas, John Vinson, Zhi-Xun Shen, Dung-Hai Lee, Thomas P. Devereaux, Wei-Sheng Lee, Robert J. Birgeneau

Materials Science

Exploring the Origins of Anti-Ambipolarity in BBL Polymer: Links to Redox Chemistry, Electronic Structure, and Structural Dynamics

Maryam Ghotbi, Alejandro Aviles and Perla B. Balbuena

We examine the intrinsic physical-chemical properties of the conjugated ladder-type polymer poly(benzimidazobenzophenanthroline) (BBL) in response to electron transfer. We aim at explaining the origin of the anti-ambipolar behavior behind the observed BBL nonlinear response associated with specific device architectures. To elucidate this point, we use theory and computation based on first principles, including density functional theory optimizations, ab initio molecular dynamics, time-dependent DFT, and Marcus-theory analysis. Our results reveal that this redox response is not simply monotonic but follows an alternating odd/even pattern in which gap narrowing and reopening occur sequentially before near-gapless behavior emerges at high charging. Converging theoretical evidence in this work demonstrates that bell shaped conductivity in BBL originates in its fundamental electronic structure and supramolecular organization.
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Materials Science

Role of structure and charge trapping on the bipolaron formation and magnetic-field response of gated conjugated polymers

Zuchong Yang, Vincent Lemaur, Melissa Berteau-Rainville et al. (+3 more)

Conjugated polymers exhibit unique spin-dependent phenomena arising from weak yet critical hyperfine interactions. Understanding these spin effects, particularly the spin-dependent formation and decay of correlated spin pairs, is important for advancing both organic electronics and polymer-based spintronics. Intrinsic magnetic-field responses such as magnetoresistance have primarily been investigated in diode architectures, where electrons and holes coexist. However, such systems are less suitable for probing bipolaron formation in unipolar transport, and the relationship between polymer structure and bipolaron formation in lightly doped polymers remains unclear. Here, we systematically investigate intrinsic magnetoresistance in representative conjugated polymers using field-effect transistors and observe a generally positive magnetoresistance. First-principles simulations reveal that bipolarons preferentially form on short conjugated segments associated with amorphous regions. Moreover, comparisons across these polymers show that enhanced charge trapping correlates with stronger magnetoresistance, implying promoted bipolaron formation. Bipolaron-incorporated energylevel-alignment modeling near metal/polymer interfaces suggests that charge traps can increase the bipolaron density.
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All authors Zuchong Yang, Vincent Lemaur, Melissa Berteau-Rainville, Olivier Bardagot, Yoann Olivier, Emanuele Orgiu

Materials Science

What drives performance in molecular MPNNs? An operator-level factorial benchmark

Panyu Jiao, Shuizhou Chen, Yiheng Shen et al. (+3 more)

Message-passing neural networks (MPNNs) are widely used for molecular property prediction, but their deployment as monolithic architectures makes it difficult to identify how specific message-passing operators affect performance. We present an operator-level factorial benchmark that decomposes 2D molecular MPNNs into the three families of message-seed initialization, node-edge fusion, and node update operators. The resulting 84 configurations are benchmarked on ten MoleculeNet datasets under a shared experimental setup and statistical analysis protocol. Across this controlled design, performance variation is associated primarily with message construction rather than update complexity. Message-seed initialization shows significant family-level effects for both regression and classification, node-edge fusion shows a significant family-level effect for regression with descriptive advantages for concatenation-based mixing, and the update family shows no statistically supported effect for either endpoint family. A representation probe into the Quinethazone molecule further demonstrates that concatenation-based mixing can better differentiate chemically distinct heteroatoms and withstand oversmoothing than Hadamard gating. Representative configurations selected separately for classification and regression recover competitive performance relative to established molecular graph neural network (GNN) baselines, ranking numerically best on eight of ten benchmark datasets. These empirical results are interpreted through concise mechanistic analyses of representative node-edge fusion and update operators. Our findings provide empirical design heuristics for molecular MPNNs by turning model design from a search over monolithic architectures into a targeted assessment of where and how chemical information enters the message-passing pipeline.
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All authors Panyu Jiao, Shuizhou Chen, Yiheng Shen, Yuyang Wang, Runhai Ouyang, Wei Xie