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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Saturday 18 July

Materials Science

Operando observation of strain relaxation in fatigued pearlitic steel

Louis Lesage, Johan Ahlström, Yubin Zhang et al. (+1 more)

Pearlitic steels are the material of choice for railway wheels and rails, where their lamellar ferrite-cementite structure balances cost, strength, and wear resistance. However, in use, cyclic loading combined with frictional heat softens the steel, promoting fatigue and eventual failure. Here we use Dark-Field X-ray Microscopy (DFXM) to follow, operando, the grain-scale response of a fatigued pearlitic colony during annealing up to 550 {\deg}C. Orientation maps reveal negligible lattice rotation and no sub-cell formation, indicating that the cementite lamellae suppress long-range dislocation motion. Strain maps nonetheless show pronounced relaxation: the elastic strain spread narrows by nearly 40%, with recovery starting below 250 {\deg}C, within the operating temperatures of railway wheels. We attribute this relaxation to short-range annihilation of dislocations confined between lamellae, linking grain-scale strain recovery to the macroscopic softening of pearlitic railway steels in service.
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All authors Louis Lesage, Johan Ahlström, Yubin Zhang, Can Y{\i}ld{\i}r{\i}m

Materials Science

Specimen design for material parameter identification using topology optimization

Adeline Wihardja and Kaushik Bhattacharya

Constitutive relations close the equations of continuum mechanics, and serve as a surrogate for a material in the design and engineering process. They are often specified in a parameterized form with parameters identified by experiment. In this paper, we propose a framework for identifying experimental configurations that are maximally informative for material parameter discovery. The framework strongly couples modeling and experimentation: the model leverages high-dimensional data from full-field measurements, while the current uncertainty in the model guides the design of future experiments. We formulate this goal by integrating Bayesian optimal experimental design with topology optimization. The Bayesian design criterion quantifies expected information gain, which drives the topology optimization of the specimen geometry.
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Materials Science

Electrical Control of Altermagnetism in a Quasi-1D Magnet

Alberto M. Ruiz, Cuiju Yu, Diego López-Alcalá et al. (+3 more)

Altermagnetism is a collinear magnetic state characterized by momentum-dependent spin splitting in fully compensated materials. While widely investigated in systems governed by three- or two-dimensional exchange interactions, its extension to quasi-one-dimensional magnets remains almost unexplored. Focusing on the experimentally established AgCrP$_2$S$_6$ van der Waals magnet, we demonstrate that antiferromagnetic chains embedded in a two-dimensional lattice provide a general route to altermagnetism. Combining first-principles calculations and spin-space-group analysis, we show that out-of-plane symmetry breaking can generate a nonrelativistic d-wave spin splitting. An external out-of-plane electric field validates this mechanism, where the induced splitting increases linearly with field strength and reverses sign with field direction. We rationalize such behaviour by constructing an effective tight-binding model, which links the altermagnetic response to anisotropic third-neighbor interchain hoppings. Additionally, we show that Janus substitution also induces a d-wave spin texture, while ferroelectric interfacing with CuInP$_2$S$_6$ enables polarization-controlled spin-split bands in a fully compensated ferrimagnetic state. Our results establish quasi-one-dimensional antiferromagnets as building blocks for altermagnetism.
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All authors Alberto M. Ruiz, Cuiju Yu, Diego López-Alcalá, Jose L. Lado, Adolfo O. Fumega, José J. Baldoví

Materials Science

Lattice initialisation and finite-size effects of non-equilibrium molecular dynamics simulations for heat transfer across graphene-copper interfaces

L.A. van Goor, W.N. Edeling, D. Jafari et al. (+5 more)

We study thermal transport across copper-graphene-copper interfaces using Non-Equilibrium Molecular Dynamics (NEMD), focusing on the influence of finite domain length and domain configuration, including lattice initialisation and associated graphene wrinkling, on the predicted thermal conductivity and Kapitza resistance. In the literature, NEMD simulations identified trends in the Kapitza resistance of graphene-copper interfaces. However, the simulation outcomes and reliability may depend heavily on configuration choices that are underexplored in the literature. We identify a strong sensitivity of the Kapitza resistance to domain configuration choices that affect the lattice constants and atomic density. We show that two conventional lattice initialisation strategies yield a factor of two difference in the Kapitza resistance, despite differences of only a few per cent in the lattice parameters. This behaviour is accompanied by strain-dependent shifts in the graphene and copper phonon spectra, and by increased phonon overlap at lower strain. Counter to conventional expectations, greater phonon-mode overlap coincides with higher Kapitza resistance, showing that spectral overlap alone cannot capture the interfacial heat-transfer dynamics. We suggest that in lattices initialised with lower residual strain, a damping boundary layer develops near the interface, and increases thermal resistance, as indicated by increased local structural disorder and local spectral broadening over a wider interfacial region. Beyond strain- and density-related effects associated with the lattice constants, Kapitza resistance shows no significant dependence on domain length or boundary temperature enforcement in this study. By contrast, the copper lattice conductivity exhibits clear domain-size and temperature dependence, consistent with phonon mean-free-path limitations and supported by phonon spectral analysis.
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All authors L.A. van Goor, W.N. Edeling, D. Jafari, H. Lee, E. Luesink, W.W. Wits, A.V. Lyulin, B.J. Geurts

Materials Science

Measuring momentum-resolved dissipation of phonon-polaritons in LiNbO$_3$ with terahertz driving

Megan F. Biggs, Rossella Acampora, Niccolò Sellati et al. (+5 more)

Mapping the dispersion of polaritons, hybrid quasiparticles arising from light-matter coupling, can provide key insights into the material dielectric response, coupling strength, and energy transfer pathways with other excitations. In this work, we present THz pump-Raman probe (TP-RP) as a versatile method for mapping the polariton dispersion in polar non-centrosymmetric materials, demonstrated here for the case of phonon-polaritons in LiNbO$_3$. By resonantly driving polaritonic modes with a broadband THz pump and probing them with a tunable NIR Raman pulse, TP-RP allows for the extraction of the momentum-dependence of both their frequency and damping rate with high accuracy. The spectral features observed in the pump-probe signal, including the polaritonic response as well as pulse artifacts, are reproduced within a many-body theoretical approach. Applying the technique to study the E(TO$_1$) phonon of LiNbO$_3$ enables the combined analysis of theory and experiments to uncover a nontrivial frequency dependence of the phonon intrinsic damping rate, revealing possible anharmonic couplings to other modes.
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All authors Megan F. Biggs, Rossella Acampora, Niccolò Sellati, Mattia Udina, Lara Benfatto, Elsa Abreu, Steven L. Johnson, Jeremy A. Johnson

Materials Science

Period-dependent suppression of Fourier peaks for topography images: Analysis of periodicity of triple-step arrays on vicinal Si(h h m) surfaces

A. Yu. Aladyshkin, A. N. Chaika, V. N. Semenov et al. (+3 more)

Reliable determination of the periodicity of multiatomic steps on high-Miller-index vicinal surfaces is often complicated by (i) the presence of relatively narrow terraces tilted at large angles relative to the scanning plane, and (ii) unavoidable distortions in the lateral direction resulting from creep and improper calibration of a piezo scanner. This work paves a way to overcome these obstacles using the period-dependent Fourier peaks suppression, which is invariant to affine distortions of the atomically resolved scanning probe microscopy images and to defects of the terrace atomic structure. We argue that the period of the triple-step arrays fabricated on vicinal Si(5 5 6) and Si(5 5 7) single-crystal wafers can be determined from raw scanning tunneling microscopy data, without preliminary corrections, with precision approaching the interatomic distance. We demonstrate that the intensities of the Fourier peaks in the differential maps, derived from raw topography images and containing stripes with the $7\times7$ reconstruction, strongly depend on the period of the stripes. The suppression of the ninth Fourier peak indicates that the regular array of triple steps formed on the Si(5 5 7) wafers has a period of $18b=5.99$ nm in projection onto the Si(1 1 1) terrace plane, where $b=0.333$ nm is the distance between atomic rows of the $1\times 1$ lattice in the $[\bar{1} \bar{1} 2]$ direction. This means that the nominally (5\,5\,7)-oriented Si wafers may correspond locally to the Si(8 8 11) orientation. The method can be applied to the precise analysis of other vicinal surfaces with narrow and wide terraces containing an integer number of Si(1 1 1)$7\times7$ unit cells.
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All authors A. Yu. Aladyshkin, A. N. Chaika, V. N. Semenov, A. S. Aladyshkina, A. M. Ionov, S. I. Bozhko

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

Unconventional superconductivity in ScIr$_2$ chiral crystal with a kagome lattice

Keqi Xia, Jianzhou Zhao, Igor Plokhikh et al. (+6 more)

Materials with a kagome lattice host exotic quantum phenomena driven by the interplay between band topology, spin-orbit coupling, magnetism, and electronic correlations. While magnetism of kagome materials has been widely investigated, their unconventional superconductivity (SC) remains largely unexplored due to the limited availability of suitable materials. Here, we report evidence of unconventional SC in the ScIr$_{2-x}$Si$_{x}$ family by combining muon-spin spectroscopy measurements with band-structure calculations. The parent ScIr$_2$ undergoes a structural phase transition from a high-$T$ cubic- to a low-$T$ rhombohedral phase, while the Ir kagome layer remains, albeit slightly distorted. Although the structural transition is suppressed by Si substitution, the superconducting pairing of ScIr$_{2-x}$Si$_{x}$ remains well described by a two-gap model. Since at least one of the gaps has nodes, this indicates an unconventional SC. Its unconventional nature can be explained by the distinct flat bands occurring near the Fermi level, leading to strong electronic correlations in the ScIr$_{2-x}$Si$_{x}$ family. Moreover, the low-$T$ phase of ScIr$_2$ exhibits an Ir chiral chain; therefore, it can be classified as a topological chiral crystal. Overall, the unusual properties of the ScIr$_{2-x}$Si$_{x}$ family make it an interesting, albeit rare, system for studying the interplay between unconventional SC, flat bands, and chirality.
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All authors Keqi Xia, Jianzhou Zhao, Igor Plokhikh, Marisa Medarde, Yang Xu, Qingfeng Zhan, Dariusz Jakub Gawryluk, Toni Shiroka, Tian Shang

Materials Science

Three Million Years Opposite State Data Retention in Partially Switched Wurtzite Ferroelectrics

Maike Gremmel, Roberto Guido, Victor Witte et al. (+3 more)

Ferroelectric memories based on the wurtzite-structured ferroelectrics are projected to store information for more than 3 million years at 150C. These results are extracted by combining standard domain wall motion limited switching kinetics with the near-by-electrode injection model for opposite state retention in ferroelectric random access memory. This impressive performance is greatly aided by switching only a fraction of the total polarization to store data, in order to limit the initial imprint variation of the devices - an effect that is universally observed in films with different thicknesses (60 nm - 270 nm) and different compounds (AlScN and AlScBN). Paradoxically, yet systematically, this reduction in initial imprint consistently results in larger switching polarization after a given time, compared to the fully switching state and 5-7 orders of magnitude improved opposite state retention. Finally, partial switching is able to simultaneously boost endurance against premature polarization loss and breakdown, making it a promising strategy for improved operation of ferroelectric devices with large spontaneous polarization, in particularly wurtzite-structured compounds.
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All authors Maike Gremmel, Roberto Guido, Victor Witte, Thomas Mikolajick, Uwe Schröder, Simon Fichtner

Materials Science

High-entropy perovskites, architectured by s0/d0/d10 cations, as novel electrolytes for solid oxide fuel cells

Ho Truong Nam Hai, Rishad Kunafiev, Kwati Leonard et al. (+1 more)

Solid oxide fuel cells enable efficient conversion of hydrogen into electricity. However, the limited availability of materials for their cathode, anode, and electrolyte remains a concern. This study introduces three high-entropy oxide perovskites as novel electrolyte materials for fuel cells (Ba0.50Sr0.50)(Ti0.33Zr0.33Hf0.33)O3 with s0/d0 cations, (Ba0.50Sr0.50)(Ga0.33In0.33Sn0.33)O3 with s0/d10 cations, and (Ba0.50Sr0.50)(Ti0.33Zr0.33Sn0.33)O3 with mixed s0/d0/d10 cations. Through sequential sintering by high-pressure torsion processing and calcination, these perovskites were synthesized and then printed with a thickness of about 6-10 microns on a Ni-SrZr0.5Ce0.4Y0.1O3 substrate as an anode and then coated with Ba0.5La0.5CoO3 as a cathode. Electrochemical analysis and impedance spectroscopy show that (Ba0.50Sr0.50)(Ti0.33Zr0.33Sn0.33)O3 with s0/d0/d10 cations exhibits the best performance with negligible current leakage and lowest ohmic resistance, while its maximum power density reaches 0.53 W.cm-2 at 973 K. Complementary synchrotron X-ray absorption and photoelectron spectroscopy analyses indicate that the superior performance of (Ba0.50Sr0.50)(Ti0.33Zr0.33Sn0.33)O3 correlates with its heterogeneous electronic structure characterized by tailored unoccupied d-orbital states, and favorable local metal-oxygen bond lengths and extrinsic oxygen vacancies. This investigation demonstrates the significance of high-entropy perovskites with mixed s0/d0/d10 cations as new rare-earth metal-free ion-conducting electrolytes, particularly for protonic solid oxide fuel cells.
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All authors Ho Truong Nam Hai, Rishad Kunafiev, Kwati Leonard, Kaveh Edalati

Materials Science

Beyond Janus Atomic Ordering: High-Throughput First-Principles Search for Hidden MoSO Monolayer Structures

Zhijing Huang, Tingting Zeng, Lin Zhang et al. (+5 more)

Despite the growing interest in two-dimensional (2D) MoSO systems, existing studies have exclusively focused on conventional Janus structures. In this work, we perform high-throughput first-principles calculations to explore novel stable 2D MoSO monolayers. Combined with random sampling strategy, graph theory and group theory, we successfully screen out three novel non-Janus 2D MoSO monolayers from 1325 candidate structures, namely Reversed 2H-MoSO, Hybrid 2H-MoSO, and Hybrid 1T'-MoSO. Compared with Janus MoSO monolayers, the non-Janus MoSO counterparts possess lower binding energies, varying from -4.38 to -4.51 eV/atom. A systematic combination of dynamic, thermodynamic, and mechanical stability analyses corroborates their excellent structural robustness. Ab initio molecular dynamics (AIMD) simulations confirm their superior thermal resistance, with the structures remaining stable at temperatures beyond 2000 K. Interestingly, unlike the semiconducting Janus MoSO, the Hybrid 1T'-MoSO monolayer exhibits distinct metallic characteristics. Furthermore, we found that strain and curvature can enable controlled phase transitions of MoSO among semiconducting, semimetallic, and metallic phases. More importantly, the Hybrid 1T'-MoSO exhibits favorable HER activity with a Gibbs free energy of -0.002 eV, rendering it a promising candidate for hydrogen evolution catalysis. This work not only expands the family of 2D MoSO materials but also provides a reliable strategy for discovering stable functional 2D materials via high-throughput computation.
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All authors Zhijing Huang, Tingting Zeng, Lin Zhang, Zhibin Gao, Longyuzhi Xu, Li Yang, Shuming Zeng, Zonglin Gu

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

3D Topologically Polarized Elastic Metamaterials Enable Asymmetric Energy Isolation at Low Frequencies

Shaoyuan Zhang, Xuejian Gong, Fangyuan Ma et al. (+5 more)

Topologically polarized elasticity has been extensively studied in lower-dimensions, yet its three-dimensional (3D) counterpart remains largely unexplored. Here, we demonstrate omnidirectional topological elasticity in 3D structures that incorporate bending stiffness, which elevates zero-frequency topological mechanical states into finite-frequency phononic modes. These modes are localized at a single boundary, creating a pronounced stiffness contrast in both static and finite-frequency dynamic regimes. This three-dimensional structure exhibits highly polarized mechanical behavior across all spatial dimensions, establishing omnidirectional asymmetric topological elasticity. Experimental and numerical results confirm robust, asymmetric energy isolation, arising from the interplay between bulk topological polarization and boundary-localized surface modes. Our findings establish a paradigm for 3D metamaterials, with promising applications in vibration shielding and directional wave manipulation.
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All authors Shaoyuan Zhang, Xuejian Gong, Fangyuan Ma, Zheng Tang, Ying Wu, Di Zhou, Feng Li, Yugui Yao

Materials Science

Harnessing disorder to decouple extension and shear in kirigami metamaterials

Haomin Yu, Hanxun Jin, Mingxuan Bi et al. (+5 more)

Kirigami turns stiff sheets into compliant, shape-morphing structures, but its reliance on periodic cut patterns comes at a cost: correlated panel rotations couple extension to shear, so stretching one axis drives a parasitic shear that cannot be suppressed, and also confine anisotropic stiffness to a narrow, discrete set of responses that cannot be tuned independently. Biological tissues overcome an analogous constraint through controlled disorder, such as graded fiber orientations in skin and hierarchical anisotropy in myocardium, achieving direction-dependent mechanics unavailable to regular architectures. Here, we show that engineered disorder is a design degree of freedom for kirigami, with stochastic kirigami accessing a continuous and far broader region of mechanical response than periodic patterns. This includes programmable anisotropy with near-complete elimination of extension-shear coupling. Because disordered patterns lack a simple parameterization, we navigate this design space with a geometry-aware graph neural network (GNN) that maps cut topology to the full nonlinear, bidirectional stress-strain response, coupled to a genetic algorithm that inverse-designs patterns reproducing target responses along two perpendicular axes. The GNN trains an order of magnitude faster and more accurately than image-based models. Fabricated elastomer samples reproduce the predicted nonlinear, anisotropic responses, closing the loop from design to physical component. By turning disorder into a variable to control directional stiffness, this work develops architected materials that stretch without parasitic shear, from soft actuators to tissue-interfacing devices matched to the anisotropy of living tissue.
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All authors Haomin Yu, Hanxun Jin, Mingxuan Bi, Mohammad Jafari, Feng Helen Long, Michael J Greenberg, Farid Alisafaei, Guy Genin

Materials Science

Ordinary Disordered Materials Can Carry Hyperuniform Physical Fields

Liyu Zhong, Haina Wang and Yang Jiao

Fluctuations in disordered matter play a central role in determining material properties and physical responses. Recent studies have identified an exotic class of systems known as structurally hyperuniform materials, in which large-scale density fluctuations are anomalously suppressed through special spatial organization of particles, phases, or microstructural features. Here we demonstrate that ordinary, structurally nonhyperuniform disordered materials can nevertheless support hyperuniform physical scalar, vector, and tensor fields such as charge, bound current, vorticity, defect density, and stress. We develop a general theoretical framework in which a physical field is generated from a more primitive parent field through a local physical operator. In Fourier space, the spectrum of the derived field is determined by the product of the parent-field spectrum and the Fourier symbol of the operator. When the operator embodies a local gauge-like constraint, its Fourier symbol possesses zeros at small wavenumber, eliminating the corresponding long-wavelength fluctuations. As a consequence, the derived field exhibits complete suppression of infinite-wavelength intensity fluctuations, irrespective of the large-scale disorder and nonhyperuniformity of the parent field. We demonstrate this mechanism in elastic, electrostatic, and magnetostatic settings, showing that operator-generated incompatibility, bound charge, and bound-current fields can become hyperuniform even when their parent eigenstrain, polarization, or magnetization fields remain conventionally disordered. These findings broaden the notion of hyperuniformity from a structural property of matter to a universal field phenomenon generated by local physical constraints.
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Materials Science

Mapping Order in Semicrystalline Polymers using Machine Learning of Nanobeam Electron Diffraction

Nicholas Marchese, Arthur R. C. McCray, Yael Tsarfati et al. (+4 more)

Organic mixed ionic electronic conductors (OMIECs) are a promising class of polymer materials for applications spanning neuromorphic computation to energy efficient electronics and bioelectronics. Despite being highly tunable, the relationship between structural features and key performance properties such as charge carrier mobility is poorly understood. Scanning nanodiffraction in the transmission electron microscope (TEM) is a powerful probe for elucidating this structure-property relationship, but produces large, noisy datasets that are difficult to interpret because polymer reflections exhibit several distinct morphologies. To address the complexity, we trained a machine learning (ML) model to detect these polymer diffraction peaks and their intensities from synthetic data. Compared to correlative peak detection algorithms, the conventional method for analyzing nanobeam 4D scanning transmission electron microscopy (4DSTEM) data, we show that the ML model is significantly faster and outperforms correlative algorithms in almost all cases, opening up the possibility of near-live visualization of 4DSTEM experiments.
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All authors Nicholas Marchese, Arthur R. C. McCray, Yael Tsarfati, Karen Bustillo, Adam Marks, Alberto Salleo, Colin Ophus

Materials Science

Signal amplification in simple metal-insulator transition devices

Victor Palin, Nareg Ghazikhanian, Matthew Frame et al. (+3 more)

Signal dissipation in large-scale neural networks can lead to information loss and ultimately to computational failures, necessitating local signal amplification at neuron - synapse connections. In biological nervous systems, axons are responsible for local signal amplification. Translating axon functionality into hardware, i.e., the ability to amplify and transmit signals without loss, is non-trivial because emulating the human brain implies building networks composed of ~10 billion interconnected neurons, each requiring a dedicated compact and scalable amplifier. Here, we demonstrate signal amplification in simple two-terminal devices made of a metal-insulator transition material. By operating the devices on the verge of the phase transition and taking advantage of negative differential resistance, we achieve robust signal amplification up to a factor of ~11.5. We also demonstrate the amplification of spiking sequences generated by a real neuristor, opening new exciting opportunities for the direct integration of artificial neurons and axons. The amplification can be controlled by easily adjustable experimental parameters, including DC bias, AC excitation, series resistance, and temperature. We further propose a model that predicts the gain using readily observable transport characteristics. Our results establish a framework for developing and optimizing axon-like amplification functionalities in nonlinear electronic materials.
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All authors Victor Palin, Nareg Ghazikhanian, Matthew Frame, Yayoi Takamura, Ivan K. Schuller, Pavel Salev

Friday 17 July

Materials Science · Cross-listed from cs.IR

Dual-Level Atomic and Coordination Geometry Learning for Crystal Property Prediction Using Graph Neural Networks

Sanjay Chakraborty

Accurate prediction of crystal properties remains a key challenge in computational materials science. While graph neural networks (GNNs) such as CGCNN, MEGNet, ALIGNN, and SchNet have shown strong performance, they primarily represent crystals at the atomic level and implicitly learn local chemical environments through message passing. However, many material properties are governed by coordination polyhedra, the fundamental structural units formed by atoms and their neighboring atoms. To address this limitation, we propose the Coordination Polyhedron Graph Network (CPGN), a multi-scale GNN that jointly learns atomic, bond, and coordination-polyhedron representations. CPGN constructs three coupled graphs: an atom graph encoding elemental and bonding information, a line graph capturing angular interactions, and a coordination polyhedron graph describing Voronoi-derived local environments through corner-, edge-, and face-sharing relationships. Physically meaningful geometric descriptors are incorporated for each polyhedron, while an interleaved message-passing mechanism with bidirectional cross-attention enables effective information exchange across structural levels. Extensive evaluations on the Materials Project, JARVIS-DFT, and QM9 benchmark datasets demonstrate that CPGN outperforms existing state-of-the-art GNN models. It achieves a formation-energy MAE of 0.060 eV/atom and a band-gap MAE of 0.292 eV on the Materials Project, while providing competitive multi-property prediction on JARVIS-DFT and superior HOMO prediction on QM9. The results highlight that explicit modeling of coordination polyhedra improves crystal representation learning and enables accurate, physically interpretable prediction of material properties.
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Materials Science

Phase nucleation, coarsening and evolution pathways of a sputtered nanostructured Inconel 725 alloy during heat treatment

Ruqing Cao, Ikponmwosa J. Iyinbor, Andrea M. Hodge et al. (+1 more)

Physical vapor deposition enables the fabrication of nanostructured superalloys with unique defect architectures, yet their phase evolution pathways can differ significantly from those of conventionally processed alloys. In this study, the effects of solution and aging treatments on phase selection and precipitation behavior in sputtered Inconel 725 films with an initially uniform columnar nanotwinned structure were systematically investigated. Direct aging at relatively low temperatures promoted extensive {\delta}-phase precipitation at twin boundaries and defect-rich regions, which depleted Nb from the {\gamma} matrix and suppressed {\gamma}'/{\gamma}" precipitation. In contrast, high-temperature solution treatment induced recrystallization and eliminated the nanotwinned structure, significantly reducing {\delta}-phase precipitation and increasing Nb availability to enable the formation of ultrafine spherical {\gamma}'/{\gamma}" precipitates within a refined {\gamma} matrix (<1 {\mu}m). Subsequent aging treatments promoted elemental partitioning and drove the morphological evolution of {\gamma}'/{\gamma}" precipitates from spherical to lenticular forms, while {\delta} precipitation became increasingly concentrated along grain boundaries. This spatial separation of intragranular {\gamma}'/{\gamma}" and grain-boundary {\delta} phases enabled simultaneous precipitation strengthening and grain stabilization, resulting in hardness values approaching 9 GPa. As a whole, this study demonstrates that the initial templates provided by defect structures can govern phase selection and precipitation pathways, providing a strategy for tailoring microstructure and achieving synergistic strengthening in nanostructured superalloys.
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All authors Ruqing Cao, Ikponmwosa J. Iyinbor, Andrea M. Hodge, Timothy J. Rupert

Materials Science

Instability-Avoiding Active Learning for Cluster Expansions in Complex Multielement Materials

Michael J. Waters and James M. Rondinelli

The high efficiency of cluster expansions make them appealing for studying chemical disorder in complex composition spaces such as in multi-principal element alloys (MPEAs). Several works have attempted to address the rapidly growing training cost with number of chemical species through active learning, transfer learning, and chemical embedding. However, many composition spaces have large regions where the host lattice becomes dynamical unstable, which are often avoided a priori so as to not generate expensive but inapplicable training data. Here, we demonstrate a procedure for integrating stability classification within an active learning workflow to autonomously avoid calculations for unstable structures. Our workflow augments the stability classification procedure with Mahalanobis distance-based structure selection to ensure model robustness by training set diversification. We benchmark our methods by training a cluster expansion for the complex FCC MPEA spanning the Ni-Fe-Cr-Al-Ti-Si alloy space, in which only Ni and Al are thermodynamically stable as FCC
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Materials Science

Bond reconstruction and vacancy clustering in monolayer silicon carbide from first principles

Péter Udvarhelyi

Bond reconstruction in vacancy-related structures affects their formation energies, symmetries, and electronic and optical properties. Using density functional theory, we investigate bond reconstruction mechanisms of monovacancies and vacancy aggregates in monolayer silicon carbide. Multiple bond descriptors reveal that isolated monovacancies undergo both in-plane reconstruction and out-of-plane distortion, which together shape their stability and electronic structure. For compact vacancy aggregates, we show that bond reconstruction acts as a key stabilization mechanism. However, in carbon monovacancy, reconstruction suppresses optical activity. In contrast, a highly stable aggregate composed of three carbon vacancies surrounding a silicon vacancy emerges as a promising infrared color-center candidate, combining a triplet ground state with a favorable Debye-Waller factor of the emission. These results highlight the role of bond reconstruction in defining the quantum properties of vacancy defects in two-dimensional silicon carbide.
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Materials Science · Cross-listed from cond-mat.soft

String Model Predicts Relaxation in Sheared Glass-Forming Liquids

Zi-Long Wang, Qi-Lu Yuan, Yun-Jiang Wang et al. (+4 more)

Understanding how structural relaxation evolves from equilibrium to nonequilibrium conditions remains a central problem in glass physics. Using simulations of model glass formers under steady shear, we show that the String Model, which links stringlike cooperative rearrangements to relaxation in equilibrium glass-forming liquids, predicts the structural relaxation time across the full range of temperatures and shear rates investigated without additional nonequilibrium fitting parameters, when combined with a shear-dependent effective temperature that is captured by a generalized fluctuation-dissipation relation. These results indicate that equilibrium and nonequilibrium relaxation are governed by the same underlying cooperative mechanism, but they occur under different effective thermodynamic conditions under steady shear. More broadly, our study provides a unified microscopic description of thermal and mechanically driven dynamics in glass-forming liquids.
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All authors Zi-Long Wang, Qi-Lu Yuan, Yun-Jiang Wang, Jack F. Douglas, Matteo Baggioli, Zhao-Yan Sun, Wen-Sheng Xu

Materials Science

Valley polarization, Rashba interaction, and weak altermagnetism in inversion-asymmetric MnPS$_\text{3}|$WS$_\text{2}$ van der Waals heterostructures

Purba Dutta, Soumajyoti Bid and Nirmal Ganguli

The deliberate breaking of inversion ($\mathcal{P}$) symmetry in antiferromagnets has recently emerged as an effective means to induce various features, such as the emergence of Berry curvature, spin-valley locking, magnetoelectric coupling, and the transition from conventional antiferromagnetism to altermagnetism. Conversely, in non-magnetic systems, inversion symmetry breaking in the presence of strong spin-orbit interaction (SOI) gives rise to momentum-dependent spin splitting via the Rashba effect, enabling tunable spin polarization through external electric fields. Motivated by recent advances in two-dimensional materials, we perform first-principles calculations based on density functional theory to investigate the van der Waals (vdW) heterostructure formed by a $\mathcal{P}$-symmetric MnPS$_3$ monolayer and a WS$_2$ monolayer. We demonstrate that the interface hosts a rich interplay of emergent phenomena, including an altermagnetic phase, Rashba spin splitting, spin-valley locking, and valley polarization. Our results demonstrate that the heterostructure exhibits semiconducting behavior with a direct band gap of approximately 1.65~eV and a type-I band alignment. Remarkably, the electronic structure and band alignment can be effectively tuned between type-I and type-II regimes via an external electric field and in-plane biaxial strain. Furthermore, field-induced modulation enables strong control over the altermagnetic phase and the valley splitting. These findings establish the proposed vdW heterostructure as a highly tunable platform with significant potential for spintronic and valleytronic applications.
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Materials Science

Atomically precise triple-step staircase on a vicinal silicon surface: Is it Si(5 5 7), Si(7 7 10) or Si(8 8 11)?

A. N. Chaika, A. Yu. Aladyshkin, V. N. Semenov et al. (+3 more)

Scanning tunneling microscopy studies of periodic arrays of triple steps fabricated on single-crystalline Si(5 5 7) wafers demonstrate several possible atomic structures of consecutive steps and Si(1 1 1) terraces maintaining the same periodicity on micrometer-sized surface areas. Detailed analysis of the atomically resolved data reveals the formation of Si(8 8 11) triple-step staircase with a period of 18b=5.99 nm in projection onto the terrace plane, where b=0.333 nm is the distance between atomic rows for the Si(1 1 1)1x1 surface. Schematic models for several possible configurations of either 7x7 or 5x5-reconstructed terraces and triple steps are proposed.
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All authors A. N. Chaika, A. Yu. Aladyshkin, V. N. Semenov, A. S. Aladyshkina, A. M. Ionov, S. I. Bozhko

Materials Science

A Dynamical Phase-Field Model for the Optical Properties of Ferroelectrics

Aiden Ross, Anya Frazer, Venkatraman Gopalan et al. (+1 more)

Ferroelectric materials are promising platforms for controllable photonic devices because of the strong coupling between their spontaneous polarization and optical properties. Yet, these materials remain challenging to design because of the close connection between the ferroelectric domain structure and optical response, which no existing theoretical approach can capture. Here, we develop a dynamical phase-field model that directly couples the ferroelectric order to the local optical response by introducing an electronic polarization field. This approach enables the prediction of the spatially resolved temperature- and wavelength-dependent optical properties in complex ferroelectric microstructures. Applying this method to BaTiO3 thin films, we investigate the evolution of the local refractive index and electro-optic response under varying electric fields and temperatures. We show that the ferroelectric domain structure strongly modifies the local electro-optic response, exceeding 4000 pm/V near domain walls, several times larger than the bulk single crystal value (r_51=1300 pm/V). Our simulations quantitatively reproduce the electro-optic coefficient measured in BaTiO3 on silicon films and capture the temperature-dependent behavior across multiple ferroelectric phase transitions, revealing the role of phase competition and coexistence in determining the electro-optic response. More broadly, this work establishes a general approach for predicting light-matter interactions in complex ferroelectric microstructures, enabling the computational design of ferroelectric materials for photonics.
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All authors Aiden Ross, Anya Frazer, Venkatraman Gopalan, Long-Qing Chen

Materials Science

Atomistic mechanism of corrosion-induced grain boundary migration in NiCr alloys in molten FLiNaK

Sadia Khan, Hamdy Arkoub and Miaomiao Jin

Corrosion of Ni-Cr structural alloys in molten fluoride salts is a persistent material degradation problem, yet the atomistic role of grain boundaries in this process remains poorly understood. Here we use reactive molecular dynamics to investigate corrosion of NiCr alloys in molten FLiNaK across four representative grain boundaries ($\Sigma3(111)$, $\Sigma11(113)$, $\Sigma5(012)$, and $\Sigma5(013)$) and corresponding bulk surfaces. Surface crystallography controls the initial dissolution stage, while grain boundary character governs the spatial localization and longer-time evolution of corrosion. We further identify a corrosion-driven grain boundary migration mechanism in which fluorine localization, preferential chromium dissolution, and vacancy-mediated mobility together drive interfacial motion away from the dealloyed region. The coherent $\Sigma3(111)$ boundary suppresses these processes, indicating low-energy special boundaries as targets for grain boundary engineering of corrosion-resistant Ni-Cr alloys.
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Materials Science

Subgrain-resolved Analysis of Degradation in Cu Metallization via Scanning 3DXRD and Thermomechanical Modeling

Nikhil Prabhu, Laura Neumann, Michael Reisinger et al. (+7 more)

Metallization layers play a key role in the performance and reliability of modern power semiconductor devices. During short-circuit events, rapid heating of power metallization layers induces thermomechanical incompatibility stresses, which may contribute to material degradation and impact device performance. In this work, potential degradation hotspots associated with thermomechanical loading in Cu power metallization are investigated using a combined experimental–computational approach. Scanning three-dimensional X-ray diffraction measurements are coupled with thermomechanical crystal plasticity simulations to probe the evolution of grain-resolved plastic deformation during rapid cyclic loading. This integrated approach provides insight into the microstructural processes governing degradation hotspot formation, laying the groundwork for future microstructure-informed, physics-based reliability assessment of Cu metallization.
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All authors Nikhil Prabhu, Laura Neumann, Michael Reisinger, James A. D. Ball, Cedric Corley-Wiciak, Manuel Petersmann, Agnieszka Corley-Wiciak, Jonathan Wright, Carsten Detlefs, Martin Diehl

Materials Science

Emergent Interfacial Magnetism in Epitaxial RuO$_2$

Yudi Yang, Zhuang Qian, Shi Liu et al. (+1 more)

The magnetic ground state of the altermagnet candidate RuO$_2$ remains controversial, with magnetic signatures observed mainly in epitaxial films. Here we show, using first-principles calculations, that magnetism in epitaxial RuO$_2$ can emerge as an interfacial boundary phase at TiO$_2$/RuO$_2$ interfaces. While TiO$_2$-induced epitaxial strain alone does not make (001)-oriented RuO$_2$ magnetic, explicit TiO$_2$/RuO$_2$ interfaces stabilize sizable Ru moments confined to the first few Ru layers. Charge-density and orbital-resolved analyses reveal interfacial electronic reconstruction, and substrate doping provides a route to tune the induced moments. In symmetric TiO$_2$/RuO$_2$/TiO$_2$ heterostructures, the two magnetic interfaces couple through the metallic RuO$_2$ spacer, producing a thickness-dependent alternation between weak-ferromagnetic and compensated altermagnetic states. Our results identify interface engineering as a practical route to stabilize and control fragile magnetism in RuO$_2$.
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All authors Yudi Yang, Zhuang Qian, Shi Liu, Congjun Wu

Materials Science

Structural Relaxation Enables Millisecond Infrared Photodetection in Selenium Iodine Semiconductors

Biman Jana

The optoelectronic performance of amorphous and partially crystalline semiconductors is strongly governed by structural disorder, yet establishing direct correlations between structural evolution and carrier transport remains challenging. Here, we show that the solid state optoelectronic response of selenium iodine (SeI2) is dictated by its transformation from a metastable glassy phase into an ordered lamellar structure. Vertically resolved transport measurements reveal pronounced depth-dependent electrical conductivity within thick SeI2 films, arising from compositional and structural inhomogeneity developed during solidification. Immediately after solidification, the glassy SeI2 network exhibits sluggish carrier transport and persistent photoconductivity. Upon prolonged structural relaxation, however, the material undergoes significant transport enhancement, enabling millisecond-scale infrared photodetection with a response time of 4.3 ms, stable operation up to 8 kHz modulation frequency, and shot-noise-limited detectivities of 108 Jones at 1550 nm and 1011 Jones in the visible. Spatial photocurrent mapping demonstrates highly uniform carrier collection despite the self-assembled lamellar morphology, while infrared thermal imaging confirms practical imaging capability over a broad temperature range. These results establish structural relaxation as a powerful strategy for engineering carrier transport in selenium-based semiconductors and position SeI2 as a promising solution-processable platform for infrared photodetection and thermal imaging.
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Materials Science

Nonuniform pressure helps structural superlubricity

Melisa M. Gianetti, Viet Hung Ho, Bjørn Haugen et al. (+2 more)

Structural superlubricity, nearly vanishing friction between two structurally incommensurate crystalline surfaces, is a promising avenue for reducing friction in applications, but requires very specific and well-controlled conditions. One of those conditions is perfectly uniform atomically flat surfaces. Real-world surfaces are generally rough, leading to nonuniform pressure distributions. We investigate the effects of nonuniform pressure distributions on structural superlubricity, using analytical calculations for rigid contacts as a basis, and molecular-dynamics simulations for a simple model to include the crucial effects of elasticity. We show that a key ingredient is the vanishing pressure at the edge of the contact, and that this leads to improved scaling depinning and scaling behaviour, leading to lower friction. We thus show that nonuniform pressure distributions actually help structural superlubricity, rather than hinder it.
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All authors Melisa M. Gianetti, Viet Hung Ho, Bjørn Haugen, Graham Cross, Astrid S. de Wijn

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

Property-dependent material times

Aude Y. Amari, Lorenzo Costigliola and Jeppe C. Dyre

We analyze simulations of physical aging following large temperature up-jumps from equilibrated, slowly relaxing states. Specifically, we consider up-jumps from temperatures T=0.43 and T=0.37 to T=0.48 in a binary Lennard-Jones mixture. The Tool-Narayanaswamy (TN) concept of a universal material time was recently shown to become less effective in rationalizing the aging response for such large jumps [Amari et al., Phys. Rev. E 113, 045411 (2026)]. Here, we investigate whether the performance of the TN formalism can be improved by assigning a separate material time to each observable. We examine the potential-energy time-autocorrelation function, the self-intermediate scattering function, and the time-dependent mean-square displacement. As part of this study, we perform a detailed analysis of the extent to which the triangular relation, a necessary condition for the existence of a material time, is satisfied. We find that, for all three properties, the best data collapse is obtained when each property is parameterized by its own material time. The degree of improvement varies considerably among the observables, however; it is most pronounced for the mean-square displacement.
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Materials Science · Cross-listed from cond-mat.mes-hall

Electrothermal control of spin-reorientation transition in Co/Fe_3GaTe_2 heterostructures

Po-Wei Chen, Ming-Hsien Hsu, Cheng-Ying Hsiao et al. (+12 more)

Electrical control of magnetic anisotropy in van der Waals (vdWs) magnets is a key step toward reconfigurable two-dimensional spintronics, yet how a conventional metallic ferromagnet competes with a van der Waals magnet across a direct interface has remained largely unexplored. Here we demonstrate reversible thermal and electrothermal control of a spin-reorientation transition in Co/Fe_3GaTe_2 (FGaT) heterostructures. As Joule heating weakens the FGaT anisotropy, the heterostructure switches from an out-of-plane- to an in-plane-dominated state at a reorientation temperature of approximately 311 K, well below the Curie temperature, consistent with an exchange-mediated anisotropy competition between the Co overlayer and FGaT. An electrically driven device shows a closely matching loop evolution within an 80-100 mW power window, reversibly over five measurement cycles, consistent with an electrothermal origin. In a Co-free FGaT device, Kerr microscopy traces the switching to a power-tunable domain nucleation barrier and demonstrates power-thresholded, field-assisted magnetization reversal at a threshold near 15 mW. These results demonstrate electrothermal anisotropy competition as a route to heat-assisted and device-level control of vdWs magnetism.
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All authors Po-Wei Chen, Ming-Hsien Hsu, Cheng-Ying Hsiao, Ming-Yang Ho, Masahiro Haze, Yan-Ru Chu, Yu-Cheng Shao, Po-Chun Chang, Chen-Yu Ou, Ruei Chen, Ko-Fan Chen, Chung-Ting Ke, Chao-Hung Du, Yukio Hasegawa, Wen-Chin Lin.