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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Tuesday 13 January

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

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

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

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

Materials Science

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

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

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

Materials Science

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

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

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

Materials Science

Machine Learning-Driven Creep Law Discovery Across Alloy Compositional Space

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

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

Materials Science

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

Abhishek Banerjee, Stefano Deledda and Olena Zavorotynska

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

Forbidden second harmonics in centrosymmetric bilayer crystals

Haoning Tang, Zhitong Ding, Tianyi Ruan et al. (+7 more)

Optical spectroscopy based on second-order nonlinearity is a critical technique for characterizing two-dimensional (2D) crystals as well as bioimaging and quantum optics. It is generally believed that second-harmonic generation (SHG) in centrosymmetric crystals, such as graphene and other bilayer 2D crystals, is negligible without externally breaking the inversion symmetry. Here, we show that with a new homodyne detection technique, we can apparently circumvent this symmetry-imposed constraint and observe robust SHG in pristine centrosymmetric crystals, without any symmetry-breaking field. With its exceptional sensitivity, we resolve polarization-resolved SHG in bilayer hexagonal boron nitride (h-BN), bilayer 2H-WSe$_2$, and remarkably, Bernal-stacked bilayer graphene, allowing us to unambiguously identify the crystallographic orientation in these crystals via SHG for the first time. We also demonstrate that the new technique can be used to non-invasively detect uniaxial strain and optical geometric phase in these crystals. The observed SHG in our experiments is attributed to second-order nonlinearity in the quadrupole channel, which is controlled by the presence of the $C_2$ symmetry instead of the inversion symmetry. Our new technique expands the capability of nonlinear optical spectroscopy to encompass a large class of centrosymmetric materials that could never be measured before, and can be used for quantum sensing of moiré materials and twisted epitaxial films.
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All authors Haoning Tang, Zhitong Ding, Tianyi Ruan, Zeyu Hao, Kenji Watanabe, Takashi Taniguchi, Haozhe Wang, Ali Javey, Feng Wang, Yuan Cao

Materials Science

Cyclic- and helical-symmetry-adapted phonon formalism within density functional perturbation theory

Abhiraj Sharma and Phanish Suryanarayana

We present a first-principles framework for the calculation of phonons in nanostructures with cyclic and/or helical symmetry. In particular, we derive a cyclic- and helical-symmetry-adapted representation of the dynamical matrix at arbitrary phonon wavevectors within a variationally formulated, symmetry-adapted density functional perturbation theory framework. In so doing, we also derive the acoustic sum rules for cylindrical geometries, which include a rigid-body rotational mode in addition to the three translational modes. We implement the cyclic- and helical-symmetry-adapted formalism within a high-order finite-difference discretization. Using carbon nanotubes as representative systems, we demonstrate the accuracy of the framework through excellent agreement with periodic plane-wave results. We further apply the framework to compute the Young's and shear moduli of carbon nanotubes, as well as the scaling laws governing the dependence of ring and radial breathing mode phonon frequencies on nanotube diameter. The elastic moduli are found to be in agreement with previous density functional theory and experimental results, while the phonon scaling laws show qualitative agreement with previous atomistic simulations.
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Materials Science · Cross-listed from cond-mat.mes-hall

Dynamical stability by spin transfer in nearly isotropic magnets

Hidekazu Kurebayashi, Joseph Barker, Takumi Yamazaki et al. (+9 more)

Spin transfer torques (STTs) control magnetisation by electric currents, enabling a range of nano-scale spintronic applications. They can destabilise the equilibrium magnetisation state by counteracting magnetic relaxation. Here, we maximise the STT effect through a dedicated growth-annealing protocol for CoFeB thin films, such that magnetic anisotropies originating from the interface and shape almost cancel each other. The nearly isotropic magnets enable low-current dynamical stabilisation of the magnetisation in the direction opposite to an applied magnetic field, thereby realising a spintronic analogue of the Kapitza pendulum. In an intermediate current regime, the STT drives large magnetisation vector fluctuations that cover the entire Bloch sphere. The continuous variable associated with the stochastic magnetisation direction may serve as a resource for probabilistic computing and neuromorphic hardware. Our results establish isotropic magnets as a platform to study as-yet-uncharted, far-from-equilibrium spin dynamics including anti-magnonics, with promising implications for unconventional computing paradigms.
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All authors Hidekazu Kurebayashi, Joseph Barker, Takumi Yamazaki, Varun K. Kushwaha, Kilian D. Stenning, Harry Youel, Xueyao Hou, Troy Dion, Daniel Prestwood, Gerrit E. W. Bauer, Kei Yamamoto, Takeshi Seki

Materials Science · Cross-listed from physics.optics

Excitonic Landscape of Monolayer Transition-Metal Dichalcogenides: Experimental Discrepancies, Theoretical Advances, and Strain Dependence

Cem Sevik, Purushothaman Manivannan, Fulvio Paleari et al. (+1 more)

Excitons in monolayer transition-metal dichalcogenides (TMDs) have garnered significant attention because of their large binding energies due to weakly screened Coulomb interaction, and direct bandgap at the K/K$^\prime$ point in the hexagonal Brillouin zone featuring spin-polarised bands due to spin-orbit coupling and lack of inversion symmetry. This makes them prospective for next-generation optoelectronic and quantum devices. However, despite the intense research activity, the reported values for exciton binding energies, quasiparticle gaps, and spectral features exhibit substantial variation across both experimental and theoretical studies. In this article, we present a comprehensive and critical assessment of the current understanding of excitonic properties in single-layer TMDs, integrating results from the angle-resolved photoemission spectroscopy (ARPES), photoluminescence (PL) measurements, and other experimental techniques with first-principles theoretical insights. Special emphasis is placed on the comparison and reconciliation of discrepancies observed across different experimental setups and sample qualities. Furthermore, we highlight our state-of-the-art GW-BSE calculations, which include both equilibrium and laterally strained systems, to systematically analyse the behaviour of direct and indirect excitons. By evaluating the effect of strain as a tunable control variable, we demonstrate its potential to engineer excitonic properties, supported by cross-validation against prior theoretical predictions and experimental findings. In doing so, we clarify the sources of discrepancies in the literature and offer a unified perspective on excited-state engineering strategies in two-dimensional TMDs.
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All authors Cem Sevik, Purushothaman Manivannan, Fulvio Paleari, Milorad V. Milosevic

Materials Science

Fractional-Monolayer 2D-GaN/AlN Structures: Growth Kinetics and UVC-emitter Applications

V.N. Jmerik, D.V. Nechaev, E.A. Evropeitsev et al. (+11 more)

The paper reports on fundamental properties of the GaN/AlN quantum wells (QWs) with nominal subcritical thicknesses of 0.75-2 monolayers (MLs). They are grown by plasma-activated molecular beam epitaxy, varying either the nominal thickness or the gallium-to-nitrogen flux ratio. In situ monitoring reveals difference in 2D nucleation and step-flow growth modes of the QWs. The emission charactestics of QWs with integer thicknesses of 1 and 2 MLs depend weakly on the growth mechanism. In contrast, the intensity and spectral position luminescence of QWs with fractional-ML thicknesses are determined by the growth mechanism. Using ab initio calculations, a phenomenological model is proposed that describes fractional-ML QWs either as arrays of 2D quantum disks or as arrays of 2D quantum ribbons, in cases where 2D nucleation or step-flow growth mechanisms predominate, respectively. This model is generally consistent with experimental data on photo- and cathodoluminescence of heterostructures with multiple (250) GaN/AlN QWs. These heterostructures, when pumped by electrom beam at an energy 12.5 keV with a maximum pulse current of 2 A, exhibit linear current dependences of optical peak powers up to 1 and 37 W for wavelengths of 228 and 256 nm, respectively, making them promising for use as powerfull ultraviolet-C emitters.
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All authors V.N. Jmerik, D.V. Nechaev, E.A. Evropeitsev, E.M. Roginskii, A.N. Semenov, M.A. Yagovkina, P.A. Alekseev, V.I. Kozlovsky, M.M. Zverev, N.A. Gamov, Tao Wang, Xinqiang Wang, T.V. Shubina, A.A. Toropov

Materials Science

Effect of Interatomic Potential Choice on Fracture Modes of Graphene with Parallel Cracks

Suyeong Jin, Jung-Wuk Hong and Alexandre F. Fonseca

Defect engineering via parallel cracks has been proposed as a route to tailor the fracture response of graphene. However, atomistic fracture predictions can be strongly sensitive to the interatomic potential. Here, we quantify the effect of potential choice by revisiting H-passivated graphene containing two parallel cracks separated by a gap $W_{\text{gap}}$ loaded in tension along the armchair (AC) and zigzag (ZZ) directions. Molecular dynamics simulations using the AIREBO potential under the same geometry and loading protocol previously studied with ReaxFF, are employed, so enabling a direct comparison. Stress-strain responses, Young's modulus, an effective mode-I stress intensity factor, and energy absorption are evaluated as functions of $W_{\text{gap}}$. Compared with ReaxFF, AIREBO predicts lower peak stresses and earlier catastrophic softening, leading to reduced post-peak deformation capacity and energy absorption. Ductility and energy absorption are shown to be highly potential-dependent, underscoring the need for careful potential selection in defect-engineered graphene fracture simulations.
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Materials Science

Giant Hole-doping in 2H-WSe2 via Ta Substitution

Minhee Kang, Woojin Choi, Choongyu Hwang et al. (+1 more)

The family of transition metal dichalcogenides (TMDCs) has been regarded as promising candidates for future electronics, valleytronics, spintronics, and optoelectronics. While most of TMDCs are intrinsic n-type semiconductors due to electron donation from chalcogen vacancies, realizing intrinsic p-type TMDCs and achieving precise control over their electronic properties remain challenging. In this work, we introduce a powerful approach to obtain intrinsic hole doping by substituting Ta atom into 2H-WSe2. A combining study of molecular beam epitaxy growth and in-situ angle-resolved photoemission spectroscopy characterization clearly reveals that Ta substitution induces a significant hole doping and provides a possible way of a semiconductor-to-metal transition in 2H-WSe2.
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All authors Minhee Kang, Woojin Choi, Choongyu Hwang, Jinwoong Hwang

Materials Science

Influence of Local Icosahedral Short-Range Order on the Magnetization Dynamics of Amorphous Cobalt-Iron Nanodisks

Erick Burgos-Parra and Matías Sepulveda-Macías

The microscopic origin of soft magnetic properties in amorphous alloys is fundamentally linked to the interplay between local topological disorder and magnetic exchange interactions. In this work, we employ a multiscale Spin-Lattice Dynamics (SLD) approach to investigate the magnetostructural correlations in amorphous Co$_{x}$Fe$_{1-x}$ nanodisks ($x=35, 50, 65$). By integrating classical molecular dynamics with a generalized magnetic Hamiltonian, we capture the dynamic feedback loop between lattice vibrations and spin precession. Topological analysis via Voronoi tessellation reveals a persistent species-dependent structural heterogeneity: Cobalt atoms preferentially adopt "solid-like" icosahedral packing, forming a rigid structural backbone, whereas Iron atoms exhibit a higher propensity for "liquid-like" disordered environments. We demonstrate that this topological disparity dictates the macroscopic magnetic response. The Cobalt-driven structural stiffness preserves a robust exchange network that maximizes saturation magnetization, while the local disorder inherent to Iron-rich regions introduces exchange fluctuations that act as an intrinsic damping mechanism, delaying magnetic relaxation. These findings provide an atomistic explanation for the stability of ferromagnetic order in Co-Fe metallic glasses and offer a pathway for tuning damping parameters in amorphous spintronic devices through stoichiometric control.
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Materials Science

Pressure-Induced Martensitic Phase Transformation and Microstructure Evolution in nanograined $\text{Fe}\text{-}7\%\text{Mn}$ Alloy

Mrinmay Sahu, Sorb Yesudhas, Valery I. Levitas et al. (+1 more)

The Fe-Mn-based alloys are receiving immense attention due to their applications in the third generation of advanced high-strength steels, owing to their high strength and ductility. A detailed in situ high-pressure structural phase transformation and microstructural evolution in nanograined $\text{Fe}\text{-}7\%\text{Mn}$ alloy has been performed using the axial synchrotron X-ray diffraction technique. The ambient BCC phase of $\text{Fe}\text{-}7\%\text{Mn}$ undergoes pressure-driven structural PT to the HCP phase at 11.4 GPa. Both BCC and HCP phases coexist up to 15.9 GPa; thereafter, they transform into a pure HCP phase, which remains stable up to the maximum pressure of 30.3 GPa. The XRD study reveals that the $(110)_{\mathrm{b}}$ dense crystallographic plane of the BCC lattice transforms into a densely packed $(002)_{\mathrm{h}}$ peak of the HCP lattice following the orientational relationship $(110)_{\mathrm{b}} \parallel (0001)_{\mathrm{h}}$ via diffusionless $ \mathrm{Burger's} $ martensitic crystallographic PT pathway. The evolution of crystallite size and microstrain with pressure shows a distinct change during the structural PT. The microstrain exhibits a sharp anomaly at around 10 GPa, suggesting that the microstructural changes precede the structural PT.
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All authors Mrinmay Sahu, Sorb Yesudhas, Valery I. Levitas, Dean Smith

Materials Science

Autonomous Materials Exploration by Integrating Automated Phase Identification and AI-Assisted Human Reasoning

Ming-Chiang Chang, Maximilian Amsler, Duncan R. Sutherland et al. (+9 more)

Autonomous experimentation holds the potential to accelerate materials development by combining artificial intelligence (AI) with modular robotic platforms to explore extensive combinatorial chemical and processing spaces. Such self-driving laboratories can not only increase the throughput of repetitive experiments, but also incorporate human domain expertise to drive the search towards user-defined objectives, including improved materials performance metrics. We present an autonomous materials synthesis extension to SARA, the Scientific Autonomous Reasoning Agent, utilizing phase information provided by an automated probabilistic phase labeling algorithm to expedite the search for targeted phase regions. By incorporating human input into an expanded SARA-H (SARA with human-in-the-loop) framework, we enhance the efficiency of the underlying reasoning process. Using synthetic benchmarks, we demonstrate the efficiency of our AI implementation and show that the human input can contribute to significant improvement in sampling efficiency. We conduct experimental active learning campaigns using robotic processing of thin-film samples of several oxide material systems, including Bi$_2$O$_3$, SnO$_x$, and Bi-Ti-O, using lateral-gradient laser spike annealing to synthesize and kinetically trap metastable phases. We showcase the utility of human-in-the-loop autonomous experimentation for the Bi-Ti-O system, where we identify extensive processing domains that stabilize $\delta$-Bi$_2$O$_3$ and Bi$_2$Ti$_2$O$_7$, explore dwell-dependent ternary oxide phase behavior, and provide evidence confirming predictions that cationic substitutional doping of TiO$_2$ with Bi inhibits the unfavorable transformation of the metastable anatase to the ground-state rutile phase. The autonomous methods we have developed enable the discovery of new materials and new understanding of materials synthesis and properties.
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All authors Ming-Chiang Chang, Maximilian Amsler, Duncan R. Sutherland, Sebastian Ament, Katie R. Gann, Lan Zhou, Louisa M. Smieska, Arthur R. Woll, John M. Gregoire, Carla P. Gomes, R. Bruce van Dover, Michael O. Thompson

Materials Science

Magnetoelectric torque in polar magnetic bilayers

Zhong Shen, Jun Chen, Xiaoyan Yao et al. (+1 more)

Energy-efficient fast switching of spin orientations or textures is a core issue of spintronics, which is highly demanded but remains challenging. Different from the mainstream routes based on spin-transfer torque or spin-orbit torque, here we propose another mechanism coined as magnetoelectric torque to switch the magnetization in polar magnetic bilayers via pure electric field. In some magnetic van der Waals bilayers, when the electrostatic energy of polarization can compensate the interlayer magnetic coupling, a magnetoelectric torque is generated to fastly flip spins within a few picoseconds, which is demonstrated by combining the first-principles calculations, analytic model, as well as atomistic simulations. Such a magnetoelectric torque doesn't rely on the spin-orbit coupling and is generally active in polar magnetic homostructures and heterostructures. Our work provides an alternative route to switch magnetization in nanoscale, which may benefit the energy-saving and fast-response spintronic devices.
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All authors Zhong Shen, Jun Chen, Xiaoyan Yao, Shuai Dong

Materials Science

Symmetry-aware Conditional Generation of Crystal Structures Using Diffusion Models

Takanori Ishii, Kaoru Hisama and Kohei Shinohara

The application of generative models in crystal structure prediction (CSP) has gained significant attention. Conditional generation–particularly the generation of crystal structures with specified stability or other physical properties has been actively researched for material discovery purposes. Meanwhile, the generative models capable of symmetry-aware generation are also under active development, because space group symmetry has a strong relationship with the physical properties of materials. In this study, we demonstrate that the symmetry control in the previous conditional crystal generation model may not be sufficiently effective when space group constraints are applied as a condition. To address this problem, we propose the WyckoffDiff-Adaptor, which embeds conditional generation within a WyckoffDiff architecture that effectively diffuses Wyckoff positions to achieve precise symmetry control. We successfully generated formation energy phase diagrams while specifying stable structures of particular combination of elements, such as Li–O and Ti–O systems, while simultaneously preserving the symmetry of the input conditions. The proposed method with symmetry-aware conditional generation demonstrates promising results as an effective approach to achieving the discovery of novel materials with targeted physical properties.
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Monday 12 January

Materials Science

Multiscale Analysis of Plasma-Modified Silk Fibroin and Chitosan Films

Jordan Nashed, Tomasz Bartkowiak, Alexandru Horia Marin et al. (+2 more)

Biological interactions with material surfaces span a wide range of length scales, yet conventional surface measurements often fail to account for scale, limiting the insights they provide for surface engineering. Here, we investigate how multiscale surface descriptors of plasma-modified silk fibroin and chitosan surfaces modify bacterial and immune cell response. Surface chemistry and topography were characterized using X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM), followed by sliding bandpass filtration and multiscale curvature tensor-based methods to measure scale-dependent topographic features. Macrophage response and biofilm growth were assessed by fluorescence microscopy. Correlation strength showed scale-dependence with respect to surface features and biological structure: individual bacteria and small colonies correlated more strongly with fine-scale topographic features, whereas macrophage morphology correlated more strongly with larger-scale surface features. Notably, measured surface chemical descriptors generally did not correlate strongly with biofilm formation; nonetheless, chitosan and silk fibroin showed distinct trends in bacterial support, suggesting that material identity was not captured by the measured surface properties and that prevention of biofilms likely benefits from combinatorial approaches as opposed to physical surface modification alone. These results show that different biological structures interact with material surfaces at distinct length scales, as well as demonstrate the utility of multiscale analysis in identifying scales of interest in biological interactions with surfaces. Moreover, the data suggests that tailoring topographic feature size to the characteristic scale of the targeted biological entity is a potential strategy for antibacterial wound-healing materials without incurring cytotoxicity.
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All authors Jordan Nashed, Tomasz Bartkowiak, Alexandru Horia Marin, Tine Curk, Viviana Marcela Posada-Perez

Materials Science · Cross-listed from cs.LG

DataScribe: An AI-Native, Policy-Aligned Web Platform for Multi-Objective Materials Design and Discovery

Divyanshu Singh, Doguhan Sar{\i}türk, Cameron Lea et al. (+3 more)

The acceleration of materials discovery requires digital platforms that go beyond data repositories to embed learning, optimization, and decision-making directly into research workflows. We introduce DataScribe, an AI-native, cloud-based materials discovery platform that unifies heterogeneous experimental and computational data through ontology-backed ingestion and machine-actionable knowledge graphs. The platform integrates FAIR-compliant metadata capture, schema and unit harmonization, uncertainty-aware surrogate modeling, and native multi-objective multi-fidelity Bayesian optimization, enabling closed-loop propose-measure-learn workflows across experimental and computational pipelines. DataScribe functions as an application-layer intelligence stack, coupling data governance, optimization, and explainability rather than treating them as downstream add-ons. We validate the platform through case studies in electrochemical materials and high-entropy alloys, demonstrating end-to-end data fusion, real-time optimization, and reproducible exploration of multi-objective trade spaces. By embedding optimization engines, machine learning, and unified access to public and private scientific data directly within the data infrastructure, and by supporting open, free use for academic and non-profit researchers, DataScribe functions as a general-purpose application-layer backbone for laboratories of any scale, including self-driving laboratories and geographically distributed materials acceleration platforms, with built-in support for performance, sustainability, and supply-chain-aware objectives.
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All authors Divyanshu Singh, Doguhan Sar{\i}türk, Cameron Lea, Md Shafiqul Islam, Raymundo Arroyave, Vahid Attari

Materials Science · Cross-listed from physics.ins-det

Achieving Ultrahigh Resolution with High Efficiency: Optical Design of the 2D-RIXS Spectrometer at NanoTerasu BL02U

Jun Miyawaki

A state-of-the-art Resonant Inelastic X-ray Scattering (RIXS) facility, composed of a dedicated beamline and a 2D-RIXS spectrometer, has been constructed and commissioned at BL02U in NanoTerasu, Japan. This paper reports the optical design and optimization of this spectrometer, aiming for an ultrahigh energy resolution of <10 meV in the soft X-ray range. Conventional RIXS spectrometers using monochromatic incident X-rays suffer from a severe trade-off between energy resolution and measurement efficiency, which makes achieving resolutions of <10 meV practically unfeasible. To overcome this limitation, we adopted the $h\nu^2$ concept using dispersive incident X-rays, based on a comparative study. This approach decouples the energy resolution from the incident bandwidth. We estimate that our 2D-RIXS spectrometer improves efficiency by more than a factor of 10 compared to conventional spectrometers. The 2D-RIXS spectrometer has been successfully commissioned, demonstrating that sub-10 meV resolution measurement is achievable with practical throughput. While development continues towards the ultimate design resolution, the successful implementation validates the design strategy and offers a pathway for future high-performance RIXS instrumentation.
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Materials Science

Low-temperature Spark Plasma Sintering of fine refractory composite powders core-shell: A case of the powders W@Ni

A. V. Nokhrin, E. A. Lantcev, L. S. Alekseeva et al. (+9 more)

The mechanisms of fast low-temperature Spark Plasma Sintering (SPS) of W + 10% wt. Ni powders were investigated. The powder compositions were obtained in two methods: (i) by mixing W and Ni powders in a specified ratio (hereinafter referred to as W + Ni); (ii) by Ni deposition on the surface of submicron W particles allowing the formation of particles with a core W - shell Ni structure (hereinafter referred to as W@Ni). To reduce the concentrations of oxygen and oxides, the powders were annealed in hydrogen. The solid-phase sintering was performed at various temperatures (1000-1150{\deg}C), pressures (40-80 MPa), heating rates (50-500{\deg}C/min), and isothermal holding times (0-20 min). The sintering temperatures corresponded to the onset of intense dissolution of W in Ni. The samples had high relative density and small grain sizes. The activation energy of SPS of the mixed powders was close to the one of the grain boundary diffusion. The key mechanism for the compaction of W@Ni particles in the SPS process is Coble creep. The increasing of the sintering temperature was shown to lead to an increase in the solubility of W in Ni and, consequently, to an increase in the number of secondary Ni4W particles formed during cooling down. The grain growth has a minor effect on the mechanical properties of the W alloy compared to the changes in its phase composition.
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All authors A. V. Nokhrin, E. A. Lantcev, L. S. Alekseeva, N. V. Malekhonova, M. S. Boldin, Yu. V. Blagoveshchenskiy, N. V. Isaeva, A. V. Terentyev, K. E. Smetanina, N. V. Sakharov, N. V. Melekhin, V. D. Chupriyanova

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

Ising Supercriticality and Universal Magnetocalorics in Spiral Antiferromagnet Nd$_3$BWO$_9$

Xinyang Liu, Enze Lv, Xueling Cui et al. (+8 more)

The celebrated analogy between the pressure-temperature phase diagram of a liquid-gas system and the field-temperature phase diagram of a ferromagnet has long been a cornerstone for understanding universality of phase transitions and critical phenomena. Here we extend this analogy to a highly frustrated antiferromagnet, the spiral Ising compound Nd$_3$BWO$_9$ with kagome layers. In its phase diagram, we identify a metamagnetic transition line with a critical endpoint (CEP) located at $\mu_0H_{\mathrm{c}} \simeq 1.04$ T and $T_{\mathrm{c}} \simeq 0.3$ K. Above the CEP, an Ising supercritical regime emerges with crossover lines that follow a universal scaling law, as evidenced by the specific heat, magnetic susceptibility, and magnetocaloric measurements. Remarkably, we observe highly sensitive magnetic cooling near the emergent CEP, characterized by a divergent magnetic Grüneisen ratio $\Gamma_H \propto 1/t^{\beta+\gamma-1}$, with $\beta + \gamma \simeq 1.563$ the sum of critical exponents of the 3D Ising universality class and $t \equiv (T-T_{\rm c})/T_{\rm c}$ the reduced temperature. Adiabatic demagnetization from 2 K and 4 T reaches a minimum temperature of 195 mK, via a self-cascading process that combines supercritical and topological cooling. Our findings open a new avenue for studying supercritical phenomena and magnetic refrigeration with the frustrated rare-earth compounds RE$_3$BWO$_9$ and, more broadly, in Ising-anisotropic antiferromagnets such as spin ices.
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All authors Xinyang Liu, Enze Lv, Xueling Cui, Han Ge, Fangyuan Song, Zhaoming Tian, Gang Su, Kan Zhao, Junsen Xiang, Peijie Sun, Wei Li

Materials Science

A DFT study of B-doped graphene as a metal-anchor: effects of oxidation and strain

Nikola Veličković, Natalia V. Skorodumova and Ana S. Dobrota

In this work, we present a systematic DFT investigation of the interaction between B-doped graphene and four selected metals: Mg and Zn, relevant for next-generation metal-ion batteries, and Cu and Pt, important for single-atom catalysis. Three different boron doping concentrations were considered to elucidate how dopant density influences the binding strength, charge transfer, and electronic structure of the resulting systems. In addition, the effects of biaxial strain and surface oxidation were examined to assess their impact on the reactivity and stability of B-doped graphene. The results show that boron doping substantially enhances graphene's affinity toward metal adsorption, though the extent and nature of this effect depend strongly on the metal type and doping level. For some of the metals investigated, the interaction is found to be almost entirely charge-transfer driven, with minimal orbital hybridization. Mechanical strain is found to enable fine-tuning of the metal/substrate interaction, while surface oxidation introduces a more pronounced effect by enabling direct interaction between metal atoms and oxygen functional groups in most cases, thereby significantly altering adsorption geometry and strength. These findings provide valuable insights into the design of boron-doped graphene materials for energy conversion and storage applications.
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Materials Science

Resolving the energy alignment between methylammonium lead iodide and C60: an in-situ photoelectron spectroscopy study

Alberto García-Fernández, Karen Radetzky, Stefania Riva et al. (+6 more)

Understanding and controlling the energy level alignment at interfaces between lead halide perovskites and electron transport layers is crucial for optimizing perovskite-based devices such as solar cells. In this work, we investigated the energy level alignment of C60 on in-situ cleaved MAPbI3 single crystals in multiple repeat experiments using photoelectron spectroscopy aiming to resolve inconsistencies reported in earlier studies. Our results show that both materials remain chemically stable upon interface formation, in contrast to the strong reactions typically seen when metals are evaporated on perovskite surfaces. By analyzing the Pb 4f and C 1s binding energies in detail, we determined that C60 consistently exhibits a downward energy shift toward MAPbI3, which works against efficient charge extraction. The magnitude of this shift, however, varies between different sample positions, highlighting that small variations in sample surfaces can lead to significant differences in energetic alignment. These findings underscore the decisive role of surface chemistry on interfacial energetics, explain performance variability in perovskite devices, and demonstrate the need to control and accurately measure surface properties. Furthermore, the observed energetic alignment can explain why further interface modification by charge blocking layers or surface passivation is needed for optimized device efficiencies.
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All authors Alberto García-Fernández, Karen Radetzky, Stefania Riva, Birgit Kammlander, Brian Rydgren, Evelyn Johannesson, Rahul Mahavir Varma, Håkan Rensmo, Ute B. Cappel

Materials Science

Ultrafast control of spin order by linearly polarized light in noncollinear antiferromagnetic metals

J. Kimak, M. Nerodilova, K. Carva et al. (+15 more)

The non-thermal optical control of magnetic order offers a promising route to ultrafast, energy-efficient information technologies. Although optical manipulation of magnetism in metals has been extensively studied, experimentally demonstrated effects have so far been limited to heat-driven dynamics or helicity-dependent mechanisms. Here, we report ultrafast non-thermal control of spin order in noncollinear antiferromagnetic Mn-based antiperovskite nitrides Mn3NiN and Mn3GaN, driven solely by the polarization orientation of linearly polarized femtosecond laser pulses. Using time-resolved magneto-optical pump-probe experiments based on the Voigt effect, we observe sub-picosecond changes in magnetic order followed by picosecond relaxation. The magneto-optical response depends on the relative orientation of the pump and probe polarization planes, with linear-polarization dependence reaching up to 95%, a value unprecedented in metallic magnets. This phenomenon is observed in two different materials and persists over a wide range of excitation wavelengths, fluences, and temperatures, demonstrating its robustness. Symmetry analysis and microscopic modeling indicate that optically induced torques alone cannot fully explain the observed dynamics. We therefore propose laser-induced formation of transient spin-spiral states as a possible excitation mechanism.
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All authors J. Kimak, M. Nerodilova, K. Carva, S. Ghosh, J. Zelezny, T. Ostatnicky, J. Zemen, F. Johnson, D. Boldrin, F. Rendell-Bhatti, B. Zou, A.P. Mihai, X. Sun, F. Yu, E. Schmoranzerova, L. Nadvornik, L.F. Cohen, P. Nemec

Materials Science

PFT: Phonon Fine-tuning for Machine Learned Interatomic Potentials

Teddy Koker, Abhijeet Gangan, Mit Kotak et al. (+2 more)

Many materials properties depend on higher-order derivatives of the potential energy surface, yet machine learned interatomic potentials (MLIPs) trained with a standard loss on energy, force, and stress errors can exhibit error in curvature, degrading the prediction of vibrational properties. We introduce phonon fine-tuning (PFT), which directly supervises second-order force constants of materials by matching MLIP energy Hessians to DFT-computed force constants from finite displacement phonon calculations. To scale to large supercells, PFT stochastically samples Hessian columns and computes the loss with a single Hessian-vector product. We also use a simple co-training scheme to incorporate upstream data to mitigate catastrophic forgetting. On the MDR Phonon benchmark, PFT improves Nequix MP by 55% on average across phonon thermodynamic properties and achieves state-of-the-art accuracy among models trained on Materials Project trajectories. PFT also generalizes to improve properties beyond second-derivatives, improving thermal conductivity predictions that rely on third-order derivatives of the potential energy.
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All authors Teddy Koker, Abhijeet Gangan, Mit Kotak, Jaime Marian, Tess Smidt

Materials Science

Geometric Time-Dependent Density Functional Theory

Éric Cancès, Théo Duez, Jari van Gog et al. (+3 more)

We provide a new formulation of Time-Dependent Density Functional Theory (TDDFT) based on the geometric structure of the set of states constrained to have a fixed density. Orbital-free TDDFT is formulated using a hydrodynamics equation involving a new density-to-current functional map. In the corresponding Kohn–Sham equation, the density is reproduced using a non-local operator. Finally, we present numerical simulations for one-dimensional soft-Coulomb systems.
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All authors Éric Cancès, Théo Duez, Jari van Gog, Asbjørn Bækgaard Lauritsen, Mathieu Lewin, Julien Toulouse

Materials Science

Geometric theory of constrained Schrödinger dynamics with application to time-dependent density-functional theory on a finite lattice

Eric Cancès, Théo Duez, Jari van Gog et al. (+3 more)

Time-dependent density-functional theory (TDDFT) is a central tool for studying the dynamical electronic structure of molecules and solids, yet aspects of its mathematical foundations remain insufficiently understood. In this work, we revisit the foundations of TDDFT within a finite-dimensional setting by developing a general geometric framework for Schrödinger dynamics subject to prescribed expectation values of selected observables. We show that multiple natural definitions of such constrained dynamics arise from the underlying geometry of the state manifold. The conventional TDDFT formulation emerges from demanding stationarity of the action functional, while an alternative, purely geometric construction leads to a distinct form of constrained Schrödinger evolution that has not been previously explored. This alternative dynamics may provide a more mathematically robust route to TDDFT and may suggest new strategies for constructing nonadiabatic approximations. Applying the theory to interacting fermions on finite lattices, we derive novel Kohn–Sham schemes in which the density constraint is enforced via an imaginary potential or, equivalently, a nonlocal Hermitian operator. Numerical illustrations for the Hubbard dimer demonstrate the behavior of these new approaches.
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All authors Eric Cancès, Théo Duez, Jari van Gog, Asbjørn Bækgaard Lauritsen, Mathieu Lewin, Julien Toulouse

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

From perovskite to infinite-layer nickelates: hole concentration from x-ray absorption

R. Pons, M. Flavenot, K. Fürsich et al. (+12 more)

The difficulty of determining cation concentrations and oxygen stoichiometry in infinite-layer nickelate thin films has so far prevented clear experimental identification of the nickel electron configuration in the superconducting phase. We used soft x-ray absorption spectroscopy to study the successive changes in PrNiO$_x$ thin films at various intermediate stages of topotactic reduction with $x=2-3$. By comparing the Ni-$L$ edge spectra to single and double cluster ligand-field calculations, we find that none of our samples exhibit a pure $d^9$ configuration. Our quantitative analysis using the charge sum rule shows that even when films are maximally reduced, the averaged number of nickel $3d$ holes is 1.35. Superconducting samples have even higher values, calling into question the previously assumed limit of hole doping. Concomitant changes in the oxygen $K$-edge absorption spectra upon reduction indicate the presence of oxygen $2p$ holes, even in the most reduced films. Overall, our results suggest a complex interplay of hole doping mechanisms resulting from self-doping effects and oxygen non-stoichiometry.
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All authors R. Pons, M. Flavenot, K. Fürsich, E. Schierle, E. Weschke, M. R. Cantarino, E. Goering, P. Nagel, S. Schuppler, G. Kim, G. Logvenov, B. Keimer, R. J. Green, D. Preziosi, E. Benckiser

Materials Science

Spin-lattice model simulations of tetragonal FePt system

Jakub Šebesta and Dominik Legut

Magnetic materials play a key role in the contemporary industry, providing unique features with a wide application potential. To study physical phenomena and design new materials, it is important to possess an appropriate tool, a model allowing simulation of desired behavior. Spin-lattice model simulations can be used to investigate spacious systems containing thousands of atoms, while complex phenomena arising from the interplay of lattice and spin dynamics can be modeled. One of the important phenomena that can be modeled in the spin lattice simulation is magnetoelastic behavior, offering direct conversion between the mechanical and magnetic energy. However, so far, only models for systems with cubic symmetry have been introduced. Therefore, here, a spin-lattice model for a system with tetragonal symmetry is proposed, where its strength is manifested by simulation of magnetoelastic properties of a characteristic representative L1$_{0}$ FePt system.
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