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Physics Condensed Matter Materials Science

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Saturday 30 May

Materials Science

Compressibility and High-Pressure Structure of CaMg$_2$Bi$_2$ and YbMg$_2$Bi$_2$

Compounds with the formula $AM_2X_2$ in the CaAl$_2$Si$_2$ structure type have garnered increasing interest across various solid-state research domains, such as quantum topological and thermoelectric materials. Prior studies have identified high-pressure phase transitions in several compounds, including Mg$_3$Sb$_2$, Mg$_3$Bi$_2$, CaMn$_2$Bi$_2$, and SrAl$_2$Si$_2$. In this study, we investigate the structural behavior of CaMg$_2$Bi$_2$ and YbMg$_2$Bi$_2$ under varying pressure conditions. We synthesized crystals using the molten metal flux method and examined them through single-crystal synchrotron X-ray diffraction, employing diamond anvil cells to exert pressures up to 20 GPa. Our analysis reveals insights into the anisotropic compressibility of these materials, highlighting the more compressible and flexible octahedral $A$-Bi bonds as the primary contributors to this anisotropy. Moreover, we observed a phase transition in both CaMg$_2$Bi$_2$ and YbMg$_2$Bi$_2$ at pressures above 9.6 GPa and 8.7 GPa, respectively. The newly identified high-pressure phase exhibits a distortion of the original CaAl$_2$Si$_2$ structure with space group $C2/m$. This high-pressure structure is distinct from that of related compounds (e.g., CaMn$_2$Bi$_2$, MgMg$_2$Bi$_2$), the latter exhibiting a square pyramidal coordination for the $M$ site.
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All authors Mario Calderón-Cueva, Allison Pease, Cheng Peng, Wanyue Peng, Megan Rylko, Weiwei Xie, Susannah M. Dorfman, Alexandra Zevalkink

Materials Science

Autonomous scanning electrochemical cell microscopy enables rapid exploration of large compositionally complex material spaces

Alloying is a central strategy in electrocatalysis, enabling fine-tuning of electronic structure. In particular, compositionally complex solid solutions (CCSS) often called high-entropy alloys are of high interest as they allow active site design. However, the "combinatorial explosion" in the number of possible compositions poses a critical bottleneck for the discovery of active CCSS electrocatalysts. We present an autonomous scanning electrochemical cell microscopy (SECCM) system for ultrahigh-throughput and large-scale CCSS activity screening. The platform rapidly establishes composition-electrocatalytic activity relationships for large compositional spaces across multiple thin-film CCSS materials libraries via active learning and automated library exchange. Embedding analytical expressions of voltammetry in the algorithm enables the learning of whole voltammograms rather than a single selected metric. As a demonstration, we investigated hydrogen evolution reaction (HER) activities of Au-Ir-Rh, where Ir and Rh exhibit strong metal-hydrogen binding and Au exhibits relatively weak binding as derived from the HER volcano plot. The composition-activity trend was accurately predicted after measuring only 15% of all 966 measurement areas. Au30Ir20Rh50 and Au10Ir35Rh55 exhibit highest activities with standard rate constants of about 0.012 cm/s, demonstrating positive synergistic contributions from elemental mixing. The autonomous robotic SECCM platform is broadly applicable to a wide range of electrocatalytic reactions, providing a general pathway for accelerating CCSS electrocatalyst discovery and optimization.
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All authors Felix Thelen, Moonjoo Kim, Geovane Arruda de Oliveira, Jan Lukas Buergel, Wolfgang Schuhmann, Alfred Ludwig

Materials Science

Thermodynamic origin of entropy-assisted stabilization in multicomponent rock-salt oxides

High entropy oxides are commonly associated with high configurational entropy ($\Delta S_{conf}\geq$ 1.61R) corresponding to five equimolar cations occupying a crystallographic sublattice. However, recent experimental observations indicate that medium-entropy compositions may also exhibit entropy-stabilized rock-salt phases, raising an important question regarding the minimum entropy required for phase stabilization. In this work, we employ a first-principles thermodynamic framework to investigate the stability of rock-salt oxides containing two to five principal cations components analogous to (Ni$_{0.8}$Cu$_{0.2}$)O, (Ni$_{0.6}$Cu$_{0.2}$Zn$_{0.2}$)O, (Ni$_{0.4}$Cu$_{0.2}$Zn$_{0.2}$Co$_{0.2}$)O, (Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$Co$_{0.2}$Mg$_{0.2}$)O. Density functional theory, MCSQS-based structural modeling, and finite-temperature Gibbs free-energy analysis are combined to quantify the roles of enthalpy mixing ($\Delta H_{mix}$), configurational ($\Delta S_{conf}$), vibrational ($\Delta S_{vib}$), electronic and magnetic ($\Delta S_{mag}$) contributions towards ($\Delta S_{elec}$) entropy change in governing phase stability. The results show that $\Delta S_{conf}$ alone is not a universal descriptor of phase stability. While the two-cation system is enthalpy-stabilized but three-, four- and five-cation systems become thermodynamically stable at high-temperature due to entropy-driven reduction of the Gibbs free energy. These findings demonstrate that single-phase rock-salt oxides are not restricted to the conventional high-entropy limit and that medium-entropy compositions can also be stabilized under suitable thermodynamic conditions.
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Materials Science

Impact of Cu-Mn ratio on Structure and Defects in Layered Multiferroic Cu1-xMn1+ySiTe3

Multiferroic materials exhibit the coexistence of magnetic and ferroelectric order, enabling control of magnetism through electric fields and vice versa. These properties make them attractive for spintronic and memory device applications. Recent studies on Cu1-xMn1+ySiTe3 (0.04 \leq x \leq 0.26; 0.03 \leq y \leq 0.15) have revealed strong magnetoelectric coupling, with variations in Mn-to-Cu concentration leading to variations in optical, electronic, and magnetic responses. Despite these findings, the influence of nanoscale structure and defects on the observed properties remains poorly understood. In this study, we investigate the structure and nanoscale defects in Cu-deficient Cu1-xMn1+ySiTe3 (Cu:Mn ratio <1, i.e., with 0.04 \leq x \leq 0.26 and 0.03 \leq y \leq 0.15) and Cu-rich Cu1+xMn1-ySiTe3 (Cu:Mn ratio >1, i.e., with 0.04 \leq x \leq 0.3 and 0.13 \leq y \leq 0.31) crystals using scanning/transmission electron microscopy and single-crystal X-ray diffraction. Cu-deficient crystals exhibit extensive stacking faults correlated with chemical inhomogeneity between Mn and Cu, along with variations in Te stacking. In contrast, Cu-rich crystals show fewer stacking faults but contain other local structural variations, such as needle-shaped precipitates and loop-like features. These distinct local structural features between Cu-rich and Cu-deficient crystals can be correlated to variations in their observed properties. Complementary density functional theory calculations confirm that the Cu-rich structure is more polar than the Cu-deficient structure. Overall, this study provides a comprehensive understanding of how subtle changes in chemistry influence the nanoscale structure, defect distribution, and functional properties in Cu1-xMn1+ySiTe3, offering guidance for designing multiferroic materials with tailored performance.
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All authors Sai Venkata Gayathri Ayyagari, Boyang Zheng, Sreekant Anil, Subrata Ghosh, Yuxi Zhang, Yu Liu, Chandan De, Ke Wang, Jeffrey Shallenberger, Weiwei Xie, Vincent H. Crespi, Zhiqiang Mao, Nasim Alem

Materials Science

A Visible-Frequency Excitonic Reststrahlen Band in (PEA)$_2$PbI$_4$ Slabs

Layered halide perovskites host exceptionally strong excitons, whose optical signatures are usually interpreted as absorptive resonances on a smooth dielectric background. Strong excitons, however, can also reshape the dielectric response itself and drive the real permittivity negative, opening a reflective band: the visible, excitonic analogue of an infrared Reststrahlen band. Whether bare (PEA)$_2$PbI$_4$ slabs reach this regime has remained unclear. Here we show that low-temperature transmission of (PEA)$_2$PbI$_4$ slabs, driven by the intralayer-exciton manifold, evolves with increasing thickness from an excitonic dip into a broad near-zero-transmission interval with compressed Fabry-Pérot-like fringes. Transfer-matrix analysis with an effective Lorentz-oscillator dielectric response reproduces this crossover, reconstructs a finite negative-Re($\varepsilon$) window, and implies near-ultrastrong exciton-photon coupling. Calculated field maps show suppressed in-plane field penetration within this interval and a driven longitudinal response near the high-energy ($\varepsilon=0$) edge. These results identify (PEA)$_2$PbI$_4$ slabs as a cavity-free visible-frequency excitonic Reststrahlen material.
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All authors Michael Pfeufer, Patrick Grenzer, Friedrich Schöppler, Tobias Hertel

Materials Science

Manifold Diffusion for Structure Generation of Transition Metal Complexes

Transition metal complexes are central to catalysis, drug design, and materials science, with relevant properties strongly sensitive to their three-dimensional geometry. However, the electronic diversity and unconventional bonding environments of transition metal complexes pose a major challenge for accurate structure generation. In this work, we introduce TMCgen, a manifold diffusion machine learning model that efficiently and accurately generates geometries of transition metal complexes. By formulating the diffusion process over the metal-ligand coordination angles, combined with torsional and rotational diffusion of the ligands, TMCgen focuses on the key geometric degrees of freedom of transition metal complexes. TMCgen shows strong performance in generating accurate coordination environments on a diverse set of experimentally derived bioinorganic and organometallic complexes while requiring only few inference steps, enabling efficient generation. Our results demonstrate the potential of manifold-based generative modeling for data-efficient geometry generation, paving the way for property-conditioned design of transition metal complexes.
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Materials Science

Impact of Disorder Dynamics and Multi-Domain Kinetics on the Sliding Ferroelectricity of CVD-Grown 3R-WSe2 Bilayers

Sliding ferroelectricity in van der Waals (vdW) layered systems has emerged as a promising route toward non-volatile nanoscale devices, where interlayer displacement in non-centrosymmetric bilayers generates an out-of-plane polarization. In particular, 3R-stacked bilayer transition metal dichalcogenides (TMDs) grown via chemical vapor deposition (CVD) have been shown to host such polarization due to broken inversion symmetry. However, a detailed investigation of the 2D ferroelectric (FE) properties of CVD-grown 2D films, particularly the role of intrinsic disorder, such as structural defects and domain structure, remains poorly understood. Here, we investigate the FE switching characteristics of CVD-grown 3R-stacked WSe2 using a graphene-based ferroelectric field-effect transistor (graphene-FE-FET) architecture, where graphene serves as a highly sensitive probe of induced charge modulation due to polarization switching of FEs. We show that the growth-induced structural disorder significantly impacts polarization switching, while multi-domain kinetics governs the evolution of the FE response. These findings provide important insights into the design and optimization of FE devices based on vdW materials.
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All authors Sourav Paul, Prasenjit Ghosh, Krishna Prasad Maity, Vineet Pandey, Abhijith M.B., Premananda Chatterjee, Kenji Watanabe, Takashi Taniguchi, Nicholas R. Glavin, Ajit K. Roy, Atindra Nath Pal, Vidya Kochat

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

Sliding contact creates universal self-affine fractal surfaces

Surface roughness evolves during sliding, a process known as run-in, and the resulting topography controls friction, leakage, and failure from machines to geological faults. Yet the physical rule selecting this state remains unclear. We show that metals, rocks, and glasses develop universal self-similar roughness at short wavelengths, while retaining a material-dependent roll-off. A two-process model explains this behavior: junction formation and rupture drive universal roughening, whereas larger-scale deformation and/or fracture limit its growth.
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All authors Ruibin Xu, Haohao Ren, Adriane Clerc, Guilhem Mollon, Wenbo Sheng, Feng Zhou, B.N.J. Persson

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

Noncollinear spin textures and 90{\deg} domain walls in twisted XY magnets

Twisted moiré magnets are promising in exploring noncollinear magnetic phases, yet current experimental studies have been restricted to uniaxial magnets, limiting the accessible phase space. Here, we demonstrate noncollinear moiré magnetism based on XY magnet CrCl3. The tunneling magnetoconductance of twisted CrCl3 exhibits multiple field-driven transitions in small-twist-angle devices, attributed to the coexisting antiferromagnetic and ferromagnetic domains with distinct susceptibilities. The inferred spin configuration depends on the layer number, reflecting the interlayer coupling strength between twisted layers. This moiré magnetism is remarkably robust, persisting up to twisted double nine-layer stacks. Combined with micromagnetic simulations, we identify the ground state as the predicted "twisted-s" phase featuring 90{\deg} domain walls. Finally, we demonstrate voltage control of these noncollinear phases, highlighting the electrically tunable twist-spintronics.
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All authors Guanghui Cheng, Shiva T. Konakanchi, Andres E. Llacsahuanga Allcca, Sanjeev Khare, Nithin Abraham, Yuqing Cao, Hechang Lei, Kenji Watanabe, Takashi Taniguchi, Pramey Upadhyaya, Yong P. Chen

Materials Science

Giant Thermal-Conductivity Enhancement from Chiral-Phonon Pseudo-Angular Momentum Conservation

Pseudo-angular momentum (PAM) underlies optical selection rules for chiral phonons, but whether it also constrains thermally populated finite-wave-number phonon-phonon scattering has remained unresolved. We show that rotational or screw eigenphase conservation imposes a PAM residue rule on cubic anharmonic vertices, revealing a hidden selection rule for heat transport. In screw-symmetric helical Te, an exact platform, implementing this rule as a projector in first-principles Boltzmann transport leaves spectra and force constants unchanged but removes roughly two thirds of kinematically allowed triplets, suppresses resistive Umklapp relaxation, and enhances lattice thermal conductivity by a factor of 5.30 at 300 K, remaining above fivefold up to 400 K. A bulk chiral-crystal benchmark further shows that explicit eigenphase organization can increase the calculated lattice thermal conductivity by about 24%, comparable to the reported first-principles underestimation of experiment. These results establish PAM conservation as an anharmonic selection principle for chiral-phonon heat transport and as a fundamental principle to guide the prediction and control of thermal conductivity in chiral crystals and nanoscale phononics.
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All authors Tingting Wang, Dabao Zha, Hao Chen, Jiangbin Gong, Lifa Zhang

Materials Science

Synthesis of single-layered fluorographdiyne nanosheets via selective on-surface 2D covalent polymerization

Two-dimensional conjugated polymers (2DCPs) are significant macromolecular materials with intriguing and tunable physicochemical properties that depend on their geometries. Graphdiyne and its derivatives are exemplary 2DCPs featuring sp-sp2 hybridized skeletons. However, achieving single-layered, large-domain/regular graphdiyne and its derivatives on surfaces remains a formidable challenge due to the lack of selective 2D covalent polymerization methods. Here, we report a selective on-surface 2D covalent polymerization method via the combination of cobalt catalysis and coronene templating, achieving the synthesis of single-layered fluorographdiyne nanosheets up to 60*60 nm2 on Au(111) surface. Using scanning probe techniques, we visualize the sequential polymerization process and characterize cobalt-activated coupling intermediates at the atomic level. Experimental and theoretical analyses suggest that strong d-{\pi} coupling between cobalt and alkynyl transforms a robust Csp-Au bond into a weaker Csp2-Au bond, thereby facilitating the demetallization C-C coupling. Besides, the templating effect of coronene suppresses kinetically trapped defects and improves the selectivity of hexagonal-ring formation in the complex 2D covalent polymerization process.
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All authors Chen-Hui Shu, Yi Zheng, Tao Lin, Li-Xia Kang, Zhang Qu, Zhi-Yu Wang, Ying Wang, Zheng-Yang Huang, Qian Liu, Hang Xu, Chong Chen, Yangfan Wu, Longteng Xiao, Mengxi Liu, Xiaohui Qiu, Pei-Nian Liu, Deng-Yuan Li

Friday 29 May

Materials Science · Cross-listed from cs.DL

APTLAS: An Indexed APT Literature Repository

Atom probe tomography (APT) literature is broad, rapidly growing, and dispersed across a wide range of journals, which can make it difficult to identify prior work on a given material system, instrument, or analytical approach. Conventional search engines (e.g., Google Scholar) excel at general retrieval but do not preserve the domain-specific metadata that often determines the relevance of an APT publication (e.g., analysis mode, laser wavelength, or instrument configuration). Herein, APTLAS is presented, which is an indexed repository of published APT literature. At present, the database contains ~2,300 records, each accompanied by metadata extracted from the source publication. The accompanying web tool, available at https://aptlas.bavleyguerguis.com/, allows users to browse and filter by material system, instrument, application, publication type, or keyword search.
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Materials Science

Data-Driven Discovery of Unconventional Antiferromagnets

Unconventional antiferromagnets combine zero net magnetization with spin-split electronic bands, offering a distinct, important platform for spintronics. Their discovery, however, has so far depended largely on case-by-case studies and on a limited number of compounds with experimentally resolved magnetic structures. Here, we overcome these bottlenecks by resolving magnetic ground states across a broad materials database. We narrow down 37163 magnets from the Materials Project to 189 collinear antiferromagnets by combining physics-informed prescreening, high-throughput exchange calculations and Luttinger-Tisza analysis. Among these, symmetry analysis identifies 36 altermagnets and 11 Luttinger-compensated ferrimagnets (LCFs), including 22 altermagnets and 9 LCFs that have not been reported previously. The identified unconventional antiferromagnets can support nonrelativistic spin Hall effects and doping-tunable spin transport with switchable polarization and giant anisotropy. Our framework converts broad structural databases into a curated, symmetry-classified set of experimentally testable compensated spin-split magnets, establishing a scalable route for the efficient discovery of functional antiferromagnets.
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All authors Qirui Cui, Chenxu Liu, Anna Delin, Kaiyou Wang

Materials Science

Microscopic origin of polytype-dependent melting in SiC revealed by machine-learning molecular dynamics

Predicting how crystal structure influences high-temperature stability remains a key challenge in materials modelling and design. Silicon carbide (SiC), one of the most thermally and chemically stable materials known, provides an ideal system for studying this problem because its many polytypes preserve similar local tetrahedral bonding while differing in long-range stacking geometry. Here, we combine phase-coexistence machine-learning molecular dynamics with finite-temperature phonon analysis, enabled by a fine-tuned MACE interatomic potential that accurately describes crystalline, high-temperature, and disordered configurations across multiple SiC polytypes. We identify a clear relative stability ordering, 3C > 2H > 9R, reflected consistently in structural disordering, interlayer sliding, and finite-temperature phonon spectra. Across all polytypes, melting initiates through the formation of short C-C contacts and carbon-rich local regions, followed by a progressive loss of tetrahedral Si-C connectivity. The reduced stability of the long-period 9R polytype is traced to low-frequency transverse-acoustic shear modes associated with relative bilayer sliding, which are already present in the 0 K phonon spectra and soften further at high temperature. These modes generate larger lateral bilayer displacements, linking enhanced interlayer sliding to local chemical disordering and ultimately melting. More broadly, our results show that high-temperature stability in polytypic covalent materials is governed not only by local bond strength, but also by stacking-dependent transverse dynamics.
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All authors Ljiljana Stojanović, Samuel J. Magorrian, Lara Kabalan, Richard N. White, Fabian L. Thiemann, Viktor Zólyomi

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

Data-Driven Spectral Prediction for Accelerating Large-Scale Electronic Structure Calculations

Simulating large molecular systems comprising thousands of atoms requires highly scalable methodologies. While modern Density Functional Theory (DFT) codes exhibit linear scaling, solving the associated large, sparse generalized eigenproblems remains a critical computational bottleneck on exascale architectures. In the context of the LimitX project, we propose a data-driven framework to accelerate these calculations. By shifting the machine learning target from discrete eigenvalues to the coefficients of an interpolating Chebyshev polynomial, and by comparing both all-atom and fragment-based structural representations, we successfully overcome the dimensionality constraints of large-scale spectral prediction. We investigate three machine learning models (Kernel Ridge Regression, Graph Neural Networks, and Random Forests) trained on a novel 2 TB dataset of protein dimers. The predicted spectra provide initial guesses that effectively bypass early Self-Consistent Field (SCF) iterations in BigDFT. Ultimately, these spectral predictors will be deployed to dynamically optimize upcoming rational filter-based eigensolvers, such as FrASE, which is currently in initial development.
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All authors Abhiram Badrinarayanan, Davor Davidovic, Edoardo Di Napoli, Jurica Novak, Luigi Genovese, Gustavo Ramirez-Hidalgo, Xinzhe Wu

Materials Science

Robust control over polar skyrmion bubble density with a combined optical and electrical approach

Polar skyrmion bubbles are nanoscale ferroelectric domain configurations with swirling polarization textures, and often emerge in ferroelectric oxide systems. Owing to their inhomogeneous polarization patterns, which endow them with distinct topologies and electrical responses from homogeneous monodomains, polar skyrmion bubbles are envisaged to be promising candidates for non-volatile memory devices. In such device, the recorded information density is directly proportional to the density of bubbles, underscoring the need for precise control over bubble nucleation. Here, using first-principles-based calculations, we demonstrate that when assisted with a DC electric field, twisted light, which has a spatially inhomogeneous field pattern, can robustly tune the density of polar skyrmion bubbles in ferroelectric ultrathin films between $10^2\sim 10^4 \rm{bit}/\mu m^2$. Moreover, by modulating DC and optical field strengths together with the beam radius, the nucleation rate, which characterizes the creation and annihilation speed of polar skyrmion bubbles, can also be well controlled. These findings highlight the unique response of ferroelectric nanofilms to optical and electric fields, which is crucial for employing polar skyrmion bubbles in the next-generation of ultrahigh-density memory technologies.
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Materials Science

Microstructure-specific mechanisms define multistage relaxation dynamics in a metallic model-glass

Deciphering complex relaxation pathways in disordered solids is a central challenge across polymeric, oxide, and metallic glasses, which traditionally relies on the interpretation of mechanical spectroscopy and resulting damping modes. Here we demonstrate the direct observation of dominant atomic-scale relaxation mechanisms during isothermal annealing of an as-quenched binary model glass towards incipient crystallization. Assessed via simulated x-ray photon correlation spectroscopy, a multi-state structural decorrelation is uncovered via speckle-pattern analysis of the full three-dimensional diffraction sphere across the first peak of the structure factor. Over a simulation time of up to 10 $\mu$s, three distinct and subsequent decorrelation stages of thermal vibration, glassy network evolution, and structural and chemical ordering towards crystallization are identified. These findings promote a picture where specific dynamically-separated mechanisms drive the microstructural evolution during glass relaxation and suggest a much richer multi-mode relaxation behavior of metallic glasses than hitherto identified.
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All authors Achraf Atila, Zengquan Wang, Birte Riechers, Robert Maaß

Materials Science · Cross-listed from cs.AI

Coupling Language Models with Physics-based Simulation for Synthesis of Inorganic Materials

Modern generative machine learning (ML) models can propose novel inorganic crystalline materials with targeted properties; however, synthesis planning of these materials remains difficult due to the complexity of the associated physical processes and limited availability of computational tools. We introduce a novel hybrid framework to evaluate Large Language Models (LLMs) in inorganic synthesis planning by combining thermodynamic databases with simplified kinetics models to approximate realistic synthesis conditions. As a case study, we focus on the niobium-oxygen system, which features multiple industrially relevant oxide phases with well-characterized data. In computational simulations, we compare LLM-generated synthesis routes with classical path-planning algorithms, showing that the implicit priors in LLMs can yield more viable strategies. In our evaluation setting, classical search methods serve primarily as a foil rather than a direct competitor. This illustrates the relative complexity of the problem and highlights where the LLM's implicit priors add value.
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All authors Edward W. Staley, Tom Arbaugh, Michael Pekala, Alexander New, Christopher D. Stiles, Nam Q. Le, Gregory Bassen, Wyatt Bunstine, Tyrel McQueen

Materials Science

Co-adsorption mechanism drives CO oxidation on defective ZnS

Reactivity on wide-bandgap semiconductor surfaces relies critically on the generation of active sites. In the case of CO oxidation, however, the mere presence of defects is insufficient to drive reactivity. Here, we investigate CO oxidation on a defective ZnS single-crystal surface by combining near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT) calculations. NAP-XPS measurements reveal CO$_2$-like surface intermediates only under oxygen-rich conditions, consistent with oxygen-assisted CO oxidation. DFT calculations support an oxygen-assisted co-adsorption pathway in which CO interacts preferentially with adsorbed oxygen species stabilized near Zn-deficient sites, forming weakly bound CO$_2$-like structures. These results identify oxygen coverage, rather than defect density alone, as the key factor controlling CO$_2$-like intermediate formation on defective ZnS and establish defective ZnS as a model platform for studying oxygen-assisted surface chemistry on non-oxide semiconductors.
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All authors P.R.A. de Oliveira, C.Codeço, M.G.Menezes, P.Venezuela, F.Stavale, J.A.Boscoboinik

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

Electron vs. hole doping in infinite-layer nickelates: electronic structure, magnetism and correlations

The observation of superconductivity in undoped infinite-layer nickelates $R$NiO$_2$ ($R$ = rare earth) challenges our current understanding and calls for a re-examination of the underlying electronic structure of this family of materials. In this context, it is particularly important to extend the investigation of $R$NiO$_2$ compounds from the intensively studied hole-doped regime to the almost unexplored electron-doped one. Here, we use a combination of density-functional theory and dynamical mean-field theory to study the evolution of the electronic structure of infinite-layer nickelates in these two doping regimes. We find a striking asymmetry in the self-doping of the Ni-$d_{x^2-y^2}$ band due to the $R(5d)$ states: while this effect is strongly suppressed upon hole doping, electron doping instead leads to an increase in the size of the $R(5d)$ electron pockets, but without effectively hole-doping the Ni-$d_{x^2-y^2}$ band. This asymmetry has an important impact on the magnetic response as antiferromagnetism is rapidly suppressed upon hole doping, whereas it remains the ground state upon electron doping. Despite these differences, electronic correlations on both sides of the phase diagram are dominated by the Ni $d_{x^2-y^2}$ orbital, suggesting that a single-band description may be appropriate for infinite-layer nickelates in both the electron- and hole-doped regimes.
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All authors Ezra Day-Roberts, Fabio Bernardini, Harrison LaBollita, Yi-Feng Zhao, Andres Cano, Antia S. Botana

Materials Science · Cross-listed from cs.LG

AI-Guided Design and Optimization of Graphite-Based Anodes via Iterative Experimental Feedback

This study presents an iterative AI-guided workflow that accelerates graphite-based anode development by improving both formulation feasibility and process robustness. Sequential learning via AI/ML-guided multiobjective inverse design for anode optimization was implemented using the Citrine Platform. Starting from a noisy, incomplete dataset, the Citrine Platform was used to generate early surrogate models, which despite low predictive certainty highlighted missing process constraints. By iteratively adding feasibility labels and boundary condition failures, the workflow rapidly converged toward manufacturable, higher-performing formulations. Fabrication reliability improved from frequent process failures to 100% successful cell production, while the fraction of cells delivering $\geq$ 350 mAh g$^{-1}$ increased from 28.4% to 84.8%, with capacity retention rising from 42.1% to 97.3%. These results demonstrate that structured, feedback-driven AI workflows can transform imperfect industrial data into actionable guidance, enabling faster, more reproducible optimization of battery electrode manufacturing.
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All authors Qian Du, Mark M. Sullivan, James E. Saal, Florian Huber

Materials Science

Advances in electrical contacts to single crystals of emerging materials for transport measurements

Transport measurements that probe electrical resistivity of a material under varying external stimuli, such as temperature, magnetic field, optical illumination, and gate voltage, are among the most important experimental techniques in condensed matter physics. These measurements provide critical insights into the fundamental electronic properties of materials. In recent years, they have facilitated the discovery and exploration of intriguing physical phenomena (e.g., superconductivity and quantum oscillations) and unique device functionalities (e.g., photoresponse and electrostatic gating effects) in various emerging materials, particularly in the form of single crystals. However, unlike large-scale wafers or thin films, newly synthesized single crystals often pose substantial challenges in establishing reliable electrical contacts due to their irregular geometries, limited dimensions, inherent structural characteristics, and potential susceptibility to degradation. In this review, we highlight recent technological advancements in the fabrication of high-quality, lithographically defined multi-terminal electrodes on both exfoliable and non-exfoliable single crystals for transport measurements. Our work provides a practical guide for researchers seeking to select appropriate contact-fabrication strategies tailored to unique characteristics of emerging crystals.
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Materials Science · Cross-listed from cs.CE

Can dents and gouges compromise the structural integrity of hydrogen transport pipelines?

Repurposing natural gas pipelines for hydrogen transport requires understanding how external defects, like dents and gouges, affect structural integrity under H$_2$ exposure. To address this, we combine experiments with a new hydrogen embrittlement model aimed at large plastic straining scenarios, which integrates: (i) multi-trap hydrogen transport, (ii) finite-strain plasticity, and (iii) a hydrogen- and triaxiality-dependent damage law. Each constituent of the model is validated with experiments on X65 pipeline steel: (i) hydrogen permeation, (ii) full-scale pipe-indentation, and (iii) mechanical testing at different hydrogen and triaxiality levels. The validated model is used to study passive (indent before H$_2$ exposure) and active (indent with H$_2$) dents and gouges. Results reveal that hydrogen does not significantly increase the damage severity of those defects, unless hydrogen egress is completely precluded at the outer surface of a pipeline that is being pressurised internally and contains a pre-existing passive dent with a gouge.
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Materials Science

Multiplet-Selective Photoelectron Diffraction from an Altermagnet

Direct real-space probes of altermagnetic order remain scarce. Here we introduce multiplet-selective photoelectron diffraction (PED), a methodology in which different regions of a transition-metal core-level multiplet act as distinct photoemission source waves. Using multiple-scattering calculations for the metallic altermagnet candidate CrSb, we show that selected Cr $3p$ multiplet features with predominantly $Y_1^{+1}$ and $Y_1^{-1}$ character generate robust diffraction asymmetries sensitive to altermagnetic domains. We demonstrate that both circularly and linearly polarized light provide access to the effect, while suitable combinations of domains, light polarizations, and multiplet-energy windows suppress nonmagnetic diffraction backgrounds. The proposed approach can be implemented using standard momentum-resolved photoemission instrumentation and establishes core-level PED as a practical route toward domain-resolved studies of altermagnets.
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Materials Science

General-purpose LLMs as Constrained Crystal Composition Generators

The targeted discovery of inorganic materials remains challenging due to the vastness of compositional design spaces and the high cost of exhaustive screening. Task-specific generative artificial intelligence represents a particularly efficient alternative to screening, yet demands tedious collection of training data before providing real benefit. General-purpose large language models (LLMs) have recently shown tremendous potential for the targeted generation of single, optimal materials compositions without the need for task-specific fine-tuning. However, it is unclear whether LLMs generally pose an advantage compared to specialized generative models, in particular in large design spaces. Here, we demonstrate that such models are capable of covering entire regions of the targeted property space effectively and systematically. Using Elpasolite materials as an established benchmark for generative tasks in large chemical spaces, we find that an iterative prompt-and-response framework is able to recover on average 96% of all low-energy Elpasolites in the target region. This performance, driven mainly by iterative in-context learning, surpasses the generative abilities of previous, task-specific models. Our results establish general-purpose LLMs as flexible and accessible components for inverse materials design workflows.
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All authors Hedda Oschinski, Maximilian L. Ach, Konstantin S. Jakob, Christian Carbogno, Karsten Reuter

Materials Science

Ab Initio Spinor Kadanoff-Baym Approach to Nonequilibrium Electron, Phonon and Magnon Dynamics in Itinerant Ferromagnets

This work introduces a theoretical framework based on the Kadanoff-Baym equations in spinor space to study ultrafast magnetization dynamics in itinerant ferromagnetic systems from first principles. By incorporating spin-orbit coupling into the ab initio Hamiltonian and generalizing the self-energies to include terms beyond the charge sector, I derive scattering integrals within the Markov approximation and quasiparticle renormalizations for electrons and phonons in the presence of spin-dependent effective interactions within a many-body perturbation theory approach. I explicitly discuss how magnons emerge in this framework, and derive, through suitable approximations, a closed and tractable set of equations for coupled electron, phonon and magnon dynamics that can be solved from first principles. I discuss the equations of motion within a minimal ferromagnetic model, where the coupled equations are solved numerically. This approach allows one to treat coherent and incoherent magnetic dynamics on an equal footing, paving the way for a first principles understanding of ultrafast magnetic dynamics and demagnetization, and opening to a truly predictive theory of femtomagnetism in periodic systems.
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Materials Science · Cross-listed from cond-mat.supr-con

What controls the superconducting dome of electron-doped FeSe?

Superconducting domes are conspicuous features of the phase diagrams of most unconventional and high-temperature superconductors. The superconducting transition temperature ($T_{c}$) of FeSe can be dramatically enhanced with electron doping, but unlike all other high-temperature and unconventional superconductors, its full phase diagram and superconducting dome have yet to be fully explored. Here, we employ a combination of molecular beam epitaxy synthesis, alkali surface doping, in-vacuum electrical transport, and angle-resolved photoemission spectroscopy to investigate the entire superconducting dome of electron-doped FeSe, achieving a fully metallic state where superconductivity is suppressed in the heavily overdoped regime. We discover a robust scaling between $T_{c}$ and the residual resistivity ($\rho_{0}$) which holds across the entire superconducting dome, suggesting that the evolution of $T_{c}$ is heavily influenced by the evolution of the elastic scattering rate in the high-$T_{c}$ electron-doped phase. This in turn suggests that the superconducting dome in electron-doped FeSe appears to be fundamentally different than that of other unconventional superconductors where doping plays the primary role, and may be driven primarily by the sensitivity of the superconductivity to disorder.
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All authors Paul T. Malinowski, Chad J. Mowers, Yaoju Tarn, Darrell G. Schlom, Brendan D. Faeth, Kyle M. Shen

Materials Science

Strain-Engineered s-C$_3$N$_6$ Monolayer for Efficient Water Splitting: A first-principles study

Photocatalytic water splitting offers a sustainable route for solar-to-hydrogen energy conversion, yet identifying stable, metal-free semiconductors with suitable electronic, optical, and band-alignment properties remains challenging. Here, we investigate the structural, mechanical, electronic, optical, and photocatalytic properties of the two-dimensional s-C$_3$N$_6$ monolayer using first-principles calculations. Ab initio molecular dynamics and elastic constant analysis confirm its thermal and mechanical stability. Hybrid HSE06 calculations reveal pristine s-C$_3$N$_6$ is a direct-band-gap semiconductor (2.62 eV). However, its conduction-band minimum lies below the hydrogen reduction potential, preventing spontaneous hydrogen evolution. To overcome this limitation, we employ biaxial and uniaxial strains (-10% to +10%) to modulate its electronic structure. We find that compressive biaxial strains of -8% and -10% uniquely tune the band edges to straddle the redox potentials, enabling spontaneous overall water splitting. Crucially, these photocatalytically active states remain mechanically and thermally stable. Optical properties calculations show the fundamental gap in both pristine and strained structures is optically dark, with the primary absorption peak in the UV region. Furthermore, a strain-induced mobility mismatch between electrons and holes facilitates efficient charge separation. However, thermodynamic modeling of surface kinetics reveals that the s-C$_3$N$_6$ surface binds intermediates strongly, necessitating a co-catalyst to overcome kinetic barriers. Our results establish strain engineering as an effective strategy to tailor band-edge alignment, carrier dynamics, and optical transitions in s-C$_3$N$_6$, highlighting its potential for stable 2D photocatalytic water splitting.
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Materials Science

Odd-Parity Magnons

Magnons, as charge-neutral spin excitations, can transport spin information without Joule heating and therefore offer a promising platform for low-power spintronics. However, in collinear magnets, the effective time-reversal symmetry forbids odd-parity magnon band splitting. Here we propose odd-parity magnons and establish a general mechanism for realizing them in collinear antiferromagnets. We provide a complete spin-point-group classification of odd-parity magnon splitting in two-dimensional collinear antiferromagnets by identifying the leading splitting types and their symmetry-allowed basis functions. This classification serves as a practical guide for searching for odd-parity magnons. We show that breaking effective time-reversal symmetry, for example by circularly polarized light or loop currents, can induce highly tunable $p$- and $f$-wave magnon splitting. In bilayer systems, the dynamical modulation can drive a topological magnon phase transition, accompanied by chiral edge modes and an abrupt jump in the magnon thermal Hall conductivity. Material-specific first-principles calculations further demonstrate the feasibility of this mechanism in real van der Waals antiferromagnets. Our study identifies the odd-parity magnons as a new class of spin excitations and provides a theoretical foundation for odd-parity magnons and ultrafast optically controlled topological magnonic devices.
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All authors Pu Zhang, Sun-Bo Xie, Junxi Yu, Yichen Liu, Cheng-Cheng Liu

Materials Science

Crystallisation kinetics of supercooled liquid palladium

In this study, we employ classical molecular dynamics (MD) simulations to investigate the crystallisation kinetics of supercooled liquid palladium and relate the results to time-resolved X-ray diffraction measurements on rapidly quenched Pd thin films. Crystal nucleation and growth rates are determined over the temperature range $700$–$1150~\mathrm{K}$ ($0.38$–$0.65 T_{\mathrm{m}}$) by analysing the evolution of the microstructure during the liquid-to-crystal transition. The self-diffusion coefficient of Pd, obtained from the atomic mean-squared displacement, follows Arrhenius behaviour over the investigated temperature range, with an activation energy of $467(6)~\mathrm{meV/atom}$, consistent with available data for supercooled liquid metals. The steady-state homogeneous nucleation rate exhibits a maximum of approximately $4 \times 10^{35}~\mathrm{m^{-3} s^{-1}}$ near $0.5 T_{\mathrm{m}}$. Crystal growth occurs at velocities of the order of metres per second, with a temperature dependence consistent with diffusion-limited Wilson-Frenkel kinetics rather than the collision-limited regime. Based on multiple statistically independent simulations, a time-temperature-transformation (TTT) diagram for crystallisation onset is constructed. The TTT curve exhibits a nose near $0.5 T_{\mathrm{m}}$ and $100~\mathrm{ps}$, corresponding to a critical cooling rate for vitrification on the order of $10^{13}~\mathrm{K s^{-1}}.$ The simulations reproduce the crystallisation onset time and temperature observed in time-resolved X-ray diffraction experiments on optically molten Pd thin films quenched at $5 \times 10^{11}~\mathrm{K s^{-1}}.$ These results indicate that homogeneous, rather than heterogeneous, nucleation governs the achievable supercooling in the experimentally studied films.
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All authors Zuzanna Kostera, Przemyslaw Dziegielewski, Christian Bressler, Wojciech Gawelda, Konstantinos Georgarakis, Dmitry Khakhulin, Oleksii I. Liubchenko, Adam Olczak, Angel Rodriguez-Fernandez, Ryszard Sobierajski, Klaus Sokolowski-Tinten, Peihao Sun, Robert W.E. van de Kruijs, Hazem Yousef, Peter Zalden, Jerzy Antonowicz