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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Monday 10 August

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

Openable Force-Balanced Halbach Magnets: From Fibonacci Sphere Simulations to Icosahedral Realizations

Ingo Rehberg, Helmut Soltner and Peter Blümler

A long-standing goal in magnet design is to completely surround a volume of highly homogeneous magnetic field with permanent magnets while maintaining practical access to that volume. In this work, we present a theoretical and experimental investigation of mechanically accessible spherical magnets in Halbach configuration that can be opened with minimal or vanishing force. Focusing on dipolar Halbach spheres composed of discrete magnetic subunits, we derive conditions for force-free opening along specific cutting planes. These conditions define a continuous set of geometries for which tensile magnetic forces cancel, leaving only shear components, enabling mechanically effortless opening. The theoretical predictions are validated experimentally using icosahedral approximations of the Halbach sphere, for which both opening forces and magnetic field properties are measured. The results demonstrate that excellent field homogeneity can be preserved while reducing opening forces by orders of magnitude. Although discussed in detail for the dipolar case, the theoretical framework is general and applicable to higher-order multipole Halbach systems. Finally, the concepts are extended to spherocylindrical Halbach configurations, highlighting their potential for large-volume, highly homogeneous, and mechanically accessible permanent-magnet systems for magnetic resonance
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Materials Science · Cross-listed from cond-mat.mes-hall

Size-Dependent Band-Tail Localization in Oxide Semiconductors Revealed by Direct Density-of-States Mapping

Chang Niu, Kisoo Nam, Aravindh Shankar et al. (+5 more)

Disorder-induced localization is expected to become increasingly important as amorphous oxide semiconductor transistors are scaled toward low-dimensional channels, yet the electronic states responsible for this transport regime remain difficult to resolve experimentally. Here, we use a lock-in-based electric-field penetration technique to directly map the effective density of states (DOS) in In-based oxide semiconductor thin-film transistors (TFTs). The extracted quantum capacitance, carrier density, and chemical potential reveal a disorder-dominated transport regime in which band-tail states are not merely passive traps, but become screening-active and partially transport-active. Geometry-dependent DOS mapping shows an exponential suppression of the effective DOS with channel length, demonstrating size-dependent band-tail localization and providing a microscopic origin for a distinct localization-induced threshold-voltage roll-off mechanism. Temperature-dependent measurements show that the disorder-dominated DOS is strongly suppressed at low temperatures, while extended diffusive states remain nearly unchanged, confirming the localization origin. By tuning film thickness, O2 annealing, and In/Ga/Zn composition, we further demonstrate systematic suppression of disorder and effective-DOS localization. This work establishes direct DOS mapping as a device-level probe of localization physics and provides a pathway for engineering disorder in low-dimensional oxide semiconductor electronics.
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All authors Chang Niu, Kisoo Nam, Aravindh Shankar, Jian-Yu Lin, Sanjeev Khare, Sumi Lee, Pramey Upadhyaya, Peide D. Ye

Materials Science

Machine-learning octet $AB$-type binary compounds across chemical space with domain knowledge of the interatomic bond

Rohan Kumar, Mariano D. Forti, Aakash A. Naik et al. (+2 more)

The prediction of the structural stability of octet $AB$-type binary compounds is a classical materials informatics problem. The challenge is to capture the relative stability of 4-fold coordinated atoms in zincblende ($\beta$-ZnS) structure and 6-fold coordinated atoms in rocksalt (NaCl) structure, modulated by charge transfer and atomic-size differences. Previous structure maps and machine-learning approaches used atomic features such as valence-electron count, ionization potential and atomic radii, using either physical intuition or symbolic regression. Here, we demonstrate that explicitly incorporating the domain knowledge of the interatomic bonds can significantly and systematically improve the prediction of $\beta$-ZnS/NaCl stability. We encode this bonding information through a coarse-grained representation of the local electronic structure obtained by a recursive solution of a tight-binding bond model. The underlying pairwise Hamiltonians are taken from downfolded eigenstates of density-functional theory calculations for diatomic molecules and thereby include domain knowledge of the bond between specific $A-B$ pairs. The benefit of this description is demonstrated with an ensemble of independently trained Kernel Ridge or symbolic regression models combined with sequential feature selection. The obtained models are compared to a previous symbolic-regression model using the same set of ab initio calculations for octet binaries as training data. We find a significant improvement in the prediction of the formation energy difference of $AB$ compounds as compared to previous works and demonstrate that an increasing amount of bond-informed recursion features improves the predictive accuracy.
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All authors Rohan Kumar, Mariano D. Forti, Aakash A. Naik, Luca M. Ghiringhelli, Thomas Hammerschmidt

Materials Science

All-Electron Single-Atom Reference Correction for Absolute Transition Energies in Fixed-Reference PAW-XCH Calculations

Yinan Wang and Teruyasu Mizoguchi

The transition energy of a core-loss spectrum comprises a transferable atomic core-reference contribution and a material-dependent response that determines chemical shifts. Density functional theory calculations commonly underestimate absolute transition energies. In VASP, the same PAW dataset is used for the ground and core-excited occupations, retaining the ground-state atomic reference when the core occupation changes and thereby omitting the associated all-electron atomic reference change. We evaluate this change using self-consistent single-atom calculations and construct a residual atomic reference correction from the valence reference change and isolated-atom total-energy response. Comparisons with an independent ultrasoft-pseudopotential implementation demonstrate numerical consistency of the all-electron reference for K, L1, and L2,3 core holes, while representative corrected spectra approach the experimental absolute energy scale. For a fixed element, edge, and core-hole scheme, the atomic reference terms cancel from energy differences, showing that same-element chemical shifts are governed by the double difference of the supercell total energy. At the Al and Si L2,3 edges, the near-edge spectral shape additionally depends strongly on the PAW representation of low-lying 3d-like unoccupied states.
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Materials Science

Multitask Scanning Probe Microscopy

Aditya Raghavan, Yu Liu, Ian Mercer et al. (+2 more)

Scanning probe microscopy provides nanoscale access to structural, electrical, electromechanical, magnetic, and mechanical properties of materials. Its increasing use for wafer-scale characterization and combinatorial materials exploration creates a need to distribute measurements efficiently across large spatial domains. This is particularly important when available modalities differ in acquisition time and potential for tip and sample damage, making exhaustive multimodal mapping over spatial grids impractical. Here, we demonstrate multitask scanning probe microscopy, a live, closed-loop workflow in which a multitask Gaussian process learns spatial and cross-modal relationships and autonomously selects both the next measurement location and the next experimental protocol. The approach is implemented on an automated large-sample atomic force microscope and demonstrated on a composition-spread AlScN wafer using tapping-mode and Dual AC Resonance Tracking (DART) measurements. Paired initial measurements establish the relation between the tasks, after which noncoincident measurements are used to update both response landscapes. The resulting workflow extends active learning in scanning probe microscopy from spatial sampling to autonomous allocation of measurement modalities and provides a basis for combining rapid, weakly perturbative imaging with slower contact, electrical, electromechanical, magnetic, or spectroscopic measurements.
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All authors Aditya Raghavan, Yu Liu, Ian Mercer, JP Maria, Sergei Kalinin

Materials Science

Self-induced crystalline fluctuation spin-glass state in Mn7C3 binary compounds

Zekun Yu, Chao Zhou, Kuo Bao et al. (+12 more)

Crystalline spin glasses are attractive compounds owing to their unique nature and applications. Here, we synthesised a bulk Pnma-type Mn7C3 spin glass by a high-temperature, high-pressure method. Experimental characterisation including X-ray diffraction and magnetic susceptibility measurements demonstrated that the compound has a triangular Ising-model-based structure, high freezing temperature of 37.4 K, and novel competition mechanism. Theoretical calculations and simulations revealed that the triangular Mn units are spontaneously frustrated and bridge neighbouring Mn units via polarised C atoms and messenger Mn atoms. Triangular C units each share one electron within a three-pronged electron cloud. This electron is the direct cause of frustration and competition in Mn7C3. The competition within the triangular Mn units suggests that the possible magnetic configurations are highly degenerate and that the Mn7C3 spin glass has high robustness. This work introduces a new family of spin glasses with ordered microgeometries that drive electronic structure disorder, and an application-friendly spin-glass material for use in fields like high-efficiency hardware and algorithm design in artificial intelligence.
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All authors Zekun Yu, Chao Zhou, Kuo Bao, Xiaofeng Wang, Zhaoqing Wang, Jinming Zhu, Enxuan Li, Andong Yao, Yuhan Meng, Yufei Ge, Xingbin Zhao, Shuailing Ma, Pinwen Zhu, Qiang Tao, Tian Cui

Materials Science

Altermagnetism-Induced Spin-resolved electronic structure in Janus FeX0.5Y0.5 Monolayers (X, Y = S, Se, Te)

Mengyang Zhang, Jie Li, Yifei Chen et al. (+3 more)

Realizing the spin-resolved electronic properties in superconducting materials stands as a critical frontier, offering both novel fundamental physics and potential for dissipationless spin-based devices. Here, we predict a series of Janus FeX0.5Y0.5 monolayers derived from iron-based superconductors (e.g., FeSe, FeTe, and FeS) by using Kondo-type model and first-principles calculations. These Janus structures exhibit significant spin-splittingelectronic states, large topological band gaps (51.4 meV) and high Néel temperatures (415 K). We further reveal that valley polarization can be effectively tuned via applied in-plane strain and the resulting valley-polarized anomalous Hall conductivity can be manipulated by shifting the Fermi level. Our work suggests a new strategy based on altermagnetism for engineering spin-splitting states in superconducting systems and inspires further exploration of superconducting spintronics.
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All authors Mengyang Zhang, Jie Li, Yifei Chen, Shifang Li, Zhentao Fu, Jianxin Zhong

Materials Science

Electronic conductivity in anharmonic crystals: Phonon dephasing in the electron-phonon interaction

Mingran Kong and Bartomeu Monserrat

The electron-phonon interaction underpins many material properties, for example, the conductivity of metals and the optoelectronic response of semiconductors. First-principles calculations of the electron-phonon interaction are a powerful tool to quantitatively describe many of these properties in increasingly complex materials. However, one key assumption of all calculations is that phonons have infinite lifetimes, an approximation that may break down when anharmonic phonon-phonon interactions are strong. In this work, we present a theory for the interaction of electrons with finite-lifetime phonons experiencing dephasing. Using a first-principles implementation of the theory, we find that anharmonic dephasing dramatically enhances electron-phonon scattering rates in metallic MgB2. Microscopically, phonon-phonon interactions create new scattering channels that increase the phase space available for electron-phonon scattering. As a result, anharmonic dephasing strongly suppresses conductivity in MgB2, bringing the calculated values substantially closer to experiment within the Boltzmann transport equation framework. This example establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon scattering, and the microscopic mechanism suggests that anharmonic dephasing could play an important role in the conductivity of many metals. More broadly, our theory and first-principles implementation of anharmonic dephasing in the electron-phonon interaction provides a solid foundation to explore this regime in other materials.
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Materials Science

Wrinkling in Selected Polymer Thin Films Induced by Combined Ion Beam and Humidity Exposure

Alessia Danagoulian, Benli Jiang, Nicholas Russo et al. (+13 more)

This study investigates ion beam sputtering (IBS)-induced surface wrinkling phenomena in three polymers with varying hydrophilicity: poly-hydroxy-ethyl-methacrylate (pHEMA), poly-4-vinyl pyridine (p4VP), and poly-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (pV4D4). It is observed that pHEMA and p4VP films wrinkle only when exposed to ion bombardment and subsequent water vapor exposure. No wrinkling is observed in pV4D4 under these same conditions. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are performed before IBS, after IBS, and after exposure to humidity. XPS shows that IBS drives chemical changes within the surface layer, creating a graphitized film at the surface. For the polymer films that exhibit wrinkling (pHEMA and p4VP), XPS and FTIR indicate water absorption in both the surface and the bulk of the films, resulting in swelling. We conjecture that the formation of wrinkles arises from this swelling being mechanically constrained by the rigid underlying silicon substrate and the stiff graphitized surface layer. In contrast, the absence of wrinkle formation in pV4D4 under the same experimental conditions can be attributed to its comparatively low water absorption and the correspondingly limited swelling response.
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All authors Alessia Danagoulian, Benli Jiang, Nicholas Russo, Colette Abadie, Jalal Karimzadeh Khoei, Grace Pettis, Jocelyn Zhang, Neil Baker, Eda Güney, Omid Moradi, Wei-Jing Chen, Jiaqi Tang, Robert Sims Jr, Kevin E. Smith, Gozde Ozaydin Ince, Karl F. Ludwig Jr

Materials Science

Anharmonic dephasing in the electron-phonon interaction

Mingran Kong and Bartomeu Monserrat

Electron-phonon coupling has been a central topic in condensed matter physics for decades, and firstprinciples methods have demonstrated remarkable success in quantitatively capturing its role in a wide variety of physical phenomena and materials. Conventional calculations of electron-phonon coupling typically assume that phonons have infinite lifetimes, but phonons can exhibit finite lifetimes due to anharmonic phonon-phonon interactions. In this work, we derive an expression for the electron-phonon coupling scattering rates including the effects of anharmonic three-phonon interactions, which lead to phonon dephasing and finite phonon lifetimes. We also describe a first-principles implementation of this anharmonic electron-phonon coupling which can be seamlessly integrated within existing workflows for the evaluation of electron-phonon and phonon-phonon coupling interactions. Finally, we present calculations of electron-phonon scattering rates including phonon dephasing in a range of materials, and discuss the different microscopic mechanisms by which anharmonic phonons influence electron-phonon coupling. This study establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon coupling, and provides a platform to explore these effects in a wide range of materials and phenomena.
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Materials Science

Energy-efficient spin Hall nano-oscillators using near-compensated CoGd ferrimagnets

Jiayu Lei, Raghav Sharma, Shishun Zhao et al. (+5 more)

Conventional spin Hall nano-oscillators (SHNOs) based on ferromagnets face practical limitations due to high threshold current densities and large external magnetic field requirements. Ferrimagnets provide an attractive alternative due to their unique magnetic dynamics and potential for energy-efficient spintronic devices. In this study, we report rare-earth-transition-metal (RE-TM) ferrimagnetic SHNOs utilizing Co1-xGdx alloys, in which compositional tuning enables high-performance operation near the magnetization compensation. The optimized SHNO operates at a low current density (1.43*10^7 A/cm^2), a small magnetic field (5 mT), and exhibits a narrow linewidth (0.61 MHz) simultaneously, showing an order-of-magnitude improvement over its ferromagnetic counterparts. This enhanced performance arises from high spin-orbit torque efficiency, low magnetic anisotropy, reduced effective magnetization, and minimized nonlinearity near the compensation point. These results establish RE-TM ferrimagnets as a promising material platform for next-generation spintronic devices and offer new strategies for realizing energy-efficient, high-performance spintronic oscillators.
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All authors Jiayu Lei, Raghav Sharma, Shishun Zhao, Fanrui Hu, Yuchen Pu, Chenhui Zhang, Rahul Mishra, Hyunsoo Yang

Materials Science · Cross-listed from physics.optics

Wafer-scale monolithic integration of Ce:YIG films and magneto-optical isolators on silicon

Tianchi Zhang, Yucong Yang, Weihao Yang et al. (+9 more)

Silicon integrated cerium doped yttrium iron garnet (Ce:YIG) thin films are promising candidates for integrated nonreciprocal photonic devices, cryogenic photonic modulators and optical computing applications. However, previously reported Ce:YIG thin film on silicon is limited to milimeter sizes. Wafer-scale integration and non-destructive characterization of high quality Ce:YIG thin films on silicon has been elusive. Here, we report growth of 4-inch wafer-scale Ce:YIG thin films on silicon substrates by radio-frequency magnetron sputtering. Strong Faraday effect of 2318 deg/cm, low propagation loss of 80 dB/cm and excellent thickness uniformity of 3.5% is demonstrated across the 4-inch silicon wafer. Furthermore, a custom designed wafer-scale, non-destructive magneto-ellipsometry was established to characterize the film thickness, optical constants and magneto-optical constants across the wafer. Wafer-scale integration of ring resonator type magneto-optical isolators are also demonstrated. Our work demonstrates a step forward toward wafer-scale heterogeneous integration and characterization of magneto-optical thin films on silicon, providing material candidates for non-reciprocal photonic device arrays, magneto-optical in-memory computing networks and integrated magneto-optic magnetometers.
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All authors Tianchi Zhang, Yucong Yang, Weihao Yang, JieJun Su, Tianyi Ma, Xuan Zhao, Junxian Wang, Di Wu, Zhenyuan Ren, Yi Shuai, Zixuan Wei, Lei Bi

Sunday 9 August

Materials Science

Detection of acoustic phonons in carbon by Raman spectroscopy

Konstantin Iakoubovskii, Andrey Katrusha, Weihua Peng et al. (+1 more)

We detected acoustic phonons in graphite and diamond by Raman spectroscopy supported by density functional theory calculations. The activation of these normally forbidden Raman modes was achieved via lattice amorphization in case of graphite and by boron doping in case of diamond. The doping-induced Raman signal in diamond was identified with substitutional boron of tetrahedral symmetry via its dependences on excitation wavelength and polarization. Comparison of the Raman spectra of amorphized graphite and heavily boron-doped diamond suggests the emergence of graphitic-like disorder in the diamond lattice. The reported approach is not limited to carbon and can be extended to a wide range of other materials.
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All authors Konstantin Iakoubovskii, Andrey Katrusha, Weihua Peng, Jianguo Peng

Materials Science

Temperature-Driven Sequential Modeling for the Prediction of Annual Power Conversion Efficiency Profiles of Organic Photovoltaic Materials: Douala Case Study

Steve Cabrel Teguia Kouam, Rockefeller Rockefeller, Raoult Dabou Teukam et al. (+4 more)

Organic photovoltaic (OPV) materials are promising candidates for distributed solar energy in tropical regions, yet existing virtual screening tools report static power conversion efficiency (PCE) values at standard testing conditions (STC) that fail to capture the temperature-driven performance degradation experienced under real deployment conditions. Here we introduce a Climate-Native computational framework that forecasts the annual PCE profile of OPV donor molecules under geographically realistic operating conditions. The framework combines GFN2-xTB molecular dynamics with an equivariant graph neural network surrogate ($268$ Neyman-stratified CEP molecules; $120,600$ training geometries; $\sim 1050\times$ speedup over explicit quantum chemistry) and sequential deep learning models trained on annual time series anchored in NASA POWER climate data for Douala, Cameroon, and validated by zero-shot transfer to Yaoundé and Maroua. Applied to $\sim 30,000$ molecules from the Harvard Clean Energy Project (CEP) and validated against $350$ HOPV15 experimental device measurements, the framework demonstrates that sequential models trained on full molecular dynamics trajectories outperform time-averaged baselines ($35\%$-$48\%$ relative MAE improvement over static baselines), confirming that thermal conformational dynamics carry information beyond mean geometry. We further introduce a seasonal stability score that reranks OPV candidates by performance consistency under tropical conditions, identifying molecules whose deployment suitability differs substantially from their static PCE ranking.
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All authors Steve Cabrel Teguia Kouam, Rockefeller Rockefeller, Raoult Dabou Teukam, Jean-Pierre Tchapet Njafa, Patrick Sorrel Mvoto Kongo, Jean-Pierre Nguenang, Serge Guy Nana Engo

Materials Science · Cross-listed from physics.optics

Nonresonant optomechanical control of structural phases

Jiaojian Shi, Yijing Huang, Christian Heide et al. (+24 more)

Optical tweezers demonstrate how light can exert forces to trap, repel, and manipulate microscopic particles without absorption. Recent theory has suggested that such forces can extend beyond particle manipulation to drive structural phase transitions in solids. Here we apply this optomechanical principle to tin selenide (SnSe), a material where proximity to several different structural phases gives rise to its high thermoelectric figure of merit and makes it a candidate for a switchable topological crystalline insulator. Whereas the force for standard optical tweezers arises from a gradient in the intensity of a light field, the optomechanical force is mediated by a gradient in the dielectric constant as a function of phonon coordinate. Unlike conventional methods that rely on resonant excitation and absorption through the imaginary part of the dielectric function, this approach operates dispersively through the real part and can be directly driven by Raman processes, enabling selective transitions with reduced energy cost and ultrafast response. Using time-domain Raman scattering, we show that above a critical mid-infrared field strength the $A_g$ Raman modes disappear abruptly without softening, signaling the formation of a new structural phase. This phase, distinct from those induced by heating or carrier excitation, exhibits large-amplitude and long-lived modulations in its optical response. Complementing this observation, we show also evidence for an equivalent DC-field-driven structural phase transformation to a higher symmetry phase, as observed by atom probe tomography. Our study demonstrates the concept of nonresonant optomechanical phase control and defines novel opportunities for synthesizing hidden structural phases with unique functional properties.
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All authors Jiaojian Shi, Yijing Huang, Christian Heide, Elias Hilderbrand, Carl Friedrich Schon, Jan Kottgen, Matthias Wuttig, Burak Guzelturk, Isabel Sedwick, Yukun Li, Haowei Xu, Yuejun Shen, Pooja Donthi Reddy, Viktoryia Shautsova, Mohammad Taghinejad, Duan Luo, Mark L. Brongersma, Kunal Mukherjee, Yuki Kobayashi, Andrew F. May, Eamonn Hughes, Mariano Trigo, David A. Reis, Ju Li, Jian Zhou, Shambhu Ghimire, Aaron M. Lindenberg

Materials Science

A Dataset of Equilibrium State Configurations of Adsorption in Zeolites

Marko Petković, Rachna Ramesh, Vlado Menkovski et al. (+1 more)

Zeolites are crystalline nanoporous materials widely used in adsorption, separation, and catalytic processes. Molecular simulations are commonly used to predict adsorption properties, but most high-throughput adsorption datasets report only ensemble-averaged quantities such as loadings or isotherms, rather than the molecular configurations from which these averages are obtained. Here, we present AdsZeo, a coordinate-resolved dataset of equilibrium methane adsorption configurations in aluminium-substituted, sodium-containing zeolite frameworks. The processed release contains 4,775 framework realisations derived from 191 zeolite topologies. Each framework realisation was simulated at 13 methane pressures between 0.1 and 100 bar at 298 K using grand canonical Monte Carlo simulations, giving 62,075 production simulations in total. In addition to scalar adsorption records, the dataset stores production-frame methane pseudo-atom coordinates, mobile Na$^+$ cation coordinates, framework atomic coordinates, per-frame loading and energy statistics, and simulation metadata in a processed DuckDB database. The release contains 12,415,000 saved production-frame records and 1,245,376,215 saved particle-coordinate records. AdsZeo provides coordinate-resolved adsorption data across variations in framework topology, aluminium content and distribution, sodium cation arrangement, pressure, and methane loading, enabling reuse for adsorption analysis, spatial statistics, density estimation, and machine-learning models for molecular configuration generation in charged zeolite pores.
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All authors Marko Petković, Rachna Ramesh, Vlado Menkovski, Sofía Calero

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

Layer-Locked Chiral Topological Superconductivity

Yijie Mo and Zhongbo Yan

We uncover a universal mechanism for realizing layer-locked topological phases. Guided by it, we investigate the realization of layer-locked chiral topological superconductivity-the superconducting analogue of the quantum anomalous layer Hall effect-in a nonsymmorphic bilayer antiferromagnetic system with s-wave pairing. We identify three distinct gate-tunable topological phases and establish a direct correspondence between the nearly quantized layer-resolved Chern numbers and the layer-locking behavior of chiral Majorana edge states, vortex-core Majorana zero modes, and nearly quantized thermal Hall responses.
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Materials Science

Light-Stabilized Metastable Electronic State in NiO with Enhanced Orbital Hybridization

Thomas C. Rossi, Fabio G. Santomauro, Lars Mewes et al. (+19 more)

Light-driven control of electronic structure in correlated metal oxides offers new opportunities for optimizing materials used in photovoltaic and photoelectrochemical technologies. We show that photoexcitation of NiO, a prototypical transparent semiconductor and hole-transport material, across its charge-transfer gap produces a long-lived metastable state with enhanced Ni 3d-O 2p orbital hybridization. We characterize this state using Ni K-edge X-ray absorption spectroscopy, which probes how structural and electronic changes affect the unoccupied p density of states during continuous and pulsed ultraviolet excitation. Under pulsed excitation, high carrier densities of approximately 10^20 per cubic centimeter generate a state with a lifetime of approximately 600 picoseconds, in which enhanced hybridization coexists with lattice heating. By contrast, continuous ultraviolet irradiation at much lower carrier densities of approximately 10^13 per cubic centimeter stabilizes a similar electronic state with negligible lattice heating, demonstrating that its formation is not solely thermally driven. First-principles DFT+U+V calculations attribute the spectral changes to stronger Ni 3d-O 2p hybridization, which alters the unoccupied Ni 4p states probed by dipole-allowed K-edge transitions. We attribute this change to the dynamic screening of on-site electronic correlations following photoexcitation, which redistributes the charge density. Because orbital hybridization governs carrier transport and charge-transfer energetics, our results identify photoinduced screening as a mechanism for dynamically tuning correlated oxides and suggest new design principles for optoelectronic materials.
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All authors Thomas C. Rossi, Fabio G. Santomauro, Lars Mewes, Janina Löffler, Dominik Kinschel, Giacomo Rossi, Mario Gutiérrez, Oliviero Cannelli, Boris V. Sorokin, Jochen Rittmann, Jakob Kel, James Budarz, Anna Wach, Adam H. Clark, Emiliano Dal Molin, Maged F. Bekheet, Albert Gili, Sebastian Praetz, Daniel Grötzsch, Delphine Cabaret, Renske M. van der Veen, Majed Chergui

Materials Science

Distribution of Relaxation Times analysis of evolution of Oxygen Reduction Pathways for ionic conductor infiltration on MIEC cathode

Rakhi Saha, Preethi Sudarsan, Manju Kumari et al. (+4 more)

Solid oxide fuel cells (SOFCs) are promising electrochemical energy conversion devices; however, the sluggish cathodic oxygen reduction reaction (ORR) remains a major limitation for intermediate-temperature operation. ORR subprocesses can be modified by infiltrating ionic Sm0.2Ce0.8O2-delta (SDC) on mixed ionic electronic SrFe0.9Ti0.1O3-delta (STF). However, the processes are indistinguishable in most cases and poorly understood using conventional equivalent circuits. Distribution of Relaxation Times (DRT) analysis distinguishes these processes to identify the dynamics with temperature and surface reconstruction. Such analysis is being reported, revealing the connection between increase of active sites, temperature, and polarization resistance (RP). SDC infiltration preferentially accelerates oxygen surface exchange and activation processes over the relatively high frequency charge transfer process related to cathode surface at elevated temperatures for the infiltrated cells. RP was reduced substantially with the systematic redistribution of each process to as low as 0.04 ohm.cm2 at 800 degC. This work underlines the deconvolution of the processes using DRT as a tool, and SDC infiltrated STF as a model cathode system to provide a mechanistic insight of understanding ORR kinetics and design a rationale for developing high-performance SOFC air electrodes
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All authors Rakhi Saha, Preethi Sudarsan, Manju Kumari, Hee Jung Park, Abdelkrim Mekki, Khalil Harrabi, Somaditya Sen

Materials Science

Microscopic Origin of Spin Splitting in Altermagnetic CrSb Thin Films

Dai Mingyang, Song Hongquan, Kang Zhuo et al. (+2 more)

Altermagnets have recently emerged as promising materials for spintronic applications owing to their momentum-dependent spin splitting. Among them, metallic CrSb is particularly attractive owing to its giant spin splitting and high Néel temperature. However, the microscopic origin of the distinct spin-splitting behaviors in bulk and thin-film CrSb remains unresolved. Here, we systematically investigate the electronic structures of CrSb slabs with different surface orientations using first-principles calculations. Although all considered slabs preserve spin-group symmetries compatible with altermagnetism, they exhibit markedly different electronic structures: the (2$\bar{1}\bar{1}$0) slab retains pronounced altermagnetic spin splitting, whereas the (0001) and (10$\bar{1}$0) slabs display nearly spin-degenerate bands. We demonstrate that dimensional reduction fundamentally changes the microscopic origin of altermagnetic spin splitting. Unlike bulk CrSb, altermagnetic spin splitting in thin films requires long-range inter-unit-cell coplanar Cr–Sb hopping, while Sb–Sb hopping provides an additional contribution. The preservation or suppression of these hopping pathways explains the strong surface dependence of the spin splitting. Our findings establish a microscopic mechanism for understanding altermagnetism in reduced dimensions and provide a general principle for engineering spin splitting in low-dimensional altermagnetic materials.
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All authors Dai Mingyang, Song Hongquan, Kang Zhuo, Xu Yuanji, Tian Fuyang

Materials Science

An Automated Magnetron Sputtering Chamber for Ferroelectric Thin Film Deposition

Stanislav A. Udovenko, Ian Mercer, Sarah Olandt et al. (+5 more)

Optimization of next-generation materials synthesis and manufacturing processes can be accelerated by effective use of digital datasets. However, a majority of existing custom research infrastructure, including that for thin film deposition, is primarily manually operated and not compatible with this new research paradigm. Here, a template is provided for upgrading existing manual deposition chambers to enable automated and autonomous experimentation. As an example, the upgrade of an existing magnetron sputtering chamber dedicated to synthesis of wurtzite ferroelectrics is presented. Focus is placed on automation of instrumentation; system and deposition control; and synchronized and automated data collection strategies. An example use case of the system for semi-autonomous determination of process-property relationships is presented, specifically minimization of coercive field in wurtzite Al$_{1-x-y}$Sc$_x$B$_y$N thin films.
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All authors Stanislav A. Udovenko, Ian Mercer, Sarah Olandt, Ric Wilburn, Kevin Dressler, Susan Trolier-McKinstry, Jon-Paul Maria, Darren C. Pagan

Materials Science

High Thermal Conductivity of Back-End-of-Line Compatible Diamond Films

Jinwen Liu, Chufei Cheng, Feifei Tan et al. (+6 more)

Back-end-of-line (BEOL) thermal management requires electrically insulating heat-spreading dielectric that can be integrated within thermal budgets below 400 C. Here, we report polycrystalline diamond films grown directly on Si at a substrate temperature below 400C. Two films with average thickness of 760 and 1000 nm were characterized by Raman spectroscopy, scanning electron microscopy (SEM), and time-domain thermoreflectance (TDTR). Raman spectra show a sharp diamond peak with minor signatures of non-diamond carbon, while SEM reveals lateral growth and large grain size. Temperature dependent TDTR measurements were performed from room temperature to 100C. Sensitivity analysis indicates that the sensitivity of cross-plane thermal conductivity is comparative to the in-plane thermal conductivity. Accordingly, the films were analyzed using an isotropic thermal model by considering the nearly-isotropic grain structure, yielding room temperature effective thermal conductivity of 73 and 86 W m-1 K-1, respectively. These values are about two orders of magnitude higher than those of conventional dielectric materials and demonstrate the potential of diamond films grown at low temperatures as dielectric heat-spreading layers.
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All authors Jinwen Liu, Chufei Cheng, Feifei Tan, Jinquan Zhang, Di Lu, Bing Dai, Jiaqi Zhu, Runsheng Wang, Zhe Cheng

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

Spin-Orbital Hall Nano-Oscillators using PtCr/NiFe

Utkarsh Shashank, Akash Kumar, Daegeun Jo et al. (+11 more)

The orbital Hall effect provides a promising route for generating angular-momentum currents beyond conventional spin Hall physics. PtCr alloys exhibit unusually large current-induced torques, but the contribution of orbital transport and the ability of these torques to sustain coherent nonlinear magnetization dynamics remain unresolved. Here we demonstrate spin-orbital Hall nano-oscillators by exploiting a homogeneous heavy-metal/light-metal alloy in which orbital Hall currents generated by Cr are converted by Pt into spin currents, producing giant spin-orbit torques. Using PtCr/NiFe heterostructures, the effective torque efficiency increases from ~0.14 in Pt/NiFe to ~0.40 in Pt0.38Cr0.62/NiFe despite substantial Pt dilution, enabling coherent auto-oscillations with the threshold current density reduced from ~ 1.07 x 10^12 to ~ 4.4 x 10^11 A m^-2. First-principles calculations show that Cr alloying suppresses the intrinsic spin Hall conductivity while enhancing the orbital Hall conductivity, and reproduce the observed torque enhancement only when orbital transport is included. Our combined experimental and first-principles results show that alloy engineering enables giant spin-orbit torques through an intrinsic orbital-mediated contribution, enabling coherent auto-oscillations without engineered multilayers and establishing a scalable materials platform for low-power nonlinear spintronic and orbitronic devices.
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All authors Utkarsh Shashank, Akash Kumar, Daegeun Jo, Thi Ngoc Anh Nguyen, Jong-Guk Choi, Sambit Ghosh, Michal Strach, Lunjie Zeng, Andrew B. Yankovich, Roman Khymyn, Ahmad A. Awad, Eva Olsson, Peter M. Oppeneer, Johan Åkerman

Materials Science

Unified open-boundary electrostatics in real-space density functional theory

Rajat Kumar, David Codony, Phanish Suryanarayana et al. (+1 more)

We present an electrostatic formulation in real-space density functional theory that provides a systematic and unified treatment of the open-boundary electrostatics of isolated and partially periodic systems, including in the presence of an applied uniform electric field along the open (finite) directions. Specifically, we formulate a local electrostatic energy functional whose stationarity yields the Poisson equation for the electrostatic potential, subject to periodic and Dirichlet boundary conditions along the periodic and open directions, respectively. Using a Green's function approach, we derive analytical expressions for the Dirichlet values arising from the total charge density of the system. We also derive the expressions for the energy, atomic forces, and stress tensor. We implement the resulting expressions within the large-scale parallel real-space SPARC electronic structure code. Using representative examples, we verify the accuracy and efficiency of the framework, demonstrating exponential convergence of the computed quantities with vacuum size and excellent agreement with established plane-wave codes while requiring significantly less vacuum at comparable accuracy. Since no existing implementation provides the stresses for such systems, we instead verify them against numerical derivatives of the energy, finding close agreement. Finally, we apply the framework to compute static polarizabilities and piezoelectric coefficients, obtaining very good agreement with values reported in the literature.
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All authors Rajat Kumar, David Codony, Phanish Suryanarayana, Abhiraj Sharma

Materials Science

Thermo-mechanical Characterization of 2D hexagonal Boron Phosphide (h-BP)

Zahabul Islam

This study explores the thermo-mechanical properties of a two-dimensional (2D) monolayer hexagonal boron phosphide (h-BP). h-BP is predicted to possess a moderate band gap, high thermal stability, and excellent carrier mobility, making it suitable for advanced electronic, sensing, and energy applications. A classical molecular dynamics (MD) potential for h-BP was developed using density functional theory (DFT) calculations. The derived parameters were implemented in MD simulations to evaluate mechanical behavior under tensile loading along both zigzag and armchair directions at varying temperatures (300 K to 900 K). The results reveal significant anisotropy in mechanical performance, with higher tensile strength and elastic modulus in the zigzag direction across all temperatures. Increasing temperature reduces both tensile strength and stiffness due to thermal softening and increased atomic vibrations. The influence of structural defects was also investigated, revealing that Stone-Wales and vacancy defects reduce the tensile strength and failure strain of h-BP, with the two-atom vacancy producing the most pronounced mechanical degradation due to localized stress concentration and premature crack initiation. These findings provide a foundation for future research on the mechanical stability of h-BP in extreme environments.
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Saturday 8 August

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

Magnetoelastic coupling in stripe-domain states of yttrium iron garnet

Nimisha Arora, Daniel Prestwood, Takashi Kikkawa et al. (+4 more)

We study magnetoelastic coupling in stripe-domain magnetic states of $3\,\mathrm{\mu m}$-thick YIG thin films grown on a GGG substrate. Broadband ferromagnetic resonance reveals low-frequency stripe-domain magnon branches modulated by a field-independent phonon comb with a frequency spacing of $3.5\,\mathrm{MHz}$, matching the value predicted for confined thickness-shear modes of the GGG substrate. Analytical fitting yields coupling rates that vary between $0.33$–$0.54\,\mathrm{MHz}$ and cooperativities of order $10^{-1}$, indicating that the system is in the weak-coupling regime without resolvable avoided-crossing gaps. Magnon-phonon mode-overlap calculations using finite-element simulations show that the weak coupling arises from phase and domain-sign cancellation: the local magnetoelastic coupling is sizable, but more than $99\%$ of the coherent overlap cancels across the stripe texture. Fully coupled simulations further demonstrate phonon-mediated excitation of a remote YIG layer and show that efficient propagating-phonon generation requires spatially asymmetric magnon modes, establishing magnetic texture as a control parameter for magnon–phonon coupling.
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All authors Nimisha Arora, Daniel Prestwood, Takashi Kikkawa, Eiji Saitoh, Jack Gartside, Will Branford, Hidekazu Kurebayashi

Materials Science

Pressure-Induced Stacking Disorder and Suppression of Long-Range Sm-type Order in Medium-Entropy Rare-Earth Alloys

Raimundas Sereika, Matthew P. Clay, Kallol Chakrabarty et al. (+1 more)

Rare-earth medium-entropy alloys provide a platform for investigating how chemical disorder modifies the well-established pressure-induced structural evolution of close-packed $4f$ lanthanides. Here, we study TbHoEr and TbHoDy using synchrotron X-ray diffraction in diamond anvil cells. Both alloys transform from the ambient hexagonal close-packed (hcp) structure to a double hexagonal close-packed (dhcp) phase, while no well-resolved bulk Sm-type intermediate phase is observed. For TbHoEr, compression to 70 GPa further reveals a high-pressure rhombohedral hR24 phase. Unlike the constituent heavy lanthanides, however, both alloys bypass the intermediate Sm-type phase. Two-dimensional diffraction images further reveal streak-like diffuse scattering in the transition region, indicating stacking disorder and limited stacking coherence along the close-packed direction. These observations indicate that the transformation proceeds through a stacking-disordered close-packed state rather than through a well-ordered bulk Sm-type phase. We propose that configurational disorder, local lattice distortion, stacking-fault energetics, and transformation kinetics collectively suppress the development of long-range Sm-type order. The results demonstrate that medium-entropy alloying can fundamentally modify pressure-induced stacking pathways in rare-earth materials under extreme conditions.
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All authors Raimundas Sereika, Matthew P. Clay, Kallol Chakrabarty, Yogesh K. Vohra

Materials Science

An Interfacial Balance Rule Governs Binder-Electrolyte Coupling in Lead-Free Perovskite Energy Storage

Arun Kumar, Ayush Kumar Pandey, Ankur Yadav et al. (+4 more)

Electrode binders are conventionally regarded as inert structural components. Here, we show that in lead-free perovskite supercapacitors, the binder defines the optimal electrolyte composition. Across a factorial matrix of poly(vinylidene fluoride) (PVDF) loadings and LiTFSI concentrations in CsSnCl$_3$ electrodes, the capacitance optimum shifts systematically with binder content along a single linear relationship, described by the Interfacial Balance Rule ($\lambda+\theta=1$), where $\lambda$ and $\theta$ are the normalized lithium-supply and polymer contributions at the optimized interfacial state. The same relationship holds for hybrid MASnCl$_3$, showing that the optimum is governed by the polymer-electrolyte interface rather than the perovskite lattice chemistry. Simulations using a pre-trained MACE machine-learned interatomic potential show that PVDF adopts a planar configuration on CsSnCl$_3$ and simultaneously interacts with cationic and anionic sites. This configuration homogenizes lithium adsorption energetics, introduces fluorine-mediated coordination, and confines lithium to a two-dimensional interfacial region while preserving lateral mobility. Tuning polymer coverage through surface density and chain length reveals a finite interfacial lithium accommodation capacity that marks the onset of out-of-plane aggregation. The Interfacial Balance Rule provides a macroscopic descriptor of this finite interfacial resource, balancing polymer-mediated lithium stabilization against limited accommodation space. Binder loading is therefore an active design parameter for polymer-regulated energy-storage interfaces.
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All authors Arun Kumar, Ayush Kumar Pandey, Ankur Yadav, Vishnu Saraswat, Shiladitya Sengupta, Abhishek Tewari, Monojit Bag

Materials Science

Denoising Diffusion Monte Carlo Electron Densities with Physically Informed Variance Stabilization: From Fourier Filters to 3D UNETs

Kenneth O. Berard, Brenda Rubenstein and Jaron T. Krogel

Obtaining accurate electron densities is important for the fundamental description of molecular and condensed matter systems, as well as for the development of next-generation density functionals. Diffusion Monte Carlo (DMC), in particular, is known to produce benchmark-quality data; however, the predicted real-space electron densities contain substantial amounts of statistical noise. In this work, we study denoising approaches for DMC densities, judged on the basis of the information-theoretic Jensen-Shannon divergence. The denoising is facilitated by an approximate heteroscedastic to homoscedastic transformation leveraging the density functional theory density as a physical prior. We systematically compare a range of denoising techniques-including Fourier transform, regression, and 3D UNETs-on materials showing a wide range of density variations: carbon diamond, blue phosphorus, and rutile VO2. Our results indicate that simple flattened machine learning models and 2D image-based models introduce line artifacts and struggle to capture the full spatial correlation. In contrast, when using variance stabilization, regression methods outperform all others in both the high and low- noise limits across all materials considered. The best denoisers reduce the required cost of density-generating DMC simulations by 10-100x, providing a promising route forward for application in noise-sensitive tasks such as DFT functional inversion.
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Materials Science

Machine Learning Framework for Magnetic Candidate Discovery in Cerium-Based Compounds

Joshua A. Torres, Yaser M. Banad, Benjamin O. Tayo et al. (+1 more)

Cerium (Ce), the most abundant lanthanide, offers significant potential for addressing shortages in high-performance magnetic materials, particularly through the discovery of compounds suitable for gap magnets. However, predicting Ce-based ferromagnets with uniaxial magnetic anisotropy remains challenging because their magnetic behavior depends strongly on crystal structure, exchange geometry, and electronic interactions. Here, we present a physics-guided computational framework to screen known Ce-based crystal structures and identify promising Ising ferromagnets for future synthesis. A Random Forest classifier uses seven structural and SOAP descriptors, including unit-cell volume, density, atomic sites, space group, atomic density, Ce SOAP overlap, and transition-metal SOAP overlap, to prioritize candidate compounds. Selected crystallographic structures are then analyzed using Ising-model Monte Carlo simulations to characterize phase behavior and critical properties. Critical exponents extracted from simulated phase transitions provide quantitative insight into magnetic regimes and anisotropy-related effects. We further employ autoencoders trained on affinity-based features from simulated spin configurations to identify latent signatures of phase evolution and transition behavior. Together, this framework integrates structural screening, statistical-mechanical simulation, and machine learning to accelerate the identification of promising Ce-based magnetic materials and provide candidates for experimental synthesis and validation.
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All authors Joshua A. Torres, Yaser M. Banad, Benjamin O. Tayo, Tej Nath Lamichhane