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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Monday 29 December

Materials Science

Surface Hydrogen Coverage on Pt/Graphene Measured by Carbon Ion ERDA

Chien-Hsu Chen, Huan Niu, Hung-Kai Yu et al. (+2 more)

Graphene, a two-dimensional monolayer of sp2-bonded carbon atoms in a honeycomb lattice, possesses exceptional electronic, mechanical, and quantum properties, making it highly attractive for energy storage, spintronics, and microelectronics. Functionalizing graphene with platinum (Pt) adatoms can further enhance its properties, particularly for hydrogen storage applications. In this study, we experimentally investigate hydrogen adsorption on Pt-decorated graphene using Elastic Recoil Detection Analysis (ERDA). By irradiating the Pt/graphene film with a 4.1 MeV C2+ ion beam and detecting recoiled hydrogen atoms at a 30 degree scattering angle, we obtain the hydrogen depth profile, providing critical insights into its storage behavior.
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All authors Chien-Hsu Chen, Huan Niu, Hung-Kai Yu, Tsung Te Lin, Yao-Tung Hsu

Materials Science

Unveiling Solvent Effects on Femtosecond Laser-Irradiated Au/Fe3O4 Colloidal Nanoparticles: The Acetone Effect

Stéphane Mottin, Żaneta Świątkowska-Warkocka, Marta Wolny-Marszałek et al. (+1 more)

The interplay between laser parameters and liquid environments dictates the outcome of femtosecond laser-induced nanoparticle modification. We present a study of gold and iron oxide nanoparticles in water and a water-acetone mixture, irradiated with femtosecond lasers at 808 nm and 404 nm. While aggregation was observed in pure water at both wavelengths, the results revealed a strong stability and a rather unexpected wavelength-dependency in the acetone-water mixture. In this case, 808 nm irradiation produced some decrease in nanoparticle sizes, while 404 nm led to some nanoparticle growth. As a result, the acetone effect is found to be twofold: (i) on one hand, it helps to prevent aggregation; (ii) on the other hand, it acts as a reactive medium allowing to tune the nanoparticle size and composition simply by changing laser wavelength. So, this work emphasizes that solvent physical properties as well as laser-induced chemical processes in the solvent are not merely secondary effects but can dominate the final morphological outcome, providing a predictive framework for nanoparticle synthesis.
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All authors Stéphane Mottin, Żaneta Świątkowska-Warkocka, Marta Wolny-Marszałek, Tatiana E Itina

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

Fate of Pomeranchuk effect in ultrahigh magnetic fields

Naofumi Matsuyama, So Yokomori, Toshihiro Nomura et al. (+8 more)

The Pomeranchuk effect is a counterintuitive phenomenon where liquid helium-3 (3He) solidifies under specific pressures, not when cooled, but when heated. This behaviour originates from the magnetic entropy of nuclear spins, suggesting a magnetic field should influence it. However, its detailed response to magnetic fields remains elusive due to the small nuclear magneton of 3He and lack of analogous fermion systems. Here, we show that an electron system also exhibit the Pomeranchuk effect, where the Fermi liquid state solidifies in a high magnetic field, unlike conventional electron systems where a field melts an electron solid into a metal. Remarkably, the electron system displays a reentrant liquid state in ultrahigh fields. These responses are explained by changes in magnetic entropy and magnetisation, extending the underlying physics to 3He. Our findings clarify magnetic-field impact on the Pomeranchuk effect and open avenues for magnetic control of chemical interactions.
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All authors Naofumi Matsuyama, So Yokomori, Toshihiro Nomura, Yuto Ishii, Hiroaki Hayashi, Hajime Ishikawa, Kazuki Matsui, Hatsumi Mori, Koichi Kindo, Yasuhiro H. Matsuda, Shusaku Imajo

Materials Science

A Dual-Gate Altermagnetic Tunnel Junction Based on Bilayer Cr$_{2}$SeO

Yunfei Gao, Aolin Li, Zesen Fu et al. (+3 more)

Altermagnets demonstrate significant potential in spintronics due to their unique non-relativistic spin-splitting properties, yet altermagnetic devices still face challenges in efficiently switching logic states. Here, we report electrostatically controllable spin-momentum locking in bilayer Cr$_{2}$SeO and design a dual-gate altermagnetic tunnel junction (AMTJ), which can switch between high and low resistance states without switching the Néel vector. First-principles calculations demonstrate that vertical electric field can induce significant spin splitting in bilayer Cr$_{2}$SeO. Reversing the electric field direction can alter the spin-momentum locking in bilayer Cr$_{2}$SeO. Leveraging this electric-field-tunable spin splitting, the dual-gate AMTJ exhibits an ultrahigh tunneling magnetoresistance (TMR) ratio of $10^{7}$. This work provides theoretical support for the design of fully electrically controlled AMTJs and demonstrates their great potential for applications in spintronic devices.
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All authors Yunfei Gao, Aolin Li, Zesen Fu, Bei Zhang, Haiming Duan, Fangping Ouyang

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

Isotope Effects and the Negative Thermal Expansion Phenomena in Ice and Water

B. I. Min and J.-S. Kang

H2O is a unique substance with exceptional thermal properties arising from the subtle interplay between its electronic, phononic, and structural degrees of freedom. Of particular interest in H2O are the negative thermal expansion (NTE) phenomena, observed in its solid phase (ice) at low temperature, and in its liquid phase (water) near the freezing temperature. Furthermore, ice and water exhibit the abnormal volume isotope effect (VIE), where volume expansions occur when replacing H with its heavier isotope, deuterium (D). In order to capture more conceptual and intuitive understanding of intriguing NTE and VIE phenomena in ice and water, we have explored isotope effects in their NTE and melting properties by employing a type of Born-Oppenheimer-approximation approach and the Lindemann criterion. Our findings demonstrate that unusual isotope effects in these phenomena stem from competition between zero-point-energy phonons, thermal phonons, and the hydrogen bonding in H2O. All these components originate from nuclear quantum mechanical (QM) processes, revealing that QM physics plays a crucial role in the seemingly classical ice/water systems.
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Materials Science

Anisotropic Photostriction and Strain-modulated Carrier Lifetimes in Orthorhombic Semiconductors

Jianxin Yu, Kun Yang, Jiawen Li et al. (+3 more)

We demonstrate anisotropic photostriction in two-dimensional orthorhombic semiconductors using time-dependent density functional theory. By tracing the dynamics of photoexcited carriers, we establish a quantitative link between carrier density and lattice deformation in layered black phosphorus and germanium selenides. The structural response exhibits significant anisotropy, featuring lattice expansion along the armchair direction and contraction along the zigzag direction, which is attributed to the interplay between charge redistribution and intrinsic lattice anisotropy. Both the magnitude and orientation of the photostrictive strains can be tuned by photodoping densities, enabling precise control over the photoinduced response. Notably, the photoinduced strains significantly increase carrier recombination lifetimes by suppressing nonradiative recombination, primarily due to the enlarged bandgap and weakened nonadiabatic coupling. These results provide microscopic insight into the origin of anisotropic photostriction in low-dimensional systems and lay the groundwork for light-controllable, directionally sensitive optomechanical devices at the atomic scale.
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All authors Jianxin Yu, Kun Yang, Jiawen Li, Sheng Meng, Xinghua Shi, Jin Zhang

Sunday 28 December

Materials Science

Compositional and Oxygen-Vacancy Effects on Phase Stability and Electronic Properties in Ceria-Based Lanthanide High-Entropy Oxides

Mary Kathleen Caucci, Billy E. Yang, Gerald R. Bejger et al. (+5 more)

Cerium-based lanthanide high-entropy oxides (LN-HEOs) are promising candidates for solid-state electrolyte (mass transport) applications due to their ability to accommodate high concentrations of oxygen vacancies while retaining a fluorite-derived structure. However, synthesis often yields undesired ordered oxygen-deficient phases, such as bixbyite, depending on composition and processing conditions. We utilize first-principles density functional theory (DFT) calculations to systematically investigate phase stability in the model system Ce$_x$(YLaPrSm)$_{1-x}$O$_{2-\delta}$, with the aim of elucidating the thermodynamic factors governing fluorite-bixbyite competition and identifying structure-property relationships to oxygen transport. By independently varying cerium concentration and oxygen vacancy content, we predict that the transition from disordered fluorite to ordered bixbyite is driven primarily by compositional and vacancy-ordering effects, rather than through changes in cation valence. Free-energy analysis reveals that at high vacancy concentrations, bixbyite is enthalpically favored due to ordered oxygen vacancies, while fluorite is stabilized at lower vacancy concentrations and higher cerium content through configurational entropy of the anion sublattice. These DFT results clarify the competing energetic contributions that control phase stability and structure-valence relationships in LN-HEOs and establishes a mechanistic framework for designing vacancy-tolerant oxide electrolytes with tunable phase behavior.
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All authors Mary Kathleen Caucci, Billy E. Yang, Gerald R. Bejger, Jacob T. Sivak, Christina M. Rost, Saeed S.I. Almishal, Jon-Paul Maria, Susan B. Sinnott

Materials Science

A Simple and Efficient Non-DFT-Based Machine Learning Interatomic Potential to Simulate Titanium MXenes

Luis F. V. Thomazini and Alexandre F. Fonseca

Titanium MXenes are two-dimensional inorganic structures composed of titanium and carbon or nitrogen elements, with distinctive electronic, thermal and mechanical properties. Despite the extensive experimental investigation, there is a paucity of computational studies at the level of classical molecular dynamics (MD). As demonstrated in a preceding study, known MD potentials are not capable of fully reproducing the structure and elastic properties of every titanium MXene. In this study, we present a simply trained, but yet efficient, non-density functional theory-based machine learning interatomic potential (MLIP) capable of simulating the structure and elastic properties of titanium MXenes and bulk titanium carbide and nitride with precision comparable to DFT calculations. The training process for the MLIP is delineated herein, in conjunction with a series of dynamical tests. Limitations of the MLIP and steps towards improving its efficacy to simulate titanium MXenes are discussed.
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Materials Science · Cross-listed from physics.comp-ph

Masgent: An AI-assisted Materials Simulation Agent

Guanghen Liu, Songge Yang and Yu Zhong

Density functional theory (DFT) and machine learning potentials (MLPs) are essential for predicting and understanding materials properties, yet preparing, executing, and analyzing these simulations typically requires extensive scripting, multi-step procedures, and significant high-performance computing (HPC) expertise. These challenges hinder reproducibility and slow down discovery. Here, we introduce Masgent, an AI-assisted materials simulation agent that unifies structure manipulation, automated VASP input generation, DFT workflow construction and analysis, fast MLP-based simulations, and lightweight machine learning (ML) utilities within a single platform. Powered by large language models (LLMs), Masgent enables researchers to perform complex simulation tasks through natural-language interaction, eliminating most manual scripting and reducing setup time from hours to seconds. By standardizing protocols and integrating advanced simulation and data-driven tools, Masgent lowers the barrier to performing state-of-the-art computational methodologies, enabling faster hypothesis testing, pre-screening, and exploratory research for both new and experienced practitioners.
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Materials Science

A fluctuation-free pathway for a topological magnetic phase transition

Riccardo Battistelli, Lukas Körber, Kai Litzius et al. (+27 more)

Topological magnetic textures are particle-like spin configurations stabilized by competing interactions. Their formation is commonly attributed to fluctuation-driven, first-order nucleation processes requiring activation over a topological energy barrier. Here, we demonstrate an alternative barrier- and fluctuation-free pathway for nucleating topological magnetic textures, triggered in our experiments by an excitation-induced spin reorientation transition. By combining x-ray imaging, scattering and micromagnetic simulations, we show that the system follows a deterministic cascade of symmetry-breaking phase transitions after excitation. First, the system undergoes a second-order phase transition from a homogeneous state to weak stripe domains, then a first-order transition to topologically trivial bubbles, and finally a topological switching event into skyrmionic textures. Through simulations, we generalize our findings and demonstrate that this pathway is active in a vast range of low-anisotropy materials. This previously unrecognized, spontaneous transition pathway suggests strategies for rapid, low-energy generation of topological spin textures and points to a general role of intrinsic modulational instabilities in phase transitions beyond magnetism.
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All authors Riccardo Battistelli, Lukas Körber, Kai Litzius, Matthieu Grelier, Krishnanjana Puzhekadavil Joy, Michael Schneider, Steffen Wittrock, Daniel Metternich, Tamer Karaman, Lisa-Marie Kern, Christopher Klose, Simone Finizio, Josefin Fuchs, Christian M. Günther, Tim A. Butcher, Karel Prokeš, Raluca Boltje, Manas Patra, Sebastian Wintz, Markus Weigand, Sascha Petz, Horia Popescu, Jörg Raabe, Nicolas Jaouen, Stefan Eisebitt, Vincent Cros, Bastian Pfau, Johan H. Mentink, Nicolas Reyren, Felix Büttner

Materials Science

Fast and accurate Fe-H machine-learning interatomic potential for elucidating hydrogen embrittlement mechanisms

Kazuma Ito

Understanding the mechanisms of hydrogen embrittlement (HE) is essential for advancing next-generation high-strength steels, thereby motivating the development of highly accurate machine-learning interatomic potentials (MLIPs) for the Fe-H binary system. However, the substantial computational expense associated with existing MLIPs has limited their applicability in practical, large-scale simulations. In this study, we construct a new MLIP within the Performant Implementation of the Atomic Cluster Expansion (PACE) framework, trained on a comprehensive HE-related dataset generated through a concurrent-learning strategy. The resulting potential achieves density functional theory-level accuracy in reproducing a wide range of lattice defects in alpha-Fe and their interactions with hydrogen, including both screw and edge dislocations. More importantly, it accurately captures the deformation and fracture behavior of nanopolycrystals containing hydrogen-segregated general grain boundaries-phenomena not explicitly represented in the training data. Despite its high fidelity, the developed potential requires computational resources only several tens of times greater than empirical potentials and is more than an order of magnitude faster than previously reported MLIPs. By delivering both a high-precision and computationally efficient potential, as well as a generalizable methodology for constructing such models, this study significantly advances the atomic-scale understanding of HE across a broad range of metallic materials.
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Materials Science

Spin-Reorientation Dynamics and Strong-Spin Phonon Coupling in Ce-substituted SmCrO$_3$

Shaona Das, Ravi Kiran Dokala and Subhash Thota

We report the influence of Ce$^{3+}$ substitution on the magnetic structures and phonon dynamics in SmCrO$_3$ perovskites. Magnetic landscapes are spanned by long-range canted anti-ferromagnetism, AFM with Neel temperatures $\sim$196 K accompanied by spin-reorientation transitions, T$_{SRPT}$ at 42 K. In Sm$_{0.9}$Ce$_{0.1}$CrO$_3$ (SCCO), Ce$^{3+}$ substitution at Sm$^{3+}$ sites transform the weak ferromagnetic (FM) $\Gamma_4$ state into robust AFM $\Gamma_1$ configuration through a gradual crossover. Such coexistence of magnetic spin configurations $\Gamma_1$(AFM) to $\Gamma_4$ (WFM) results in the enhanced high coercive field and a pronounced exchange bias-field, $H_{\mathrm{EB}}$ $\sim$ 2 kOe. Spin-only driven magneto-crystalline anisotropy of Cr$^{3+}$ and spin-orbit driven magnetic moment in Sm$^{3+}$, and Ce$^{3+}$ exhibits spin-phonon coupling through $A_{1g}(6)$ mode in SCCO are consistent with the temperature dependent spectral features of the isostructural magnetic systems and quite significant in SCCO which is in accordance with the higher structural distortion in SCCO. These results demonstrate that site-specific R$^{3+}$ substitution modulates lattice distortions, spin-phonon coupling, and spin-orbit interactions, offering pathways to optimize perovskites for diverse spintronic applications.
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Materials Science

Giant-Magnetocaloric effect and phonon dynamics in (GdCe)CrO$_3$

Ravi Kiran Dokala, Shaona Das and Subhash Thota

We investigate the effect of Ce$^{3+}$ substitution on the magnetic ordering and phonon dynamics of the GdCrO$_3$ orthorhombic perovskite. The Ce doped compound exhibits long-range canted antiferromagnetism with Neel transitions, T$_N$ at $\sim$ 173 K, accompanied by spin-flip, T$_{SF}$ at $\sim$ 10 K. Ce$^{3+}$ incorporation drives a modification of the spin-flip transition from the $\Gamma{(G_x,A_y,F_z)}$ configuration to $\Gamma$ inducing a reorientation of the spin axis between the (001) and (001) crystallographic planes. This spin reorientation is governed by Zeeman energy and produces pronounced field-induced irreversibility between FCC and FCW magnetization processes. The substituted compound Gd$_{0.9}$Ce$_{0.1}$CrO$_3$ (GCCO) exhibits a remarkably large magnetic entropy change, $\Delta$ S $\sim$ 45-40 J/kg-K for $\Delta$ H = 90-70 kOe at 3 K among the highest reported for rare-earth orthochromites. The interplay of spin-only magnetocrystalline anisotropy from Cr$^{3+}$ and spin-orbit-driven magnetic moments of Gd$^{3+}$ and Ce$^{3+}$ results in pronounced spin-phonon coupling, manifested through the A$_{1g}$(6) vibrational mode. The observed temperature-dependent spectral evolution is consistent with behaviour reported in isostructural magnetic perovskites.
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Materials Science

Real-time Observation of Thermal Surface Recovery in $SrVO_3$

Amit Cohen, Jonathan Ludwick, Ward Yahya et al. (+4 more)

$SrVO_3$ (SVO), a model correlated metal and a promising transparent conducting oxide, develops a several-nanometer-thick near-surface region (NSR), rich in $V^{5+}$ species under ambient conditions. This oxidized layer obscures the intrinsic correlated-metallic $V^{4+}$ character and limits both fundamental studies of the physics and the material's integration into electronic devices. Here, we demonstrate a direct and controllable approach for recovering the metallic SVO surface by thermally reducing the NSR under ultra-high vacuum. Real-time in-situ X-ray photoelectron spectroscopy (XPS) reveals a sharp transformation from a $V^{5+}$-dominated surface to mixed valence states, dominated by $V^{4+}$, and a recovery of its metallic character. Ex-situ X-ray diffraction (XRD), atomic force microscopy (AFM), and high-resolution scanning electron microscopy (HR-SEM) suggest that this transformation is accompanied by mass redistribution and partial oxygen loss, leading to nanoscale surface reorganization and modest lattice expansion. While thermodynamic considerations motivate evaluation of a $V_2O_5$ volatilization pathway, the combined experimental evidence instead points toward a predominantly structural surface reorganization. These findings establish a practical method for obtaining predominantly $V^{4+}$ SVO surfaces without protective capping layers, a capability that expands the utility of SVO for advanced spectroscopies, interface engineering, and oxide-electronics device integration.
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All authors Amit Cohen, Jonathan Ludwick, Ward Yahya, Maria Baskin, Lishai Shoham, Tyson C. Back, Lior Kornblum

Materials Science

Plastic inorganic Sn2BiS2I3 semiconductor enabled deformable and flexible electronic tongue for heavy metal detection

Qiao Wang and Pengyue Zhao

Deformable and flexible electronics have garnered significant attention due to their distinctive properties; however, their current applications are primarily limited to the thermoelectric domain. Expanding the range of these electronics and their application scope represents a pivotal trend in their development. In this work, a plastic inorganic semiconductor material, Sn2BiS2I3, with a band gap of 1.2 eV was synthesized and fabricated into a three-electrode flexible and portable electronic tongue capable of detecting heavy metal elements. The electronic tongue device exhibits exceptional linearity and demonstrates resistance against interference from impurity ions. The linear regression equation is expressed as Y=0.24+19.06X, yielding a linear coefficient of approximately 0.96, and the detectable limit stands at around 1.1 ppb, surpassing the 2.0 ppb limit of the ICP-AES instrument. Furthermore, mechanical testing reveals the favorable plasticity of Sn2BiS2I3, as evidenced by the absence of cracks during nanoindentation. The indentation hardness of Sn2BiS2I3 is approximately 1.67 GPa, slightly exceeding the hardness of Cu, which is 1.25 GPa. This study expands the repertoire of deformable and flexible electronics, offering a new and exceptional choice for biomimetic tongue sensor materials.
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Saturday 27 December

Materials Science

Enabling high giant magnetoresistance in simple spin valves with ultrathin seed and free layers

Sachli Abdizadeh, Rachel E. Maizel, Dylan L. Haymore et al. (+3 more)

Emerging spin-orbit-torque devices based on spin valves require a thin magnetic free layer to maximize the torque per moment. However, reducing the free-layer thickness to $\lesssim 2$ nm deteriorates the giant magnetoresistance (GMR) signal for electrical readout. Here, we demonstrate that the addition of a 1-nm Cu seed layer promotes sharp interfaces in simple polycrystalline Co-based spin valves, enabling high GMR ratios of 5-7% at sub-2-nm free-layer thicknesses. Our work offers a pathway for engineering high-signal GMR readout in spin-orbit-torque digital memories and neuromorphic computers.
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All authors Sachli Abdizadeh, Rachel E. Maizel, Dylan L. Haymore, Jing Zhao, F. Marc Michel, Satoru Emori

Materials Science · Cross-listed from physics.optics

Elastomer-based whispering gallery mode microlasers with low Young's modulus for biosensing applications

Melisa A. Bayrak, David Ripp, Joseph S. Hill et al. (+1 more)

Sensing biological forces with microscopic lasers is an emerging technique that offers significant advantages over conventional fluorescent probes and imaging-based techniques. However, the limited availability of suitable deformable or elastic microlaser materials is restricting the scale of forces that can be detected which strongly narrows their overall applicability. Here, we describe the synthesis of spherical whispering gallery mode microbead lasers from a commercially available elastomer material in a microfluidic system with high viscosity. Upon doping with an organic dye, the microbeads show multimode lasing with thresholds in the range of 2-11 nJ. Measurements of the mechanical properties reveal that the width of the laser modes is directly proportional to the applied external force. The measured mean Young's modulus is 36 kPa, comparable to the stiffness of single cells and soft tissues. We also demonstrate that elastomer microlasers are stable under cell culture conditions for several days and observe splitting of the laser modes for intracellular microlasers. The observed properties render elastomer microlasers as a robust material platform for biointegrated lasers that also allows further tuning of the mechanical and optical properties for tailored force sensing inside cells, tissues, and small animals.
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All authors Melisa A. Bayrak, David Ripp, Joseph S. Hill, Marcel Schubert

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

Orbital homology of p and t2g orbitals in models and materials

Gang v. Chen and Congjun Wu

The nominal divide between $p$- and $d$-electron systems often obscures a deep underlying unity in condensed matter physics. This review elucidates the orbital homology between the $p$ and $t_{2g}$ orbital manifolds, establishing the correspondence that extends from minimal model Hamiltonians to the complex behaviors of real quantum materials. We demonstrate that despite their distinct atomic origins, these orbitals host nearly identical hopping physics and spin-orbit coupling, formalized through an effective ${l=1}$ angular momentum algebra for the $t_{2g}$ case. This equivalence allows one to transpose physical intuition and theoretical models developed for $p$-orbital systems directly onto the more complex $t_{2g}$ materials, and vice versa. We showcase how this paradigm provides a unified understanding of emergent phenomena, including non-trivial band topology, itinerant ferromagnetism, and unconventional superconductivity, across a wide range of platforms, from transition metal compounds, two-dimensional oxide heterostructures, and iron-based superconductors, to $p$-orbital ultracold gases. Ultimately, this $p$-$t_{2g}$ homology serves not only as a tool for interpretation but also as a robust design principle for engineering novel quantum states.
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Materials Science

Temperature and crystallographic orientation dependence of the anisotropic magnetoresistance in epitaxial Fe65Co35 thin films

A. Paz Jalca, W. H. Painado Lozano, D. E. Gonzalez-Chavez et al. (+7 more)

In this work, we study the anisotropic magnetoresistance (AMR) behavior of [001] epitaxial Fe65Co35 thin films along different crystallographic directions as a function of temperature. The AMR ratio is found to strongly depend on the current orientation relative to the crystal axes, reaching 0.16 % and 0.10 % at room temperature when the current is applied along the magnetic hard and easy axes, respectively. Moreover, the AMR ratio decreases at different rates as the temperature is reduced to 80 K. The longitudinal and transverse magnetoresistance curves were fitted using the Stoner-Wohlfarth formalism to describe the magnetization reversal path and to extract the magnetic anisotropy constants. The fitted cubic and uniaxial anisotropy constants are Kc = -2.36 kJ/m3 and Ku = 2.18 kJ/m3, verifying the change in the cubic anisotropy compared to Fe-richer Fe100-xCox compositions. These results demonstrate that by tailoring the crystalline orientation and temperature dependence of AMR, epitaxial Fe65Co35 thin films can enable the design of magnetic sensors with tunable sensitivity.
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All authors A. Paz Jalca, W. H. Painado Lozano, D. E. Gonzalez-Chavez, L. Saba, D. Pérez-Morelo, J. E. Gómez, A. Butera, A. Gutarra Espinoza, L. M. Leon Hilario, L. Avilés-Félix

Materials Science

Unravelling 2,4-D – biochar interactions by molecular dynamics: adsorption modes and surface functionalities

Rosie Wood, Ondřej Mašek and Valentina Erastova

We report a molecular dynamics investigation of 2,4-dichlorophenoxyacetic acid (2,4-D) adsorption at the aqueous-biochar interface using experimentally constrained woody biochar models representative of softwood-derived biochars produced at 400, 600 and 800 ${\deg}$C. The models reproduce experimental descriptors (H/C, O/C, aromaticity, true density, and surface functionality) of their experimental counterparts, and simulations enable calculation of adsorption isotherms that align with available experimental measurements. Our results reveal that 2,4-D$^{-}$ uptake is governed by a synergy of three interaction classes: (i) ${\pi}$-${\pi}$ and ${\pi}$-Cl contacts with graphitic domains with either parallel or perpendicular alignments, (ii) polar interactions including H-bonding to surface -OH and other oxygen-containing groups, and (iii) Na$^{+}$-mediated cation bridging that links 2,4-D$^{-}$ anion to surface oxygens, that would have an increasing relevance for biochars near or above the pH at point of zero charge. Notably, we found that low-temperature produced biochars, which retain higher densities of surface O functionalities, exhibit higher adsorption per unit surface area due to cooperative polar interactions alongside ${\pi}$-${\pi}$ binding, whereas medium-to-high temperature biochars rely more on ${\pi}$-${\pi}$ and cation-bridging mechanisms. The distinct adsorption distances measured emphasize surface heterogeneity and porosity. Taken together, these atomistic insights corroborate experimental observations and yield actionable guidance for the rational design of biochars for remediation of anionic herbicides, highlighting how surface functionality and solution chemistry can be tuned to optimize sorption. Our approach provides a general framework to interrogate pollutant-biochar interactions and to inform remediation strategies.
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Materials Science · Cross-listed from cs.AI

Multi-AI Agent Framework Reveals the "Oxide Gatekeeper" in Aluminum Nanoparticle Oxidation

Yiming Lu, Tingyu Lu, Di Zhang et al. (+2 more)

Aluminum nanoparticles (ANPs) are among the most energy-dense solid fuels, yet the atomic mechanisms governing their transition from passivated particles to explosive reactants remain elusive. This stems from a fundamental computational bottleneck: ab initio methods offer quantum accuracy but are restricted to small spatiotemporal scales (< 500 atoms, picoseconds), while empirical force fields lack the reactive fidelity required for complex combustion environments. Herein, we bridge this gap by employing a "human-in-the-loop" closed-loop framework where self-auditing AI Agents validate the evolution of a machine learning potential (MLP). By acting as scientific sentinels that visualize hidden model artifacts for human decision-making, this collaborative cycle ensures quantum mechanical accuracy while exhibiting near-linear scalability to million-atom systems and accessing nanosecond timescales (energy RMSE: 1.2 meV/atom, force RMSE: 0.126 eV/Angstrom). Strikingly, our simulations reveal a temperature-regulated dual-mode oxidation mechanism: at moderate temperatures, the oxide shell acts as a dynamic "gatekeeper," regulating oxidation through a "breathing mode" of transient nanochannels; above a critical threshold, a "rupture mode" unleashes catastrophic shell failure and explosive combustion. Importantly, we resolve a decades-old controversy by demonstrating that aluminum cation outward diffusion, rather than oxygen transport, dominates mass transfer across all temperature regimes, with diffusion coefficients consistently exceeding those of oxygen by 2-3 orders of magnitude. These discoveries establish a unified atomic-scale framework for energetic nanomaterial design, enabling the precision engineering of ignition sensitivity and energy release rates through intelligent computational design.
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All authors Yiming Lu, Tingyu Lu, Di Zhang, Lili Ye, Hao Li

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

Magnetic field and pressure tuning of the heavy fermion antiferromagnet CePdIn

Bin Shen, Feng Du, Rui Li et al. (+8 more)

Frustrated Kondo lattices are ideal platforms for studying how both the Kondo effect and quantum fluctuations compete with the magnetic exchange interactions that drive magnetic ordering. Here, we investigate the effect of tuning the heavy-fermion compound CePdIn, which crystallizes in the geometrically frustrated ZrNiAl-type structure, using applied magnetic fields and hydrostatic pressure. At ambient pressure, CePdIn exhibits two magnetic transitions, one at $T_{\rm{N}} \approx 1.65$ K and another at $T_{\rm{M}} \approx 1.15$ K, which are both suppressed by applied $c$-axis fields. Upon applying pressure in zero magnetic field, there is a non-monotonic evolution of $T_{\rm{N}}$, which decreases to 0.8 K at 2.3 GPa, before abruptly increasing to 1.5 K at 2.6 GPa. At higher pressures, $T_{\rm{N}}$ has a weak pressure dependence, and vanishes near 5 GPa. Together with the high-pressure phase being more robust to applied fields, these results suggest two distinct antiferromagnetic phases in CePdIn, which are separated near 2.6 GPa, and this change may be driven by the evolution of the underlying electronic structure due to enhanced Kondo hybridization under pressure.
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All authors Bin Shen, Feng Du, Rui Li, Hang Su, Yasuyuki Shimura, Takahiro Onimaru, Kazunori Umeo, Xin Lu, Toshiro Takabatake, Michael Smidman, Huiqiu Yuan

Materials Science · Cross-listed from quant-ph

Quantum Noise Spectroscopy of Nanoscale Charge Defects in Silicon Carbide at Room Temperature

Jinpeng Liu, Yuanhong Teng, Yu Chen et al. (+8 more)

The nanoscale charge environment critically influences semiconductor physics and device performance. While conventional bulk characterization techniques provide volume-averaged defect properties, they lack the spatial resolution to resolve nanoscale charge heterogeneity and identify microscopic noise sources. Here, we utilize single PL5 centers in 4H-SiC as room-temperature broadband quantum sensors to fill in the gap. We report the first real-time, nanoscale observation of singlecharge tunneling dynamics in a commercial semiconductor at room temperature, by monitoring the random telegraph noise using optically detected magnetic resonance (ODMR). This capability enables an electrical noise imaging technique, showing distinct noise variations across different wafer substrates. By employing dynamical decoupling, we extend noise spectroscopy from near-DC to MHz frequencies, uncovering significant noise spectral density correlations across frequency bands. Finally, we probe MHz-GHz noise and identify its origin via T1 relaxation spectroscopy, obtaining the first nanoscale electron paramagnetic resonance (EPR) spectroscopic fingerprint of charge defects in SiC. These techniques open avenues for characterizing noise environments in semiconductor devices, providing critical insights for optimizing SiC fabrication processes, defect control, and advancing quantum technologies.
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All authors Jinpeng Liu, Yuanhong Teng, Yu Chen, Yixuan Wang, Chihang Luo, Jun Yin, Hao Li, Lixing You, Ya Wang, Qi Zhang, Fazhan Shi

Materials Science

Chemical state detection and charge transfer in complex oxide heterostructures via in situ Auger Electron Spectroscopy

Harish Kumarasubramanian and Jayakanth Ravichandran

Understanding and controlling the chemical states both in the bulk and at the interfaces of complex oxide thin films is essential for engineering a wide range of electronic, optical, and magnetic functionalities, which arise through emergent phenomena such as two-dimensional electron gases, interfacial magnetism, and associated phase transitions. Here, we demonstrate the use of in situ Auger Electron Spectroscopy (AES) as a powerful tool for probing oxidation states and dynamic chemical processes during the growth of complex oxide heterostructures. By leveraging the chemical sensitivity of AES to subtle changes in valence electron populations, we show that this technique can distinguish distinct oxidation states in multivalent perovskite manganate and vanadate systems with high fidelity during deposition. Furthermore, we show evidence for dynamic chemical phenomena, specifically charge transfer processes at the polar-nonpolar LaMnO3/SrTiO3 interface. Our results establish in situ AES as a powerful diagnostic tool for monitoring and controlling interfacial chemistry during thin film growth, offering a pathway toward the atomic-scale engineering of chemical states in functional oxide heterostructures.
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Materials Science

Kitaev interaction and possible spin liquid state in CoI2 and Co2/3Mg1/3I2

Yaozhenghang Ma, Ke Yang, Yuxuan Zhou et al. (+1 more)

Kitaev materials are of great interest due to their potential in realizing quantum spin liquid (QSL) states and applications in topological quantum computing. In the pursuit of realizing Kitaev QSL, a Mott insulator with strong bond-dependent frustration and weak geometric frustration is highly desirable. Here we explore Kitaev physics in the van der Waals triangular antiferromagnet (AF) CoI$_2$, through the spin-orbital states and Wannier function analyses, exact diagonalization and density matrix renormalization group study of the electronic structure and magnetic properties. We find that the high-spin Co$^{2+}$ ion is in the $J_\mathrm{eff}=1/2$ state because of strong spin-orbit coupling, and the weak trigonal elongation and crystal field contribute to the observed weak in-plane magnetic anisotropy. The strong $t_{2g}$-$e_g$ hopping via the strong Co 3$d$-I 5$p$ hybridization gives rise to a strong Kitaev interaction ($K_1$) at the first nearest neighbors (1NN), and the long Co-Co distance and the weak $t_{2g}$-$t_{2g}$ hoppings determine a weak Heisenberg interaction $J_1$. The resultant $|K_1/J_1|$ = 6.63 confirms a strong bond-dependent frustration, while the geometric frustration due to the 3NN Heisenberg interaction $J_3$ gets involved, and they all together result in the experimental helical AF order in CoI$_2$. We then propose to suppress the $J_3$ using a partial Mg substitution for Co, and indeed we find that Co$_{2/3}$Mg$_{1/3}$I$_2$ has the much reduced geometric frustration but hosts the robust bond-dependent frustration, and thus it would be a promising Kitaev material being so far closest to the QSL state.
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All authors Yaozhenghang Ma, Ke Yang, Yuxuan Zhou, Hua Wu

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

Effect of superconductivity by Nb and V substitution in kagome CaPd5

Dan Li, Zhengxuan Wang, Chuanguang Zhang et al. (+8 more)

Materials featuring kagome lattices have attracted significant research interest due to their unique geometric frustration, which gives rise to rich physical phenomena such as non-trivial topology, spin fluctuations, and superconductivity. In this work, using CaPd5 as the prototype structure, we discover and systematically investigate a new class of kagome superconductors, CaMxPd5-x (M = Nb and V) alloys. First-principles calculations confirm that these compounds are non-magnetic metals, among which four are dynamically stable: CaNb5, CaV5, CaNb2Pd3, and CaV2Pd3. CaNb5 is identified as a strong electron-phonon coupling (EPC) superconductor with the highest superconducting transition temperature (Tc) of 10.1 K, which can be further increased to 12.8 K under external pressure. In contrast, CaV5, CaNb2Pd3, and CaV2Pd3 exhibit weaker EPC and correspondingly lower Tc values. Furthermore, by applying the method of symmetry indicators, we systematically classify the topological and nodal characteristics of CaNb5, providing valuable insights for determining its superconducting pairing symmetry. Our findings demonstrate that Nb and V substitution in kagome CaPd5 provides an effective route for designing a new type of kagome superconductor with relatively high Tc. This study also offers new perspectives on topological superconductivity in kagome systems and establishes a useful guideline for discovering other superconducting materials with unique properties.
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All authors Dan Li, Zhengxuan Wang, Chuanguang Zhang, Chunlan Ma, Shijing Gong, Chuanxi Zhao, Shuaikang Zhang, Tianxing Wang, Xiao Dong, Wuming Liu, Yipeng An

Materials Science

The Role of THz Phonons in the Ionic Conduction Mechanism of $Li_7La_3Zr_2O_{12}$ Polymorphs

Amy K. Lin, Lauren F. Illa, Natan A. Spear et al. (+2 more)

Superionic conduction in solid-state materials is governed not only by static factors, such as structure and composition, but also by dynamic interactions between the mobile ion and the crystal lattice. Specifically, the dynamics of lattice vibrations, or phonons, have attracted interest because of their hypothesized ability to facilitate fast ionic conduction. Herein, we use laser-driven ultrafast impedance spectroscopy (LUIS) to resonantly excite phonons using a THz field and probe ion hopping with picosecond time resolution. We apply LUIS to understand the dynamical role of phonons in $Li_7La_3Zr_2O_{12}$ (LLZO). When in its cubic phase (c-LLZO), this garnet-type solid electrolyte has an ionic conductivity two orders of magnitude greater than its tetragonal phase (t-LLZO). Upon excitation of phonons in the 0.5-7.5 THz range, the ionic conductivity of both polymorphs is enhanced. Furthermore, we observe a similar time decay constant of the perturbation between t-LLZO and c-LLZO despite their distinct Li sublattices and migration mechanisms. Along with Raman spectra and MD-computed vibrational density of states, these findings suggest that low-energy optical phonons perturb the lattice to enhance ionic conduction independently of the underlying static properties. We propose that it does so by increasing the population of phonons which directly modulate the ion hopping pathway and by increasing the entropy of migration thereby partially counteracting the migration barrier set by the Li sublattice. Overall, this work highlights the interplay of static and dynamic factors that enables improved ionic conductivity in both highly and poorly conducting inorganic solids alike.
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All authors Amy K. Lin, Lauren F. Illa, Natan A. Spear, Geoffrey A. Blake, Scott K. Cushing

Friday 26 December

Materials Science · Cross-listed from physics.optics

Nonlinear Anisotropy in Phase-Tuned Wide-Gap Halides

L. Landivar Scott, L. M. Vogl, C. Klenke et al. (+2 more)

Silver iodide (AgI) thin films offer a compelling platform for studying nonlinear optical phenomena due to their intrinsic noncentrosymmetric lattice and direct band gap. Here, we investigate the nonlinear optical properties of AgI thin films grown by physical vapor deposition that selectively produce zincblende (\zbAgI) and wurtzite (\wzAgI) phases. Using a combination of polarization-resolved second harmonic generation (SHG) and two-photon photoluminescence (2PPL) spectroscopy, we identify clear phase- and morphology-dependent anisotropic nonlinear responses. Triangular \zbAgI $(111)$ flakes exhibit sixfold SHG symmetry and isotropic 2PPL emission, while rod-shaped \wzAgI $(101)$ samples display twofold-symmetric patterns in both SHG and 2PPL, which are explained by theories that integrate explicit polarization analysis using second- and third-order nonlinear susceptibilities. We estimate $\chi^{(2)}_\mathrm{eff}$ of 0.45 pm/V (\zbAgI) and 0.16 pm/V (\wzAgI), respectively, after correcting for multiple internal reflections and generation of SHG within the AgI film and optical interference effect in the dielectric layers. These results identify AgI as a useful single-composition halide platform for studying phase-dependent nonlinearity and establish a realistic methodology for evaluating nonlinear susceptibilities in layered materials or thin films supported by a substrate.
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All authors L. Landivar Scott, L. M. Vogl, C. Klenke, S. Puri, H. Nakamura

Materials Science · Cross-listed from cs.AI

HalluMat: Detecting Hallucinations in LLM-Generated Materials Science Content Through Multi-Stage Verification

Bhanu Prakash Vangala, Sajid Mahmud, Pawan Neupane et al. (+2 more)

Artificial Intelligence (AI), particularly Large Language Models (LLMs), is transforming scientific discovery, enabling rapid knowledge generation and hypothesis formulation. However, a critical challenge is hallucination, where LLMs generate factually incorrect or misleading information, compromising research integrity. To address this, we introduce HalluMatData, a benchmark dataset for evaluating hallucination detection methods, factual consistency, and response robustness in AI-generated materials science content. Alongside this, we propose HalluMatDetector, a multi-stage hallucination detection framework that integrates intrinsic verification, multi-source retrieval, contradiction graph analysis, and metric-based assessment to detect and mitigate LLM hallucinations. Our findings reveal that hallucination levels vary significantly across materials science subdomains, with high-entropy queries exhibiting greater factual inconsistencies. By utilizing HalluMatDetector verification pipeline, we reduce hallucination rates by 30% compared to standard LLM outputs. Furthermore, we introduce the Paraphrased Hallucination Consistency Score (PHCS) to quantify inconsistencies in LLM responses across semantically equivalent queries, offering deeper insights into model reliability.
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All authors Bhanu Prakash Vangala, Sajid Mahmud, Pawan Neupane, Joel Selvaraj, Jianlin Cheng

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

Effect of hybrid field coupling in nanostructured surfaces on anisotropic signal detection in nanoscale infrared spectroscopic imaging methods

Ayona James, Maryam Ali, Zekai Ye et al. (+21 more)

Anisotropic intensity distributions on nanostructured surfaces and polarization-sensitive spectra have been observed in a number of nanoscale infrared spectroscopic imaging methods, including nano-FTIR [Bakir et al., Molecules, 2020, 25, 4295], photothermal induced resonance (PTIR) [Waeytens et al., Analyst, 2021, 146], tapping AFM-IR [Hondl et al., ACS Meas. Sci. Au, 2025, 5, 469; Luo et al., APL, 2022, 121, 23330], infrared photoinduced force microscopy (PiF-IR) [Anindo et al., JPCC, 2025, 129, 4517; Shcherbakov et al., Rev Methods Primers, 2025, 5, 1; Ali et al., Anal. Chem., 2025, 97, 23914] and peak force infrared microscopy (PFIR) [Xie et al., JPCC, 2022, 126, 8393; Anindo, JPCC, 2025]. A recent work combining modeling and experiment demonstrated that the hybrid field coupling of the IR illumination E0 with a polymer nanosphere and a metallic AFM probe is nearly as strong as the plasmonic coupling in case of a gold nanosphere [Anindo, JPCC, 2025]. For p-polarized illumination, this results in enhanced IR absorption on the surface perpendicular to the propagation of E0 which can explain the observed anisotropic intensity distribution. An additional anisotropy may be introduced by aligned surface molecules with oriented vibrational transition moments [Bakir et al., Molecules, 2020, 25, 4295; Luo, APL, 2022]. PiF-IR is strongly surface sensitive combining an unprecedented spatial resolution < 5 nm with high spectral resolution [Shcherbakov, Rev Methods Primers, 2025; Ali, Anal. Chem., 2025], which allows, for example, to visualize nanoscale chemical variation on the surface of bacteria cells affected by antimicrobial interaction [Ali, Anal. Chem., 2025]. We compare PiF-IR hyperspectra of aligned perylene Langmuir Blodgett monolayers on nanostructured and planar gold substrates and use quantum chemical calculations of the oriented vibrational oscillators to interpret the observations.
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All authors Ayona James, Maryam Ali, Zekai Ye, Phan Thi Yen Nhi, Sharon Xavi, Mashiat Huq, Sajib Barua, Meng Luo, Yisak Tsegazab, Anna Elmanova, Robin Schneider, Olga Ustimenko, Sarmiza-Elena Stanca, Marco Diegel, Andrea Dellith, Uwe Hübner, Christoph Krafft, Jasmin Finkelmeyer, Maximilian Hupfer, Kalina Peneva, Matthias Zeisberger, Christin David, Martin Presselt, Daniela Täuber