Materials Science · Cross-listed from cs.LG
Learning ORDER-Aware Multimodal Representations for Composite Materials Design
Xinyao Li, Hangwei Qian, Jingjing Li et al. (+2 more)
Artificial intelligence has shown remarkable success in materials discovery and property prediction, particularly for crystalline and
polymer systems where material properties and structures are dominated by discrete graph representations. Such graph-central paradigm breaks down on composite materials, which possess continuous and nonlinear design spaces. General composite descriptors, e.g., fiber volume and misalignment angle, cannot fully capture the fiber distributions that determine microstructural characteristics, necessitating the integration of heterogeneous data sources through
multimodal learning. Existing
alignment-oriented frameworks have proven effective on abundant
crystal or
polymer data under discrete, unique graph-property mapping assumptions, but fail to address the highly continuous composite design space under extreme data scarcity. In this work we introduce ORDinal-aware imagE-tabulaR
alignment (ORDER), a
multimodal pretraining framework that establishes ordinality as a core principle for material representations. ORDER ensures that materials with similar target properties occupy nearby regions in the latent space, which effectively preserves the continuous nature of composite properties and enables meaningful interpolation between sparsely observed designs. We evaluate ORDER on a Nanofiber-reinforced composite
dataset and a carbon fiber T700
dataset. ORDER and its variants outperform both
alignment-oriented and customized property-aware contrastive baselines across property prediction, cross-modal
retrieval, and microstructure generation tasks. We further introduce physics-based ordinal surrogate signals avoiding the need for full property annotation during pretrain. Our work demonstrates learning continuous
multimodal features are fundamental for composite materials, and provides a reliable pathway toward data-efficient universal
multimodal intelligent systems.
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All authors Xinyao Li, Hangwei Qian, Jingjing Li, Lei Zhu, Ivor Tsang
Materials Science · Cross-listed from physics.chem-ph
A combined criterion of surface free energy and roughness to predict the wettability of non-ideal low-energy surfaces
Majid Shaker and Erfan Salahinejad
The significance of wettability between solid and
liquid substances in different fields encourages scientists to develop accurate models to estimate the resultant apparent contact angles. Surface free energy (SFE), which is principally defined for ideal (flat) surfaces, is not applicable to predict the wettability of real (rough) surfaces. This paper introduces a new parameter, namely normalized surface free energy (NSFE) as a combination of SFE and roughness, to predict the contact angle of
liquids on non-ideal low-energy surfaces. The remarkable consistency of the predicted and measured contact angles of
liquids on some rough surfaces also confirm the validity of the approach.
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Materials Science
Symmetry-protected topological polarons
Kaifa Luo, Jon Lafuente-Bartolome and Feliciano Giustino
Emergent quasiparticles in solids often exhibit unique topological properties as a result of the complex interplay between charge, orbital,
spin and
lattice degrees of freedom. Among these quasiparticles, the polaron occupies a special place as the first known manifestation of the interaction between a
fermion and a
boson field. While polarons have been investigated for almost a century, whether these quasiparticles exhibit topological properties and why remain open questions. Here, we establish the universal
symmetry principles governing the
topology of polar textures in large polarons. Using a group-theoretic analysis, we identify four distinct classes of polar textures in time-reversal-invariant systems, and we show that they carry integer topological charges. We validate this classfication by performing state-of-the-art first-principles calculations of materials representative of each class. For these materials, we compute the fingerprints of polaron
topology in Huang diffuse scattering, and propose ultrafast electron and X-ray scattering experiments to detect these quasiparticles.
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Materials Science
Embedded Ferroelectric Nanoclusters can drive Polarization Reversal in a Non-Ferroelectric Polar Film via the Proximity Effect
Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin et al. (+3 more)
Heterogeneous nucleation from defects dominates the electric field required for polarization switching of ferroelectrics. Here, we consider the switching of a nominally non-switchable polar thin film of AlN due to the proximity effect arising from embedded ferroelectric nanoclusters of Al1-xScxN. Using a Landau-Ginzburg-Devonshire thermodynamic approach and finite element modeling, we study the influence of nanocluster shape on polarization switching and domain nucleation emerging in AlN. The ferroelectric nanocluster boundary is modeled as a thin layer transitioning from Al1-xScxN to AlN. We analyze the conditions under which polarization switching in the AlN film occurs at coercive fields significantly lower than its dielectric breakdown field. In the presence of spike-like Al1-xScxN nanoclusters, the proximity effect enables switching of the spontaneous polarization in AlN and significantly reduces the corresponding coercive field. The internal field, which is depolarizing inside the AlN (due to its larger spontaneous polarization) and polarizing within the ferroelectric Al1-xScxN nanoclusters (due to its smaller spontaneous polarization), lowers the potential barrier in the clusters and nucleates nanodomains at the Al1-xScxN-AlN interface, forming localized regions of reversed polarization. Proximity effect can thus provide a pathway towards "thawing" previously "frozen" ferroelectrics through engineered nucleation for
memory, actuation and optical technologies.
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All authors Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin, Long-Qing Chen, Dean R. Evans, Venkatraman Gopalan
Materials Science
Minimal model for vortex nucleation and reversal in spherical magnetic nanoparticles
Michael P. Adams and Andreas Michels
Magnetic nanoparticles beyond the single-domain limit often develop
vortex-like magnetization textures arising from the competition between exchange and magnetostatic energies. While such states are routinely studied using micromagnetic simulations, transparent analytical descriptions of
vortex-mediated hysteresis and nucleation remain scarce. Here, we develop a semi-analytical minimal framework for
vortex states in spherical
magnetic nanoparticles. Guided by micromagnetic simulations, we introduce a parametrized
vortex magnetization Ansatz based on
hyperbolic functions that continuously interpolates between uniform and
vortex states. In this way, we achieve a complexity reduction leading to a minimal
Hamiltonian, which enables the efficient computation of magnetization curves and provides insight into
vortex-mediated magnetization reversal. As an application, we derive analytical estimates for the critical
vortex nucleation radius and field, recovering the functional form of Brown's classic result and extending it within a variational framework.
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Materials Science
Materials design based on a material-motif network and heterogeneous graphs
Anoj Aryal, Weiyi Gong, Huta Banjade et al. (+1 more)
Machine learning models for functional materials design require precise and informative representations of material systems. Common representations encode atomic composition and bonding but often do not include local coordination environments across chemically diverse
crystals. Recurring structural motifs provide a motif level description of crystalline solids and can serve as interpretable descriptors for structure property learning. To analyze the motif connectivity in materials, we construct a bipartite material motif network from 131,548 Materials Project entries, with materials and motifs as the two node sets. Edges connect materials to their constituent motifs and are weighted by motif distortion, which quantifies the strength of each material motif association. Network connectivity is analyzed to identify motif-defined material clusters that capture recurring local geometries relevant to structure property trends. Most shared motifs act as hubs that connect otherwise disconnected regions of the network, enabling motif guided screening by expanding from known motifs to nearby materials in the same neighborhoods. A network
embedding step converts this weighted connectivity into vector representations of materials. Using these motif informed
embeddings, property prediction yields a formation energy mean absolute error (MAE) of 0.157 eV per atom and a bandgap MAE of 0.601 eV. These results indicate that motif connectivity provides a compact, interpretable representation that complements existing descriptors for scalable screening and structure property modeling.
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All authors Anoj Aryal, Weiyi Gong, Huta Banjade, Qimin Yan
Materials Science
Discontinuous character of the ultrafast exciton Mott transition in monolayer WS$_2$
Subhadra Mohapatra, Samuel Palato, Nicholas Olsen et al. (+2 more)
There are conflicting predictions and reports on the character of the
exciton Mott transition (EMT) in monolayer transition metal dichalcogenides. It could be either a discontinuous or a continuous transition from the excitonic to the
plasma phase, with important implications for devices such as photoswitches. To resolve the nature of the transition in monolayer WS$_2$, we study its ultrafast optical response upon resonant photoexcitation of the A
exciton across a broad range of photoexcitation densities. In agreement with previously reported measurements we observe that the A
exciton quenches gradually with increasing excitation density. However, a detailed lineshape analysis unveils an abrupt red shift in the transient peak positions of the A and B
exciton resonances above an excitation density threshold. This is attributed to band gap renormalization arising from the formation of free charge carrier
plasma, i.e., the EMT. The
plasma phase decays with a time constant of 0.65 ps back into the excitonic state. The abrupt appearance of the
plasma phase at the threshold density suggests that the EMT is a discontinuous and not a continuous transition. This work demonstrates how transient optical spectroscopy combined with lineshape analysis of two excitonic resonances simultaneously can be used to investigate the EMT in 2D materials.
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All authors Subhadra Mohapatra, Samuel Palato, Nicholas Olsen, Julia Stähler, Lukas Gierster
Materials Science
Thermodynamics of Ferroelectric and Optical Properties in KNbO3
Aiden Ross, Venkatraman Gopalan and Long-Qing Chen
Potassium niobate (KNbO3) is a prototypical perovskite ferroelectric with large electro-optic and nonlinear optical responses, high optical damage thresholds and a rich sequence of temperature-driven phase transformations, making it a promising platform for tunable photonic devices. In this work, we develop a thermodynamic model for the coupled ferroelectric and optical properties of KNbO3. By separating the total polarization into
lattice and electronic contributions, the model provides a unified description of both the anisotropic ferroelectric and optical properties. The thermodynamic coefficients are determined by fitting to experimental measurements of the spontaneous polarization, dielectric susceptibilities,
lattice parameters, and refractive indices. Without any further fitting, the model quantitatively predicts the temperature dependence of the electro-optic and piezoelectric coefficients in close agreement with experimental measurements. By utilizing the electronic polarization equation of motion, the model further captures the optical dispersion in the near infrared to visible spectrum. This work provides the thermodynamic foundation for future studies of coupled ferroelectric and optical phenomena in KNbO3.
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Materials Science
On-the-Fly Machine-Learned Force Fields for High-Fidelity Polymer Glass Transition Simulations
Ashutosh Srivastava, Sakshi Agarwal, Shivank Shukla et al. (+2 more)
Predicting
polymer glass transition temperatures (Tg) with first-principles fidelity has long remained out of reach, as cooling multi-thousand-atom systems over a broad temperature range at acceptable rates exceeds the computational limits of ab initio molecular dynamics (AIMD). Here we employ a hybrid scheme that merges AIMD with accelerated on-the-fly (OTF) machine-learned force-field (MLFF) construction, enabling Tg prediction at
quantum-mechanical accuracy with near-classical computational cost. The OTF protocol to construct MLFFs adaptively triggers first-principles calculations only when newly encountered configurations lie outside the current model's domain of confidence, allowing robust, parameter-free MLFFs to be built from merely 1000 AIMD-sampled configurations per
polymer. These MLFFs are then utilized to perform long-time cooling simulations on amorphous supercells containing several thousand atoms. Applied across twelve
polymers spanning aromatic, aliphatic, heteroatomic, and branched chemistries, the method yields predictions in excellent accord with experiment while reducing computational cost by approximately six orders of magnitude relative to AIMD. This work establishes a new paradigm for predictive
polymer modeling, demonstrating that OTF-MLFFs provide a generalizable, accurate, and scalable route to simulating the thermophysical behavior of complex disordered materials at near
quantum-mechanical fidelity.
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All authors Ashutosh Srivastava, Sakshi Agarwal, Shivank Shukla, Harikrishna Sahu, Rampi Ramprasad
Materials Science
Detecting the full photoemission cone from laser-based ARPES experiments by leveraging deflector technology
Nicolas Gauthier, Benson Kwaku Frimpong, Dario Armanno et al. (+8 more)
Angle-resolved photoemission spectroscopy (ARPES) provides a direct access to the electronic band structure of solid and molecular systems. The momentum range accessible by this technique depends directly on the
photon energy used, and low-
photon-energy sources are insufficient to photoemit electrons over the full Brillouin zone of most
quantum materials. In addition, while electrons are emitted over a 2$\pi$ solid angle, conventional hemispherical analyzers only collect a small subset of those electrons. A previous work [RSI 92, 123907 (2021)] demonstrated that electrons emitted over a larger field-of-view can be acquired in one fixed configuration by accelerating them towards the analyzer with a bias voltage. Here, we extend this work by leveraging the deflector technology of novel ARPES hemispherical analyzers. We demonstrate the ability to detect all $2\pi$ photoemitted electrons in a fixed configuration for various materials such as gold, cuprates and transition-metal dichalcogenides. This approach is especially advantageous for time-resolved ARPES, as electron dynamics over a large momentum range can be accessed with identical measurement conditions.
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All authors Nicolas Gauthier, Benson Kwaku Frimpong, Dario Armanno, Akib Jabed, Francesco Goto, Vicky Hasse, Claudia Felser, Genda Gu, Heide Ibrahim, Francois Légaré, Fabio Boschini
Materials Science
Tunable Edelstein effect in intrinsic two-dimensional ferroelectric metal PtBi$_{2}$
Weiyi Pan and Jaroslav Fabian
The Edelstein effect, which enables charge-to-
spin conversion and is therefore highly promising for future spintronic devices, can be realized and non-volatilely manipulated in ferroelectric materials owing to their broken inversion
symmetry and switchable polarization states. To date, most ferroelectric systems reported to exhibit the Edelstein effect are
semiconductors, requiring extrinsic doping for functionality. In contrast, the Edelstein effect has rarely been reported in metallic ferroelectric systems, where doping is unnecessary. Using first-principles calculations, we predict that a pronounced Edelstein effect can be realized in the recently proposed intrinsic two-dimensional ferroelectric metal PtBi$_{2}$ monolayer, where the sign of the Edelstein coefficient is coupled to the direction of ferroelectric polarization through the polarization-switching-induced reversal of
spin textures, thereby enabling non-volatile control of charge-
spin conversion. The Edelstein effect reaches a magnitude of $10^{11}~\hbar/(\textup{A} \cdot \textup{cm})$, which is sizable compared to previously reported ferroelectric systems. Microscopically, the Edelstein effect in a PtBi$_2$ monolayer originates from competing contributions of inner Rashba-like electron pockets and outer hole pockets with opposite signs; an upward shift of the
Fermi level alters their balance and can reverse the sign of the Edelstein effect. Upon applying biaxial strain, the
Fermi-surface electronic structure is strongly modified, resulting in a pronounced change of the Edelstein effect: a 2 % compressive strain suppresses the Edelstein effect by about 50 %. Our results not only identify a promising material platform for tunable charge-
spin conversion but also provide new insights into the functional potential of metallic ferroelectric systems.
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Materials Science
Atomically Resolved Acoustic Dynamics Coupled with Magnetic Order in a van der Waals Antiferromagnet
Faran Zhou, Kyle Hwangbo, Sung Soo Ha et al. (+22 more)
Magnetoelastic coupling in van der Waals (vdW)
magnetic materials enables a unique interplay between the
spin and
lattice degrees of freedom. Characterizing the elastic responses with atomic and femtosecond resolution across the
magnetic transition is essential for guiding the design of magnetically tunable actuators and strain-mediated spintronic devices. Here, ultrafast x-ray diffraction employed at a free-electron
laser reveals that the atomic displacements, wave vectors, and dispersion relations of acoustic
phonon modes in a vdW antiferromagnet FePS$_3$ are coupled with the
magnetic order, by tracking both in-plane and out-of-plane Bragg peaks upon optical excitation across the Néel temperature (T$_N$). One transverse mode shows that a quasi-out-of-plane atomic displacement undergoes a significant directional change across T$_N$. Its quasi-in-plane wave vector is derived by the comparison between the measured sound velocity and the first-principles calculations. The other transverse mode is an interlayer shear acoustic mode whose amplitude is strongly enhanced in the
antiferromagnetic phase, exhibiting eight times stronger amplitude than the longitudinal acoustic mode below T$_N$. The atomically resolved characterization of acoustic
phonon dynamics that couple with
magnetic ordering opens opportunities for harnessing unique magnetoelastic coupling in vdW magnets on ultrafast timescales.
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All authors Faran Zhou, Kyle Hwangbo, Sung Soo Ha, Xiao-Wei Zhang, Sae Hwan Chun, Jaeku Park, Intae Eom, Qianni Jiang, Zekai Yang, Marc Zajac, Sungwon Kim, Sungwook Choi, Zhaodong Chu, Kyoung Hun Oh, Yifan Su, Alfred Zong, Elton J. G. Santos, Ting Cao, Jiun-Haw Chu, Stephan O. Hruszkewycz, Nuh Gedik, Di Xiao, Hyunjung Kim, Xiaodong Xu, Haidan Wen
Materials Science
Connecting bond switching to fracture toughness of calcium aluminosilicate glasses
Sidsel Mulvad Johansen, Tao Du, Johan F. S. Christensen et al. (+5 more)
Fracture toughness is a critical mechanical property of glasses, but a detailed understanding of its link to composition and structure is still missing. Here, focusing on the industrially important family of calcium aluminosilicate glasses, we measure the fracture toughness of two glass series using the single-edge precracked beam method, one based on tectosilicate compositions with varying silica contents and the other covering both percalcic and peraluminous compositions with varying Al/Ca ratio. To elucidate the structural origins of the variation in fracture toughness, we perform X-ray total scattering measurements and molecular dynamics simulations. Our findings show that local coordination changes of especially Al atoms, so-called bond switching, feature an overall positive correlation with fracture toughness. We also compare this variation with that in other mechanical properties, including elastic
moduli, hardness, and crack initiation resistance. We find that various structural aspects need to be considered to describe and understand the mechanical properties of calcium aluminosilicate glasses.
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All authors Sidsel Mulvad Johansen, Tao Du, Johan F. S. Christensen, Anders K. R. Christensen, Xuan Ge, Theany To, Lars R. Jensen, Morten M. Smedskjaer
Materials Science
Łucja Kipczak, Tomasz Woźniak, Chinmay K. Mohanty et al. (+10 more)
Understanding the coupling between
lattice vibrations and
magnetic order is crucial for controlling properties of two-dimensional
magnetic materials. Here, we investigate the vibrational properties of bulk and thick-flake CrCl$_\textrm{3}$ using polarization-resolved Raman spectroscopy, complemented by photoluminescence, photoluminescence excitation, and optical absorption measurements.
Symmetry analysis, supported by first-principles
phonon calculations, enables the unambiguous assignment of all eight Raman-active modes, four $\textrm{A}_\textrm{g}$ and four $\textrm{E}_\textrm{g}$, previously predicted only theoretically. Excitation-energy-dependent measurements reveal that the strong enhancement of selected
phonon modes originates primarily from interference effects rather than resonant Raman scattering. Temperature-dependent Raman spectroscopy further reveals pronounced signatures of
spin-
phonon coupling across the transition from a fully
antiferromagnetic phase, through an intermediate regime with local, domain-like
ferromagnetic order, to the paramagnetic phase, accompanied by a clear rhombohedral-to-monoclinic structural transition. Together, these results demonstrate how
lattice, electronic, and
magnetic degrees of freedom collectively govern the Raman response of CrCl$_\textrm{3}$.
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All authors Łucja Kipczak, Tomasz Woźniak, Chinmay K. Mohanty, Igor Antoniazzi, Jakub Iwański, Przemysław Oliwa, Jan Pawłowski, Meganathan Kalaiarasan, Zdeněk Sofer, Andrzej Wysmołek, Adam Babiński, Maciej Koperski, Maciej R. Molas
Materials Science · Cross-listed from cond-mat.stat-mech
Statistical mechanics of a 2D material in a gas reservoir
Moon-ki Choi and Ellad B Tadmor
We derive and validate a partition function for low-dimensional systems interacting with a heat bath, addressing the general issue of thermodynamic modeling of nanoscale systems. In contrast to bulk systems in the canonical (NVT) ensemble where the partition function is solely determined by the
Hamiltonian of the system and the temperature of the heat bath, our formulation demonstrates that accounting for the interactions with the heat bath is essential for describing the statistical mechanics of low-dimensional materials. To validate our theoretical findings, we develop a molecular dynamics (MD)
algorithm for directly modeling the heat bath as a gas reservoir. We first validate our approach using a 1D harmonic oscillator, calculating its length distribution through explicit numerical integration and confirming these results with MD simulations. We then extend our method to investigate the out-of-plane fluctuations of a 2D
graphene monolayer immersed in a gas at finite temperature and pressure. Comparisons with conventional NVT ensemble simulations controlled by a thermostat reveal that environmental interactions significantly influence the properties of the 2D material system.
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Materials Science
Charting the Landscape of Oxygen Ion Conductors: A 60-Year Dataset with Interpretable Regression Models
Seong-Hoon Jang, Shin Kiyohara, Hitoshi Takamura et al. (+1 more)
Oxygen ion conductors are indispensable materials for such as solid
oxide fuel
cells, sensors, and membranes. Despite extensive research across diverse structural families, systematic data enabling comparative analysis remain scarce. Here, we present a curated
dataset of oxygen ion conductors compiled from $84$ experimental reports spanning $60$ years, covering $483$ materials. Each record includes activation energy ($E_a$) and prefactor ($A$) derived from Arrhenius plots, alongside detailed metadata on structure, composition, measurement method, and data source. When the original papers derive these using an erroneous Arrhenius equation $\sigma_T=A\exp{\left(-\frac{E_a}{RT}\right)}$, where ($\sigma_T$ is the oxygen ion conductivity at temperature $T$ and $R$ is the gas constant), we replotted these using the correct one, $\sigma_{T}T=A\exp{\left(-\frac{E_a}{RT}\right)}$. To illustrate how the database can be used, we constructed interpretable regression models for predicting oxygen ionic conductivity. Two symbolic regression models for E_a and A suggest that oxygen ion transport is primarily governed by local coordination environment and the electrostatic interactions, respectively. This
dataset establishes a reliable foundation for data-driven discovery and predictive modeling of next-generation oxygen ion conductors.
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All authors Seong-Hoon Jang, Shin Kiyohara, Hitoshi Takamura, Yu Kumagai
Materials Science · Cross-listed from cond-mat.mes-hall
Twisted bilayer graphene from first-principles: structural and electronic properties
Albert Zhu, Daniel Bennett, Daniel T. Larson et al. (+3 more)
We present a comprehensive first-principles study of twisted
bilayer graphene (tBLG) for a wide range of twist angles, with a focus on structural and electronic properties. By employing density functional theory (DFT) with an optimized local basis set, we simulate tBLG, obtaining fully relaxed commensurate structures for twist angles down to 0.987{\deg}. For all angles the
lattice relaxation agrees well with continuum elastic models. For angles accessible to plane-wave DFT (VASP), we provide a detailed comparison with our local basis DFT (SIESTA) calculations, demonstrating excellent agreement in both the atomic and electronic structure. The dependence of the
Fermi velocity and band width on the twist angle shows qualitative agreement with results from an `exact' $\mathbf{k \cdot p}$ continuum model, but reveals a small twist angle offset. Additionally, we provide details of the low-energy wavefunction character, band inversion and
symmetries. Our results provide an ab initio reference point for the microscopic structure and electronic properties of tBLG which will serve as the foundation for future studies incorporating many-body effects.
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All authors Albert Zhu, Daniel Bennett, Daniel T. Larson, Mohammed M. Al Ezzi, Efstratios Manousakis, Efthimios Kaxiras
Materials Science
Unified First-Principles Formula for Time-Resolved ARPES Spectra of Coherent and Incoherent Excitons
Gianluca Stefanucci and Enrico Perfetto
Despite major experimental progresses in time-resolved and angle-resolved photoemission spectroscopy, a quantitative, microscopic framework for interpreting
exciton-induced modifications of electronic band structures – applicable even beyond the low-density limit – is still lacking. Here we close this gap by introducing a unified approach that links the dynamics of coherent and incoherent
excitons to distinct and experimentally observable excitonic sidebands. Our central result is a general, first-principles formula for time-resolved photoemission spectra, applicable across a broad range of temperatures, excitation densities, and pump-probe delays. This advance provides a predictive tool for quantitatively tracking excitonic dynamics in complex materials.
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Materials Science
Controlling Mixed Mo/MoS$_2$ Domains on Si by Molecular Beam Epitaxy for the Hydrogen Evolution Reaction
Eunseo Jeon, Vincent Masika Peheliwa, Marie Hrůzová Kratochvílová et al. (+2 more)
Molybdenum disulfide (MoS$_2$) is a prototypical layered transition-metal dichalcogenide whose electrocatalytic performance is governed by a delicate balance between crystallinity, defect density, and electronic conductivity. Here we report a systematic molecular beam epitaxy (MBE) study in which annealing temperature, deposition cycle number, and Mo/S thickness ratio were independently varied to control the structural and electronic properties of MoS$_2$ thin films. The successful epitaxial growth of atomically uniform MoS$_2$ directly on Si substrates enables strong interfacial coupling and efficient charge transfer, offering a viable route toward
semiconductor-integrated catalytic architectures. X-ray diffraction, Raman spectroscopy, and X-ray absorption analyses reveal that higher annealing temperatures and excessive deposition cycles enhance crystallinity but reduce edge-site density and electrical conductivity, leading to diminished hydrogen
evolution reaction (HER) activity. In contrast, intermediate cycle numbers and sulfur-deficient growth conditions yield
heterostructures composed of MoS$_2$ with residual metallic Mo and sulfur vacancies, which activate otherwise inert basal planes while providing conductive pathways. These defect-engineered films deliver the best catalytic performance, achieving overpotentials as low as -0.33 V at -10 mA cm$^{-2}$, enlarged electrochemical surface area (ECSA) up to 8.0 cm$^2$, and mass-based turnover frequencies exceeding 23 mmol H$_2$ g$^{-1}$ s$^{-1}$, more than double those of stoichiometric counterparts. Our findings establish sulfur stoichiometry and growth kinetics as powerful levers to tune the interplay between structural order and catalytic activity in MBE-grown MoS$_2$ and point toward a broader strategy for engineering layered catalysts at the atomic scale.
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All authors Eunseo Jeon, Vincent Masika Peheliwa, Marie Hrůzová Kratochvílová, Tim Verhagen, Yong-Kul Lee
Materials Science
Engineering the electronic structure of TiO$_2$ by transition metal doping: A First Principles DFT Study
Vikash Mishra, Shashi Pandey, Swaroop Ganguly et al. (+1 more)
By means of first-principles density-functional theory (DFT) calculations, we perform a comparative analysis of the electronic and
magnetic properties of transition metal-doped TiO$_2$. The electronic band gaps of Ti$_x$M$_{1-x}$O$_2$, where M represents 3d-transition metals such as Sc, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn have been determined using the PBE functional within the generalized-gradient approximation (GGA) scheme, and also using the hybrid HSE06 functional. In the context of pure TiO$_2$, the partial density of states (PDOS) reveals that the electronic band gap emerges between the O-2p and Ti-3d orbitals. It is suggested that the Ti-3d ($t_{2g}$) states play a more prominent role in bonding compared to the Ti-3d ($e_g$) states. We performed DFT calculations to investigate the impact of doping with other 3d transition metal atoms, leading to the emergence of
impurity states within the band gap. The hybridization between the oxygen 2p orbitals and the titanium 3d orbitals in TiO$_2$ is altered by the introduction of doping with 3d transition metals because of the change in the oxidation state of titanium, shifting from solely 4+ to a combination of 4+ and 3+ states. The calculation of
spin-polarized density demonstrates the emergence of
ferromagnetic properties, particularly in titanium dioxide doped with chromium (Cr), manganese (Mn), and iron (Fe) with large
magnetic moments. Our work demonstrates the significant impact of doping transition metals on TiO$_2$, allowing for the precise manipulation of electrical and
magnetic properties, and thus holds great potential for the development of
spin-based
memory devices with possible neuromorphic applications.
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All authors Vikash Mishra, Shashi Pandey, Swaroop Ganguly, Alok Shukla
Materials Science
Control of helix orientation in chiral magnets via lateral confinement
Maurice Colling, Mariia Stepanova, Mario Hentschel et al. (+7 more)
Helimagnetic materials offer a versatile platform for
spin-based device concepts owing to their long-range, tunable spiral order. Here, we demonstrate controlled manipulation of the helimagnetic propagation vector q by geometrical confinement, using FeGe as a model Dzyaloshinskii-Moriya interaction (DMI)-driven
chiral magnet. Micromagnetic simulations based on the nonlinear sigma model reveal that open boundaries give rise to a
chiral surface twist acting as an effective surface anisotropy, which dictates the preferred helix orientation in the absence of magnetostatic shape effects. This geometry-induced anisotropy is quantitatively captured by an analytical model derived from the DMI boundary condition.
Magnetic force microscopy measurements on focused-ion-beam structured FeGe confirm the predicted orientation behavior and establish geometry-controlled helimagnetic order as a robust, tunable mechanism for steering DMI-stabilized
spin-spiral states. The concept provides a general route toward device-level control of
chiral magnetic order in non-centrosymmetric systems.
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All authors Maurice Colling, Mariia Stepanova, Mario Hentschel, Somasree Bhattacharjee, Erik Lysne, Kasper Hunnestad, Naoya Kanazawa, Yoshinori Tokura, Jan Masell, Dennis Meier
Materials Science
AI-enhanced discovery and accelerated synthesis of metal phosphosulfides
Javier Sanz Rodrigo, Nicholas A. Kryger-Nelson, Lena A. Mittmann et al. (+3 more)
Metal phosphosulfides have emerged as unique multifunctional materials, but they present unique synthesis challenges compared to more established material classes such as
oxides and nitrides. As a consequence, experimental development and theoretical understanding of phosphosulfides have focused on individual compounds rather than on accelerated broad-range exploration. In this work, we first evaluate the synthesizability and band gaps of 909 hypothetical ternary phosphosulfides by density functional theory. We find 19 previously unknown thermodynamically stable compounds, including the first Si- and Ge-based phosphosulfides. For rapid band gap prediction, we then develop a multi-fidelity machine learning model to translate semilocal density functional theory band gaps into experimentally calibrated band gaps. Importantly, we extend the accelerated material development workflow to the experimental domain by demonstrating a route to high-throughput synthesis and characterization of virtually any phosphosulfide material system. The method is based on thin-film combinatorial libraries and yields over 100 unique compositions in each experiment, enabling us to synthesize four distinct phosphosulfide compounds in only four combinatorial experiments without prior synthesis recipes and without compromising on material quality. Thus, we argue that accelerated materials development workflows combining theory, artificial intelligence, synthesis, and characterization can be viable even for experimentally challenging inorganic materials.
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All authors Javier Sanz Rodrigo, Nicholas A. Kryger-Nelson, Lena A. Mittmann, Eugène Bertin, Ivano E. Castelli, Andrea Crovetto
Materials Science · Cross-listed from cond-mat.mes-hall
Observation of an isolated flat band in the van der Waals crystal NbOCl$_2$
Changhua Bao, Vincent Eggers, Manuel Meierhofer et al. (+11 more)
Dispersionless electronic bands lead to an extremely high density of states and suppressed kinetic energy, thereby increasing electronic correlations and instabilities that can shape emergent ordered states, such as excitonic,
ferromagnetic, and superconducting phases. A flat band that extends over the entire momentum space and is well isolated from other dispersive bands is, therefore, particularly interesting. Here, the band structure of the van der Waals
crystal NbOCl$_2$ is revealed by utilizing photoelectron momentum microscopy. We directly map out an electronic band that is flat throughout the entire Brillouin zone and features a width of only $\sim$100 meV. This band is well isolated from both the conduction and remote valence bands. Moreover, the quasiparticle band gap shows a high tunability upon the deposition of caesium atoms on the surface. By combining the single-particle band structure with the optical transmission spectrum, the optical gap is identified. The fully isolated flat band in a van der Waals
crystal provides a qualitatively new testbed for exploring flat-band physics.
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All authors Changhua Bao, Vincent Eggers, Manuel Meierhofer, Jakob Helml, Lasse Münster, Suguru Ito, Leon Machtl, Sarah Zajusch, Giacomo Inzani, Ludwig Wittmann, Marlene Liebich, Robert Wallauer, Ulrich Höfer, Rupert Huber
Materials Science · Cross-listed from cond-mat.soft
Simulation of the carbon dioxide hydrate-water interfacial energy
Jesús Algabaa Esteban Acuña, José Manuel Míguez, Bruno Mendiboure et al. (+2 more)
Carbon dioxide hydrates are ice-like nonstoichiometric inclusion solid compounds with importance to global
climate change, and gas transportation and storage. The thermodynamic and kinetic mechanisms that control carbon dioxide nucleation critically depend on hydrate-water interfacial free energy. Interfacial energies show large uncertainties due to the conditions at which experiments are performed. Under these circumstances, we hypothesize that accurate molecular models for water and carbon dioxide combined with computer simulation tools can offer an alternative but complementary way to estimate interfacial energies at coexistence conditions from a molecular perspective. We have evaluated the interfacial free energy of carbon dioxide hydrates at coexistence conditions (three-phase
equilibrium or dissociation line) implementing advanced computational methodologies, including the novel Mold Integration methodology. Our calculations are based on the definition of the interfacial free energy, standard statistical thermodynamic techniques, and the use of the most reliable and used molecular models for water (TIP4P/Ice) and carbon dioxide (TraPPE) available in the literature. We find that simulations provide an interfacial energy value, at coexistence conditions, consistent with the experiments from its thermodynamic definition. Our calculations are reliable since are based on the use of two molecular models that accurately predict: (1) The ice-water interfacial free energy; and (2) the dissociation line of carbon dioxide hydrates. Computer simulation predictions provide alternative but reliable estimates of the carbon dioxide interfacial energy. Our pioneering work demonstrates that is possible to predict interfacial energies of hydrates from a truly computational molecular perspective and opens a new door to the determination of free energies of hydrates.
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All authors Jesús Algabaa Esteban Acuña, José Manuel Míguez, Bruno Mendiboure, Iván M. Zerón, Felipe J. Blas
Materials Science
Microscopic Origin of Piezomagnetism in Mn$_3$Sn: A Dual Real- and $k$-Space Picture
Soichiro Kikuchi, Yuki Yanagi, Thi Ngoc Huyen Vu et al. (+1 more)
We present a comprehensive first-principles study on the origin of the piezomagnetic effect in the non-collinear antiferromagnet Mn$_3$Sn, a material known for exhibiting a large anomalous
Hall effect. We investigate strain-induced variations of electronic and
magnetic states and elucidate the mechanism of the piezomagnetic effect from both real-space and momentum-space perspectives. In real space, the emergence of piezomagnetism is understood to arise from rotations of the
magnetic moments at specific Mn sites, which directly couple to the strain. Through detailed electronic structure analysis, we identify the
Fermi surfaces that play a crucial role in the emergence of piezomagnetism. Our results reveal that specific
Fermi surface features undergo pseudo-degeneracy lifting under applied strain, which significantly contributes to the induced net magnetization. By combining these complementary real-space and momentum-space pictures, our dual-space analysis provides deep insight into the microscopic origins of strain-driven magnetization in Mn$_3$Sn.
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All authors Soichiro Kikuchi, Yuki Yanagi, Thi Ngoc Huyen Vu, Michi-To Suzuki
Materials Science
Role of defects in the thermodynamic stability of grain boundary phases at asymmetric tilt boundaries in copper
Swetha Pemma, Lena Langenohl, Saba Saood et al. (+5 more)
Grain boundaries can exist as different grain boundary phases (also called complexions) with individual atomic structures. The thermodynamics of these defect phases in high-angle grain boundaries were studied mostly with atomistic and phase field computer simulations, but almost exclusively for special, symmetric boundaries. Here, we use molecular dynamics simulations combined with structure search methods, as well as scanning transmission electron microscopy experiments to take a step towards understanding more general grain boundaries. Using the example of $\Sigma$37c $[11\overline{1}]$ tilt boundaries in Cu, we show how the grain boundary phase transition on a symmetric boundary plane is changed by the geometrically necessary defects introduced in inclined, asymmetric boundaries. We analyze the disconnections - which are dislocation-like line defects of grain boundaries - both in the simulations, as well as in experimental Cu and Al samples. A main finding is that defect energies can have a major influence on the stability of grain boundary phases, even at small inclinations. Furthermore, some defects are not able to effect large inclinations. At that point, defective asymmetric GB phases compete with grain boundaries faceting into the adjacent symmetric GB phases.
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All authors Swetha Pemma, Lena Langenohl, Saba Saood, Yoonji Choi, Rebecca Janisch, Christian H. Liebscher, Gerhard Dehm, Tobias Brink
Materials Science · Cross-listed from cond-mat.mes-hall
Enhanced Terahertz Photoresponse via Acoustic Plasmon Cavity Resonances in Scalable Graphene
Domenico De Fazio, Sebastián Castilla, Karuppasamy P. Soundarapandian et al. (+11 more)
Precise control and nanoscale confinement of terahertz (THz) fields are essential requirements for emerging applications in photonics,
quantum technologies, wireless communications, and sensing. Here, we demonstrate a polaritonic cavity enhanced THz photoresponse in an
antenna coupled device based on chemical vapor deposited (CVD) monolayer
graphene. The dipole
antenna lobes simultaneously serve as two gate electrodes, concentrate the impinging THz field, and efficiently launch acoustic
graphene plasmons (AGPs), which drive a strong photo-thermoelectric (PTE) signal. Between 6 and 90 K, the photovoltage exhibits pronounced peaks, modulating the PTE response by up to 40%, that we attribute to AGPs forming a Fabry Pérot THz cavity in the full or half
graphene channel. Combined full wave and transport thermal simulations accurately reproduce the gate controlled plasmon wavelength, spatial absorption profile, and the resulting nonuniform electron heating responsible for the PTE response. The lateral and vertical maximum confinement factors of the AGP wavelength relative to the incident wavelength are 165 and 4000, respectively, for frequencies from 1.83 to 2.52 THz. These results demonstrate that wafer scalable CVD
graphene, without hBN encapsulation, can host coherent AGP resonances and exhibit an efficient polaritonic enhanced photoresponse under appropriate gating,
antenna coupling, and AGP cavity design, opening a route to scalable, polarization and frequency selective,
liquid nitrogen cooled, and low power consumption THz detection platforms based on plasmon thermoelectric transduction.
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All authors Domenico De Fazio, Sebastián Castilla, Karuppasamy P. Soundarapandian, Tetiana Slipchenko, Ioannis Vangelidis, Simone Marconi, Riccardo Bertini, Vlad Petrica, Yang Hao, Alessandro Principi, Elefterios Lidorikis, Roshan K. Kumar, Luis Martín-Moreno, Frank H. L. Koppens
Materials Science
Synergistic effects of ferromagnetic elements and LAGP solid electrolyte in suppressing and trapping polysulfide shuttle transfers in lithium-sulfur batteries
Giovanni Ceccio, Jiri. Vacík, Mykhailo Drozdenko et al. (+4 more)
The large - scale commercialization of promising lithium - sulfur (Li - S) batteries remains limited by the polysulfide shuttle effect, which causes rapid capacity fading and poor cycle life. In this study, we present a scalable strategy to mitigate this challenge by modifying polyethylene (PE) separators with
ferromagnetic and solid - state ionic coatings. Thin films of nickel (Ni), cobalt (Co), and the Li - ion - conducting ceramic Li1.5Al0.5Ge1.5(PO4)3 (LAGP) were deposited via ion beam sputtering, while Ni ion implantation was also employed to modify the PE substrate. The electrochemical performance of pristine and modified separators was evaluated using electrochemical impedance spectroscopy (EIS) and staircase voltammetry (SV) in
liquid electrolyte within H -
cell configurations. Surface morphology and elemental composition were characterized by scanning electron microscopy (SEM) and Rutherford backscattering spectroscopy (RBS). The results show that LAGP-based coatings significantly enhance separator stability and effectively suppress polysulfide
diffusion, leading to lower redox peak intensities and improved cycling performance. In contrast, Ni coatings exhibited poor long - term stability, likely due to parasitic reactions or delamination during its life time. The combined LAGP/Co architecture provided the most effective suppression of the polysulfide shuttle, attributed to synergistic ionic and catalytic effects that promote interfacial stability and selective ion transport. Ni implantation into PE showed only a negligible effect. This study highlights the potential of integrating solid ionic conductors with
ferromagnetic layers to design multifunctional separators for high-performance Li - S batteries.
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All authors Giovanni Ceccio, Jiri. Vacík, Mykhailo Drozdenko, Romana Mikšová, Josef Novak, Eva Štěpanovská, Mayur Khan
Materials Science
Electronic structure, phase stability, and transport properties of the AlTiVCr lightweight high-entropy alloy: A computational study
Christopher D. Woodgate, Hubert J. Naguszewski, Nicolas F. Piwek et al. (+1 more)
We investigate the thermodynamics and phase stability of the AlTiVCr lightweight high-
entropy alloy using a combination of ab initio electronic structure calculations, a concentration wave analysis, and atomistic Monte Carlo simulations. In
alignment both with experimental data and with results obtained using other computational approaches, we predict a $\textrm{B2}$ (CsCl) chemical ordering emerging in this
alloy at comparatively high temperatures, which is driven by Al and Ti moving to separate sublattices, while V and Cr express weaker site preferences. The impact of this $\textrm{B2}$ chemical ordering on the electronic transport properties of the
alloy is investigated within a Kubo-Greenwood linear response framework and it is found that, counter-intuitively, the
alloy's residual resistivity increases as the material transitions from the $\textrm{A2}$ (disordered bcc) phase to our predicted $\textrm{B2}$ (partially) ordered structure. This is understood to result primarily from a reduction in the density of electronic states at the
Fermi level induced by the chemical ordering. At low temperatures, our atomistic Monte Carlo simulations then reveal subsequent sublattice orderings, with the ground-state configuration predicted to be a fully-ordered, single-phase structure with vanishing associated residual resistivity. These results give fresh, insight into the atomic-scale structure and consequent physical properties of this well-studied, technologically relevant material.
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All authors Christopher D. Woodgate, Hubert J. Naguszewski, Nicolas F. Piwek, David Redka
Materials Science
Mobile charges in MoS2/high-k oxide transistors: from abnormal instabilities to memory-like dynamics
Shaokai Zhou, Haihui Cai, Yehao Wu et al. (+6 more)
MoS$_2$ field-effect transistors (FETs) with high-k
oxides currently lag behind silicon standards in bias and temperature stability due to ubiquitous border
oxide traps that cause clockwise (CW) hysteresis in gate transfer characteristics. While suppressing this effect is typically mandatory for logic FETs, here we explore an alternative strategy where the initial CW hysteresis can be dynamically overcome by stronger counterclockwise (CCW) hysteresis towards
memory-like dynamics. We systematically compare hysteresis in similar back-gated MoS$_2$/HfO$_2$ and MoS$_2$/Al$_2$O$_3$ FETs up to 275\textdegree C. At room temperature, both devices initially show sizable CW hysteresis. However, at 175\textdegree C MoS$_2$/HfO$_2$ FETs exhibit dominant CCW dynamics coupled with self-doping and negative differential resistance (NDR) effects. Our compact model suggests that this behavior is caused by the drift of mobile oxygen vacancies (V\({}_{\mathrm{O}}^{+}\) or V\({}_{\mathrm{O}}^{2+}\)) within HfO$_2$ which also causes negative $V_{\mathrm{th}}$ shift under a constant positive bias stress. This alternative mechanism effectively overrides the initial CW hysteresis and enables intrinsic
memory functionality that can be enhanced by using narrower gate bias sweep ranges. In contrast, the MoS$_2$/Al$_2$O$_3$ FETs display only minor CCW dynamics even at 275\textdegree C due to higher drift activation energies for the same vacancies, thereby maintaining superior stability. Our results reveal an
insulators selection paradigm: Al$_2$O$_3$ layers are better suited to suppress detrimental negative $V_{\mathrm{th}}$ shifts in MoS$_2$ logic FETs at high temperatures, whereas their HfO$_2$ counterparts can serve as active
memory layers that would exploit these abnormal instabilities.
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All authors Shaokai Zhou, Haihui Cai, Yehao Wu, Yufeng Min, Renchen Yuan, Yezhu Lv, Jianming Huang, Yuanyuan Shi, Yury Yuryevich Illarionov