Materials Science
From Mono- to Hexa-Interstitials: Computational Insights into Carbon Defects in Diamond
Nima Ghafari Cherati, Arsalan Hashemi and Ádám Gali
We present a comprehensive first-principles investigation of carbon self-interstitial defects in diamond, ranging from mono- to hexa-interstitial complexes. By
quantum mechanical density functional theory, empowered by interatomic potential models, we efficiently sample the complex configurational landscape and identify both known and previously unreported defect geometries. Our results reveal a pronounced energetic driving force for aggregation: the formation energy per interstitial decreases systematically from isolated split interstitials to compact multi-interstitial clusters, with the tetra-interstitial platelet emerging as a particularly stable structural motif. Additionally, charge analysis indicates that the predominantly covalent bonding in diamond becomes more polar within the defect centers. Analysis of defect energy levels shows that only the investigated mono-, di-, penta-, and hexa-interstitial complexes introduce in-gap electronic states, whereas the tri- and tetra-interstitial clusters are electronically inert. Vibrational spectroscopies further reveal that self-interstitials generate characteristic signatures. Short carbon-carbon bonds inside the defect cores give rise to high-frequency vibrational modes between 1375 and 1925 cm$^{-1}$, which are strongly IR-active but exhibit weak Raman activity. Through a systematic analysis of metastable configurations, we identify the 3H defect center as a neutral di-interstitial defect. Based on this identification, we further suggest that the TR12 center may arise from a 3H-containing defect like a metastable hexa-interstitial configuration. Taken together, these findings provide a coherent picture of the structural, electronic, and vibrational characteristics of carbon self-interstitials and establish a robust framework for their experimental identification.
Read the full abstract ▾
Materials Science
Simultaneous measurement of thermal conductivity and specific heat in quasi-two-dimensional membranes using the 3{\omega} method
Yiwei Le, Erdong Song, Jason Li et al. (+1 more)
Toward measuring the thermal properties of exfoliated atomically thin materials, we demonstrate simultaneous measurements of the thermal conductivity and specific heat in suspended membranes. We use the 3{\omega} technique applied to quasi-two-dimensional silicon nitride membranes having a metal line heater patterned on the surface to both deliver heat and directly measure the thermal impedance of the membrane at the heating frequency, Z(2{\omega}). We derive an expression for the complex thermal impedance as a function of frequency, approximating the actual rectangular membranes with a one dimensional model. The derivation accounts for potential parasitic heat loss mechanisms including conduction along the heater line, and by the gas load in an imperfect
vacuum. Qualitatively, the thermal impedance response resembles a low-pass filter, owing to the combination of the total thermal resistance and total specific heat. Fitting Z(2{\omega}) to measurements across a few decades in frequency, we extract values of the thermal conductivity and specific heat of silicon nitride in agreement with literature values. We also study the dependence on the heating current, and compare to measurements of the thermal conductivity at zero frequency.
Read the full abstract ▾
All authors Yiwei Le, Erdong Song, Jason Li, Erik A. Henriksen
Materials Science
Non-reciprocal Magnetoresistances in Chiral Tellurium
Shuchen Li, Chang Niu, Peide D. Ye et al. (+1 more)
Materials with broken fundamental
symmetries, such as
chiral crystals, provide a rich playground for exploring unconventional
spin-dependent transport phenomena. The interplay between a material's chirality, strong
spin-orbit coupling, and charge currents can lead to complex non-reciprocal effects, where electrical resistance depends on the direction of current and
magnetic fields. In this study, we systematically investigate the angular dependencies of magnetoresistance in single-crystalline
chiral Tellurium (Te). We observe distinct non-reciprocal magnetoresistances for
magnetic fields applied along three orthogonal directions: parallel to the current along the
chiral axis (z), in the sample plane but perpendicular to the current (y), and out of the sample plane (x). Through detailed analysis of the chirality- and thickness-dependence of the signals, we successfully disentangle multiple coexisting mechanisms. We conclude that the Edelstein effect, arising from the
chiral structure's radial
spin texture, is responsible for the non-reciprocity along the z-axis. In contrast, the chirality-independent signal along the y-axis is attributed to the Nernst effect, and the non-reciprocity along the x-axis may originate from intrinsic orbital magnetizations. These findings elucidate the complex interplay of
spin, orbital, and thermal effects in Te, providing a complete picture of its non-reciprocal transport properties.
Read the full abstract ▾
All authors Shuchen Li, Chang Niu, Peide D. Ye, Axel Hoffmann
Materials Science
Ferromagnetic Phase Transition of DPPH Induced by a Helical Magnetic Field
Emmanouil Markoulakis, John Chatzakis, Antonios Konstantaras et al. (+2 more)
We report the results and unique instrument configuration of a novel experiment in which we successfully transitioned a DPPH sample from its natural paramagnetic state and essentially a non-
magnetic material to a
ferromagnetic state at room temperature. This was achieved using a specifically applied helical flux
magnetic field. The DPPH sample (2,2-diphenyl-1-picrylhydrazyl) remained
ferromagnetic for at least one hour after the experiment, indicating that a transformation in the material was induced by the external field rather than being merely a temporary
magnetic phase transition observed only during the experiment. The external
magnetic field used had a helical pitch angle of approximately $54.7{\deg}$, known mathematically as the Magic Angle, relative to the +z-axis, which is aligned with the normal S to N external field's
magnetic moment vector. Based on the phenomenology of the experiment and results, we suggest that this specific magic angle corresponding to the known quantization precession
spin angle of free electrons under a homogeneous straight flux
magnetic field potentially enhances the percentage of unpaired valence electrons within the DPPH material, allowing them to align in parallel with the applied external field. Typically, in paramagnetic materials, the distribution of unpaired electrons'
quantum spins relative to an external field is nearly random, showing roughly a 50% chance of either parallel or antiparallel
alignment. Only a slight majority preference exists in one
alignment direction due to the Boltzmann thermal distribution, which contributes to the paramagnetic nature of these materials. In our measurements, we found that the induced ferromagnetism of the DPPH sample resulted in an abnormal thousand-fold decimal value increase in relative
magnetic permeability at ${\mu}{\approx}1.4$, compared to its typical paramagnetic value of $1.0001$ for this material.
Read the full abstract ▾
All authors Emmanouil Markoulakis, John Chatzakis, Antonios Konstantaras, Iraklis Rigakis, Emmanuel Antonidakis
Materials Science
Adsorption energies are necessary but not sufficient to identify good catalysts
Shahana Chatterjee, Alexander Davis, Lena Podina et al. (+7 more)
As a core technology for green chemical synthesis and electrochemical energy storage, electrocatalysis is central to decarbonization strategies aimed at combating
climate change. In this context, computational and machine learning driven catalyst discovery has emerged as a major research focus. These approaches frequently use the thermodynamic overpotential, calculated from adsorption free energies of reaction intermediates, as a key parameter in their analysis. In this paper, we explore the large-scale applicability of such overpotential estimates for identifying good catalyst candidates by using
datasets from the Open Catalyst Project (OC20 and OC22). We start by quantifying the uncertainty in predicting adsorption energies using ab initio methods and find that $\sim$0.3-0.5 eV is a conservative estimate for a single adsorption energy prediction. We then compute the overpotential of all materials in the OC20 and OC22
datasets for the hydrogen and oxygen
evolution reactions. We find that while the overpotential allows the identification of known good catalysts such as platinum and iridium
oxides, the uncertainty is large enough to misclassify a broad fraction of the
datasets as “good”, which limits its value as a screening criterion. These results question the reliance on overpotential estimation as a primary evaluation metric to sort through catalyst candidates and calls for a shift in focus in the computational catalysis and machine learning communities towards other metrics such as synthesizability, stability, lifetime or affordability.
Read the full abstract ▾
All authors Shahana Chatterjee, Alexander Davis, Lena Podina, Divya Sharma, Yoshua Bengio, Alexandre Duval, Oleksandr Voznyy, Alex Hernández-Garcia, David Rolnick, Félix Therrien
Materials Science
Valence Modifications in Hygroscopic VI3 Degraded Crystals via Soft X-Ray Synchrotron Radiation
A. De Vita, V. Polewczyk, G. Panaccione et al. (+1 more)
Among van der Waals
crystals, transition metal trihalide VI3 has driven
attention for its
magnetic and orbital properties. However, its chemical instability under ambient conditions make its exploitation challenging for technological implementation. In this context, here we show how synchrotron radiation soft X-rays partially restore stoichiometric chemical and electronic properties of VI3
crystals. By combining X-ray absorption and X-ray photoemission spectroscopies, we show as-cleaved and aged (in ultra-high
vacuum conditions) chemical degradation of VI3
crystal surface, with the formation of vanadates, and its, at least partial, recovery under high-flux soft X-ray beam exposure, revealing that superficial hygroscopic contamination couples relatively weakly to the
crystal surface.
Read the full abstract ▾
All authors A. De Vita, V. Polewczyk, G. Panaccione, G. Vinai
Materials Science
Magnetic and moiré Proximity Effects in WSe2/WSe2/CrI3 Trilayers
Junyi Liu, Xu Zhang and Gang Lu
Integrating
magnetic order to moiré superlattices is of significant scientific and technological interest. Based on first-principles calculations, we study the interplay of
magnetic proximity and moiré proximity in WSe2/WSe2/CrI3 trilayers with different stackings and twist angles. Large valley splitting is observed due to redistribution of the
exciton charge density across layers via a super-exchange-like mechanism, and its electric-field dependence bears similarity to electrically tunable and valley-selective Feshbach resonances. The valley splitting can be magnified in moiré superlattices owing to the superposition of Umklapp
excitons folded from moiré minibands, yielding spatially modulated and enhanced
magnetic proximity. The moiré proximity effect is demonstrated via an imprinted moiré potential on CrI3 layer and its feedback to the direct moiré potential on WSe2
bilayers is observed. The cooperation between the direct and imprinted moiré potentials is shown to yield novel topological and correlated states.
Read the full abstract ▾
Materials Science
A Machine Learning Framework for Predicting Glass-Forming Ability in Ternary Alloy Systems
Fatemeh Mahmoudi
Predicting the glass-forming ability (GFA) of chemical compositions remains a fundamental challenge in materials science, especially for
oxide glasses with broad compositional diversity. Traditional empirical and thermodynamic approaches often fail to capture the complex, nonlinear factors governing vitrification. In this study, we applied two ensemble machine learning
algorithms-Random Forest (RF) and Extreme Gradient Boosting (XGB)-to the glass_ternary_hipt
dataset to predict the GFA of ternary
oxide glasses directly from composition-derived descriptors. Both models achieved excellent predictive accuracy (R^2 > 0.92, MAE < 0.04), confirming that GFA is learnable from compositional features alone. Feature importance analysis revealed that electronegativity variance, atomic size mismatch, and valence electron descriptors are the most influential factors, while cohesive energy and ionic radius provided secondary contributions. These chemically interpretable features align with established theories of glass formation, thereby bridging predictive performance with physical understanding. The novelty of this work lies in systematically extending ML-based predictive modeling to ternary
oxide glasses, a class less studied compared to metallic and binary systems. Our results demonstrate that ensemble learning not only enables accurate GFA prediction but also provides actionable insights for designing new glass compositions with enhanced stability.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.str-el
Uncovering surface states of the Dirac semimetal BaMg2Bi2
A. De Vita, J. Bakkelund, H. Świątek et al. (+13 more)
BaMg2Bi2 is a Dirac semimetal characterized by a simple Dirac cone crossing the
Fermi level at the center of the Brillouin zone, protected by C3 rotational
symmetry. Together with its Sr-based analogue SrMg2Bi2, it has been proposed as a promising candidate for a chemically driven topological switch: while SrMg2Bi2 is an
insulator, BaMg2Bi2 exhibits non-trivial topological features. A detailed understanding of its electronic structure is essential to elucidate its electronic and transport properties. Previous photoemission studies confirmed the Dirac nature of BaMg2Bi2, but were limited to high
photon energies, which hindered direct comparison with density functional theory calculations (DFT), due to reduced resolution and higher-frequency
matrix-element modulation in that regime. In this work, we combine high-resolution angle-resolved photoemission spectroscopy (ARPES) and DFT calculations to get full insight on the valence band states, providing a comprehensive picture of the low-energy electronic structure. Our measurements reveal the presence of previously unobserved surface states. We found that they are topologically trivial, but they unlock a more comprehensive understanding of the material's behavior, reconciling previous discrepancies between experiment and theory.
Read the full abstract ▾
All authors A. De Vita, J. Bakkelund, H. Świątek, M. J. Winiarski, S. Malick, C. V. B. Nielsen, F. Bertran, A. J. H. Jones, P. Majchrzak, F. Miletto Granozio, J. A. Miwa, R. Ernstorfer, T. Pincelli, T. Klimczuk, C. Bigi, F. Mazzola
Materials Science
Relating the dynamics of photo de-mixing in mixed bromide-iodide perovskites to ionic and electronic transport
Ya-Ru Wang, Marko Mladenović, Eugene Kotomin et al. (+9 more)
The observation of reversible de-mixing phenomena in mixed-halide perovskites under illumination is one of the most challenging as well as intriguing aspects of this class of materials. On the one hand, it poses critical constraints to the compositional space that allows reliable design of absorbers for perovskite photovoltaics. On the other hand, it holds potential for the development of novel optoionic devices where an ionic response is triggered via optical stimuli. Funda-mental questions about the origin of such photo de-mixing process remain unanswered, both in terms of its mechanism as well as thermodynamic description. Here, we relate in-situ measurements of ionic and electronic transport of mixed bromide-iodide perovskite thin films performed during photo de-mixing with the
evolution of their optical and morpho-logical properties. The results point to the definition of different stages of the de-mixing process which, based on micros-copy and spectroscopic measurements, we assign to regimes of spinodal decomposition and nucleation of quasi-
equilibrium iodide- and bromide-rich phases. Combined with density functional theory calculations, we explore the role of dimensionality in the mechanism and reversibility of photo de-mixing and dark re-mixing processes, referring to elec-tronic and ionic contributions to the de-mixing driving force. Additionally, our data emphasizes the role of the surface, as significantly different de-mixing dynamics, in terms of extent and reversibility, are observed for films with or without encapsulation. Our comprehensive analysis of transport, phase and optical properties of mixed-halide perovskites pro-vides guidelines for future materials design as well as for the more general fundamental understanding of light-induced ionic phenomena.
Read the full abstract ▾
All authors Ya-Ru Wang, Marko Mladenović, Eugene Kotomin, Kersten Hahn, Jaehyun Lee, Wilfried Sigle, Jovana V. Milić, Peter A. van Aken, Ursula Rothlisberger, Michael Grätzel, Davide Moia, Joachim Maier
Materials Science · Cross-listed from cond-mat.mes-hall
Resolving Abrikosov vortex entry in superconducting nano-string resonators via displacement-noise spectroscopy in cavity-optomechanics
Thomas Luschmann, Tahereh Sadat Parvini, Lukas Niekamp et al. (+3 more)
Abrikosov
vortices in type-II
superconductors critically influence current flow and coherence, thereby imposing fundamental limits on superconducting
quantum technologies.
Quantum circuits employ superconducting elements at micro- and mesoscopic scales, where individual
vortices can significantly impact device performance, necessitating investigation of
vortex entry, motion, and pinning in these constrained geometries. Cavity-optomechanical platforms combining flux-tunable microwave resonators with superconducting nanomechanical elements offer a promising route to the single-
photon strong-coupling regime and enable highly sensitive probing of the mechanical degree of freedom under elevated
magnetic fields. Here, we exploit this platform to investigate
vortex entry processes at the single-event level. We observe discrete jumps of the mechanical resonance frequency attributable to individual
vortex entry, corresponding to attonewton-scale forces and allowing quantitative extraction of single-
vortex pinning energies. These signatures are superimposed on a smooth power-law background characteristic of the collective Campbell-regime of
vortex elasticity. Our results establish optomechanics-inspired sensing as a powerful method for exploring fundamental superconducting properties and identifying decoherence pathways in
quantum circuits. Beyond advancing
vortex physics, this work opens new opportunities for integrating mechanical sensing into superconducting device architectures, bridging condensed matter physics and
quantum information science.
Read the full abstract ▾
All authors Thomas Luschmann, Tahereh Sadat Parvini, Lukas Niekamp, Achim Marx, Rudolf Gross, Hans Huebl
Materials Science
Time-Temperature-Transformation (TTT) Diagrams to rationalize the nucleation and quenchability of metastable $\alpha$-Li$_3$PS$_4$
Akira Miura, Woohyeon Baek, Yuta Fujii et al. (+12 more)
$\alpha$-Li$_3$PS$_4$ is a promising solid-state electrolyte with the highest ionic conductivity among its polymorphs. However, its formation presents a thermodynamic paradox: the $\alpha$-phase is the
equilibrium phase at high temperature and transforms to the stable $\gamma$-Li$_3$PS$_4$ polymorph when cooled to room temperature; however, $\alpha$-Li$_3$PS$_4$ can be synthesized and quenched in a metastable state via rapid heating at relatively low temperatures. The origin of this synthesizability and anomalous stability has remained elusive. Here, we resolve this paradox by establishing a comprehensive time-temperature-transformation (TTT) diagram, constructed from a computational temperature-size phase diagram and experimental high-time-resolution isothermal measurements. Our density functional theory calculations reveal that at the nanoscale, the $\alpha$-phase is stabilized by its low surface energy, which drastically lowers the nucleation barrier across a wide temperature range. This size-dependent stabilization is directly visualized using in-situ synchrotron X-ray diffraction and electron microscopy, capturing the rapid nucleation of nano-sized $\alpha$-phase and its subsequent slow transformation. This work presents a generalizable framework that integrates thermodynamic and kinetic factors for understanding nucleation and phase transformation mechanisms, providing a rational strategy for the targeted synthesis of functional metastable materials.
Read the full abstract ▾
All authors Akira Miura, Woohyeon Baek, Yuta Fujii, Kiyoharu Tadanaga, Rana Hossain, Aichi Yamashita, Yoshikazu Mizuguchi, Chikako Moriyoshi, Shintaro Kobayashi, Shogo Kawaguchi, Jiong Ding, Shigeo Mori, Atsushi Sakuda, Akitoshi Hayashi, Wenhao Sun
Materials Science · Cross-listed from cond-mat.mes-hall
Boltzmann transport theory of magnon-exciton drag
Zakhar A. Iakovlev, Akashdeep Kamra and Mikhail M. Glazov
We develop a microscopic theory of
magnon-
exciton drag effect in a
bilayer van der Waals
antiferromagnetic semiconductor CrSBr. Effective
exciton-
magnon coupling arises from an orbital mechanism:
Magnons tilt the layer magnetizations, enabling charge carrier tunneling that mixes intra- and interlayer
excitons and thereby modulate the
exciton energy. We derive the effective
Hamiltonian of
exciton-
magnon coupling, based on our calculation of the
magnon spectrum taking into account short-range exchange interaction between Cr-ion
spins, single-ion anisotropy, and long-range dipole-dipole interactions. The latter produces a negative group velocity of
magnons at small wavevectors. We show that despite rather small renormalization of
exciton's energy and effective mass by the
exciton-
magnon interaction, the three key two-
magnon processes:
exciton-
magnon scattering, two-
magnon absorption by
exciton, and two-
magnon emission are highly efficient. By solving the Boltzmann kinetic equation, we evaluate short
exciton-
magnon scattering time which is in the sub-ps range and strongly decreases with the increase of
magnon population. Hence,
exciton-
magnon scattering is likely to be dominant over other scattering processes related to the
exciton-
phonon and
exciton-disorder interactions. We demonstrate that
magnons can efficiently drag
excitons, resulting in a large and nearly isotropic
exciton propagation that can significantly exceed the intrinsic anisotropic
diffusion. Our results provide a theoretical basis for recent observations of anomalous
exciton transport in CrSBr [F. Dirnberger, et al., Nat. Nano. (2025)] and establish
magnon-
exciton drag as a powerful mechanism for controlling
exciton propagation in
magnetic systems.
Read the full abstract ▾
Materials Science · Cross-listed from physics.chem-ph
Enhanced quantum transport in bilayer two-dimensional materials
José Campos-Martínez and Marta I. Hernández
Two-dimensional (2D) materials have been proposed, among many other applications, as a efficient tool for the separation of atomic and molecular species and their corresponding isotopes, given the confinement provided by their subnanometric dimensions. In this work we present three dimensional
quantum wave packet calculations revealing an enhancement in the
quantum transport in
bilayer over monolayer graphdiyne membranes, one of the most popular 2D materials which is commonly employed for this purpose. Besides, resonances emerge superimposed over the typical monolayer profile for transmission probabilities, a feature that is general to other
bilayer nanoporous 2D
heterostructures and that shows a strong dependence on the interlayer separation.
Read the full abstract ▾
Materials Science
Machine-learning-enabled interpretation of tribological deformation patterns in large-scale MD data
Hendrik J. Ehrich, Marvin C. May and Stefan J. Eder
Molecular dynamics (MD) simulations have become indispensable for exploring tribological deformation patterns at the atomic scale. However, transforming the resulting high-dimensional data into interpretable deformation pattern maps remains a resource-intensive and largely manual process. In this work, we introduce a data-driven workflow that automates this interpretation step using unsupervised and supervised learning. Grain-orientation-colored computational tomograph pictures obtained from CuNi
alloy simulations were first compressed through an autoencoder to a 32-dimensional global feature vector. Despite this strong compression, the reconstructed images retained the essential microstructural motifs: grain boundaries, stacking faults, twins, and partial
lattice rotations, while omitting only the finest defects. The learned representations were then combined with simulation metadata (composition, load, time, temperature, and spatial position) to train a CNN-MLP model to predict the dominant deformation pattern. The resulting model achieves a prediction accuracy of approximately 96% on validation data. A refined evaluation strategy, in which an entire spatial region containing distinct grains was excluded from training, provides a more robust measure of generalization. The approach demonstrates that essential tribological deformation signatures can be automatically identified and classified from structural images using Machine Learning. This proof of concept constitutes a first step towards fully automated, data-driven construction of tribological mechanism maps and, ultimately, toward predictive modeling frameworks that may reduce the need for large-scale MD simulation campaigns.
Read the full abstract ▾
Materials Science
Size-effects on shift-current in layered CuInP$_2$S$_6$
Francesco Delodovici, Brahim Dkhil and Charles Paillard
Two-dimensional ferroelectrics have recently emerged as a promising avenue for next-generation optoelectronic and photovoltaic devices. Due to the intrinsic absence of inversion
symmetry, 2D ferroelectrics exhibit bulk photovoltaic effect (BPVE), which relies on hot, non-thermalized photo-excited carriers to generate a photo-induced current with enhanced performances thanks to efficient charge separation mechanisms. The absence of a required p-n junction architecture makes these materials particularly attractive for nanoscale energy harvesting. Recent studies have reported enhanced BPVE in nanometer-thick CuInP$_2$S$_6$ ferroelectric embedded between two
graphene wafers, driven by relatively strong polarization and reduced dimensionality. Short
circuit photocurrent density values have been observed to reach up to mA/cm$^2$. In this paper, we demonstrate that the shift-current mechanism alone cannot fully account for these high conductivity values, suggesting that additional mechanisms may play a significant role. Furthermore, our work confirms the existence of a strong size effect, which drastically reduces the shift-conductivity response in the bulk limit, in agreement with experimental observations.
Read the full abstract ▾
Materials Science
Symmetry-driven phonon confinement in 2D halide perovskites
Mustafa Mahmoud Aboulsaad, Olivier Donzel-Gargand, Rafael B. Araujo et al. (+1 more)
Quantum confinement not only reshapes electronic states but also reorganizes the vibrational landscape of low-dimensional
semiconductors. In halide perovskites, however, the role of confinement in governing
symmetry effects on vibrational modes has remained unresolved. Here we synthesize 2D CsPbBr3 nanoplatelets with atomically defined thicknesses for 2-5 monolayers (MLs) and perform
exciton absorption and emission analysis, crystalline phase determination, and
phonon analysis. The lowest dimensional structure (2 MLs) reveal a co-existence of cubic and orthorhombic structure, energetically converging to orthorhombic for 3 MLs and beyond. Through polarization-resolved Raman spectroscopy and first-principles theory for 2-5 MLs, a striking
symmetry contrast is found: B1g modes intensify and evolve in line with the
phonon-confinement model, while Ag modes deviate, reflecting their distinct spatial localization. First principles calculations show that B1g vibrational modes largely reside in the xy-plane, Pb-Br-Pb units connect octahedra along the xy-direction with increased
lattice dynamics as inner layers accumulate, whereas A1g vibrations couple to out-of-plane distortions and remain susceptible to surface disorder and finite-size effects. This
symmetry-driven dichotomy provides a general framework for understanding
phonon localization in layered halide perovskites. Beyond mechanism, we establish Raman fingerprints, particularly the A1g/B1g intensity ratio in cross-polarized geometry, as a calibrated, non-destructive metrology for 2D nanoplatelet thickness through 2-5 MLs. These results bridge electronic and
phonon confinement and highlight
symmetry engineering as a route to understand and control
phonons,
excitons, and their interactions in low-dimensional optoelectronic materials.
Read the full abstract ▾
All authors Mustafa Mahmoud Aboulsaad, Olivier Donzel-Gargand, Rafael B. Araujo, Tomas Edvinsson
Materials Science
Angle and time-resolved polarization change induced by Kerr effect in amorphous and crystalline SiO2
Lample Pierrick, Weis Mateusz, Boschetto Davide et al. (+1 more)
We measure the polarization change of a beam reflected from the surface of both crystalline alpha and amorphous SiO2 samples while they are photo-excited by an intense light pulse, at intensities above the nonlinear excitation threshold yet below the damage threshold. The polarization change varies with the angle between the polarization of pump and probe light, but is found to be independent of their orientation relative to the
crystal axes. This behavior differs between the reflected and transmitted beams, and can be modeled by taking into account a birefringence induced by the electric field of the pump. These polarization-change effects can be very strong, with polarization rotation exceeding 90{\deg}, at pump intensities well below the damage threshold. We also observe a markedly different behavior of the reflected beam depending on whether the material is crystalline or amorphous.
Read the full abstract ▾
All authors Lample Pierrick, Weis Mateusz, Boschetto Davide, Guizard Stéphane
Materials Science · Cross-listed from physics.chem-ph
Comparing the latent features of universal machine-learning interatomic potentials
Sofiia Chorna, Davide Tisi, Cesare Malosso et al. (+3 more)
The past few years have seen the development of “universal” machine-learning interatomic potentials (uMLIPs) capable of approximating the ground-state potential energy surface across a wide range of chemical structures and compositions with reasonable accuracy. While these models differ in the architecture and the
dataset used, they share the ability to compress a staggering amount of chemical information into descriptive latent features. Herein, we systematically analyze what the different uMLIPs have learned by quantitatively assessing the relative information content of their latent features with feature reconstruction errors, and observing how the trends are affected by the choice of training set and training protocol. We find that uMLIPs encode the chemical space in significantly distinct ways, with substantial cross-model feature reconstruction errors. When variants of the same model architecture are considered, trends become dependent on the
dataset, target, and training protocol of choice. We also observe that fine-tuning of a uMLIP retains a strong pre-training bias in the latent features. Finally, we discuss how atom-level features, which are directly output by MLIPs, can be compressed into global structure-level features via concatenation of progressive cumulants, each adding significantly new information about the variability across the atomic environments within a given system.
Read the full abstract ▾
All authors Sofiia Chorna, Davide Tisi, Cesare Malosso, Wei Bin How, Michele Ceriotti, Sanggyu Chong
Materials Science
Exe.py: Ab initio fine structure parameters for trigonal defect qubits within the E$\otimes$e Jahn-Teller case
Balazs Toth, Adam Gali and Gergo Thiering
Trigonal solid-state defects are often subjects of spontaneous
symmetry breaking driven by the $E\otimes e$ Jahn-Teller effect, reflecting strong electron-
phonon coupling. These systems, particularly paramagnetic defect
qubits in solids are central for
quantum technology applications, where accurate knowledge of their fine-structure parameters $-$ shaped by the complex interplay of
spin-orbit and electron-
phonon interactions $-$ is essential. We introduce the Exe.py code part of the jahn-teller-dynamics package, a Python code that implements the first-principles approach of [Phys. Rev. X 8, 021063 (2018)] to accurately compute the
spin-orbit-
phonon entanglement in trigonal defects utilizing the output from density functional theory calculations (DFT). By employing $\Delta$SCF calculations, the method extends naturally to excited states and predicts fine-structure parameters of zero-
phonon lines (ZPLs), including Zeeman shifts under external
magnetic fields. The approach is applicable not only to solid-state defects but also to Jahn-Teller active trigonal molecules such as the $X$CH$_3$ family. We demonstrate the capabilities of Exe.py through applications to negatively charged Group-IV$-$vacancy (G4V) defects in diamond: SiV$^-$, GeV$^-$, SnV$^-$, PbV$^-$ and the neutral N$_3$V$^0$ defect in diamond, and the CH$_3$O methoxy radical.
Read the full abstract ▾
Materials Science
In situ mapping of indentation-induced densification and cracking in vitreous silica by nanofocus X-ray scattering
Johan F. S. Christensen, M. Faizal Ussama Jalaludeen, Søren S. Sørensen et al. (+9 more)
The practical strength of
oxide glasses is greatly reduced by surface flaws that form during processing and use. Instrumented indentation can mimic such real-life damage events and induce flaws and cracking under controlled conditions. At the same time, instrumented indentation allows for systematic examination of the deformation and structural changes of the regions of the glass being indented. However, structural probing is nearly always performed after rather than during the sharp contact event, limiting our understanding of the indentation process. To overcome this, we here demonstrate the use of nanofocus X-ray scattering experiments to probe the local mechanical and structural response of vitreous silica during indentation. Two-dimensional mapping of the scattering pattern in the zone below a sharp diamond wedge indenter reveals local changes in the atomic structure and density as well as cracking behavior. These in situ experiments during indentation reveal the formation and
evolution of the densification zone and cracking with nanoscale resolution. Understanding the interplay between structural densification and cracking behavior in glasses is deepened through this work, which is crucial for the development of more damage-resistant and thus stronger glasses as well as fundamental understanding of glass deformation mechanisms.
Read the full abstract ▾
All authors Johan F. S. Christensen, M. Faizal Ussama Jalaludeen, Søren S. Sørensen, Anders K. R. Christensen, Xuan Ge, Tao Du, Yuanzheng Yue, Anton Davydok, Christina Krywka, Lothar Wondraczek, Henning F. Poulsen, Morten M. Smedskjaer
Materials Science
Improving 2D-ness to enhance thermopower in oxide superlattices
Dongwon Shin, Inseo Kim, Min-Su Kim et al. (+6 more)
The transport dynamics of itinerant charge carriers and their interactions with the environment. For two-dimensional
oxide thermoelectrics, predominantly represented by doped SrTiO3-based superlattices, reduced spatial dimensions and increased effective mass are known to enhance thermopower (S). However, because of their large effective Bohr radius resulting from their high dielectric constant, SrTiO3-based systems have limitations in exhibiting the 2D characteristic. Here, we focus on EuTiO3 as an alternative perovskite platform in which fractional LaxEu1-xTiO3/EuTiO3 artificial superlattices demonstrate the improvement in 2D nature for the dimensionality-induced improvement of S. We observed a quasi-2D thermopower S2D of -950 uV K-1 and S2D/S3D of ~20 resulting from the improved 2D confinement. Thermopower measurements, combined with hybrid density functional theory calculations, show the enhanced S originates from the confinement of Ti 3dxy-states within the LaxEu1-xTiO3 layers and the associated increase in the 2D density of states. In detail, a smaller effective Bohr radius and modified electronic band structures, in conjunction with the presence of the Eu 4f-states in EuTiO3 which modified the local electronic potential and strengthened the spatial confinement of Ti 3d-states. This approach to improving the dimensional confinement establishes a small effective Bohr radius and Eu 4f-state assisted 2D confinement provides valuable insights into the design of high-performance applications in artificial
oxide superlattices.
Read the full abstract ▾
All authors Dongwon Shin, Inseo Kim, Min-Su Kim, Yu-Qiao Zhang, Woo Tack Lim, Si-Young Choi, Minseok Choi, Hiromichi Ohta, Woo Seok Choi
Materials Science · Cross-listed from cond-mat.mes-hall
Toward a Theoretical Roadmap for Organic Memristive Materials
Salvador Cardona-Serra
Neuromorphic computing aspires to overcome the intrinsic inefficiencies of von Neumann architectures by co-locating
memory and computation in physical devices that emulate biological
neurons and synapses. Memristive materials stand at the core of this paradigm, enabling non-volatile, history-dependent electronic responses. While inorganic
oxides currently dominate the field, molecular and polymeric systems can offer untapped advantages in terms of chemical tunability, structural flexibility, low-cost processing, and biocompatibility. However, progress has been hindered by the absence of a theoretical framework able to rationalize how molecular structure translates into memristive function. Here, a multiscale computational perspective is presented, outlining how
quantum chemistry and molecular dynamics, among other approaches, can be integrated into a coherent methodology to design next-generation organic memristors. Three mechanisms, ionic migration, redox-driven switching, and conduction interplay in
chiral molecules are examined as representative routes toward molecular neuromorphic hardware. The opportunities and challenges associated with each mechanism are discussed, together with a view on how a theoretically guided roadmap can accelerate the emergence of chemically engineered synaptic materials.
Read the full abstract ▾
Materials Science
Suppression of stripe-ordered structural phases in monolayer IrTe$_2$ by a gold substrate
Kati Asikainen, Frédéric Chassot, Baptiste Hildebrand et al. (+12 more)
Metal-assisted exfoliation of two-dimensional (2D) materials has emerged as an efficient route to isolating large-area monolayer
crystals, yet the influence of the supporting metal substrate on their intrinsic properties remains poorly understood. Here, we demonstrate successful gold-assisted exfoliation of monolayer IrTe$_2$ up to the millimeter scale. Angle-resolved photoemission spectroscopy (ARPES), combined with first-principles calculations, reveals that the low-energy electronic structure closely resembles that of a freestanding monolayer 1T-IrTe$_2$. We find that quasi-covalent hybridization together with substrate-induced strain leads to only modest modifications of the electronic bands. Although strain contributes to phase stability, it is essentially hybridization that drives the stabilization of the 1T-phase of the monolayer IrTe$_2$ by suppressing stripe-ordered phase transitions. These results establish gold-assisted exfoliation as a robust route to prepare a large-area monolayer IrTe$_2$ and highlight the role of metal-substrate interaction in engineering 2D materials with tailored structural phases.
Read the full abstract ▾
All authors Kati Asikainen, Frédéric Chassot, Baptiste Hildebrand, Aymen Mahmoudi, Joel Morf, Mahault Berset, Pascal Turban, Matti Alatalo, S. Assa Aravindh, Marko Huttula, KeYuan Ma, Fabian O. von Rohr, Jean-Christophe Le Breton, Thomas Jaouen, Claude Monney
Materials Science
Prussian Blue and Prussian Blue Analogs as Emerging Memristive Materials
L.B. Avila
Prussian blue analogues (PBAs) and related organic materials are promising platforms for next-generation
memory and energy-storage technologies due to their redox activity, ionic mobility, and compatibility with low-cost and scalable fabrication. Electrodeposited Prussian Blue (PB) and Prussian White (PW) thin films show robust resistive switching with ON/OFF ratios from one to three orders of magnitude in both bipolar and unipolar modes. Structural and spectroscopic analyses reveal homogeneous films with well-defined grain boundaries and ionic pathways that enable filamentary conduction. Current-voltage measurements, impedance spectroscopy, and
quantum transport modeling indicate switching mechanisms governed by ohmic or space-charge-limited conduction, driven by potassium-ion migration and reversible redox processes. PB-based devices also exhibit conductance quantization with discrete steps at integer and half-integer multiples of G0, consistent with ballistic electron transport through atomic-scale channels. Complementary studies on perylene-based
liquid crystals and FeHCF on
graphene oxide highlight the versatility of PBAs for
memory and supercapacitor applications. Together, these results demonstrate the multifunctionality and scalability of PBAs for future ReRAM, neuromorphic computing, multilevel
memory, cryptographic hardware, and high-performance energy-storage devices.
Read the full abstract ▾
Materials Science
Revealing interstitial energetics in Ti-23Nb-0.7Ta-2Zr gum metal base alloy via universal machine learning interatomic potentials
Miroslav Lebeda, Jan Drahokoupil, Veronika Mazáčová et al. (+1 more)
Understanding the behavior of light interstitial elements in multicomponent
alloys remains challenging due to the complexity of local chemical environments and the high computational cost of first-principles calculations. Here we demonstrate that three universal machine-learning interatomic potentials (uMLIPs) - MACE-MATPES-PBE-0, Orb-v3, and SevenNet-0 can efficiently map the energetics of C, N, O, and H interstitials in a Ti-23Nb-0.7Ta-2Zr (at.%) gum metal base
alloy while being several orders of magnitude faster than density functional theory (DFT). All uMLIPs predict broad energy distributions (~1-3 eV) across the four interstitial elements, reflecting their strong sensitivity to local
lattice chemistry. Despite
alloy disorder, MACE-MATPES-PBE-0 and Orb-v3 reproduce the expected site preferences of the bcc structure: C, N, and O relax into octahedral sites, whereas H stabilizes in tetrahedral positions. In contrast, SevenNet-0 predicts H to be most stable in octahedral coordination, indicating a limitation of this model. Correlation analysis reveals two dominant chemical trends: Ti-rich environments strongly stabilize interstitials, whereas close proximity to Nb is destabilizing. Zr and Ta show no statistically significant influence, likely due to their low concentrations. Benchmarking representative O interstitial configurations against DFT confirms that the uMLIPs reasonably reproduce the energetic ordering of chemically distinct environments. DFT validation confirms that tetrahedral configurations are energetically more favorable than octahedral sites for H interstitials, further illustrating the SevenNet-0 limitation. Overall, we demonstrated that uMLIPs enable computationally efficient, statistically broad characterization of defect energetics in Ti-23Nb-0.7Ta-2Zr gum metal base
alloy and provide insight into how local chemical environments govern interstitial stability.
Read the full abstract ▾
All authors Miroslav Lebeda, Jan Drahokoupil, Veronika Mazáčová, Petr Vlčák
Materials Science · Cross-listed from cond-mat.str-el
Interplay of Orbital Degeneracy and Vacancies in Stabilizing Collinear Magnetic Order in Cr$_{1+\delta}$Te$_2$
Prasanta Chowdhury, Jyotirmoy Sau, Mohamad Numan et al. (+7 more)
Cr$_{1+\delta}$Te$_2$, a two-dimensional van der Waals ferromagnet, displays a contested
magnetic structure, poised between collinear and non-collinear
spin configurations. In this work, we investigate the
magnetic structure of Cr$_{1.33}$Te$_2$ at the microscopic level by combining single-
crystal neutron diffraction, X-ray absorption spectroscopy, and first-principles calculations.
Neutron diffraction measurements reveal a distinct collinear
spin alignment, whereas spectroscopic analyses reveal inherent structural vacancies at both Cr and Te sites. These vacancies lead to local
symmetry breaking that elevates the orbital degeneracy of the Cr 3$d$ states, as demonstrated by our first-principles analysis. The resulting modification of magnetocrystalline anisotropy emerges as the key mechanism stabilising the collinear
magnetic ground state over the non-collinear one in the presence of vacancies. Our findings uncover a vacancy-driven route to control
spin anisotropy and
magnetic ordering in layered ferromagnets, offering new insights into the design of tunable 2D
magnetic materials.
Read the full abstract ▾
All authors Prasanta Chowdhury, Jyotirmoy Sau, Mohamad Numan, Jhuma Sannigrahi, Matthias Gutmann, Gangadhar Das, D. T. Adroja, Saurav Giri, Manoranjan Kumar, Subham Majumdar
Materials Science · Cross-listed from cond-mat.str-el
Sub 1 K Adiabatic Demagnetization Refrigeration with Rare-Earth Borates Ba$_3$XB$_9$O$_{18}$ and Ba$_3$XB$_3$O$_9$, X = (Yb, Gd)
Marvin Klinger, Tim Treu, Felix Kreisberger et al. (+4 more)
Adiabatic demagnetization refrigeration (ADR) is regaining relevance for the refrigeration to temperatures below 1 K as global helium-3 supply is increasingly strained. While ADR at these temperatures is long established with paramagnetic hydrated salts, more recently frustrated rare-earth
oxides were found to offer higher
entropy densities and practical advantages since they do not degrade under heating or evacuation. We report structural,
magnetic and thermodynamic properties of the rare-earth borates Ba$_3$XB$_9$O$_{18}$ and Ba$_3$XB$_3$O$_9$ with X = (Yb, Gd). Except for Ba$_3$GdB$_9$O$_{18}$, which orders at 108 mK, the three other materials remain paramagnetic down to their lowest measured temperatures. ADR performance starting at 2 K in a field of 5 T is analyzed and compared to literature results.
Read the full abstract ▾
All authors Marvin Klinger, Tim Treu, Felix Kreisberger, Christian Heil, Anna Klinger, Anton Jesche, Philipp Gegenwart
Materials Science
Mode-resolved logarithmic quasiballistic heat transport in thin silicon layers: Semianalytic and Boltzmann transport analysis
Jae Sik Jin
Nonequilibrium
phonon transport driven by nanoscale hotspot heating in silicon device layers governs heat dissipation in advanced microelectronics and underscores the need for a better microscopic understanding of such processes. Yet the origin of the frequently observed logarithmic (ln) dependence of the apparent thermal response on hotspot size in crystalline silicon, and the role of individual
phonon modes in this regime, remain unclear. Here, we develop a semianalytical, mode-resolved framework in the spectral
phonon mean free path (MFP) domain and validate it against a full-
phonon-dispersion Boltzmann transport model for heat removal from a 10 x 10 nm^2 hotspot in a thin Si layer (thicknesses of 41, 78, and 177 nm) representative of a silicon-on-
insulator transistor. We show that ln-type quasiballistic scaling arises only for modes that lie on a log-uniform conductivity plateau and are diffusive-side or quasiballistic with respect to the hotspot size, whereas fully ballistic long-MFP modes contribute a saturated, nonlogarithmic background, leading to extremely slow suppression of their heat-carrying capability. The resulting
phonon-modal nonlocal spectrum establishes spectral selection rules for ln-regime transport in confined Si and provides a compact basis for incorporating mode-selective quasiballistic corrections into continuum thermal models and for interpreting
phonon-resolved thermometry experiments.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.mes-hall
Quantum geometry and $X$-wave magnets with $X=p,d,f,g,i$
Motohiko Ezawa
Quantum geometry is a differential geometry based on
quantum mechanics. It is related to various transport and optical properties in condensed matter physics. The Zeeman
quantum geometry is a generalization of
quantum geometry including the
spin degrees of freedom. It is related to electromagnetic cross responses.
Quantum geometry is generalized to non-Hermitian systems and density
matrices. Especially, the latter is
quantum information geometry, where the
quantum Fisher information naturally arises as
quantum metric. We apply these results to the $X$-wave magnets, which include $d$% -wave, $g$-wave and $i$-wave altermagnets as well as $p$-wave and $f$-wave magnets. They have universal physics for anomalous
Hall conductivity, tunneling magneto-resistance and planar
Hall effect. We also study magneto-optical conductivity,
magnetic circular dichroism and Friedel oscillations in the $X$-wave magnets. Various analytic formulas are derived in the case of two-band
Hamiltonians. This paper presents a review of recent progress together with some original results.
Read the full abstract ▾