Materials Science · Cross-listed from cond-mat.soft
Spatially heterogeneous relaxational dynamics and the evolution of recoverable strain following flow cessation of a ductile nanocolloidal glass
Chloe W. Lindeman, James J. Griebler, Penelope Grace Kovakas et al. (+6 more)
We report a combined rheology and x-ray
photon correlation spectroscopy (XPCS) study of the structural and mechanical relaxation of a ductile, nanocolloidal glass following the cessation of shear flow. After the glass is sheared to 300% strain at various shear rates and then held at fixed strain, the stress undergoes a protracted, quasi-logarithmic decay with hold time that depends weakly on the initial strain rate. Recovery rheology measurements reveal that this stress relaxation is accompanied by a logarithmic decrease in the elastic component of the recoverable strain; hence, the rates of decrease of the stress and recoverable strain are proportional. XPCS measurements during the stress relaxation reveal dynamics dominated by a convection-like backflow that is divided into two dynamically distinct regions indicative of banded motion. In one region, the flow can be modeled by an affine strain, while in the other region the glass moves as a plug while undergoing slow, glassy relaxation. The rates of these dynamics approximately track the rate of loss of recoverable strain, indicating this motion is the predominant microscopic mechanism driving the conversion of recoverable to unrecoverable strain during stress relaxation. In contrast, XPCS measurements during strain recovery reveal purely affine flow with no evidence of heterogeneity and with strain rates that agree quantitatively with the rheometry measurements. Together, these results provide a unified microscopic picture connecting the evolving internal dynamics of a ductile glass to its macroscopic mechanical relaxation following flow cessation.
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All authors Chloe W. Lindeman, James J. Griebler, Penelope Grace Kovakas, Miaoqi Chu, Qingteng Zhang, Suresh Narayanan, James L. Harden, Simon A. Rogers, Robert L. Leheny
Materials Science
Accurate Evaluation of Nanoscale Spatiotemporal Dynamics with Electron Correlation Microscopy
Po-Cheng Kung, Ajay Annamareddy, Mark D. Ediger et al. (+2 more)
Electron correlation microscopy (ECM) can measure materials dynamics with nanoscale spatial resolution from intensity correlation functions. However, adopting X-ray
photon correlation spectroscopy (XPCS) normalization frameworks unchanged when calculating intensity correlations can introduce errors. Due to the constrained sampling volumes and larger speckle sizes in nanobeam electron diffraction, XPCS-style time-averaging and scattering-vector averaging introduce systematic artifacts, such as artificial anticorrelations or elevated baselines that lead to systematic errors in structural relaxation times and stretching exponents. This work presents physics-inspired, ECM-specific intensity normalizations over time- and azimuthal-averaged intensities of the first diffraction ring that limit those errors. The framework is validated using molecular dynamics simulations of a CuZr supercooled
liquid to
benchmark against the self intermediate scattering function, successfully reproducing relaxation times. When applied to experimental time-resolved 4D STEM
datasets of a Pt57.5Cu14.7Ni5.3P22.5 nanowire, the method correctly identifies highly stable, unchanging nanoscale crystalline phases that were erroneously misclassified as relaxing domains by previous frameworks. Other previous ECM research is reevaluated in light of these observation. This robust approach establishes an artifact-free pathway for evaluating localized spatiotemporal relaxation behaviors.
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All authors Po-Cheng Kung, Ajay Annamareddy, Mark D. Ediger, Dane Morgan, Paul M. Voyles
Materials Science · Cross-listed from cs.CE
Predicting Mechanical Properties of Lignin-Containing Polyurethane Rigid Foams from Microstructure Using Convolutional Neural Networks
Ilige S. Hage, Charbel Y. Seif, Jose Enrico Q. Quinsaat et al. (+5 more)
Bio-based alternatives for conventional rigid foams have proven to be good substituents owing to their enhanced sustainability and competitive performance. However, because their manufacturing processes are complex and destructive testing is often impractical, this study investigates whether microstructural features can be correlated with mechanical properties in lignin-containing rigid polyurethane (PU) foams using machine-learning approaches. Various types and percentages of lignin-based polyols were investigated as a partial polyol replacement. Scanning electron microscopy (SEM) images and corresponding mechanical compression data were used to train a custom state-of-art dual-head convolutional neural network (CNN) targeting the specific prediction of density, specific compression modulus, specific yield strength, and specific compression strength. The CNN was optimized with a weighted multi-output loss function, achieving strong predictive performance R2 values ranging from 0.850 to 0.91 and correlation coefficients above 0.92 while maintaining mean absolute error percentages below 9%. This proves the trained network capability to predict and capture morphological features governing load bearing responses. On the other hand, Grad-CAM visualization revealed that the network focused its predictions on physically meaningful microstructural regions such as
cell walls and strut junctions, which confirm that the proposed network can be classified as an interpretable, non-destructive and data-driven framework for predicting and understanding bio-based PU foams mechanical behavior, hence reducing the inconvenience caused by time consuming manufacturing and destructive testing.
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All authors Ilige S. Hage, Charbel Y. Seif, Jose Enrico Q. Quinsaat, Daniel J. van de Pas, Richard Vendamme, Walter Eeversd, Karolien Vanbroekhovend, Elias Feghalid
Materials Science · Cross-listed from cond-mat.supr-con
Yttrium Superhydrides Revisited: Advanced Experimental and Theoretical Studies of YH$_6$, YH$_9$ and YH$_{10}$
Dmitrii V. Semenok, Pedro N. Ferreira, Di Zhou et al. (+10 more)
Yttrium polyhydrides are
benchmark materials in high-pressure superconductivity, yet several key properties of the Y-H system remain insufficiently characterized. Here we combine contact transport, contactless
radio-frequency measurements, pulsed-field experiments, and first-principles calculations to reinvestigate YH$_6$, YH$_9$, and YH$_{10}$ in the pressure range 140-213 GPa. Yttrium hydrides YH$_6$ ($\textit{$T_c$}$ = 218-221 K) and YH$_9$ ($\textit{$T_c$}$ = 235-237 K) demonstrate narrow superconducting transitions ($\textit{${\Delta}$T$_c$}$ = 2-5 K), approaching the limit imposed by thermal fluctuations. Pulsed-field measurements on YH$_6$ up to 60 T establish an extended superconducting phase diagram with a linear slope $\textit{dB$_{c2}$/dT}$ = -0.52 T/K, pronounced transition broadening above 30 T, and negligible normal-state magnetoresistance. We report the
radio-frequency AC susceptibility study of YH$_6$, providing evidence for superconductivity via high-frequency field screening in a contactless geometry. Experiments involving Pd incorporation, Pd thin-film sputtering, and Al alloying show strong suppression of high-temperature superconductivity, with no transitions detected above 78-120 K. Finally, using density-functional theory with the
stochastic self-consistent harmonic approximation, superconducting density-functional theory, and full-bandwidth Migdal-Eliashberg calculations, we show that anharmonic effects substantially reduce the predicted $\textit{$T_c$}$ of cubic YH$_{10}$ to approximately 260-270 K. These results strongly disfavor room-temperature superconductivity in binary yttrium superhydrides.
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All authors Dmitrii V. Semenok, Pedro N. Ferreira, Di Zhou, Fabian Jőbstl, Andrey V. Sadakov, Kirill S. Pervakov, Burkhan I. Massalimov, Toni Helm, Ryosuke Akashi, Vladimir M. Pudalov, Viktor V. Struzhkin, Christoph Heil, Ivan A. Troyan
Materials Science
Symmetry-Dependent Mechanical and Vibrational Response of Formamidinium Lead Halide Perovskites: A DFT Study
Mahdi Faghihnasiri, Carmine Autieri and Sara Memarzadeh
Formamidinium-based hybrid halide perovskites (FAPbX3, X = Cl, Br, and I) have attracted considerable
attention for optoelectronic applications owing to their outstanding optical and electronic properties. However, the influence of
crystal symmetry reduction on their mechanical behavior and stability has not yet been comprehensively understood. In this work, density functional theory (DFT) calculations were performed to investigate the structural, elastic, dynamical, and nonlinear mechanical properties of the cubic and ps-cubic phases of FAPbX3. The elastic constants, bulk, shear, and Young's moduli, Poisson's ratio, sound velocities, and Debye temperature were evaluated and correlated with the second Piola-Kirchhoff stress-strain response under tensile and compressive loading. The results reveal that the effect of
symmetry reduction is strongly dependent on the halide composition. For FAPbCl3 and FAPbBr3, the transition from the cubic to the ps-cubic phase reduces the
lattice stiffness, decreases the acoustic
phonon velocities, and lowers the Debye temperature, whereas the opposite trend is observed for FAPbI3. The stress-strain analysis further reveals pronounced nonlinear, anisotropic, and asymmetric mechanical behavior, demonstrating that
symmetry reduction can either activate or suppress strain-accommodation mechanisms depending on the halide species, thereby governing the mechanical stability and the onset of structural softening. These findings provide microscopic insight into the relationship between
crystal symmetry,
lattice dynamics, and nonlinear mechanical response in formamidinium-based halide perovskites, offering useful guidance for the design of mechanically robust optoelectronic materials.
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Materials Science · Cross-listed from cond-mat.mes-hall
Large bias-tunable magnetoresistance from spin-dependent interlayer hybridization in van der Waals antiferromagnet CrSBr-based heterostructures
Sadeed Hameed, Aditya Kumar, Chengjie Yu et al. (+5 more)
We explore the large magnetoresistance (MR) in \ce{hBN}/few-layer-
graphene/\ce{CrSBr}/few-layer-
graphene heterostructures and reveal the mechanism behind its non-monotonic bias dependence. Using bias voltage and temperature as independent tuning knobs, we achieve MR up to \SI{350}{\percent} at \SI{20}{K}, characterized by symmetric M-shaped maxima around $\pm 0.5\,\mathrm{V}$. Continuous tuning of the magnetization angle $\theta$ via a hard-axis
magnetic field shows that the barrier band-edge offset varies linearly with $\cos(\theta/2)$, a first-order signature of
spin-dependent interlayer hybridization. This linear relationship rules out the Jullière model and a
spin-filter projection. We conclude that the
magnetic-configuration-dependent band edge, rather than electrode
spin polarization, dictates the large magnetoresistance in \ce{CrSBr} junctions.
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All authors Sadeed Hameed, Aditya Kumar, Chengjie Yu, Aravind P. Balan, Xinran Wang, Lichuan Zhang, Yuriy Mokrousov, Mathias Kläui
Materials Science
Many-Body Destabilization of Intermediate Oxygen-Hole States
Anirudh Adavi, Kayahan Saritas, Ming Lei et al. (+3 more)
Oxygen holes in transition-metal oxides can appear as localized polarons,
symmetry-delocalized ligand holes, or intermediate states whose stability is controlled by subtle electron-correlation effects. In layered Na$_{2-x}$Mn$_3$O$_7$, hybrid density functional theory (DFT) predicts an unusual bond-centered split oxygen-hole polaron stabilized near ordered Mn vacancies. Here we resolve the nature of this state using
diffusion Quantum Monte Carlo (QMC). Although hybrid DFT favors the split configuration, QMC reverses the energetic ordering and identifies the localized oxygen polaron as the lower-energy state. The result is robust to the class of trial wavefunctions used, including hybrid and generalized-gradient DFT wavefunctions. Many-body
spin densities further show that the nominal split state partially collapses toward a localized polaron. Because localized and split configurations produce similar O K-edge spectral features, this qualitative failure is not resolved by conventional X-ray absorption signatures alone. These findings identify Na$_{2-x}$Mn$_3$O$_7$ as a stringent
benchmark for oxygen-hole polarons and reveal a failure mode of hybrid functionals in correlated oxides.
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All authors Anirudh Adavi, Kayahan Saritas, Ming Lei, Das Pemmaraju, Paul R. C. Kent, Iwnetim I. Abate
Materials Science
Strain-controlled magnetism and magnetoelasticity in monolayer NiPS$_3$ and CrPS$_4$
Balázs Nagyfalusi, Alvaro Bermejillo-Seco, Linde de Jong et al. (+5 more)
We develop a first-principles framework for magnetoelastic coupling in two-dimensional magnets based on a strain-dependent Heisenberg model. In this approach, strain derivatives of the exchange interactions provide direct access to magnetostriction and to the
magnetic renormalization of the elastic tensor, establishing a microscopic link between
spin interactions and elastic response. We apply the method to monolayer NiPS$_3$ and CrPS$_4$, which exhibit contrasting magnetoelastic behavior. NiPS$_3$ shows weak and nearly isotropic
spin-
lattice coupling, consistent with a robust zigzag antiferromagnetic ground state. In contrast, CrPS$_4$ displays strong anisotropic coupling, leading to strain-driven transitions between
spin-spiral and ferromagnetic phases and significant changes in the critical temperature and elastic response. Our results demonstrate a general route to quantify magnetoelastic effects in low-dimensional magnets and highlight CrPS$_4$ as a promising platform for strain engineering of
magnetic order.
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All authors Balázs Nagyfalusi, Alvaro Bermejillo-Seco, Linde de Jong, Ritesh Das, Yaroslav M. Blanter, Herre S. J. van der Zant, Amador Garcia-Fuente, and Jaime Ferrer
Materials Science
Chemically Meaningful Textualization Enables Explainable Validation of Metal-Organic Frameworks by Large Language Models
Guobin Zhao and Xiao-Yan Li
Computation-ready metal-organic framework (MOF) databases are essential for high-throughput screening, yet many reported
crystal structures remain chemically unreasonable or disordered, compromising simulation fidelity. Existing validation approaches can identify non-computation-ready structures, but they often rely on heuristic rules, license requirement, or offer limited interpretability. Here, we show that large
language models (LLMs) can serve as interpretable validators of MOF structures when crystallographic information is transformed into chemically meaningful text. By benchmarking nine descriptors, we find that successful LLM-based validation depends not on the amount of structural information alone, but on whether local coordination, framework connectivity, and chemical context are organized into a linguistically learnable representation. Fine-tuned LLMs using specialized descriptors (mof2text) achieve performance comparable to graph-based models in identifying unreasonable MOFs. Importantly, these models extend beyond black-box classification by generating diagnostic rationales for likely error sources, including abnormal bonding, connectivity, and charge states, as well as error-category predictions for annotated
datasets. This work establishes chemically informed textualization as the key step that transforms LLMs from generic text models into practical and explainable tools for curating MOF databases.
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Materials Science · Cross-listed from quant-ph
Impact of strain and dark states on spectroscopic measurements of silicon-vacancy centers in diamond
Tommy Chin, Kesav V. Narayan, Imran Bashir et al. (+4 more)
Negatively charged silicon-vacancy (SiV$^-$) centers in diamond offer an attractive platform for the development of many forms of
quantum technology. However, questions remain in connection to how large ensembles of SiV$^-$ centers behave in concert. Here, we develop a computational model designed to simulate recent experiments where optical multidimensional coherent spectroscopy (MDCS) was used to examine a high-concentration sample of SiV$^-$ centers in diamond, revealing significant variations in spectral signature depending on the detection scheme. Simulation results reveal that strain effects are highly random in this system, with a characteristic axial strain of $2.8 \times 10^{-4}$ and a shear strain of $3.5 \times 10^{-5}$. They suggest in addition that highly strained centers (with values exceeding $1.5 \times 10^{-5}$) may become significantly decoupled from optical emission. The results have implications for the use of SiV$^-$ centers as
quantum sensors.
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All authors Tommy Chin, Kesav V. Narayan, Imran Bashir, Kelsey M. Bates, Liam G. Stanton, Ehsan Khatami, Christopher L. Smallwood
Materials Science
Structural, Optical and Magnetic Properties of Superparamagnetic Fe3O4@TiO2 and Fe3O4@SiO2@TiO2 CoreShell Nanostructures
Wagner Henrique Gamas, Rosana R. Rangela, Grecia Alejandra Gomez-Iriarteb et al. (+2 more)
Tailoring core-shell nanostructures using iron oxide core (Fe3O4) and titanium dioxide shell (TiO2) offer a promising multifunctional platform for
multimodal cancer therapies. TiO2 shell exhibits photo-responsive optical properties suitable for optical imaging and phototherapies, while Fe3O4
magnetic core enables
magnetic resonance imaging (MRI) and
magnetic hyperthermia therapy (MHT). This present work reports synthesis and characterization from core-shell Fe3O4@TiO2 and Fe3O4@SiO2@TiO2 nanostructures. Structural and physical properties were evaluated using X-ray Diffraction (XRD),
Fourier-Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), High-Resolution Scanning Electron Microscopy (HRSEM), Diffuse UV-Vis Reflectance Spectroscopy (DRS) and SQUID magnetometry. This work highlights the potential use of
magnetic (core) and optically activated (shell) nanostructures for
multimodal therapies assisted by
magnetic hyperthermia.
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All authors Wagner Henrique Gamas, Rosana R. Rangela, Grecia Alejandra Gomez-Iriarteb, Sergio Seabra. Pablo, L. Bernardo
Materials Science
Tunable chiral anomaly in electron magnetotransport in the Weyl semimetallic Pb$_{1-x}$Sn$_x$Te:Cr alloy
A. Królicka, E. Łusakowska, M. Matusiak et al. (+4 more)
We study magnetotransport properties of
semiconductor substitutional
alloy Pb$_{1-x}$Sn$_x$Te, known to exhibit Sn-content dependent properties of topological crystalline
insulators with a semimetallic zero-gap state at a specific band inversion point. We experimentally verify the theoretically predicted role of chemical disorder in this multivalley electron system, which leads to sequential band inversions in various valleys and places the Fermi level close to the pairs of Weyl nodes, as identified in the density functional theory calculations. Doping with mixed-valence Cr resonant impurities enables exploitation of the unique properties of dopant resonant states, which provide an effective means of tuning carrier concentration. The combination of these two effects results in the pinning of the Fermi level in the vicinity of the nodal touching points across a wide range of composition. To address the above issues, we grow Bridgman bulk
crystals of Pb$_{1-x}$Sn$_x$Te heavily doped with chromium and covering the full range of tin (0 $\leq x \leq$ 1), i.e. spanning both the topological crystalline
insulator and trivial electronic regimes. We observe the emergence of the three dimensional (3D) Weyl semimetal phase over a range of Sn compositions, namely for $0.25 < x < 0.45$. We provide magnetotransport evidence for this and verify the relationship between the magnitude of the experimentally determined Berry
curvature and the electrical properties of these materials.
Quantum transport regime observed in magnetoresistance is also independently confirmed by thermal conductivity measurements.
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All authors A. Królicka, E. Łusakowska, M. Matusiak, A. Mirowska, A. Łusakowski, T. Story, K. Dybko
Materials Science · Cross-listed from physics.med-ph
T1, T2, and complex permittivities of hydrogels, paramagnetic salt solutions, and oils at 0.35, 1.5, and 3 Tesla
H Michael Gach, Kerri Prinos and Hannah Sechaga
Approach: The T1, T2, and complex permittivities of candidate MRI phantom constituents (hydrogels, paramagnetic electrolytes, and oils) were measured at different
magnetic field strengths and concentrations. Data: T1 decreased with increasing concentration except for PEG. The T1 and T2 relaxivities of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), sodium polyacrylate, and deionized water did not significantly vary with field strength. The T2 relaxivities of gelatin and sodium alginate did not significantly vary with field strength. All of the hydrogels and paramagnetic electrolyte solutions had high static dielectrics (e.g., {\epsilon}s~70) similar to water. The static electrical conductivities of Miller's LB agar, gelatin, PVA, sodium alginate, sodium polyacrylate, xanthan gum, CuSO4, NiCl2, and Mn(NO3)2 rose with concentration. However, the conductivities of PEG and PVP did not rise with concentration. Conclusions: Sodium polyacrylate, PVP, and PEG hydrogels are challenging for generating consistent phantoms. Sodium alginate, Miller's LB agar, and xanthan gum were good hydrogel candidates. Mn(NO3)2 had the highest relaxivities of the tested samples. All three oils (canola, castor, and grapeseed) are good candidates for low dielectric ({\epsilon}s<10) phantoms for high field applications) but with low conductivities.
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Materials Science
Stable Glasses of Organic Semiconductor Resist Crystallization
Kushal Bagchi, Marie E. Fiori, Camille Bishop et al. (+2 more)
The instability of glassy solids poses a key limitation to their use in several technological applications. Well-packed organic glasses, prepared by physical vapor deposition (PVD), have drawn
attention recently because they can exhibit significantly higher thermal and chemical stability than glasses prepared from more traditional routes. We show here that PVD glasses can also show enhanced resistance to crystallization. By controlling the deposition temperature, resistance towards crystallization can be enhanced by at least a factor of ten in PVD glasses of the model organic
semiconductor Alq3 (Tris(8-hydroxyquinolinato) aluminum). PVD glasses of Alq3 first transform into a supercooled
liquid before crystallizing. By controlling the deposition temperature, we increase the glass to
liquid transformation time thereby also increasing the overall time for crystallization. We thus demonstrate a new strategy to stabilize glasses of organic
semiconductors against crystallization, which is a common failure mechanism in OLED (organic light emitting diode) devices.
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All authors Kushal Bagchi, Marie E. Fiori, Camille Bishop, M.F. Toney, M.D. Ediger
Materials Science
Competition between local magnetic disorder and altermagnetism in doped FeSb$_2$
Enrico Di Lucente and Michele Simoncelli
Recent experimental reports suggest that the narrow-gap nonmagnetic
semiconductor FeSb$_2$ can be transformed into an altermagnetic metal through Co doping (Co$_{0.15}$Fe$_{0.85}$Sb$_2$), or into a magnetically disordered or short-range-ordered state through Cr doping (Cr$_{0.15}$Fe$_{0.85}$Sb$_2$). Here we explore the energy landscape and
magnetic states of these doped systems from first principles, relying on Hubbard-augmented density-functional theory (DFT+U) combined with the Romeo ground-state search
algorithm. Within the established virtual-
crystal approximation (VCA), we show that Romeo finds several non-trivial
magnetic states, which inform targeted explicit simulations of doping in supercells. We rely on these findings to discuss strengths and limitations of the VCA-Romeo approach versus the explicit-doping supercell approach, and how they can be used in synergy. Overall, our simulations suggest that the ground state of the Cr-doped system is a Locally Disordered
Spin-Compensated (LDSC) configuration, formally compatible with Néel's L-type fully compensated ferrimagnetism, whereas the ground state of the Co-doped system is found to be altermagnetic (AFMo). This work shows how approximate and explicit simulations of
magnetic alloys can be mutually informative, and establishes a protocol for studying candidate metallic altermagnets.
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Materials Science · Cross-listed from cond-mat.soft
Using Deposition Rate and Substrate Temperature to Manipulate Liquid Crystal-like Order in a Vapor-deposited Hexagonal Columnar Glass
Camille Bishop, Zhenxuan Chen, Michael F. Toney et al. (+3 more)
We investigate vapor-deposited glasses of a phenanthroperylene-ester, known to form an
equilibrium hexagonal columnar phase, and show that
liquid crystal-like order can be manipulated by the choice of deposition rate and substrate temperature during deposition. We find that rate-temperature superposition (RTS), the equivalence of lowering deposition rate and raising substrate temperature, can be used to predict and control the molecular orientation in vapor-deposited glasses over a wide range of substrate temperatures (0.75Tg to 1.0Tg). This work extends RTS to a new structural motif, hexagonal columnar
liquid crystal order, which is being explored for organic electronics applications. By several metrics, including the apparent average face-to-face nearest-neighbor distance, PVD glasses of the phenanthroperylene-ester are as ordered as the glass prepared by cooling the
equilibrium liquid crystal. By other measures, the PVD glasses are less ordered than the cooled
liquid crystal. We explain the difference in the maximum attainable order with the existence of a gradient in molecular mobility at the free surface of a
liquid crystal, and its impact upon different mechanisms of structural rearrangement. This free surface equilibration mechanism explains the success of the RTS principle and provides guidance regarding the types of order most readily enhanced by vapor deposition. This work extends the applicability of RTS to include molecular systems with a diverse range of higher-order
liquid crystalline morphologies that could be useful for new organic electronic applications.
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All authors Camille Bishop, Zhenxuan Chen, Michael F. Toney, Harald Bock, Lian Yu, M.D. Ediger
Materials Science · Cross-listed from cond-mat.soft
Multi-step deformation experiment and development of a model for the mechanical behavior of polymeric glasses
Grigori A Medvedev, Enran Xing, Mark D Ediger et al. (+1 more)
Traditional models for stress-strain behavior of glassy
polymers are based on the assumption that the critical features of the stress-strain response can be explained by changes in the molecular mobility. The four-step deformation experiments consisting of (i) an initial constant strain rate loading, (ii) unloading to specified stress, (iii) creep under that stress and (iv) second constant strain rate loading, challenges that assumption. Specifically, existing models fail to predict the experimentally observed large second stress overshoot in case of a slight unloading. Until now there has remained a possibility that the mobility was actually lower in case of a partial rather than complete unloading, which would preserve the main assumption, if not particular details, of these specific constitutive models. By performing direct optical experiments using the photobleaching technique simultaneously with the mechanical four-step experiments it is shown that a lower molecular mobility upon partial unloading does not take place. As traditional models cannot account for these experimental results, a new model has been developed where the changes of molecular structure manifest not in the relaxation time, but in the shear modulus, which is function of an internal variable that is the fraction of the efficiently packed material. This fraction obeys a population balance equation, where the steady-state fraction is controlled by the applied stress. In the absence of deformation, the efficiently packed fraction increases, which explains the increase in the modulus in the course of physical aging below Tg. The model qualitatively describes the four-step experiment as well as single step loading experiments.
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All authors Grigori A Medvedev, Enran Xing, Mark D Ediger, James M Caruthers
Materials Science
Accelerated Discovery of Materials with Extreme Work Functions through Uncertainty-Aware Multi-Fidelity Screening
Jun Meng, Ryan Jacobs, Rehan Kapadia et al. (+1 more)
Work function plays a pivotal role in technologies ranging from energy conversion and electronics to catalysis. In this work, we integrated machine learning (ML) with multi-fidelity screening to develop a data-driven framework for accelerating the discovery of materials with extreme work functions. We augmented a previously published Random Forest (RF) model for work function to include prediction uncertainty calibration and domain of applicability assessment to enhance prediction robustness. By combining the augmented RF model with universal ML interatomic potential simulations and targeted ab initio calculations, we screened 5.5 million compounds from the GNoME and Alexandria databases. This workflow identified 209 surfaces with extreme low work functions below 2.0 eV and 227 surfaces with extreme high work functions above 6.0 eV, corresponding to 136 and 172 unique materials, respectively. The resulting candidates revealed trends consistent with established chemical principles, including the tendency of alkali- and alkaline-earth-terminated surfaces to exhibit low work functions. While it also uncovered less conventional motifs: lanthanide-rich surface terminations were strongly associated with extremely low work functions, whereas surfaces containing metalloids or phosphorus at the top layer were correlated with exceptionally high work functions. This work demonstrates a scalable strategy that leverages ML models and multi-fidelity computational efforts to accelerate the discovery of materials with extreme work functions for advanced electronic, energy-conversion, and catalytic applications.
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All authors Jun Meng, Ryan Jacobs, Rehan Kapadia, John Booske
Materials Science
Oxygen K-edge X-ray Absorption Spectroscopy Database for NMC811 Layered Cathode Materials
Jian He, Bowen Xiu, Feng Ryan Wang et al. (+2 more)
X-ray absorption spectroscopy (XAS) probes the local chemical environment of the absorbing atom and is one of the most powerful characterization techniques for battery materials. Here we present a database of simulated oxygen K-edge XAS spectra for the layered cathode material LiNi0.8Mn0.1Co0.1O2 (NMC811), built on the atomic structures of our recent work[1]. All spectra were obtained using the excited electron and core-hole (XCH) method with the R2SCAN meta-GGA functional, as implemented in the Vienna Ab initio Simulation Package (VASP). The database covers
benchmark binary oxides (TiO, Ti2O3, TiO2, Mn3O4, Mn2O3, MnO2) together with a realistic NMC811 supercell containing 60 transition metal sites at three states of charge. Because each spectrum is resolved at the level of individual oxygen sites, the database links O K-edge spectral features to specific oxygen environments defined by their local coordination and transition metal neighbors. All data are freely available and can serve as a reference for spectral fingerprinting, for direct comparison with experiments, and as training data for machine learning models.
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All authors Jian He, Bowen Xiu, Feng Ryan Wang, Frank MF de Groot, Nongnuch Artrith
Materials Science
Oscillation modes of skyrmion strings in a ferromagnetic film
Eugene M. Chudnovsky and Dmitry A. Garanin
It is shown that a skyrmion string in a ferromagnetic film consisting of $N$ atomic layers exhibits flexural oscillations at eigenfrequencies $|\omega_{m}|=(4J'S/\hbar)\sin^{2}[\pi m/(2N)]$, where $J'$ is the interlayer exchange coupling, $S$ is the length of the atomic
spin, and $m=1,...,N-1$. This result is confirmed numerically for individual skyrmion strings in a discrete microscopic
spin-
lattice model of up to ten atomic layers, as well as for skyrmion-string
lattices at finite temperature.
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Materials Science · Cross-listed from cond-mat.mes-hall
Anisotropic magnon spin transport in CrPS$_4$
Krishnaraajan Sundararajan, Muhammad Zohaib, Yulia Kreminska et al. (+2 more)
Crystal anisotropy provides a powerful route for realizing direction-dependent transport in solid-state systems. While its influence on electronic transport is well established, the role of anisotropy in
magnon spin transport in van der Waals magnets is largely unexplored. Here, in a nonlocal geometry, utilizing the monoclinic van der Waals antiferromagnet CrPS$_4$, we observe pronounced anisotropy in both electrically and in thermally excited
magnon spin transport. Electrically generated
magnons exhibit a
magnon spin conductivity at least 2.2 times larger and a
spin diffusion length at least 2.7 times longer for transport along the crystallographic-b axis compared to the crystallographic-a axis, where $\lambda_m^{a} \sim$ 211 nm and $\lambda_m^{b} \geq$ 575 nm. In comparison, at 8T, we find the nonlocal second-harmonic resistance associated with thermally excited
magnons to be $\sim$7 times larger along the crystallographic-b axis at 25K. We further show that a
magnon spin diffusion length cannot be reliably extracted from the nonlocal second-harmonic resistance, owing to the extended temperature profile within CrPS$_4$. Likewise, we show that the anisotropy in the
spin Seebeck coefficients cannot be reliably estimated from the thermally excited
magnon spin transport alone, as it is intertwined with the anisotropic heat conductivity of CrPS$_4$. Utilizing the electrically generated
magnon spin transport, we demonstrate that intrinsic crystalline anisotropy serves as an effective control parameter for tuning
magnon spin transport, opening new avenues for magnonic device engineering.
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All authors Krishnaraajan Sundararajan, Muhammad Zohaib, Yulia Kreminska, Sytze H. Tirion, Bart J. van Wees
Materials Science
High-pressure electride superconductor Li5N for multifunctional applications: A theoretical insight into the physical properties
M. Abdul Hadi Shah and S.H. Naqib
This study aims to unveil the physical properties of multifunctional Li5N electride under high pressure in the range of 150-350 GPa through first principles analysis within the density functional theory.
Materials Science · Cross-listed from cond-mat.str-el
Quantum Mechanism of Piezomagnetism in Higher-Spin Altermagnets
Daisuke Yamamoto and Makoto Naka
We investigate piezomagnetism in higher-
spin altermagnets with easy-plane single-ion anisotropy using a flavor-wave approach. We show that
quantum fluctuations of higher-
spin collective modes provide a microscopic origin of the piezomagnetic response. For integer
spins, the relevant branch softens and evolves into a
Higgs-like amplitude mode on approaching the large-$D$ transition, endowing the excitation with a sizable dipolar component and producing a pronounced enhancement of piezomagnetism. By contrast, in half-integer systems the higher-
spin branches are progressively separated from the low-energy dipolar sector as the anisotropy increases, which suppresses their contribution to the response. This integer-half-integer contrast directly links macroscopic piezomagnetism to the low-energy fate of multipolar excitations. Our results establish piezomagnetism as a probe of higher-
spin quantum dynamics and identify higher-
spin altermagnets as a promising setting for
quantum magnetoelastic responses.
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Materials Science
Multi-scale modeling of high strain rate deformation and spall fracture in poly-crystalline metals
S Madhavan
This thesis utilizes a multiscale method by connecting molecular dynamics (MD) based information to hydrodynamic macroscopic calculations for investigating the shock response and spallation of metals. First, shock propagation in Cu, Al, and Ni single
crystals is simulated up to $100$ GPa at strain rates $>10^6$ s$^{-1}$. Shock-Hugoniot ($U_s$-$U_p$) relations agree strongly with experiments (error $<6\%$); the Foiles EAM potential shows the least deviation for Ni. Second, a multiscale framework linking MD atomic void kinetics to hydrodynamic macro-calculations is established. Using particle swarm optimization (PSO), Nucleation and Growth (NAG) parameters are extracted for Cu, Nb, Mo, and Al, yielding free surface velocity (FSV) profiles matching experiments within $8\%$ for Al. Third, deformation across ten Al tilt (STGB) and twist (STwGB) bicrystals at rates of $10^{10}$-$10^{11}$ s$^{-1}$ proves that threshold spallation depends on boundary misorientation. Phase transitions near GBs lower spall strength at high $U_p$, whereas GB plasticity prolongs pull-back and delays spallation (e.g., $14.2^\circ$ STwGB). FSV methods are found to underestimate true peak tensile strength. Fourth, the framework is extended to polycrystals via 11 STGB and 12 STwGB configurations. Voids consistently nucleate at weakened GBs. Unique NAG parameters are fitted using PSO for all 23 bicrystals. An Average Void Growth in a Fluid Element (AVGFE) model is introduced to map these distinct boundary properties into 1D hydrodynamic codes. The combined model is validated against empirical Al flyer impacts at $518$, $1588$, and $2275$ m/s. The simulated temporal FSV curves mirror experiments, with spall strength deviations tightly bounded within $2.15\%$, $2.9\%$, and $6.0\%$, respectively, and spall thickness deviations within $2.4$-$4.0\%$.
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Materials Science · Cross-listed from physics.chem-ph
Spin Rotatory Strength as the Equilibrium Observable for Chiral-Induced Spin Selectivity
Rubén Dar\io Guerrero
We identify the
spin rotatory strength—a chirality-odd, finite-frequency
spin–dipole cross response—as the
equilibrium observable for chiral-induced
spin selectivity. Time-reversal
symmetry forces the static response to vanish, while nonzero SU(2) Wilson-loop flux is an independent necessary condition. Exact diagonalization of a Kane–Mele–Hubbard model ($N{=}4,6,8$) reveals that gapped molecules robustly suppress the response, whereas near-degenerate systems show amplification at small $N$ whose persistence at larger sizes remains open.
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Materials Science · Cross-listed from quant-ph
Nanoscale graphitization and defect evolution in silicon-vacancy center-containing nanodiamonds under high-pressure high-temperature annealing
M. De Feudis, B. Yavkin, L. Henry et al. (+6 more)
Group-IV color centers, such as the silicon-vacancy (SiV) defect, are highly promising for solid-state
quantum technologies. However, nanodiamonds typically exhibit significant
lattice strain and structural disorder, which degrade their optical properties and hinder the resolution of the fine spectral structure at cryogenic temperatures. High-pressure high-temperature (HPHT) annealing offers a potential route to relax internal strain, although the phase stability of diamond at the nanoscale under such conditions remains poorly constrained. Here, we investigate the structural
evolution of nanodiamonds during HPHT annealing using a Paris-Edinburgh press coupled with in situ synchrotron X-ray diffraction at SOLEIL. A dedicated sample assembly combining nanodiamonds - NaCl - Pt enabled accurate pressure-temperature calibration and real-time monitoring of phase transformations. The diffraction data reveal that the onset of diamond-to-graphite transition occurs at approximately 1800 K at 2 GPa and 2120 K at 4 GPa under the applied HPHT heating protocol. These experimentally determined graphitization onsets define a practical pressure-temperature processing window for HPHT annealing of nanodiamonds while avoiding detectable graphitization and provide a calibrated framework for reliable off-beam annealing treatments that avoid graphitization. Photoluminescence measurements on samples annealed below the graphitization threshold show improved optical response, with partial resolution of the SiV fine structure at 12 K. These optical measurements suggest a relationship between nanoscale phase stability and the optical response of individual SiV-containing nanodiamonds following HPHT annealing. The experimentally established HPHT processing window provides a practical framework for the controlled processing of
quantum nanodiamonds while avoiding graphitization.
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All authors M. De Feudis, B. Yavkin, L. Henry, K.O. Ho, M.-P. Adam, P. Goldner, F. Benedic, S. Desgreniers, J.-F. Roch
Materials Science
Enhanced Screening in Epitaxial Graphene via Nearly Free-Electron Metal Intercalation
Cedric Schmitt, Lukas Gehrig, Jonas Erhardt et al. (+8 more)
Graphene exhibits extraordinarily high carrier mobility, making it a promising platform for next-generation electronics. Scalable growth on SiC, however, suffers from limited dielectric screening at the
graphene-substrate interface, degrading electronic performance. In this work, we systematically enhance dielectric screening by intercalating a bilayer of indium at the
graphene-SiC interface. Using
graphene's plasmaronic signature observed in angle-resolved photoemission spectroscopy as a proxy for interaction strength, we quantitatively demonstrate strong dielectric screening arising from the interplay of both indium layers. Layer-resolved density functional theory shows that the first indium layer acts as a buffer that absorbs substrate interactions, enabling the second layer to form a nearly free-electron system that efficiently screens the
graphene layer above. Experiments with only a single intercalated indium layer reveal reduced screening, confirming the essential role of the second layer. Our results establish 2ML indium intercalation as a powerful route for engineering dielectric environments in
graphene.
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All authors Cedric Schmitt, Lukas Gehrig, Jonas Erhardt, Kilian Strauß, Stefan Enzner, Martin Kamp, Timur Kim, Giorgio Sangiovanni, Jörg Schäfer, Simon Moser, Ralph Claessen
Materials Science · Cross-listed from cond-mat.str-el
Carrier-tunable RKKY magnetism in a crystalline magnet
Xiang S.W. Huang, Bruno K. Saika, Satoshi Hamao et al. (+10 more)
In itinerant magnets governed by the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, the exchange coupling depends on both the moment-moment distance $r$ and the Fermi wavevector $k_{\mathrm{F}}$, yet in bulk synthesis the two are tightly coupled: a change in composition typically alters both. Here, we use a thin-film approach to tune these two variables independently in a single crystalline host. Using molecular-beam epitaxy (MBE), we stabilize either $2\times2\mathrm{R}0^\circ$ Cr$_{1/4}$NbSe$_2$ or $\sqrt{3}\times\sqrt{3}\mathrm{R}30^\circ$ Cr$_{1/3}$NbSe$_2$ within the same NbSe$_2$ host through separate growth windows. Controlled post-growth annealing performed across a series of temperatures then modifies the carrier density while leaving the Cr superstructure intact below a structural-transition threshold. The two as-grown phases are distinct in electronic structure,
magnetic ground state, and transport. Along this annealing series, the Hall response evolves systematically while the
magnetic response changes in a structurally insensitive manner, with ferromagnetic order emerging within the same $\sqrt{3}\times\sqrt{3}\mathrm{R}30^\circ$ structural class only above a critical annealing temperature, experimentally disentangling carrier density and moment geometry. The Hall magnitude and sign
evolution point to a low-carrier-density system in which $k_{\mathrm{F}}$ is susceptible to modest external tuning. Cr-NbSe$_2$ thus realizes carrier-sensitive RKKY magnetism in a single crystalline host, within an MBE-plus-annealing approach extensible across the intercalated transition-metal dichalcogenide family.
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All authors Xiang S.W. Huang, Bruno K. Saika, Satoshi Hamao, Yuki Majima, Yuki Settai, Hideki Matsuoka, Yuki M. Itahashi, Masato Sakano, Taro Nakajima, Shinichiro Seki, Yoshihiro Iwasa, Kyoko Ishizaka, Masaki Nakano
Materials Science
Construction of 3D-Ferroelectric Polarization Microstructure and Detection of Polarization Invariants under Induced Flexoelectric Strains
Sabarigresan Murugan, Vaishnavi S M and Ranjith Ramadurai
Ferroelectric thin films that are heterophased and polycrystalline possess strain sensitive piezoelectric behavior. However, a direct insight into polarization orientations within a given grain and how mechanical stresses reconfigures the ferro elastically coupled polarization orientations remains ambiguous. A polarization component resolved imaging in a Piezoresponse Force Microscope (PFM) was developed in combination with correlative structure and
phonon studies that provide insights into grain orientation, domains and bending stress driven phase transitions. The method correlates the polarization invariant and the respective grain orientations present underneath. The technique facilitates an experimental inverse model approach to determine crystallographic grain orientation from the ferroelectric domain. A three point bending stage introduces a flexoelectric strain in Ba0.85,Ca0.15Zr0.1Ti0.9O3_BCZT thin films and simultaneous polarization imaging. This novel technique potentially captures the formation of new polarization invariant of a monoclinic phase that appears under high pressures. The experimental findings pave way for development of inverse modelling of heterophased and polycrystalline systems.
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Materials Science · Cross-listed from cond-mat.mes-hall
Dynamics of amorphous membranes in the two-dimensional limit
Liga Jasulaneca, Alberto Martín-Pérez, Hongji Zhang et al. (+7 more)
Atomically thin mechanical resonators have been realized predominantly in crystalline two-dimensional (2D) materials, such as
graphene, where long-range crystalline order sets their elastic properties and defines their nonlinear resonant behavior. Extending these concepts to the amorphous 2D limit has remained largely unexplored. Here, we demonstrate that monolayer amorphous carbon (MAC) forms suspended membranes that support optothermal actuation and sensitive interferometric readout across both linear and nonlinear regimes of its resonant motion. We resolve thermomechanical motion, driven resonances, and multimode spectra in MAC nanodrums. The frequencies of fundamental vibration modes correspond to unusually low pretensions, placing monolayer MAC nanodrums in a regime where
geometric nonlinearities, stress heterogeneity, and mode coupling emerge at comparatively low drive powers. Consistently, we observe pronounced nonlinear dynamics, including hardening, softening, and mixed Duffing responses, nonlinear damping, parametrically excited modes, and signatures of intermodal coupling. These results establish MAC as a robust nanoelectromechanical platform and open an experimental route to disorder-governed nanomechanics in the 2D amorphous limit.
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All authors Liga Jasulaneca, Alberto Martín-Pérez, Hongji Zhang, Prertahn Munireternam, Natalia A. Mamchik, Chee-Tat Toh, Artem K. Grebenko, Barbaros Özyilmaz, Makars Šiškins, Farbod Alijani