Materials Science · Cross-listed from cs.LG
Reducing cross-sample prediction churn in scientific machine learning
Gordan Prastalo and Kevin Maik Jablonka
Scientific machine learning reports predictive performance. It does not report whether the same prediction would survive a different draw of training data. Across $9$ chemistry
benchmarks, two classifiers trained on independent bootstraps of the same training set agree on aggregate accuracy to within $1.3\text{--}4.2$ percentage points but disagree on the class label of $8.0\text{--}21.8\%$ of test molecules. We call this gap cross-sample prediction churn. The standard parameter-side techniques (deep ensembles, MC dropout,
stochastic weight averaging) do not reduce this gap; two data-side methods do. The first is $K$-bootstrap bagging, which cuts the rate $40\text{--}54\%$ on every
dataset at no accuracy cost ($K{\times}$-ERM compute). The second is twin-bootstrap, our proposal: two networks trained jointly on independent bootstraps with a sym-KL consistency loss between their predictions, which at matched $2{\times}$-ERM compute reduces churn a further median $45\%$ beyond bagging-$K{=}2$. Cross-sample prediction churn deserves a column alongside predictive performance in scientific-ML
benchmark reports, because without it the parameter-side and data-side methods are indistinguishable on the metric they actually differ on.
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Materials Science
Chiral molecule-induced contributions to ferromagnetic resonance
Jurgen Lindner, Pedro Contreras-Gallardo, Abhishek Singh et al. (+7 more)
Despite extensive research on chirality-driven
spin selectivity, most studies have focused on static
magnetic properties, while the influence of chirality on the dynamic
magnetic response remains largely unexplored. Here, we investigate how
chiral molecular interfaces affect magnetization dynamics in thin Co/Ni multilayers with perpendicular
magnetic anisotropy using broadband
ferromagnetic resonance spectroscopy. A comparison between bare (reference) films and molecule-functionalized (hybrid) samples reveals no measurable changes in either the resonance field or the linewidth that could be attributed to the presence of the
chiral environment. Motivated by our findings we develop a macrospin description that distinguishes
equilibrium modifications of the
magnetic free-energy landscape (MIPAC-type effects) from non-
equilibrium, CISS-induced
spin torques. Our analysis shows that
equilibrium modifications primarily shift the resonance condition via changes to the free energy landscape and thereby the effective field, whereas damping-like non-
equilibrium torques provide a distinct channel for varying the effective damping rate. This approach establishes clear criteria for disentangling
chiral-interface-induced energy modifications from torque-driven dynamical effects in
ferromagnetic resonance experiments.
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All authors Jurgen Lindner, Pedro Contreras-Gallardo, Abhishek Singh, Ruslan Salikhov, Anna Semisalova, Olav Hellwig, Rodolfo Gallardo, Anna Lewandowska-Andralojc, Kilian Lenz, Aleksandra Lindner
Materials Science · Cross-listed from cond-mat.mes-hall
Magnetization-dependent and stacking-tunable Edelstein effect in two-dimensional magnet 2H-VTe2
Weiyi Pan and Jaroslav Fabian
The Edelstein effect in
magnetic systems enables magnetization switching via the coupling between current-induced
spin accumulation and intrinsic
magnetic order, and is therefore highly promising for next-generation spintronic devices. Realizing and manipulating the Edelstein effect in two-dimensional (2D)
magnetic systems is particularly desirable for achieving high-efficiency and multifunctional spintronic applications. In this work, based on first-principles calculations and
symmetry analysis, we demonstrate that the Edelstein effect can intrinsically arise in the 2D in-plane
ferromagnetic semiconductor 2H-VTe2, with its behavior strongly dependent on the magnetization orientation. For monolayer 2H-VTe2 with D3h
crystal symmetry, under an applied current along the +x direction, only the time-reversal-even z component and the time-reversal-odd y(x) component of the
spin accumulation are allowed when the magnetization is aligned along +x (+y). For
ferromagnetic bilayer 2H-VTe2 in AB or BA stacking, where the
crystal symmetry is reduced to C3v, additional
spin components emerge with the presence of in-plane magnetization. Specifically, for magnetization along +x (+y), besides dSz_even and dSy_odd (dSz_even and dSx_odd), extra components such as dSy_even and dSz_odd (dSy_even) become allowed. Notably, these additional components can be reversibly switched by changing the stacking configuration from AB to BA via interlayer sliding. Our results not only deepen the understanding of current-induced
spin accumulation in 2D
magnetic systems from both
symmetry and first-principles perspectives, but also identify 2H-MX2 materials as a promising platform for realizing intrinsic and tunable Edelstein effects in high-efficiency
spin-orbit torque devices.
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Materials Science
Giant optical spin-orbit interactions in ferroelectric van der Waals waveguides
Ding Xu, Saeed Rahmanian Koshkaki, Vicente Galicia et al. (+14 more)
Optical
spin-orbit interactions (SOI) link photonic
spin to momentum, offering a route toward on-chip polarization control and beam steering. Nevertheless, achieving sufficient optical SOI and nonlinearities on sub-micrometer scales - a prerequisite for dense photonic integration - remains an outstanding challenge. Here, we show that highly birefringent van der Waals (vdW) waveguides provide an ideal, chip-compatible platform to address this limitation. We focus on the ferroelectric
semiconductor NbOI2, which exhibits record optical nonlinearities and dielectric anisotropy. Using femtosecond optical microscopy, we image light propagation and harmonic conversion beyond the total internal reflection barrier over tens of micrometers in NbOI2 slab waveguides. We report
giant optical
spin-splitting through the optical
spin Hall effect, which facilitates spatial separation of optical
spin currents on sub-micrometer scales, in quantitative agreement with a microscopic light-matter interaction model. We further leverage optical
spin-momentum locking to realize polarization-controlled waveguide steering. We generalize these observations across various vdW waveguides and empirically confirm a scaling law linking dielectric anisotropy to
geometric spin-splitting. Our results establish highly anisotropic vdW waveguides as an ideal platform for densely integrated opto-spintronic technologies.
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All authors Ding Xu, Saeed Rahmanian Koshkaki, Vicente Galicia, Chun-Ying Huang, Victoria Quirós-Cordero, Jakhangirkhodja A. Tulyagankhodjaev, André Koch Liston, Daniel G. Chica, Emma Lian, Amirhosein Amini, Yongseok Hong, Taketo Handa, P. James Schuck, Xiaoyang Zhu, Xavier Roy, Arkajit Mandal, Milan Delor
Materials Science
Nonlinear dynamic elastic moduli from equilibrium stress fluctuations
F. E. Garbuzov and Y. M. Beltukov
Fluctuation formulas for elastic and viscoelastic
moduli allow their computation from
equilibrium molecular dynamics simulations, avoiding explicit nonequilibrium deformation protocols. While such expressions are well established for the quasi-static
moduli, and also the linear dynamic
moduli, no fluctuation formula exists for the nonlinear time-dependent
moduli that govern anharmonic viscoelastic response under finite time-dependent strains. In this work we derive transient-time correlation function expressions for both the linear and the nonlinear dynamic
moduli, starting from the DOLLS/SLLOD equations of motion for irrotational motion. The resulting formulas involve
equilibrium time correlations of the stress tensor and Born-kinetic terms, and they recover the known quasi-static and linear dynamic results in the appropriate limits.
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Materials Science
High-Pressure XRD Study of Ti-3Al-2.5V Titanium Alloy: Intermediate Transition Pressure and Composition Trends in Ti-Al-V Alloys
D. Errandonea, R. Turnbull, P. Botella et al. (+3 more)
High-pressure X-ray diffraction experiments were performed on Ti-Al-V
alloys to investigate the effect of composition on structural stability, focusing on Ti-3Al-2.5V and comparing with pure Titanium and Ti-6Al-4V. Measurements using different pressure-transmitting media show a phase transition in Ti-3Al-2.5V at 17-19 GPa, intermediate between pure Ti (5-10 GPa) and Ti-6Al-4V (~30 GPa). Despite variations arising from the choice of pressure medium, the transition pressure shows a clear and systematic increase with higher Al and V content. Equation-of-state analysis indicates that the bulk modulus remains nearly unchanged across compositions. This suggests a decoupling between elastic properties and phase stability, with alloying primarily affecting the transition pressure rather than compressibility. These results highlight the role of composition in tuning high-pressure phase transformations in Ti-Al-V based
alloys.
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All authors D. Errandonea, R. Turnbull, P. Botella, R. Oliva, C. Popescu, S. MacLeod
Materials Science
Layer thickness dependent band gap of MBE grown single- to few-layer MoS$_{2}$
Maciej Bazarnik, Thorsten Deilmann, Marta Przychodnia et al. (+1 more)
In light of the rise of transition metal dichalcogenides as 2D
semiconductors for device applications, band engineering becomes very important from an application point of view. In many of these materials, such as the canonical example of MoS$_{2}$, the
semiconductor band gap depends on the layer number. It changes from indirect to direct as it evolves from a bulk
semiconductor to a monolayer. Interestingly, it was predicted and experimentally confirmed that, by thinning the material from bulk to a
bilayer, the indirect transition shows a strong blue-shift. Here, we present the results of scanning tunnelling spectroscopy measurements on MoS$_{2}$ that has been grown in situ via molecular beam epitaxy on
graphene on Ir(111) at thicknesses ranging from 1 to 5 layers. We find a drastic decrease of the band gap with increasing layer number, to values even below the band gap in bulk. We also observe that the pinning of the conduction band vanishes above 4 layers. Comparing our experimental data with density functional theory and GW calculations indicates that an additional screening is introduced by the sample growth conditions.
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All authors Maciej Bazarnik, Thorsten Deilmann, Marta Przychodnia, Anika Schlenhoff
Materials Science
OpenAaaS: An Open Agent-as-a-Service Framework for Distributed Materials-Informatics Research
Peng Kang, Bixuan Li, Xiaoya Huang et al. (+5 more)
The Materials Genome Initiative catalyzed the proliferation of centralized platforms–SaaS, PaaS, and IaaS–that aggregate computational and experimental resources for accelerated materials discovery. In parallel, breakthroughs in large
language models (LLMs) and autonomous
agents have created powerful new
reasoning capabilities for scientific research. Yet a critical "last mile" problem remains: while we possess world-class models and vast repositories of materials data, we lack the organizational infrastructure to compose these capabilities securely across institutional boundaries. The development of structural and functional materials for harsh service environments–high-temperature
alloys, radiation resistant steels, corrosion-resistant coatings–remains characterized by long-term iteration, mechanistic complexity, and high domain expertise–demands that exceed both monolithic
agent systems and traditional centralized platforms. To address this gap we propose OpenAaaS, an open-source hierarchical and distributed
Agent-as-a-Service framework that enables organized multi-
agent collaboration for intelligent materials design. OpenAaaS is built on a single foundational principle: code flows, data stays still. A Master
Agent plans and decomposes complex research tasks without requiring direct access to subordinate
agents' managed data and computational resources. Sub-
agents, deployed as near-data execution nodes, retain full sovereignty over local
datasets, proprietary
algorithms, and specialized hardware. This architecture guarantees that raw data never leaves its domain of origin while enabling cross-scale, cross-domain secure integration of previously isolated materials intelligence silos. We validate the framework through two representative case studies: (i) AlphaAgent, an evidence-grounded materials literature analysis executor that achieves 4.66/5.0 on deep analytical questions against single-pass RAG baselines; and (ii) an ultra-large-scale hexa-high-
entropy alloy descriptor database service that demonstrates secure near-data execution and domain-specific scientific workflows under strict data-sovereignty constraints. OpenAaaS establishes a principled pathway toward "organized research" via
agent collectives, offering a scalable foundation for next-generation materials intelligent design platforms. All source code is available at https://github.com/Wolido/OpenAaaS.
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All authors Peng Kang, Bixuan Li, Xiaoya Huang, Shuo Shi, Weiqiao Zhou, Zhen Li, Yu Liu, Lei Zheng
Materials Science
Magnetocaloric Effect in Nanostructured $La_{0.6}Sr_{0.4}Fe_{1-x}Co_{x}O_3$
Fabiana N. Morales Alvarez, Mariano Quintero and Joaquín Sacanell
This work presents a systematic study of the magnetocaloric effect in the nanostructured perovskite series $La_{0.6}Sr_{0.4}Fe_{1-x}Co_{x}O_3$ (x = 0, 0.2, 0.5, 0.8, and 1.0), synthesized by a pore-wetting method using polymeric membranes with pore diameters of 200 nm and 800 nm. All samples were calcined at 1000{\deg}C. Structural characterization was made by X-ray diffraction and confirmed the formation of a single-phase perovskite with distorted rhombohedral
symmetry, without detectable secondary phases. We observed significant influence of substitution of Fe by Co on the morphology, as the analysis by scanning electron microscopy revealed a clear
evolution from smaller to larger particles and from thin to thicker nanotubes, as the Co content increased.
Magnetic measurements showed that the cationic substitution enhances
ferromagnetic coupling, increasing both the saturation magnetization (MS) and the Curie temperature (TC). The magnetocaloric properties, determined through the Maxwell relations, exhibit a maximum
entropy change of 1.13 J/(kg K) under an applied field of 3 T for the sample with x = 1. These results demonstrate that the combination of Co doping and controlled nanostructuring effectively optimizes the magnetocaloric response.
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Materials Science · Cross-listed from physics.geo-ph
Assessing foundational atomistic models for iron alloys under Earth's core conditions
Tianqi Wan, Liangrui Wei, Zepeng Wu et al. (+2 more)
We assess the capability of recently developed foundational atomistic models (FAMs) to simulate iron
alloys under the extreme pressures and temperatures of Earth's core. Static equations of state for hexagonal close-packed (hcp) and body-centered cubic (bcc) iron, computed using 17 FAMs, are benchmarked against ab initio calculations. Two representative models, MatterSim and MACE, are further evaluated for their ability to reproduce
phonon spectra,
liquid structure, and melting relations of iron at core conditions. While both models capture several key properties, MACE substantially overestimates the stability of bcc iron and fails to correctly describe the stability of hcp iron. Their performance is also examined for binary
liquids, superionic phases, and a seven-component Fe-Ni-Si-S-O-H-C
liquid. Although these FAMs were not explicitly trained on data from core conditions, they can reproduce several structural and dynamical properties across a wide range of compositions. However, none of the tested models consistently reproduces all first-principles
benchmarks. By analyzing the origins of these discrepancies, we identify several limitations of current FAMs, particularly the lack of an explicit treatment of thermal electronic excitations, which significantly affect phase stability and thermodynamic properties under core conditions. We further discuss directions for improving FAMs to enable predictive simulations of core-forming materials under extreme conditions.
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All authors Tianqi Wan, Liangrui Wei, Zepeng Wu, Renata M. Wentzcovitch, Yang Sun
Materials Science
Anisotropic Dopant and Strain Architectures in WS$_2$ Nanocrystals Driven by Growth Kinetics
Frederico B. Sousa, Raphaela de Oliveira, Matheus J. S. Matos et al. (+11 more)
Dopant distribution in two-dimensional
semiconductors is typically assumed to be
stochastic, limiting deterministic defect engineering. Here, we show that non-
equilibrium growth kinetics can be harnessed to define dopant-driven strain architectures in vanadium-doped WS$_2$ monolayers. Using synchrotron X-ray fluorescence, we identify preferential vanadium incorporation, anti-correlated with tungsten content, along crystallographic bisectors. An adsorption-growth-
diffusion model with a single kinetic parameter quantitatively captures the dopant segregation arising from preferential corner adsorption and limited
diffusion during chemical vapor deposition growth. Hyperspectral Raman imaging demonstrates mechanically induced vibrational responses, revealing localized tensile strain ($\varepsilon \approx0.70\%$) channels associated with the anisotropic dopant distribution. This regime is marked by the depletion of W-site-sensitive in-plane modes and the emergence of a localized $J2$ mode (210~cm$^{-1}$), which our ab-initio calculations attribute to antiphase V$-$V oscillations. These findings establish kinetic segregation as a route to deterministic chemical and strain architectures in 2D
semiconductors, enabling programmable defect landscapes and strain engineering during synthesis.
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All authors Frederico B. Sousa, Raphaela de Oliveira, Matheus J. S. Matos, Elizabeth Grace Houser, Igor Ferreira Curvelo, Zhuohang Yu, Mingzu Liu, Felipe Menescal, Gilmar Eugenio Marques, Leandro M. Malard, Mauricio Terrones, Bruno R. Carvalho, Helio Chacham, Marcio D. Teodoro
Materials Science
Correlation-driven tunability of altermagnetism in RuO$_2$
Ina Park, Dongwook Kim, Inho Lee et al. (+3 more)
RuO$_2$ has been regarded as a prototypical candidate for metallic altermagnet, offering a potential platform for high-speed and high-efficiency spintronics. However, the
magnetic ground state of RuO$_2$ remains a topic of active debate due to conflicting experimental reports. In this work, we investigate the effect of electron correlations in RuO$_2$ using density functional theory combined with dynamical mean-field theory (DFT+DMFT). In contrast to previous DFT-based studies, DFT+DMFT captures essential dynamical correlation effects, yielding spectral functions and optical conductivities in excellent quantitative agreement with experiments, and further reveals that RuO$_2$ resides in the close vicinity of both the paramagnetic-altermagnetic phase boundary and the itinerant-localized crossover, rendering the
magnetic ground state highly susceptible to external perturbations. Indeed, even a minimal compressive strain of $\sim$0.5% is sufficient to drive the system into an altermagnetic phase. These findings elucidate the origin of the conflicting experimental observations and reveal that dynamical correlation effects are the key driving force behind the highly tunable
magnetic ground state of RuO$_2$.
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All authors Ina Park, Dongwook Kim, Inho Lee, Jisook Hong, Beomjoon Goh, Bo Gyu Jang
Materials Science
High-temperature behavior of amorphous alumina coatings: Insights from in-situ nanoindentation and X-ray diffraction studies
A. Zaborowska, L. Kurpaska, M. Zielinski et al. (+9 more)
Further development of
nuclear power plant technology relies heavily on materials durability under operating conditions. Estimating the materials performance in the operando tests is crucial. In this paper, the mechanical behavior of thin amorphous
nuclear-dedicated Al2O3 coatings deposited by pulsed
laser deposition was investigated by nanoindentation over the temperature range of 25-650C. Experimental nanomechanical analysis was supported by MD simulations. The results indicate that the hardness of the amorphous coating experiences a gradual, constant decrease with temperature, while the Young modulus value remains constant in the whole temperature range. Observed phenomena confirm the increasing plasticity of the material and it is postulated to be related to the bond-switching mechanism that accelerates at high temperatures. The post-mortem transmission electron microscopy characterization confirmed that the loaded material was non-crystalline over the entire range of the indentation temperatures. The thermal stability of the structure was further studied in-situ up to 1050C by X-ray diffraction. The implemented methodology allowed us to follow the dynamic process of phase transitions occurring in the material above 650C. First, thermally activated crystallization was observed at 700C. Intermediate alumina phases were present up to 950C, while above this temperature, exclusively the thermodynamically stable alpha-Al2O3 was observed. The in-situ high-temperature characterization of the
evolution of thin films boosts the understanding of the application limits of the coating systems at elevated temperatures. The added value is that the paper demonstrates the potential usefulness of combining high-temperature techniques to characterize the complete behavior of thin films at elevated temperatures.
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All authors A. Zaborowska, L. Kurpaska, M. Zielinski, Q. Xu, E. Wyszkowska, J. OConnell, J.H. Neethling, F. Di Fonzo, M. Frelek-Kozak, S. Papanikolaou, R. Diduszko, J. Jagielski
Materials Science
Multiple Softening Q-vectors Driving a Cascade of CDW Phases in $\mathrm{1T-VSe}_{2}$
Zheng-Hong Li, Yung-Ting Lee, Yu-Chan Tai et al. (+8 more)
Charge density wave (CDW) formation in two-dimensional materials is governed by complex competing
lattice instabilities that remain incompletely understood. Here, we investigate the structural
evolution of monolayer $\mathrm{1T-VSe}_{2}$ using first-principles electronic and
phonon calculations. The pristine phase exhibits several imaginary-frequency
phonon modes associated with dominant instability wave vectors $\mathrm{Q}_{CDW}$, which generate the first-generation CDW phases. Subsequent
phonon analyses reveal that several of these intermediate structures remain dynamically unstable and undergo further
symmetry-lowering distortions into larger superstructures. Through iterative
phonon-driven relaxations, we identify multiple transformation pathways that converge toward the same low-energy $2\sqrt{3}\times4$ CDW configuration. Although these pathways originate from distinct intermediate CDW states, they ultimately reach nearly degenerate energetically stable phases, demonstrating that different
phonon-driven routes can lead to the same ground-state configuration. The results establish a unified
phonon-driven cascade mechanism for hierarchical CDW formation in monolayer $\mathrm{1T-VSe}_{2}$ and provide a systematic framework for understanding competing ordered phases in low-dimensional
quantum materials.
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All authors Zheng-Hong Li, Yung-Ting Lee, Yu-Chan Tai, Cheng-Tien Chiang, Chien-Cheng Kuo, Meng-Kai Lin, Chun-Liang Lin, Hung-Chung Hsueh, Ming-Chiang Chung, Po-Tuan Chen, Chi-Cheng Lee
Materials Science
From Film to Flakes: Electronic Properties and Magnetization Variations in Yttrium Iron Garnet
Pia M. Düring, Seema, Roman Hartmann et al. (+7 more)
Yttrium iron garnet (YIG) is a ferrimagnetic
insulator valued for its high Curie temperature, very low
magnetic damping, and ability to support long-range
spin-wave transport. These qualities have established it as a cornerstone material in the field of spintronics and magnonics. Most studies on YIG so far have been focused on bulk
crystals, thin films, and nanoparticles, including variants with substitutions at the yttrium or iron site. New morphologies such as sub-micron flakes have drawn interest recently as their geometry and mechanical flexibility might enable different device architectures. However, detailed investigations combining their electronic structure and
magnetic behavior remain scarce. In this work, we present a comparative study of the electronic and
magnetic properties of a bulk-like YIG film and a sub-micron-sized YIG flake. Our results highlight the distinct behavior that emerges in sub-micron dimensions and point toward future uses for flake-based YIG in compact spintronics devices.
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All authors Pia M. Düring, Seema, Roman Hartmann, Sebastian Sailler, Michaela Lammel, Andrei Gloskovskii, Christoph Schlueter, Angelo Di Bernardo, Sebastian T. B. Goennenwein, Martina Müller
Materials Science · Cross-listed from cond-mat.str-el
Reentrant behavior and possible $2/3$ magnetization plateau on the double-trillium langbeinite K$_2$Ni$_2$(SO$_4$)$_3$
Matías G. Gonzalez, Yurii Skourski, Johannes Reuther et al. (+1 more)
K$_2$Ni$_2$(SO$_4$)$_3$ is a member of the langbeinite family, consisting of two intertwined $S=1$ trillium
lattices, out of which one is strongly coupled (strong-TL) and the other is weakly coupled (weak-TL). Further inter-trillium interactions give rise to a highly-frustrated Heisenberg
Hamiltonian. Despite ordering at low temperatures, K$_2$Ni$_2$(SO$_4$)$_3$ lies close in parameter space to a
spin-
liquid region that surrounds the tetratrillium limit, where each triangle belonging to strong-TL turns into a tetrahedron by connecting to a single
spin from weak-TL. Here, we compare the experimentally determined magnetization process using pulsed
magnetic fields up to $40$ T with classical Monte Carlo calculations, uncovering a series of phase transitions at both low and intermediate fields. Furthermore, we reveal a signature of a $2/3$ magnetization plateau consisting of a $1/3$ phase on strong-TL and a fully polarized phase on weak-TL. Although in the classical limit no plateau is expected, we find a very prominent dome structure reflecting the tendency of the system to stabilize this particular
spin configuration. The presence of a dome leads to a reentrant phenomenon in which the system recovers the
Hamiltonian symmetries when increasing the
magnetic field. Finally, we show that this plateau-like phase is also present in the classical Heisenberg model on the single trillium and tetratrillium
lattices, indicating its possible presence in the large family of double-trillium langbeinite compounds. Our findings motivate future studies on the presence of the plateau phase in the
quantum limit of both trillium and double-trillium materials within the langbeinite family.
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All authors Matías G. Gonzalez, Yurii Skourski, Johannes Reuther, Ivica Živković
Materials Science
Minimum energy paths for defect annihilation in finite dodecagonal quasicrystal clusters
Tiejun Zhou, Rong Liu, Gang Cui et al. (+3 more)
Defect repair in quasicrystals involves local structural rearrangements on a complex potential energy landscape. Here, we combine the string method with the spring pair method to compute a minimum energy path connecting a locally defective finite dodecagonal quasicrystal cluster to a locally repaired reference configuration in the Lennard-Jones–Gauss particle model. The computed path contains seven local minima connected through six transition states. A detailed analysis of one defective region resolves three successive stages: a phason flip, aggregation of neighboring shield-like defects, and decomposition of the aggregated motif. The phason flip restores the local outer-ring structure and relocates a shield-like defect into the interior. Subsequent collective rearrangements remove the defective motifs and yield a net decrease in the local interaction-energy measure together with an increase in local bond-orientational order. These results provide a microscopic description of a specific defect-repair pathway on the potential energy surface of a finite dodecagonal quasicrystal cluster.
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All authors Tiejun Zhou, Rong Liu, Gang Cui, Xianbo Huang, Li Peng, Kai Jiang
Materials Science · Cross-listed from physics.class-ph
Acoustic Chirality
Alex J. Vernon and Konstantin Y. Bliokh
We reveal a previously unknown continuous
symmetry and conservation law in the equations of linear isotropic elasticity, which describe the chirality of elastic waves. We show that the integral chirality is determined by the population imbalance between right- and left-handed transverse
phonons, whereas the local chirality density generally involves both transverse and longitudinal wave components. We also introduce the related concepts of acoustic helicity and “false chirality”. The theory is illustrated with simple interference fields exhibiting distinct distributions of chirality,
spin angular momentum, and false chirality. Our results establish chirality as a fundamental property of elastic waves and provide a general theoretical framework for
chiral acoustic phenomena.
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Materials Science
Conditional probability density functional theory for solids
Peiwei You, Ryan Pederson, Kieron Burke et al. (+1 more)
The recently developed conditional probability density functional theory (CP-DFT) yields direct access to the exchange-correlation hole of a system, an important correlation function that is not available in standard DFT. We present the first results for extended materials with periodic boundary conditions. We validate CP-DFT for weakly correlated Na and Si. We apply it to a stretched hydrogen chain, the prototype of strong correlation. When applied to the Kagome material CsV$_3$Sb$_5$, we find $d$-orbital correlations that are missing in standard DFT, implying an enhanced finding probability between two separated electrons and a local charge density wave related modulation.
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All authors Peiwei You, Ryan Pederson, Kieron Burke, E. K. U. Gross
Materials Science
Magnesium-graphene interphase boundaries created by high-pressure torsion enhance hydrogen storage kinetics:Mechanisms and significance of activation energy and frequency factor
Runchen Zhou, Payam Edalati, Anthony Alhayek et al. (+6 more)
A strategy to overcome sluggish hydrogenation/dehydrogenation of magnesium is demonstrated by creating magnesium-
graphene interphase boundaries via high-pressure torsion (HPT). HPT reduces the grain size of pure magnesium from 1 mm to 850 nm, with 70% of grain boundaries having high misorientation angles.
Graphene addition leads to even finer grain sizes of 10-500 nm with a bimodal morphology. The magnesium-
graphene composites exhibit superior kinetics at 623 K while maintaining high air resistance. Kinetic modeling reveals that the rate-controlling mechanism transits from interfacial reaction in coarse-grained magnesium to atomic
diffusion in magnesium-
graphene nanocomposites. Kissinger analysis shows that the activation energy for hydrogen desorption remains unchanged at 145 +/- 2 kJ/mol, regardless of the presence of grain or interphase boundaries. However, the frequency factor (number of successful attempts to overcome the activation energy) increases with the generation of interfaces, which serve as sites for hydrogen
diffusion and heterogeneous metal/hydride nucleation. These findings highlight the impact of interphase boundary engineering via severe plastic deformation for enhancing the kinetics and air resistance of hydrogen storage materials.
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All authors Runchen Zhou, Payam Edalati, Anthony Alhayek, Shivam Dangwal, Marc Novelli, Md. Amirul Islam, Baran Bidyut Saha, Thierry Grosdidier, Kaveh Edalati
Materials Science
Structural, electronic, and optical properties of hexagonal GeSn from density functional theory
Yetkin Pulcu, János Koltai, Andor Kormányos et al. (+1 more)
Unlike cubic GeSn, which undergoes an indirect-to-direct bandgap transition only above a finite Sn concentration, lonsdaleite (2H) germanium is an intrinsic direct-gap
semiconductor. We employ first-principles density functional theory to investigate the structural, electronic, and optical properties of 2H-Ge$_{1-x}$Sn$_{x}$ random
alloys in the dilute Sn regime ($x \le 0.10$). Substitutional disorder is modeled using 48-atom special quasirandom structure (SQS) supercells, and the coherent effective band structure is recovered via spectral band unfolding. We show that the semiconducting
alloy configurations retain a direct bandgap at the $\Gamma$ point, with a moderate, nearly linear reduction of the bandgap in the dilute regime that shifts the fundamental absorption edge toward the mid-infrared. As the gap approaches zero, its calculated value becomes increasingly sensitive to the atomic configuration and supercell size. Evaluation of the optical transition
matrix elements shows that the polarization anisotropy characteristic of pristine 2H-Ge remains observable under dilute Sn alloying. Although
alloy disorder relaxes the
crystal selection rules, the band edge response remains dominated by light polarized perpendicular to the
crystal $c$ axis, whereas the parallel component remains weaker. These results identify dilute hexagonal GeSn as a tunable direct-gap system with a strongly polarization-dependent optical response in the infrared.
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All authors Yetkin Pulcu, János Koltai, Andor Kormányos, Guido Burkard
Materials Science
Helium Bubbles in Liquid Lead Lithium Solutions: Pressure Inhomogeneities at Interfaces and Non Ideal Mixture Effects
Edgar Alvarez-Galera, Jordi Marti and Lluis Batet
The extremely low solubility of helium in
liquid metals may lead to rapid supersaturation, promoting spontaneous formation of helium bubbles by nucleation. Once nucleated, the stability of these bubbles is governed by the properties of the helium
liquid metal interface. In particular, interfacial tension between the immiscible phases controls bubble interactions and induces local pressure inhomogeneities. This work is motivated by the need of a better understanding of helium bubble formation in
liquid Pb Li
alloys, which are of particular relevance for the design of breeding blankets in the future
nuclear fusion reactors. We employ classical molecular dynamics simulations to investigate helium segregation in a range of lead lithium systems, including the limiting cases of pure lead and pure lithium. Changes in local pressure are evaluated from direct mechanical calculations, enabling the characterization of interfacial properties. Interfacial tension and radius of the bubble are subsequently determined across multiple thermodynamic conditions, spanning temperatures starting near the melting points of the constituent metals up to 1021 K. The impact of
curvature and composition of the
alloy on the interfacial behaviour are also investigated.
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Materials Science
Ultrafast Critical Slowing of Spin Dynamics and Emergent Nonequilibrium Fano Interference in Fe3GeTe2
Anupama Chauhan, Sidhanta Sahu, Satyabrata Bera et al. (+5 more)
Fe$_3$GeTe$_2$ is a prototypical metallic van der Waals ferromagnet with itinerant magnetism and a highly tunable Curie temperature, yet how electronic excitations couple to
spin and
lattice degrees of freedom across its
magnetic transition remains largely unexplored. Here, we use two-color pump-probe reflectivity to investigate the coupled electronic,
spin, and
lattice dynamics. The time-resolved reflectivity exhibits a tri-exponential relaxation, in which the intermediate component shows an anomaly near the Curie temperature due to enhanced interlayer
spin-
lattice interactions, while the slowest component displays pronounced critical slowing down with an exponent of ~ 0.3, revealing non-universal relaxation dynamics associated with intralayer
spin correlations. Furthermore, we observe an emergent nonequilibrium A1g
phonon Fano asymmetry that is suppressed in the
ferromagnetic phase but anomalously enhanced in the paramagnetic regime, driven by thermally activated anharmonic decay pathways that bridge the kinematic gap to a hot electronic continuum. The pronounced enhancement of the acoustic strain pulse amplitude near T$_c$ further evidences robust magnetoelastic coupling. Overall, our results reveal how
magnetic order governs the interplay among critical
spin dynamics, electronic continuum excitations, and
lattice response in metallic van der Waals ferromagnets
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All authors Anupama Chauhan, Sidhanta Sahu, Satyabrata Bera, Tuhin Debnath, Mintu Mondal, Anamitra Mukherjee, Siddhartha Lal, N. Kamaraju
Materials Science
Apparent Ferroelectric Polarization Hysteresis and a Simple Method to Observe Piezoelectric Strain Loops with a Microphone
Mamoru Fukunaga
Extra components in series to non-ferroelectric capacitance can cause apparent ferroelectric D-E hysteresis loops even with the double-wave method (DWM). Characteristics of fake loops are studied withsimple
circuit models, and suspicious loops of actual materials are found in some papers using the DWM. Inverse piezoelectric strain also reverses along with the polarization by the electric field, and S-E loops are considered more reliable to prove ferroelectricity than the D-E loops. But measurement of S-E loops usually requires expensive instruments in contrast to D-E loops with a simple
circuit. A very simple method is developed to observe S-E loops of bulk samples with an inexpensive small electret microphone and a little expansion to the
circuit for D-E loops. S-E loops of a commercial ceramic capacitor by this method reveal that its D-E loops apparent.
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Materials Science
Selective Octahedral Accommodation of Cr$^{3+}$ and Weak Magnetic Connectivity in the Sugilite Analogue KNa$_2$Cr$_2$Li$_3$Si$_{12}$O$_{30}$
Yuya Haraguchi, Taishu Aoki, Daisuke Nishio-Hamane et al. (+1 more)
We report the synthesis of the Cr analogue of sugilite, KNa$_2$Cr$_2$Li$_3$Si$_{12}$O$_{30}$, in the milarite-type framework. Rietveld refinement of a composition-conserving antisite model gives $x = 0.0024(18)$ in KNa$_2$[Cr$_{2-x}$Li$_x$][Li$_{3-x}$Cr$_x$]Si$_{12}$O$_{30}$, corresponding to a T2-site Cr occupancy of $0.0008(6)$. X-ray MEM analysis shows no detectable Cr-like density at T2.
Magnetic susceptibility indicates weak
antiferromagnetic interactions with $\theta_{\mathrm{W}} = -4.78(7)$ K and no ordering above 1.8 K.
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All authors Yuya Haraguchi, Taishu Aoki, Daisuke Nishio-Hamane, Hiroko Aruga Katori
Materials Science · Cross-listed from cond-mat.str-el
Frustrated Magnetism of the $S = 1$ Trillium-Lattice Oxide Li$_2$NiGe$_3$O$_8$
Yuya Haraguchi
We report magnetization and heat-capacity measurements on the ordered-spinel
oxide Li$_2$NiGe$_3$O$_8$, where Ni$^{2+}$ ions with $S = 1$ form a single three-dimensional trillium
lattice. Powder x-ray diffraction confirms a cubic ordered-spinel structure with space group $P4_{1}32$ or $P4_{3}32$. The inverse susceptibility $H/M$ follows Curie–Weiss behavior above 50 K with an effective
magnetic moment $\mu_{\mathrm{eff}} = 3.124(4)\,\mu_{\mathrm{B}}$ per Ni and a Weiss temperature $\theta_{\mathrm{W}} = -0.21(1)$ K, but deviates smoothly below about 10 K. The
magnetic heat capacity $C_{\mathrm{mag}}/T$ shows a broad maximum near 3 K with a wide tail to about 10 K, and the
entropy recovered between 2 and 40 K is about 88% of $R \ln 3$. The broad heat-capacity maximum is compared with Monte Carlo results for the local
ferromagnetic Ising model on the trillium
lattice using a characteristic scale $J$ of order 7 K, while the inverse susceptibility shows only qualitative similarity to the theoretical curve. These results establish Li$_2$NiGe$_3$O$_8$ as a rare $S = 1$ single-trillium
oxide with frustrated
magnetic correlations. The present data provide an experimental platform for discussing the relation between Heisenberg-like and
spin-ice-like regimes on the trillium
lattice.
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Materials Science · Cross-listed from nlin.PS
Whitham modulation equations for the regularized Boussinesq equation with cubic nonlinearity
Mark A. Hoefer and Anna Vainchtein
A regularized Boussinesq equation is studied as a dispersive, long-wave (quasicontinuum) approximation of the
Fermi-Pasta-Ulam
lattice with a general cubic interaction force. Explicit periodic traveling wave solutions in terms of Jacobi
elliptic functions are classified, and their solitary-wave, kink, and trigonometric limits are obtained. The Whitham modulation equations describing slow modulations of periodic traveling wave solutions are derived using an averaged variational principle. The convexity (strict hyperbolicity, genuine nonlinearity) of the resulting hydrodynamic-type equations is examined numerically in general and analytically in the solitary-wave and harmonic limits. In particular, the loss of hyperbolicity and the formation of complex conjugate characteristic speeds is shown to lead to modulational instability of periodic traveling waves. The onset of modulational instability is verified by numerical computations of linearized spectra for periodic traveling waves and initial value problems that also reveal additional short-wave instabilities.
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Materials Science · Cross-listed from cond-mat.soft
Topological and morphological signatures of disorder in a self-assembled, soft matter sponge network
Xueyang Feng, Suman S. Kulkarni, Michael S. Dimitriyev et al. (+4 more)
Many soft matter systems exhibit ordered, polycontinuous network morphologies, such as the cubic (double) gyroid or diamond, as well as disordered network morphologies known generically as “random sponges". While presumed to share similar local packing geometry, the structural relationship between these ordered and disordered network morphologies has remained obscure. We use slice and view scanning electron microscopy to analyze and compare multi-scale morphological features of an ordered double-gyroid morphology to the amorphous sponge morphology formed in the same block copolymer sample. We find that node valence of the minority component network of the sponge is mostly gyroidal (trivalent), with a small fraction of diamond-like (tetravalent) connections. We analyze mesoatoms – space-filling volumes occupied by chains around each network node – finding significant differences in shape and size between ordered and amorphous regions. Local block thickness and inter-domain
curvature within mesoatomic units of the disordered sponge exhibits a surprisingly similar degree of dispersity to the ordered double-gyroid. The mean differences in local packing geometry derive from topological distinction: loops of the minority networks of the ordered double-gyroid are intercatenated, while loops of the disordered sponge are not. In this way, the sponge may be viewed as disordered variant of a single-gyroidal morphology. We exploit these topological differences to demarcate the boundary region between ordered and disordered networks and highlight modulations of the mesoatom motifs at the boundary. These observations point to new questions about potential metastability of disordered networks and their possible role as kinetic precursors to long-range ordered network morphologies.
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All authors Xueyang Feng, Suman S. Kulkarni, Michael S. Dimitriyev, Dani S. Bassett, Randall D. Kamien, Edwin L. Thomas, Gregory M. Grason
Materials Science
Ultraviolet plastic scintillators based on naphthalene-doped polystyrene and polyvinyltoluene
Nicolás Agustín Molina, Victoria Alejandra Gómez Andrade, Javier Martín Abbas et al. (+6 more)
This work reports the fabrication and optical characterization of ultraviolet-emitting plastic scintillators based on polystyrene [-(CH2-CH(C6H5))n-] and polyvinyltoluene [-(CH2-CH(C6H4CH3))n-] doped with different concentrations of naphthalene (Naph). Photoluminescence (PL) measurements show that Naph incorporation enhances the emission intensity, inducing a red shift in the emission wavelength of the polystyrene (PS), while Naph-doped polyvinyltoluene (PVT) exhibits a bimodal emission with peaks around 335 and 350 nm. Time-resolved photoluminescence (TRPL) reveals fast decay components for the undoped
matrices and a dominant slow component of approximately 87 ns in the doped samples. Scintillation light yield measurements indicate moderate performance for the undoped
polymers and a significant enhancement upon Naph doping.
Proton irradiation experiments reveal a reduction in light yield for all samples, with Naph-doped PVT retaining a larger fraction of its initial light yield compared to PS-based scintillators, indicating improved radiation tolerance. Overall, these results demonstrate the effectiveness of Naph as a UV emission enhancer and highlight Naph-doped PVT as a promising candidate for compact and radiation-resistant scintillation detectors.
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All authors Nicolás Agustín Molina, Victoria Alejandra Gómez Andrade, Javier Martín Abbas, Alan Fuster, Luciano Ferreyro, Martín Alurralde, Martin Mirenda, María Dolores Pérez, Paula Guidici
Materials Science
Ultrafast electron dynamics of electron-irradiated graphene
Yifan Yao and Andre Schleife
Electron irradiation is essential for materials characterization and modification, though the fundamental interactions between incident electrons and host materials remain under investigation. Here, we employ first-principles simulations to study electron dynamics under external electron irradiation. We quantify differences in key observables, including kinetic energy loss, secondary electron emission, and backscattered electrons, between classical and
quantum mechanical descriptions of the incident electron. Around 400 eV incident energy, we identify significant differences in backscattered electron yields between classical point-charge and
quantum wave-packet descriptions, whereas the
quantum-mechanical effects diminish at incident energies above 600 eV. These differences highlight the critical importance of
quantum effects in electron irradiation phenomena that occur in a specific energy range of the incident electron. Our results provide clear guidance for selecting appropriate incident, electron descriptions based on kinetic-energy regimes, identify a targeted experimental window for isolating
quantum-only backscattering, and enable the rational design of 2D materials for nanofabrication and high-resolution electron-beam technologies.
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