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Physics Condensed Matter Materials Science

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Monday 12 January

Materials Science

Noise2Void for Denoising Atomic Resolution Scanning Transmission Electron Microscopy Images

William Thornley, Sam Sullivan-Allsop, Rongsheng Cai et al. (+3 more)

The Noise2Void technique is demonstrated for successful denoising of atomic-resolution scanning transmission electron microscopy (STEM) images. The technique is applied to denoising atomic resolution images and videos of gold adatoms on a graphene surface within a graphene liquid cell, with the denoised experimental data qualitatively demonstrating improved visibility of both the Au adatoms and the graphene lattice. The denoising performance is quantified by comparison to similar simulated data and the approach is found to significantly outperform both total variation and simple Gaussian blurring. Compared to other denoising methods, the Noise2Void technique has the combined advantages that it requires no manual intervention during training or denoising, no prior knowledge of the sample and is compatible with real time data acquisition rates of at least 45 frames per second.
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All authors William Thornley, Sam Sullivan-Allsop, Rongsheng Cai, Nick Clark, Roman Gorbachev, Sarah J. Haigh

Materials Science

A density functional theory study of amino acids on Mg and Mg-based alloys

John Bolin, Amanda Goold, Olof Hildeberg et al. (+2 more)

Magnesium (Mg) has mechanical properties similar to bone tissue, and Mg ions take part in the metabolism. This makes Mg of interest for biocompatible degradable body implants, provided that its high corrosion rate can be inhibited. Slightly alloying Mg and adding surface coatings can slow down the corrosion processes without significantly changing the mechanical properties. Use of coating molecules that are native to the body increase the likelihood of making the surface biocompatible, for example by use of amino acids. We here present a density functional theory (DFT) study of the adsorption on Mg(0001) of the amino acids glycine, L-proline, and L-hydroxyproline (Hyp), the main amino acid content of collagen. We investigate how binding of the functional groups of Hyp are affected when Mg(0001) is slightly alloyed with zinc, lithium or aluminium, and we also model the immersion of the systems in a water environment to see how this affects the binding.
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All authors John Bolin, Amanda Goold, Olof Hildeberg, Alva Limbäck, Elsebeth Schröder

Materials Science

Anisotropic anomalous Hall effect in distorted kagome GdTi3Bi4

Avdhesh K. Sharma, Bo Tai, Subhajit Roychowdhury et al. (+5 more)

Topological kagome magnets offer a rich landscape for exploring the intricate interplay of quantum interactions among geometry, topology, spin, and correlation. GdTi3Bi4 crystallizes in layered Ti based kagome nets intertwined with zigzag Gd chains along the a axis and orders antiferromagnetically below 15 K. Here, we present the temperature and field dependent electrical transport of GdTi3Bi4 in different directions. The material exhibits anomalous Hall conductivity (AHC) of 410 S cm-1 at 2 K for B parallel c and it is completely absent for B parallel a, despite the similar magnetization observed in both orientations. This behavior is quite contradictory, as anomalous Hall effect (AHE) typically scales with the magnetization. Through first principles calculations, it is demonstrated that in the presence of time reversal symmetry broken by the Gd 4f sublattice and spin orbit coupling, the magnetization direction controls the orbital mixing in the Ti t2g bands, relocating Berry curvature hot spots and producing the observed orientation selective AHC. The results establish GdTi3Bi4 as platform for investigating new avenues of AHE, such as directional AHE, and thus shed new light on the intricate coupling between magnetic and electronic structures, paving the way for exploring novel quantum phenomena.
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All authors Avdhesh K. Sharma, Bo Tai, Subhajit Roychowdhury, Premakumar Yanda, Ulrich Burkhardt, Xiaolong Feng, Claudia Felser, Chandra Shekhar

Materials Science

PEG- and PVP-assisted wet-chemical synthesis of ZnS nanocrystals via hydrothermal and co-precipitation methods for route-dependent structural and bandgap tuning

Rao Uzair Ahmad, Nasir Javed and Falak Sher

Zinc sulphide (ZnS) is a non-toxic, wide-bandgap II-VI semiconductor with well-established optoelectronic properties. This work presents a systematic, concentration-dependent comparison of PEG and PVP across two scalable aqueous routes, linking ligand chemistry to crystallite size and bandgap shifts. ZnS quantum dots (QDs) were synthesized using polymer-assisted wet-chemical methods, hydrothermal processing and room-temperature co-precipitation. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) were used as capping agents to examine their influence on particle growth, dispersion, and optical behaviour. Room-temperature co-precipitation produced QDs with crystallite sizes as small as 2.03 nm, whereas hydrothermal synthesis at elevated temperature yielded larger crystallites exceeding 6 nm. X-ray diffraction confirmed cubic zinc-blende ZnS in all samples, with peak broadening and small lattice-parameter variations consistent with nanoscale dimensions. UV-visible absorption spectra showed systematic shifts of the absorption edge, with optical bandgap values ranging from 3.60 to 3.80 eV, consistent with size-dependent quantum confinement. Fourier-transform infrared spectroscopy and dynamic light scattering verified effective polymer capping and particle size distribution, with PVP providing stronger growth suppression and improved dispersion compared to PEG. Overall, the results highlight how synthesis route and polymer-nanocrystal interactions govern the structural and optical properties of ZnS QDs. The demonstrated bandgap tuning and improved dispersion with PVP are relevant for UV optoelectronic coatings and QD-based layers used in photodetectors and LED interfaces.
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Materials Science · Cross-listed from physics.optics

Exciton coherence propagation measured with non-local four-wave mixing micro-spectroscopy

Mateusz Raczyński, Amadeusz Dydniański, Karolina Ewa Połczyńska et al. (+8 more)

Coherence transfer is a multi-disciplinary topic of interest, including chemistry, biology and physics. In quantum technologies, achieving non-local coherent coupling between solid-state qubits is of the utmost importance. Here, we demonstrate that excitons - i.e. electron-hole pairs bound by the Coulomb force within a quantum well - can act as a medium for mesoscopic optical coherence transfer in semiconductors. To this end, we use a femtosecond laser pulse to resonantly generate excitons within the light cone. These excitons can then either recombine radiatively or scatter out of the light cone, gaining an in-plane momentum in the process. In samples without disorder, such as the CdTe quantum wells used here, the resulting fast excitons can diffuse over mesoscopic distances before recombining radiatively. Using coherent nonlinear micro-spectroscopy, we carry out exciton time-of-flight measurements. Specifically, we monitor the spatio-temporal propagation of launched exciton wave packets, selectively observing their coherence or density on a scale of up to 10$\,\mu$m. Our proof-of-principle experiment demonstrates that free excitons inherit a phase modulation from the optical pulsed excitation and can generate coherent links within excitonic circuits, offerring a higher level of miniaturisation and compactness than photonic or polaritonic architectures.
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All authors Mateusz Raczyński, Amadeusz Dydniański, Karolina Ewa Połczyńska, Gabriela Szwed, Adam Szczerba, Jin-Woo Jung, Gilles Nogues, Wolfgang Langbein, Piotr Kossacki, Wojciech Pacuski, Jacek Kasprzak

Materials Science · Cross-listed from math.FA

Phase-field approximation of sharp-interface energies accounting for lattice symmetry

Sergio Conti, Vito Crismale, Adriana Garroni et al. (+1 more)

We present a phase-field approximation of sharp-interface energies defined on partitions, designed for modeling grain boundaries in polycrystals. The independent variable takes values in the orthogonal group $\mathrm{O}(d)$ modulo a lattice point group $\mathcal{G}$, reflecting the crystallographic symmetries of the underlying lattice. In the sharp-interface limit, the surface energy exhibits a Read-Shockley-type behavior for small misorientation angles, scaling as $\theta|\log\theta|$. The regularized functionals are applicable to grain growth simulation and the reconstruction of grain boundaries from imaging data.
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All authors Sergio Conti, Vito Crismale, Adriana Garroni, Annalisa Malusa

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

Reconfigurable Oxide Nanoelectronics by Tip-induced Electron Delocalization

Chengyuan Huang, Changjian Ma, Mengke Ha et al. (+15 more)

Reconfigurable oxide nanoelectronics, enabled by conductive atomic force microscope (cAFM) lithography, have established complex oxide interfaces as a promising platform for quantum engineering that harnesses emergent phenomena for advanced functionalities. However, this cAFM nanofabrication process can only occur in the air, with simultaneous device decay described under the "water-cycle" writing mechanism. These restrictions pose ongoing challenges for device optimization in the quantum regime at mK temperatures. Here, we demonstrate a "waterless" cAFM lithography approach that is compatible with vacuum and cryogenic environments. Through oxygen vacancy engineering at the LaAlO$_3$/SrTiO$_3$ interface, we have achieved nonvolatile and reconfigurable cAFM control of nanoscale interfacial polaron-electron liquid transition at mK temperatures with an ultrafine line resolution of 0.85 nm. Supported by first-principles calculations and drift-diffusion modeling, we show that tip-controlled oxygen vacancy electromigration plays a key role. This advancement bridges reconfigurable device fabrication and concurrent characterization in situ at mK temperatures, and establishes a versatile Hubbard toolbox for engineering programmable quantum phases in correlated oxides.
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All authors Chengyuan Huang, Changjian Ma, Mengke Ha, Longbing Shang, Zhenlan Chen, Qing Xiao, Zhiyuan Qin, Danqing Liu, Haoyuan Wang, Dawei Qiu, Qianyi Zhao, Ziliang Guo, Yanling Liu, Dingbang Chen, Chengxuan Ye, Zhenhao Li, Chang-Kui Duan, Guanglei Cheng

Materials Science

High isothermal magnetocaloric effect in La(Fe,Si)13 based alloys

A.P. Kamantsev, Yu.S. Koshkid`ko, O.E. Kovalev et al. (+4 more)

This work investigates the magnetocaloric effect (MCE) in LaFe_{11.6}Si_{1.4} and LaFe_{11.78}Mn_{0.41}Si_{1.32}H_{1.6} alloys under adiabatic {\Delta}T and isothermal {\Delta}Q conditions in a magnetic field of {\mu}_{0}H = 1.8 T. The studied samples exhibited high reproducibility of the {\Delta}Q-effect upon cyclic magnetic field application, which is of critical importance for magnetic cooling systems.The LaFe_{11.78}Mn_{0.41}Si_{1.32}H_{1.6} alloy demonstrate high values of the isothermal MCE, with a maximum {\Delta}Q = 3400 J/kg in a magnetic field of {\mu}0H = 1.8 T near the Curie temperature (TC) of 275 K. This value is 2.5 times higher than the well-known corresponding values for pure Gd at room temperature. Furthermore, the structural and magnetic properties of LaFe13-xSix-based alloys with Cr and Co additions were investigated using density functional theory calcula-tions. It was shown that the addition of Cr leads to a decrease in the equilibrium volume, i.e., to a com-pression of the crystal lattice, whereas Co addition causes its expansion. These changes are expected to increase or decrease the T_{C}, respectively.
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All authors A.P. Kamantsev, Yu.S. Koshkid`ko, O.E. Kovalev, N.Yu. Nyrkov, A.V. Golovchan, A.A. Amirov, A.M. Aliev

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

Field-induced magnetic phase transitions and transport anomalies in GdAlSi

Zheng Li, Sheng Xu, Yi-Yan Wang et al. (+6 more)

Magnetic topological materials hosting non-zero Berry curvature have emerged as a focus of intensive research due to their exceptional magnetoelectric coupling phenomena and potential applications in next-generation spintronic devices. In this work, we successfully synthesized high-quality GdAlSi single crystals, a prototypical member of RAlX (R = rare earth elements; X = Si/Ge) family that has been theoretically predicted to sustain a non-trivial Weyl semimetal state. Through systematic investigations of magnetic and transport properties, we identified two successive antiferromagnetic transitions at critical temperatures TN1 31.9 K and TN2 31.1 K, as evidenced by temperature-dependent resistivity, magnetic susceptibility, and specific heat measurements. Notably, applied magnetic fields exceeding 8 T induce a third magnetic transition (TN3), generating a cascade of metamagnetic transitions that collectively form a dendritic phase diagram. This complex magnetic behavior is attributed to the interplay between localized Gd-4f moments and itinerant conduction electrons, possibly mediated by Dzyaloshinskii-Moriya interactions. Transport measurements revealed striking stepwise anomalies in magnetoresistance when crossing phase boundaries, accompanied by pronounced hysteresis loops arising from magnetic moment flopping processes. Our results not only establish GdAlSi as a rich platform for investigating correlated topological states, but also demonstrate its potential for engineering topological phase transitions through magnetic symmetry manipulation in Weyl semimetals.
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All authors Zheng Li, Sheng Xu, Yi-Yan Wang, Tian-Hao Li, Shu-Xiang Li, Jin-Jin Wang, Jun-Jian Mi, Qian Tao, Zhu-An Xu

Materials Science

Analysis of contributions of plastic deformation and intergranular corrosion to corrosion-fatigue failure of Al-Mg alloys

Oleg Belkin, Vladimir Chuvil'deev, Mikhail Chegurov et al. (+2 more)

The article presents the results of corrosion-fatigue tests of industrial Al-Mg alloys were conducted in air and in a 3% NaCl aqueous solution. Fatigue curves can be characterized using the Basquin equation and the plastic deformation model at the crack tip. It has been demonstrated that the primary contributions to corrosion-fatigue failure in the Al-Mg alloys at low stresses are made by the process of pitting and intergranular corrosion, and by the plastic deformation at high stresses.
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All authors Oleg Belkin, Vladimir Chuvil'deev, Mikhail Chegurov, Aleksey Nokhrin, Anatoly Sysoev

Materials Science

Effect of the parameters of bimodal microstructure on the mechanical properties of alumina: A case of sintering regime effects

M. S. Boldin, E. A. Isupova, E. A. Lantcev et al. (+7 more)

The effect of sintering regimes on the density, microstructure parameters, and mechanical properties of Al2O3 and Al2O3 + 0.25%MgO ceramics has been investigated. The ceramics were sintered in three regimes: Regime I - heating at a constant rate (2.5, 5, 10, 20 C/min) up to the temperature T=1650C; Regime II - heating with a varied heating rate up to 1565C with the duration corresponding to sintering at the heating rate of 10 C/min in Regime I followed by a three-fold decrease in the shrinkage rate; Regime III - two-stage sintering: heating according to Regime II up to the temperature T1+1550C, then lowering the temperature down to T2 = 1300-1500C and holding for 3 h at the T2. The sintering regimes were chosen so that the ceramics had the relative density of 97-99% and a bimodal distribution of the microstructure parameters. The Al2O3 and Al2O3 + 0.25%MgO ceramics obtained in Regimes I-III had a microstructure with abnormally large grains in a fine-grained matrix. The sizes and volume fractions of the large grains depended on the sintering regime. Most abnormally large grains had elongated shapes that leads to deviations in the crack propagation trajectories from the straight line. The optimal parameters of the bimodal microstructure parameters distribution providing enhanced mechanical properties of the ceramics (hardness, indentation fracture toughness, ultimate strength) have been determined.
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All authors M. S. Boldin, E. A. Isupova, E. A. Lantcev, T. S. Pozdova, M. D. Nazmutdinov, D. A. Permin, A. A. Murashov, A. N. Sysoev, A. V. Nokhrin, V. N. Chuvil'deev

Materials Science · Cross-listed from cs.LG

Simulated Annealing-based Candidate Optimization for Batch Acquisition Functions

Sk Md Ahnaf Akif Alvi, Raymundo Arróyave and Douglas Allaire

Bayesian Optimization with multi-objective acquisition functions such as q-Expected Hypervolume Improvement (qEHVI) requires efficient candidate optimization to maximize acquisition function values. Traditional approaches rely on continuous optimization methods like Sequential Least Squares Programming (SLSQP) for candidate selection. However, these gradient-based methods can become trapped in local optima, particularly in complex or high-dimensional objective landscapes. This paper presents a simulated annealing-based approach for candidate optimization in batch acquisition functions as an alternative to conventional continuous optimization methods. We evaluate our simulated annealing approach against SLSQP across four benchmark multi-objective optimization problems: ZDT1 (30D, 2 objectives), DTLZ2 (7D, 3 objectives), Kursawe (3D, 2 objectives), and Latent-Aware (4D, 2 objectives). Our results demonstrate that simulated annealing consistently achieves superior hypervolume performance compared to SLSQP in most test functions. The improvement is particularly pronounced for DTLZ2 and Latent-Aware problems, where simulated annealing reaches significantly higher hypervolume values and maintains better convergence characteristics. The histogram analysis of objective space coverage further reveals that simulated annealing explores more diverse and optimal regions of the Pareto front. These findings suggest that metaheuristic optimization approaches like simulated annealing can provide more robust and effective candidate optimization for multi-objective Bayesian optimization, offering a promising alternative to traditional gradient-based methods for batch acquisition function optimization.
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Materials Science · Cross-listed from cond-mat.str-el

Interplay of Charge and Magnetic Orders in SmNiC$_2$ Mediated by Electron-Phonon Interaction

A. von Ungern-Sternberg Schwark, A.-A. Haghighirad, R. Heid et al. (+11 more)

We investigate the interplay between charge density wave (CDW) instabilities and ferromagnetism in SmNiC$_2$ using diffuse and inelastic x-ray scattering together with Raman spectroscopy. We identify a soft acoustic phonon driving the incommensurate CDW (I-CDW) and uncover a second Kohn anomaly at the wave vector of the commensurate CDW (C-CDW) stabilized in other $R$NiC$_2$ members ($R=$ rare earth). The marked softening of both phonons and their contrasting evolution with temperature reveal a competition between the two ordering tendencies. Alongside pronounced anomalies in the temperature dependence of the zone center and soft phonons, we observe the collective amplitude mode of the CDW, which collapses abruptly as ferromagnetism sets in. Surprisingly, the Kohn anomalies persist in the ferromagnetic state despite the degradation of Fermi-surface nesting conditions. Our experimental findings, supported by ab initio calculations, highlight the central role of the electron-phonon interaction in driving the CDW formation and tuning the balance between competing charge and magnetic orders.
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All authors A. von Ungern-Sternberg Schwark, A.-A. Haghighirad, R. Heid, P. H. McGuinness, N. Maraytta, A. Eich, M. Merz, A. Bosak, D. A. Chaney, A. Chumakova, A. Pawbake, C. Faugeras, M. Le Tacon, S. M. Souliou

Materials Science

Emergent Cooperative Superstructures via Order-Disorder Kinetics in Molecule-Intercalated NbSe2

Taiga Ueda, Hideki Matsuoka, Shungo Aoyagi et al. (+12 more)

The design of quantum states at heterointerfaces has enabled a variety of emergent phenomena. Among them, molecular intercalation superlattices have attracted attention as tunable hybrid materials, formed by inserting organic molecules into van der Waals crystals, where molecular structure and chemistry provide new degrees of freedom. Traditionally, the intercalated molecules have been regarded as inactive spacers, while possible molecular ordering and its impact on the host lattice have remained largely unexplored. Here, we report the discovery of a cooperative superstructure (CSS) phase in molecule intercalated NbSe2, where ordering of the guest molecules induce a concomitant superstructure in the NbSe2 host lattice, characterized by a moiré structure due to incommensurability between the molecular layer and the inorganic lattice. Synchrotron X-ray diffraction reveals the emergence of CSS phase, accompanied by crystal symmetry lowering. Complementary resistivity and thermal-quench measurements show that the transition is governed by unusually slow order-disorder kinetics, so that the CSS phase can be selectively accessed under standard laboratory cooling rates. This kinetic behavior arises from slow molecular dynamics coupled to the host lattice, contrasting with fast charge or magnetic ordering in inorganic solids. Our findings establish molecular ordering as a route for engineering heterointerfaces, enabling thermally programmable superstructures.
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All authors Taiga Ueda, Hideki Matsuoka, Shungo Aoyagi, Shunsuke Kitou, Yijin Zhang, Fumihiko Kimura, Kenta Hagiwara, Masato Sakano, Takahiro Iwagaki, Yuiga Nakamura, Kyoko Ishizaka, Tomoki Machida, Masayuki Suda, Taka-hisa Arima, Naoya Kanazawa

Materials Science

Thermodynamic Driving Force Activated Phonon Scattering in InN

Zaheer Ahmad, Osama A. Rana, Shakeel Ahmad et al. (+3 more)

Defect related disorder during InN growth is a major challenge for making high performance electronic and optoelectronic devices. This is partly because film quality is often described using reactor specific settings instead of general physical variables. In this study, we show that plasma assisted MOCVD growth of InN can be described using a single thermodynamic driving force coordinate. This coordinate brings together growth kinetics, defect sensitive Raman response and structural coherence across different process conditions. When we use this coordinate, the incorporation rate follows a universal activated trend with a kinetic scale of about 0.08 eV. Raman measurements show a clear crossover between a defect sparse and a defect rich regime, a disorder activated Raman metric increases quickly after the crossover, while an A1-LO control metric stays mostly the same. This suggests that short range lattice disorder, not long range polar coupling, dominates the defect activation process. X-ray diffraction shows that the out of plane coherence length stays the same for samples with the same driving force, even if reactor settings are very different. This supports the idea that structural coherence is organized by thermodynamics in this growth window. Finally, a simple kinetic Monte Carlo model using driving force biased incorporation and defect activation events matches the observed exponential trends and the two regimes, supporting the driving force approach. These results show that a transferable driving force coordinate can be used for plasma assisted InN growth and offer a quantitative way to achieve defect sparse growth conditions.
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All authors Zaheer Ahmad, Osama A. Rana, Shakeel Ahmad, Mark Vernon, Brendan Cross, Alexander Kozhanov

Materials Science

Improvement of a focused ion beam fabricated diamond pillar for scanning ensemble nitrogen-vacancy magnetometry probe using an ultrapure diamond

Dwi Prananto, Yifei Wang, Yuta Kainuma et al. (+3 more)

Scanning diamond nitrogen-vacancy probe microscopy (SNVM) is an important tool for studying nanoscale condensed-matter phenomena. Ga$^+$-ion-focused-ion-beam (FIB) milling has been introduced as a method for fabricating SNVM, while the probe diameter is limited to a few micrometers due to Ga$^+$-induced damage. We report a method for improving the quality of FIB-fabricated SNVM probes by polyvinyl alcohol and Pt/Pd capping, followed by post-fabrication UV/ozone exposure. The effectiveness of the method is confirmed by the fabrication of an 800 nm-diameter probe with shallow NV centers, demonstrating an imaging of maze-like magnetic domain structure with a resolution of a few hundred nanometers and an improved sensitivity of 6.7 $\mu$T/Hz${1/2}$, while preserving spin coherence properties.
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All authors Dwi Prananto, Yifei Wang, Yuta Kainuma, Kunitaka Hayashi, Masahiko Tomitori, Toshu An

Materials Science

Hidden half-metallicity

San-Dong Guo and Pan Zhou

Half-metals, featuring ideal 100% spin polarization, are widely regarded as key materials for spintronic and quantum technologies; however, the half-metallic state is intrinsically fragile, as it relies on a delicate balance of exchange splitting and band filling and is therefore highly susceptible to disorder, external perturbations, and thermal effects. Here we introduce the concept of hidden half-metallicity, whereby the global electronic structure of a symmetry-enforced net-zero-magnetization magnet is non-half-metallic, while each of its two symmetry-related sectors is individually half-metallic, enabling robust 100% spin polarization through a layer degree of freedom. Crucially, the vanishing net magnetization of the entire system suppresses stray fields and magnetic instabilities, rendering the half-metallic functionality inherently more robust than in conventional ferromagnetic half-metals. Using first-principles calculations, we demonstrate this mechanism in a $PT$-symmetric bilayer $\mathrm{CrS_2}$, and further show that an external electric field drives the system into a seemingly forbidden fully compensated ferrimagnetic metal in which hidden half-metallicity persists. Finally, we briefly confirm the realization of hidden half-metallicity in altermagnets, establishing a general paradigm for stabilizing half-metallic behavior by embedding it in symmetry-protected hidden sectors and opening a new route toward the design and discovery of unprecedented half-metallic phases.
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Materials Science

Percolation-Driven Magnetotransport due to Structural and Microstructural Evolution in Ultrathin Si/Fe Bilayers

S. S. Das and M. Senthil Kumar

The anomalous Hall effect (AHE) in magnetic nanofilms is highly sensitive to the microstructural and magnetic homogeneity. However, the evolution of the microstructure and morphology near the percolation threshold, and its connection to the resulting magnetic and magnetotransport behavior in low-dimensional magnetic heterostructures, remain poorly understood. In this study, we present a comprehensive analysis of the evolution of the structural, microstructural, and magnetotransport properties of Si/Fe bilayers by varying the Fe layer thickness. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and magnetisation data reveal a percolation-driven transition from a continuous metallic film to percolative network structure of grains when tFe decreases below 30 Angstrom. Transport measurements involving longitudinal resistivity (rho), and the anomalous Hall resistivity (rho_A,h,s) show clear divergence near the percolation threshold. The purely electronic conduction channels (rho) evolve more gradually as compared to the combined electronic and magnetic ones rho_A,h,s. The percolative analysis of the structural, magnetic, and magnetotransport data yields a critical exponent in the range of 0.78 to 1.16, consistent with that of 2D-disordered systems. The AHE scaling relation between the rho_A,h,s and rho reveals a crossover of the AHE mechanism from a mixed intrinsic/side-jump contribution with a minor skew scattering component (n ~ 1.42) in the thick, low-resistive samples (tFe > 30 Angstrom) to a skew-scattering-dominant mechanism (n = 0.62) in the high-resistive films (tFe <= 30 Angstrom). This crossover coincides with the onset of structural and magnetic connectivity between the grains. Furthermore, these findings underscore the interlink between microstructure, morphology, magnetism, and Hall transport under a percolation framework.
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Sunday 11 January

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

Fractional Order Thermo Piezoelectric Modelling of qP Wave Interaction and Energy Partition at Welded Interface

Hriticka Dhiman and Soniya Chaudhary

An analytical model is developed to investigate the interaction of quasi longitudinal (qP) waves with a perfectly bonded interface between a thermo piezoelectric half space and a functionally graded piezoelectric half space. The formulation is based on the fractional order Lord Shulman generalized thermoelasticity theory, which provides an enhanced description of coupled thermo electro mechanical wave behaviour. Rotational effects are incorporated into the constitutive relations and equations of motion for both media, while the lower half space is assumed to be subjected to initial stress. Closed form solutions for reflection and transmission coefficients are obtained, together with associated energy partition factors, allowing a comprehensive assessment of interface wave characteristics. Numerical simulations carried out using MATLAB demonstrate that the reflection and transmission responses are strongly influenced by initial stress, fractional order parameter, and thermal relaxation time. The calculated energy ratios of scattered waves satisfy the energy conservation condition, confirming the mathematical consistency of the formulation. The findings of this study are relevant to the design and analysis of smart sensors, rotating and aerospace structures, vibration control systems, and energy harvesting devices employing functionally graded thermo piezoelectric materials under fractional order effects.
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Materials Science · Cross-listed from cond-mat.str-el

Ferromagnetic Insulator to Metal Transition in Non-Centrosymmetric Graphene Nanoribbons

Aidan P. Delgado, Michael C. Daugherty, Weichen Tang et al. (+2 more)

Engineering sublattice imbalance within the unit cell of bottom-up synthesized graphene nanoribbons (GNRs) represents a versatile tool for realizing custom-tailored quantum nanomaterials. The interaction between low-energy zero-modes (ZMs) not only contributes to frontier bands but can form the basis for magnetically ordered phases. Here, we present the bottom-up synthesis of a non-centrosymmetric GNR that places all ZMs on the majority sublattice sites. Scanning tunneling microscopy and spectroscopy reveal that strong electron-electron correlations, leading to the Stoner magnetic instability, drive the system into a ferromagnetically ordered insulat-ing ground state featuring a sizeable band gap of Eg ~ 1.2 eV. At higher temperatures, a chemical transformation induces an insulator-to-metal transition that quenches the ferromagnetic order. Tight-binding (TB), density functional theory, and GW calculations corroborate our experimental observations. This work showcases how control over molecular symmetry, sublattice polarization, and ZM hybridiza-tion in bottom-up synthesized nanographenes can open a path to the exploration of many-body physics in rationally designed quantum materials.
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All authors Aidan P. Delgado, Michael C. Daugherty, Weichen Tang, Steven G. Louie, Felix R. Fischer

Materials Science

Case study of an exploratory high voltage NASICON-based Na$_4$NiCr(PO$_4$)$_3$ cathode material for sodium-ion batteries

Madhav Sharma, Pooja Sindhu and Rajendra S. Dhaka

We examine a new NASICON-type Na$_4$NiCr(PO$_4$)$_3$ material designed for high-voltage and multi-electron reactions for the sodium-ion batteries (SIBs). The Rietveld refinement of the X-ray diffraction pattern, using the R$\bar{3}$c space group, confirmed the stabilization of the rhombohedral NASICON framework. Furthermore, the Raman and Fourier transform infrared spectroscopy are employed to probe the structure and chemical bonding. The core-level photoemission analysis reveals the Cr$^{3+}$ and mixed Ni$^{2+}$/Ni$^{3+}$ oxidation states in the sample. Moreover, the bond valence energy landscape (BVEL) analysis, based on the refined structure, revealed a three-dimensional network of well-connected sodium sites with a migration energy barrier of 0.468 eV. The material delivered a good charge capacity at around 4.5 V, but showed no sodium-ion intercalation during discharge, resulting in negligible discharge capacity. The post-mortem analysis confirmed that the crystal structure remained intact. The calculated energy barrier values indicated a reversal in sodium site stability after cycling, though the barriers can still permit feasible ion migration. This suggests that ion transport alone cannot explain the lack of reversibility, which likely arises from intrinsically poor electronic conductivity. These findings highlight key challenges in achieving stable, reversible capacity in this system and underscore the need for doping, structural modification, and electrolyte optimization to realize its full potential as a high-voltage SIB cathode.
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Materials Science · Cross-listed from physics.chem-ph

Cation Dominated but Negatively Charged Na2SO4,aq-Graphene Interfaces

Ademola Soyemi and Tibor Szilvasi

The distribution of ions and their impact on the structure of electrolyte interfaces plays an important role in many applications. Interestingly, recent experimental studies have suggested the preferential accumulation of $SO_4^{2-}$ ions at the $Na_2SO_{4,aq}$-graphene interface in disagreement with the generally known tendency of cations to accumulate at graphene-electrolyte interfaces. Herein, we resolve the atomistic structure of the $Na_2SO_{4,aq}$-graphene interfaces in the 0.1-2.0 M concentration range using machine learning interatomic potential-based simulations and simulated sum frequency generation (SFG) spectra to reveal the molecular origins of the conundrum. Our results show that Na+ ions accumulate between the outermost and second water layers whereas $SO_4^{2-}$ ions accumulate within the second interfacial water layer indicating cation dominated interfaces. We find that the interfacial region (within ~10 ${\AA}$ of the graphene sheet) is negatively charged due to sub-stoichiometric $Na^+$/$SO_4^{2-}$ ratio at the interface. Our simulated SFG spectra show enhancement and a red-shift of the spectra in the hydrogen bonded region as a function of $Na_2SO_4$ concentration similar to measurements due to $SO_4^{2-}$-induced changes in the orientational order of water molecules in the second interfacial layer. Our study demonstrates that ion stratification and ion-induced water reorganization are key elements of understanding the electrolyte-graphene interface.
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Materials Science · Cross-listed from physics.ins-det

Benchmarking Autonomy in Scientific Experiments: A Hierarchical Taxonomy for Autonomous Large-Scale Facilities

James Le Houx

The transition from automated data collection to fully autonomous discovery requires a shared vocabulary to benchmark progress. While the automotive industry relies on the SAE J3016 standard, current taxonomies for autonomous science presuppose an owner-operator model that is incompatible with the operational rigidities of Large-Scale User Facilities. Here, we propose the Benchmarking Autonomy in Scientific Experiments (BASE) Scale, a 6-level taxonomy (Levels 0-5) specifically adapted for these unique constraints. Unlike owner-operator models, User Facilities require zero-shot deployment where agents must operate immediately without extensive training periods. We define the specific technical requirements for each tier, identifying the Inference Barrier (Level 3) as the critical latency threshold where decisions shift from scalar feedback to semantic digital twins. Fundamentally, this level extends the decision manifold from spatial exploration to temporal gating, enabling the agent to synchronise acquisition with the onset of transient physical events. By establishing these operational definitions, the BASE Scale provides facility directors, funding bodies, and beamline scientists with a standardised metric to assess risk, define liability, and quantify the intelligence of experimental workflows.
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Materials Science

Data-driven active learning approaches for accelerating materials discovery

Jiaxin Chen, Tianjiao Wan, Hui Geng et al. (+10 more)

Materials discovery is a cornerstone of modern technological advancement, yet it remains constrained by traditional trial-and-error paradigms and the inherent bias of human intuition. Artificial intelligence (AI) has emerged as a transformative tool in materials science by effectively modeling structure-property relationships. Despite substantial efforts to enhance model expressiveness, data efficiency remains an equally critical challenge, given the limited availability of experimental and computational resources. Active learning (AL), as a data-driven machine learning paradigm, has shown great promise for discovering novel materials and enabling the efficient navigation of vast materials spaces. In this review, we follow the evolution of sampling strategy design techniques in AL, from Bayesian optimization to advanced deep learning-based strategies. We then highlight how AL enhances data efficiency across various data regimes, ranging from task-specific settings with limited data to the development of general-purpose datasets and large-scale models. We further provide a systematic overview of AL applications throughout the materials research pipeline, including computational simulation, composition and structural design, process optimization, and self-driving laboratory systems. Finally, we pinpoint key challenges and future perspectives of AL in materials discovery.
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All authors Jiaxin Chen, Tianjiao Wan, Hui Geng, Liang Xiong, Guohong Wang, Yihan Zhao, Longxiang Deng, Zijian Gao, Susu Fang, Zheng Luo, Huaimin Wang, Shanshan Wang, Kele Xu

Materials Science

Dislocation distribution near a wall within the framework of the continuum theory of curved dislocations

István Groma, Dénes Berta, Lóránt Sándli et al. (+1 more)

A recently proposed generalised continuum theory of curved dislocations describes the spatial and temporal evolution of statistically stored and geometrically necessary dislocation densities as well as the curvature. The dynamics follow from a scalar plastic potential that constrains the allowed velocity fields and leads to a phase field like formulation with a nontrivial mobility function. Although conceptually related to strain gradient plasticity, the theory differs by introducing an intrinsic, evolving length scale given by the dislocation spacing. In this paper, we determine three key material independent parameters of this continuum theory by quantitatively comparing its predictions with discrete dislocation dynamics (DDD) simulations. To achieve this, we impose a narrow impenetrable wall inside the simulation volume, which blocks dislocation motion and generates characteristic spatial variations of the dislocation density fields under external loading. We show that for this geometry, the continuum equations reduce to a form that can be solved efficiently via direct numerical integration. The resulting stationary distributions of total and geometrically necessary dislocation densities are then compared to extensive 2D and 3D DDD simulations. This comparison allows us to extract the parameters that govern the back stress, the density gradient coupling, and the flow stress relation. Our results demonstrate that the continuum theory quantitatively captures the DDD observed structure of the dislocation pile up near the wall and therefore provides a reliable mesoscale description. The wall loading setup further serves as a benchmark problem to validate numerical implementations of the continuum theory in more general geometries.
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All authors István Groma, Dénes Berta, Lóránt Sándli, Péter Dusán Ispánovity

Materials Science

Size Dependent Ternary Halide Solid Solutions in Perovskite Nanocrystals

Shai Levy, Lotte Kortstee, Georgy Dosovitskiy et al. (+5 more)

Crystalline solid solutions incorporate guest atoms by substituting host lattice sites up to a solubility limit dictated by solute host similarity. Solid solutions enable tuning various material properties, such as the optoelectronic behavior of halide perovskites. In bulk, incompatibility of Cl:I halide mixtures restricts exploration throughout the ternary halide Cl:Br:I compositional range. However, solubility is extended in nanocrystals which better accommodate a wider range of ions within their lattice. Through high throughput synthesis and spectroscopic characterization of over 3000 samples, along with density functional theory and cluster expansion models, we determine the solubility boundaries of ternary halide perovskite nanocrystals and demonstrate their extended size dependent miscibility. Smaller nanocrystals, with sufficient Br content, stabilize the Cl:Br:I solid solutions, suppress planar stacking fault defects and prevent halide segregation.
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All authors Shai Levy, Lotte Kortstee, Georgy Dosovitskiy, Emma H. Massasa, Yaron Kauffmann, Juan Maria García-Lastra, Ivano E. Castelli, Yehonadav Bekenstein

Materials Science

Nanoindentation induced plasticity in equiatomic MoTaW alloys by experimentally guided machine learning molecular dynamics simulations

F. J. Dominguez-Gutierrez, T. Stasiak, G. Markovic et al. (+2 more)

Refractory complex concentrated alloys (RCCA) exhibit exceptional strength and thermal stability, yet their plastic deformation mechanisms under complex contact loading remain insufficiently understood. Here, the nanoindentation response of an equiatomic MoTaW alloy is investigated through a combined experimental and atomistically resolved modeling approach. Spherical nanoindentation experiments are coupled with large scale molecular dynamics simulations employing a tabulated low dimensional Gaussian Approximation Potential (tabGAP), enabling near DFT accuracy. A physics based similarity criterion, implemented via PCA of load-displacement curves, is used to identify mechanically representative experimental responses for quantitative comparison with simulations. Indentation stress-strain curves are constructed yielding excellent agreement in the elastic regime between experiment and simulation, with reduced Young's moduli of approximately 270 GPa. Generalized stacking fault energy calculations reveal elevated unstable stacking- and twinning-fault energies in MoTaW relative to pure refractory elements, indicating suppressed localized shear and a preference for dislocation-mediated plasticity. Atomistic analyses demonstrate a strong crystallographic dependence of plastic deformation, with symmetric {110}<111> slip activation and four-fold rosette pile-ups for the [001] orientation, and anisotropic slip, strain localization, and enhanced junction formation for [011]. Local entropy and polyhedral template matching analyses further elucidate dislocation network evolution and deformation-induced local structural transformations. Overall, this study establishes a direct mechanistic link between fault energetics, orientation-dependent dislocation activity, and experimentally observed nanoindentation behavior in RCCA.
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All authors F. J. Dominguez-Gutierrez, T. Stasiak, G. Markovic, A. Kosinska, K. Mulewska

Materials Science

Bgolearn: a Unified Bayesian Optimization Framework for Accelerating Materials Discovery

Bin Cao, Jie Xiong, Jiaxuan Ma et al. (+11 more)

Efficient exploration of vast compositional and processing spaces remains a major challenge in accelerated materials discovery. Bayesian optimization (BO) provides a principled approach to identify optimal materials with minimal experimentation, but its adoption has been limited by implementation complexity and a lack of domain-specific tools. Here, we present Bgolearn, a versatile Python framework that brings BO to materials research through intuitive interfaces, robust algorithms, and materials-focused workflows. Bgolearn supports single- and multi-objective optimization, multiple acquisition strategies, diverse surrogate models, and uncertainty quantification, enabling effective navigation of complex design spaces. Benchmark studies show that Bgolearn reduces experimental effort by 40-60% compared with random search, grid search, and genetic algorithms, while achieving comparable or superior solution quality. Its effectiveness is demonstrated across case studies, including the discovery of maximum-elastic-modulus triply periodic minimal surface structures, ultra-high-hardness high-entropy alloys, and high-strength, high-ductility medium-Mn steels, and is further supported by numerous publications. With a modular architecture that integrates seamlessly into existing materials workflows and a graphical interface (BgoFace) that removes programming barriers, Bgolearn establishes a practical, reliable platform for Bayesian optimization in materials science. The software is openly available at https://github.com/Bin-Cao/Bgolearn.
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All authors Bin Cao, Jie Xiong, Jiaxuan Ma, Yuan Tian, Yirui Hu, Mengwei He, Longhan Zhang, Jiayu Wang, Jian Hui, Li Liu, Dezhen Xue, Turab Lookman, Jun Wang, Tong-Yi Zhang

Materials Science

Absence of magnetic order in epitaxial RuO2 revealed by X-ray linear dichroism

Siyu Wang, Chao Wang, Yanan Yuan et al. (+21 more)

Recently, the topic of altermagnetism has attracted tremendous attention and RuO2 have been demonstrated to be one of the most promising altermagnetic candidates. However, disputes still remain on the existence of magnetic order in RuO2. Here in this work, we employ X-ray linear dichroism (XLD), a widely utilized technique for characterizing antiferromagnets, in conjunction with photoemission electron microscopy and multiple scattering calculation to provide clear evidence of the absence of magnetic order in epitaxial RuO2 films. The observed XLD signal is nearly invariant with temperature and independent on cooling field direction, in stark contrast to the substantial magnetic order-related XLD signal predicted by multiple scattering calculation. This finding strongly suggests a nonmagnetic origin for RuO2. Furthermore, we observed significantly distinct XLD signals at the Ru M3 and O K edges in RuO2 films grown on TiO2 substrate with different surface orientations, which can be attributed to the low-symmetry crystal field. These results unequivocally demonstrate the absence of magnetic order in RuO2 and establishes XLD measurement as a robust technique for probing the low-symmetry magnetic materials.
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All authors Siyu Wang, Chao Wang, Yanan Yuan, Jiangxiao Li, Fangfang Pei, Daxiang Liu, Chunyu Qin, Jiefeng Cao, Yamei Wang, Tianye Wang, Jiayu Liu, Jieun Lee, Guanhua Zhang, Christoph Klewe, Chenchao Yu, Fan Zhang, Dongsheng Song, Kai Chen, Weisheng Zhao, Dawei Shen, Ziqiang Qiu, Mengmeng Yang, Bin Hong, Qian Li

Materials Science

Electric field switching of altermagnetic spin-splitting in multiferroic skyrmions

Gui Wang, Yuhang Li, Bin Li et al. (+26 more)

Magnetic skyrmions are localized magnetic structures that retain their shape and stability over time, thanks to their topological nature. Recent theoretical and experimental progress has laid the groundwork for understanding magnetic skyrmions characterized by negligible net magnetization and ultrafast dynamics. Notably, skyrmions emerging in materials with altermagnetism, a novel magnetic phase featuring lifted Kramers degeneracy-have remained unreported until now. In this study, we demonstrate that BiFeO3, a multiferroic renowned for its strong coupling between ferroelectricity and magnetism, can transit from a spin cycloid to a Neel-type skyrmion under antidamping spin-orbit torque at room temperature. Strikingly, the altermagnetic spin splitting within BiFeO3 skyrmion can be reversed through the application of an electric field, revealed via the Circular photogalvanic effect. This quasiparticle, which possesses a neutral topological charge, holds substantial promise for diverse applications-most notably, enabling the development of unconventional computing systems with low power consumption and magnetoelectric controllability.
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All authors Gui Wang, Yuhang Li, Bin Li, Xianzhe Chen, Jianting Dong, Weizhao Chen, Xiaobing Chen, Naifu Zheng, Maosen Guo, Aomei Tong, Hua Bai, Hongrui Zhang, Yifan Gao, Kaiwen Shen, Jiangyuan Zhu, Jiahao Han, Yingfen Wei, Hao Jiang, Xumeng Zhang, Ming Wang, Kebiao Xu, Wu Shi, Pengfei Wang, Jia Zhang, Qihang Liu, Cheng Song, Qi Liu, Xincheng Xie, Ming Liu