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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Wednesday 3 June

Materials Science

Tunable Rashba Splitting in Janus InXPbP (X = S, Se, Te) Monolayers for Enhanced Photocatalytic Water Splitting

Vuong Van Thanh, Nguyen Minh Quan and Nguyen Tuan Hung

Janus two-dimensional (2D) materials exhibiting Rashba spin splitting have recently attracted considerable attention owing to their potential applications in spintronic devices and photocatalytic water splitting. In this work, we investigate, using first-principles calculations, the structural, mechanical, electronic, optical, and photocatalytic properties of Janus InXPbP (X = S, Se, Te) monolayers that exhibit significant Rashba effects. Our results demonstrate that all three monolayers are energetically, dynamically, and mechanically stable, as evidenced by cohesive energy calculations, phonon dispersion analysis, and elastic constants. By varying the chalcogen atom (X = S, Se, Te), the Rashba effect in InXPbP can be effectively tuned. Rashba parameters of 0.16 and 0.20 eVÅ are obtained near the conduction-band minimum (CBM) for InSPbP and InSePbP, respectively, whereas InTePbP exhibits giant Rashba spin splitting near both the CBM and valence-band maximum (VBM), with corresponding Rashba parameters of 0.90 and 0.87 eVÅ. Furthermore, the Janus InXPbP monolayers exhibit suitable band gaps of 1.21, 1.27, and 0.76 eV for InSPbP, InSePbP, and InTePbP, respectively, which are favorable for photocatalytic applications. All three monolayers possess suitable band-edge alignments for overall water splitting, yielding solar-to-hydrogen (STH) conversion efficiencies of 21.67%, 26.03%, and 29.83% for InSPbP, InSePbP, and InTePbP, respectively. Our findings not only enrich the family of Janus materials but also suggest that the Janus InXPbP monolayers are promising candidates for spintronic devices and high-performance photocatalytic water-splitting applications.
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Materials Science

Why Fe doping kills photoluminescence in CsPbCl$_3$ but not in CsPbBr$_3$: Role of midgap Fe 3$d$ states and electron-phonon coupling

Arpan Das and Saptarshi Chakraborty

Understanding the impact of transition-metal doping on the optoelectronic properties of halide perovskite nanocrystals is essential for their rational design in photonic applications. We establish the microscopic origin of photoluminescence (PL) quenching in Fe-doped CsPbCl$_3$ using spin-polarized density functional theory calculations. The emergence of Fe 3$d$ midgap states creates efficient electron-trapping centres that drive nonradiative recombination, accounting for the reduced PL intensity. Extending this analysis to Fe-doped CsPbX$_3$ (X = Cl, Br), we show experimentally that although PL intensity is suppressed in both systems relative to their pristine counterparts, their high-doping behaviour diverges: CsPbCl$_3$ becomes completely non-emissive, whereas CsPbBr$_3$ retains a finite, saturated PL intensity. Despite this contrast, electronic structure calculations reveal nearly identical midgap states in both materials, indicating that electronic effects alone cannot explain the distinct PL responses. Phonon calculations likewise fail to capture this difference. In contrast, electron-phonon coupling calculations based on the deformation potential approach reveal significantly stronger coupling in Fe-doped CsPbCl$_3$, enabling efficient dissipation of electronic excitation energy into lattice vibrations and leading to complete PL quenching. These results identify electron-phonon coupling as the key factor governing halide-dependent PL quenching and provide a unified microscopic framework for dopant-induced nonradiative processes in halide perovskites.
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Materials Science · Cross-listed from cond-mat.mes-hall

Dipolar interlayer excitons in transition metal dichalcogenide alloy heterobilayers

E. Katsipoulaki, N.G. Chatzarakis, E. Rigoutsou et al. (+6 more)

Interlayer excitons in transition metal dichalcogenide (TMD) heterobilayers possess a permanent electric dipole moment and long recombination lifetimes, making them a promising platform for exploring excitonic many-body physics. Here, we report dipolar interlayer excitons in a MoS$_{1.4}$Se$_{0.6}$/MoSe$_2$ heterobilayer encapsulated in hexagonal boron nitride. Low-temperature photoluminescence measurements reveal a distinct emission peak at $\sim1.4$ eV, attributed to radiative recombination of interlayer excitons. The emission exhibits a blueshift with increasing excitation power, indicating repulsive dipole-dipole interactions. Time-resolved photoluminescence measurements uncover nanosecond-scale lifetimes, consistent with the spatial separation of electrons and holes across the two layers. These findings establish chalcogen-alloyed TMD heterobilayers as a versatile platform for engineering dipolar excitons and tuning excitonic interactions in van der Waals materials.
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All authors E. Katsipoulaki, N.G. Chatzarakis, E. Rigoutsou, D. Katrisioti, T. Taniguchi, K. Watanabe, S. Psilodimitrakopoulos, N.T. Pelekanos, I. Paradisanos

Materials Science

Electron-Ion Path Integral Monte Carlo with Hard Core

Riccardo Fantoni

We performed numerical (restricted) path integral Monte Carlo experiments on metallic Hydrogen from first principles. We study a quantum two component plasma where one component is made of pointwise particles of negative unitary charge and the other is made of charged hard spheres of positive unitary charge. We study both the additive mixture and a nonadditive mixture where we only keep a hard core between unlike species. We specialize to the case of the electron-proton plasma with a 1:1 ratios between the molar fraction of the two species. We measured thermodynamic and structural properties of the plasma. From an analysis of the structure we see a transition from a metallic Hydrogen phase, to a molecular Hydrogen phase as the temperature is lowered. As expected at high density the correlations are diminished.
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Materials Science

Spin-polarization of the electric current in half-metallic Co$_2$MnSi Heusler thin films

José Solano Córdova, Anna Maria Friedel, Quentin Rossi et al. (+6 more)

Using propagating spin wave spectroscopy we measure the spin wave Doppler shift in patterned MgO/Co$_2$MnSi/MgO thin films and determine the degree of spin-polarization of the electric current. Our measurements reveal that the current is fully spin-polarized in the devices. This shows that the half-metallic character of the electron band structure translates into a fully spin polarized current flowing across the patterned films. Additionally, we measure a current-induced change of the spin-wave attenuation from which we estimate the non-adiabatic spin-transfer-torque parameter.
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All authors José Solano Córdova, Anna Maria Friedel, Quentin Rossi, Jérôme Robert, Yves Henry, Philipp Pirro, Sébastien Petit-Watelot, Stéphane Andrieu, Matthieu Bailleul

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

Efficient Magnetic Spin-Filtering and Persistent Spin-Currents in Lifshitz-Transitioned Altermagnets: A Route to Open-Orbit Spintronics

Wun-Hao Kang, Yu-Ting Hsiao, Jozef Genzor et al. (+3 more)

Altermagnets offer a unique venue for spin transport due to their vanishing net magnetization and momentum-dependent spin splitting. We demonstrate that a homotopic Lifshitz transition in two-dimensional altermagnets creates a regime where carriers are confined to geometrically protected, spin-selective open channels. These channels originate from non-contractible Fermi contours and act as metallic analogues of topological edge modes: they are sharply directional, spin-pure, and protected by Fermi-surface winding rather than an energy gap or boundary confinement. We predict three striking magneto-transport signatures of such topologically reconfigured altermagnets: open-orbit focusing with perfect lensing and retroreflection, high-efficiency magnetic spin filtering, and chirality-tunable spin persistent currents in altermagnetic nanotubes. Our results establish altermagnets as a platform where Fermi-surface winding directly engineers spin transport, bypassing the requirements for ferromagnetism or strong spin-orbit coupling. These findings identify Lifshitz-transitioned altermagnets as a route to topology-enabled spintronics that transcends the limitations of conventional edge-state paradigms.
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All authors Wun-Hao Kang, Yu-Ting Hsiao, Jozef Genzor, Yaroslav Zhumagulov, Ming-Hao Liu, Denis Kochan

Materials Science · Cross-listed from cond-mat.supr-con

Antiferromagnetic Quantum Criticality in Infinite-Layer Cuprates Sr1-xNdxCuO2

Bin-Jie Wu, Ze-Xian Deng, Guang-Ran Wei et al. (+8 more)

The interplay between quantum criticality and Fermi surface reconstruction is central to elucidating the phase diagram of high-temperature cuprate superconductors. While studies on electron-doped T'-structure cuprates suggest an antiferromagnetic origin of this reconstruction, quantitative consensus has been hindered by apical oxygen instabilities and uncontrolled oxygen vacancies. Here, we overcome these limitations by utilizing ozone-assisted molecular beam epitaxy to synthesize high-quality, oxygen-stoichiometric thin films of infinite-layer cuprate Sr1-xNdxCuO2 across its entire superconducting dome. Hall transport measurements reveal a sharp carrier-type transition signaling a Fermi surface reconstruction at a critical doping xc ~ 0.155. We show that a spin-density-wave tight-binding model quantitatively reproduces the transport evolution, supporting an antiferromagnetic origin of this quantum phase transition. Furthermore, upon suppressing superconductivity with magnetic fields, the normal-state resistivity exhibits a pristine strange metal behavior that persists down to 2 K in the vicinity of xc. Our findings establish an intrinsic, universal antiferromagnetic quantum criticality in electron-doped cuprates, positioning the structurally simplest infinite-layer cuprates as a clean benchmark platform for theories of unconventional superconductivity.
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All authors Bin-Jie Wu, Ze-Xian Deng, Guang-Ran Wei, Xi Zhou, Ji-Hai Zhang, Da-Zhuang Deng, Qun Zhu, Yong Zhong, Can-Li Song, Xu-Cun Ma, Qi-Kun Xue

Materials Science

Mechanical bistability and hysteresis in graphene-CNT hybrid systems: from atomistic simulations to macroscale structural responses

Mingda Ding, Nanami Sakurai, Man Shen et al. (+11 more)

Hybrid systems composed of graphene (Gr) and carbon nanotubes (CNTs), such as films and aerogels, have attracted broad attention for applications in electronics, mechanics, energy, and environmental science. Since the microstructures of Gr-CNT hybrids strongly affect their properties, it is essential to establish mechanical principles that govern these structures. In this study, we investigated the structural stability and mechanical behavior of Gr-CNT hybrid systems by combining molecular dynamics (MD) simulations and nanoindentation experiments. MD simulations of stacked Gr-CNT structures, in which two Gr layers confine CNTs between them, identified the energetically stable configurations and their governing parameters, i.e., intertube spacing, CNT diameter, and wall number. Specifically, under certain conditions, the structures exhibit mechanical bistability with two stable configurations: adhesion and separation of the Gr layers, arising from the competition between interlayer van der Waals attraction and elastic deformation of Gr and CNTs. Simulated loading–unloading curves display hysteresis and energy dissipation related to the stable configurations. In addition, reduced graphene oxide (rGO)-CNT hybrid films were experimentally fabricated as macroscopic assemblies of the unit structures modeled in the simulations. Atomic force microscopy-based nanoindentation measurements on the rGO-CNT films exhibit clear hysteresis and higher dissipation energy compared with pure rGO, in good agreement with the simulation results. These results provide valuable insights into Gr-CNT hybrid systems and offer guidance for designing microstructures with enhanced properties for advanced applications.
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All authors Mingda Ding, Nanami Sakurai, Man Shen, Taiki Inoue, Takahisa Matsuzaki, Takuo Mizuno, Kento Suzuki, John Isaac Enriquez, Harry Handoko Halim, Yuji Hamamoto, Yuta Nishina, Hiroshi Y. Yoshikawa, Yoshitada Morikawa, Yoshihiro Kobayashi

Tuesday 2 June

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

Auditing Representation-Induced Geometry in Acoustic-Emission Fracture Transients

Jose Sanchez-Andreu

Fixed convolutional representations can induce structured geometry in time-frequency data even without task-specific or source-domain training. We audit a previously reported morphology-space analysis of two granite acoustic-emission experiments. The original cumulative angular-path endpoint is reproduced to within 2.1e-7 in the Archive-B/Archive-A ratio. However, the same directional contrast is obtained with ImageNet features and with three randomly initialized EfficientNet-B0 encoders: the preserved Aether representation gives a ratio of 1.411, ImageNet gives 1.361, and the random encoders give 1.480–1.503. We therefore withdraw the attribution of this contrast to interferometric pretraining. We also correct a reversal between archived OG1/OG3 file identifiers and the physical experiments. Phase randomization and temporal shuffling alter the preserved trajectory, but these responses are reinterpreted as pipeline-dependent diagnostics rather than evidence of a learned universal elastic morphology. The corrected result is narrower: multiple fixed convolutional maps expose a reproducible contrast between two acoustic-emission datasets. The signal statistics and architectural biases responsible for that contrast remain open questions.
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Materials Science · Cross-listed from cond-mat.soft

Polyethylene-based thermo-mechanically recyclable stretchable yarns for circular sustainable textiles

SeongHyeon Kim, Duo Xu, Volodymyr Korolovych et al. (+4 more)

Most high-performance elastic textiles rely on yarns composed of chemically dissimilar polymers, rendering them difficult to recycle. Here, we demonstrate fully thermo-mechanically recyclable stretchable yarns composed of polyethylene (PE) family materials. Inspired by structure-property relationships in natural materials, we engineer a library of melt-spun PE fibers spanning mechanical properties from elastomeric to functional by tuning polymer crystallinity and chain orientation. These fibers are assembled into core-sheath yarns comprising an olefin block copolymer elastic core and a high-strength PE sheath, forming a helical architecture. The resulting yarns exceed mechanical performance of commercial PET-spandex yarns while maintaining full recyclability. We further show that PE homopolymers and copolymers can be jointly melt-processed and recycled without phase separation or loss of performance. This approach enables stretchable recyclable textiles from fibers with previously demonstrated cooling, moisture-wicking and stain-resisting performance and provides a scalable pathway toward circular garments compatible with existing polyethylene recycling streams.
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All authors SeongHyeon Kim, Duo Xu, Volodymyr Korolovych, Domingo R. Flores-Hernandez, Kaniz Moriam, Daniel J. Braconnier, Svetlana V. Boriskina

Materials Science

First-principles calculations of electronic structure

Arpan Das

The emergence of high-mobility at provides a fertile platform for exploring emergent quantum phenomena and next-generation oxide electronics. Here, using first-principles density functional theory (DFT) calculations, we uncover the microscopic origin of the formed at the interface between insulators. Despite both constituents being insulating in bulk, the heterostructure develops robust metallicity at the interface, in agreement with experimental observations. This charge redistribution stabilizes at the interface. The electronic states forming enforcing carrier motion strictly within the interfacial plane. Remarkably, the spin-up parabolic band hosting the 2DEG exhibits an exceptionally small effective mass – indicating the potential for significantly enhanced carrier mobility. Furthermore, the calculated interfacial electron density exceeds that of by nearly an order of magnitude, consistent with experimental measurement. These findings identify the heterostructure as a compelling platform for realizing and open new avenues for engineering correlated oxide interfaces for quantum electronic applications.
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Materials Science

Physical properties of R$_2$Co$_6$Al$_{20-\delta}$ (R = Gd-Tm, Y) single crystals

Sushma Kumari, Fernando A. Garcia, Juan Schmidt et al. (+6 more)

Rare-earth (R) based intermetallic compounds can often exhibit diverse physical properties and distinct magnetic anisotropies. A Notable example are the light rare earth members of the mono-clinic, R$_2$Co$_6$Al$_{19}$ series that are known to display a range of physical properties, from non-Fermi liquid behavior to antiferromagnetic (AFM) ordering, with properties that vary depending on R. In this work, we have extended this series to the heavy rare earths and systematically investigate the synthesis, crystal structure, and physical properties of single crystals of R$_2$Co$_6$Al$_{20-\delta}$ for R = Gd - Tm and Y. Single crystal X-ray diffraction reveals that these materials adopt an orthorhombic Imma-type structure with delta varying non-monotonically across the heavy rare earths; ranging from 0.73 for Dy to 0.91 for Gd. Temperature-dependent specific heat, resistivity, and magnetization measurements demonstrate AFM ordering in all materials, with the Neel temperature (TN) ranging from 1.8 K for Ho to 11.8 K for Tb. Notably, Gd and Tb-based materials exhibit two distinct AFM transitions, separated by approximately 2 - 3 K. These findings establish the heavy rare-earth members of the R2Co6Al20-delta series as anisotropic antiferromagnets with strong crystal electric field effects and exchange anisotropy. The observed deviation from de Gennes scaling and the anisotropy crossover across the series highlight the important interplay between RKKY exchange and crystal electric field interactions in this orthorhombic system.
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All authors Sushma Kumari, Fernando A. Garcia, Juan Schmidt, Tyler J. Slade, Aashish Sapkota, Ajay Kumar, Yaroslav Mudryk, Paul C. Canfield, Raquel A. Ribeiro

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

Breaking the width-scaling limit in high-performance atomically thin 2D nanoribbon transistors

Sameer Kumar Mallik, Adrian Christiansen and Saroj P. Dash

State-of-the-art transistors have been successfully scaled the gate lengths and channel thicknesses down to 5 nm for high-performance and energy-efficient information processing. However, reducing channel width below 40-50 nm remains a bottleneck, as dangling bonds, edge disorder, and lateral depletion suppress drive current and degrade device performance. Here, we break this width-scaling wall using ultra-scaled two-dimensional semiconductor (2DSC) nanoribbon transistors down to 15 nm. In contrast to the conventional scaling rule of degradation of current density upon width scaling, our atomically-thin monolayer and bilayer molybdenum disulfide nanoribbon transistors exhibit enhancement of on-current density of up to 230% and 170%,respectively, followed by a saturation for the narrowest channels down to 15 nm. The ultra-narrow nanoribbon transistors maintain the highest on/off ratios reported so far for similar device dimensions, with improved mobility and threshold-voltage stability, indicating reduced edge scattering and depletion with a stronger electrostatic control. These findings lead to a breakthrough in width scaling rules using 2DSC nanoribbons with enhanced performance at narrower channel widths, which is promising for the ultimate scaling of transistors.
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Materials Science

Emergence of Macroscopic Quantum Order via Translational Zero Modes

Kenan Gundogdu

Macroscopic quantum coherence in solids, such as in superfluids, superconductors, and condensates, is generally limited to low temperatures because order forms within a fixed excitation spectrum whose competing states become thermally populated as temperature rises. Here, we show that strong coupling between electronic excitations and a deformable lattice enables a different route. Above a critical density, this coupling nucleates self generated confining potentials that trap the very excitations generating them. Unlike rigid external traps, these potentials can translate through the host lattice without changing their internal structure, defining a translational zero mode. Coupling to this zero mode provides a shared dynamical coordinate that lowers and isolates a single collective many body configuration, opening a density dependent gap that suppresses thermal occupation of competing states and supports off diagonal long range order at elevated temperatures. As a concrete realization, we identify high-temperature superfluorescence in lead halide perovskites as the radiative instability of this zero mode dressed ordered excitonic state. More broadly, this establishes a general route to macroscopic quantum order: not cooling within a fixed spectrum, nor pairing instabilities, but a self generated mobile confining structure whose translational zero mode reconstructs the many-body spectrum to protect coherence.
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Materials Science · Cross-listed from cond-mat.soft

Controlled Chemical Signaling between Enzymatic Nanomotors

Shuqin Chen, Giorgio Lovato, Oriol Jutglar Soler et al. (+3 more)

The coordinated interactions between organisms enhance collective functionality, a feature that artificial systems such as enzymatic nanomotors seek to replicate. A key objective, yet still a major challenge, is to achieve chemical communication among nanomotors. Progress has been limited by the difficulties in verifying effective signaling processes, including chemical signal propagation and the response of receiving nanomotors. Here, we address this challenge using an enzymatic nanomotor system that demonstrates communication between two populations through generically non-reciprocal phoretic response. A primary swarm of glucose-responsive nanomotors migrates toward a glucose gradient while producing H2O2 as a diffusible communication signal. This self-generated chemical gradient then acts as a chemoattractant for a secondary swarm of catalase-powered nanomotors. Through carefully designed experiments, we visualize the propagating H2O2 gradient and quantify the spatiotemporal response of the receiver nanomotors to the chemical front. Combined experimental and theoretical analysis has revealed that the synergy between different combinations of chemo-attractive and chemo-repulsive mobilities and catalytic rates of consumption and production of substrates and products gives rise to a wealth of different collective responses in the system. This work represents a step toward programmable synthetic systems at the collective level, broadening the functionality of chemical nanomotors and opening opportunities for future hybrid living-synthetic systems.
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All authors Shuqin Chen, Giorgio Lovato, Oriol Jutglar Soler, Daniel Sánchez-deAlcázar, Ramin Golestanian, Samuel Sánchez

Materials Science

Uncertainty-Aware Symbolic Regression through Bayesian Support Selection

Satadeep Bhattacharjee

The Sure Independence Screening and Sparsifying Operator (SISSO) framework is a powerful symbolic-regression method for extracting compact and interpretable descriptors from large nonlinear feature spaces. However, standard SISSO is deterministic: it returns a single descriptor and point prediction, without quantifying uncertainty in descriptor selection, regression coefficients, or predictions. Here we introduce a probabilistic extension in which the sure independence screening (SIS) stage is kept deterministic to preserve scalability, while the sparsifying operator (SO) stage is reformulated as Bayesian inference over the SIS-screened support space. The resulting deterministic-SIS/Bayesian-SO framework yields posterior probabilities for competing descriptor supports, feature-inclusion probabilities, Bayesian-model-averaged predictions, and predictive credible intervals, while recovering the deterministic SO descriptor of standard SISSO in the maximum-a-posteriori limit. Applied to an $X_2YZ$ Heusler-alloy magnetic-moment dataset, the approach gives modest improvements in five-fold cross-validation RMSE and near-nominal empirical coverage of the 95$\%$ predictive intervals. More importantly, the posterior exposes competing, physically related symbolic descriptor families that would appear artificially unique in a deterministic analysis. These results suggest that deterministic-SIS/Bayesian-SO can be used as an uncertainty-aware diagnostic extension of SISSO: a tool for assessing descriptor confidence, stability, and non-uniqueness in small-data materials regression problems.
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Materials Science

Topological Weyl Phase of an Ideal Spin-Gapless Semiconductor KCrSe

Subhajit Mandal, Bishal Das, Himanshu Sharma et al. (+2 more)

The coexistence of topological and spin-polarized electronic states within a single material platform provides an attractive route toward emergent quantum phenomena and spintronic functionalities. However, materials simultaneously exhibiting spin-gapless semiconducting (SGS) behavior and Weyl semimetallicity remain exceedingly rare. Here, using first-principles calculations, we identify the half-Heusler compound KCrSe as an ideal spin-gapless Weyl semimetal. Transport calculations reveal a weak temperature dependence of the longitudinal conductivity and relatively small Seebeck coefficients, providing further evidence of its SGS nature. KCrSe hosts a single pair of Weyl nodes-the minimum number permitted in a Weyl semimetal-located in close proximity to the Fermi level (E$_\text{F}$), resulting in exceptionally clean bulk and surface electronic spectra. The nontrivial Berry curvature associated with these Weyl nodes gives rise to sizable anomalous transport responses, including an anomalous Hall conductivity of $\sigma_{xy}^{A}\sim 90.76~\mathrm{S\,cm^{-1}}$ and an anomalous Nernst conductivity of $\alpha_{xy}^{A}\sim 0.15~\mathrm{A\,m^{-1}K^{-1}}$ at E$_\text{F}$, with substantially enhanced values at lower energies. The combination of an ideal Weyl topology, fully spin-polarized low-energy states, and finite anomalous transport establishes KCrSe as a promising platform for designing high-efficiency topological spintronic devices.
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All authors Subhajit Mandal, Bishal Das, Himanshu Sharma, Satoru Hayami, Aftab Alam

Materials Science

Bernoulli principle in ferroelectrics

Anna Razumnaya, Yuri Tikhonov, Dmitrii Naidenko et al. (+2 more)

Ferroelectric materials, characterized by spontaneous electric polarization, exhibit remarkable parallels with fluid dynamics, where polarization flux behaves similarly to fluid flow. Understanding polarization distribution in confined geometries at the nanoscale is crucial for both fundamental physics and technological applications. Here, we show that the classical Bernoulli principle, which describes the conservation of the energy flux along velocity streamlines in a moving fluid, can be extended to the conservation of polarization flux in ferroelectric nanorods with varying cross-sectional areas. Geometric constrictions lead to an increase in polarization, resembling fluid acceleration in a narrowing pipe, while expansions cause a decrease. Beyond a critical expansion, phase separation occurs, giving rise to topological polarization structures such as polarization bubbles, curls and Hopfions. This effect extends to soft ferroelectrics, including ferroelectric nematic liquid crystals, where polarization flux conservation governs the formation of complex mesoscale states.
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All authors Anna Razumnaya, Yuri Tikhonov, Dmitrii Naidenko, Ekaterina Linnik, Igor Lukyanchuk

Materials Science

Deciphering borophene growth pathways with data-driven simulations

Colin Bousige, Jean Furstoss, Julien Lam et al. (+1 more)

Deterministic synthesis of borophene remains challenging because many polymorphs compete during nucleation and growth. Here we combine a reactive machine-learned interatomic potential with grand-canonical Monte Carlo simulations and data-driven structural classification to track borophene formation from early nuclei to extended layers on Ag(111) and Ag(100). We build temperature-pressure substrate growth maps and resolve how vacancy motifs, phase intermixing and seed structure govern polymorph selection. The simulations reproduce key experimental trends, including the prevalence of $\beta_{12}$/$\chi_3$ phases and their temperature-dependent competition, while revealing kinetic pathways that connect metastable nuclei to long-range order. We identify conditions that suppress competing motifs and promote targeted phases, providing actionable synthesis windows. These results establish a predictive framework for directing borophene growth and, more broadly, for controlling polymorphism in low-dimensional materials by coupling atomistic simulation with machine-learning-enabled phase recognition.
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All authors Colin Bousige, Jean Furstoss, Julien Lam, Pierre Mignon

Materials Science

Predicting core-level X-ray photoemission spectra of oxide surfaces from first principles – a case study for SnO$_2$

Wenxuan Cai, Stefan Kucharski, Chris Blackman et al. (+2 more)

X-ray photoemission spectroscopy (XPS) is a powerful technique to gain insight into the chemical properties of oxide surfaces. However, the interpretation of XPS spectra is notoriously difficult as realistic surfaces contain different terminations, reconstructions, adsorbates and defects all of which leave (potentially overlapping) spectroscopic fingerprints. To address this challenge, we present a first-principles approach based on the Z+1 method that allows us to predict XPS spectra of oxide surfaces which can directly be compared to experimental measurements. We present results for different SnO$_2$ (110) surfaces: the stoichiometric surface, surfaces with different types of vacancies (one of which is the fully reduced surface) and also the fully reduced surface with adsorbed OH and O$_2$ molecules. For these systems, we calculate the O 1s core-electron binding energies of all oxygen atoms and then use this to predict the XPS spectrum. We find that the fully reduced surface gives rise to a highly symmetric peak shape in agreement with recent XPS measurements. In contrast, the spectrum of the stoichiometric surface exhibits an additional feature at low binding energies caused by the bridging oxygen atoms at the surface. For the reduced surface with OH and O$_2$ adsorbates, the spectrum exhibits additional features at higher binding energies. The predicted spectra are in good agreement with experimental results obtained for reduced surfaces that have been exposed to oxygen gas. The presented method is general and can be straightforwardly applied to other surfaces.
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All authors Wenxuan Cai, Stefan Kucharski, Chris Blackman, Juhan Matthias Kahk, Johannes Lischner

Materials Science

Quantitative Detection of Molecular Oxygen in the Gas Phase with Fluorescent Nanodiamonds

Nicholas A. Nunn, Antonin Marek, Alex I. Smirnov et al. (+2 more)

The quantitative detection of paramagnetic molecular oxygen (O2) in gas mixtures using optically detected magnetic resonance (ODMR) from negatively charged nitrogen-vacancy (NV-) centers in fluorescent nanodiamonds is described. Fluorescent nanodiamonds approximately 70 nm in diameter were deposited on the glass surface of a microfluidic channel, and the oxygen concentration varied from 0 to 100% (0 to 760 mmHg O2 partial pressure) by mixing O2 and N2 gases at ambient pressure. Continuous-wave (CW) ODMR contrast was measured using a double-modulation (lock-in) detection scheme applied to both optical excitation and microwave drives. The ODMR contrast decreases linearly with oxygen partial pressure, with a sensitivity coefficient k of (-10.1 +/- 0.3) x 10^-4 % mmHg^-1. The oxygen detection limit of the experimental setup was estimated to be approximately 8 mmHg O2 partial pressure (corresponding to about 1% O2 in the gas mixture). Cycling of the content of O2 in the gas mixture in the range of 0-5% revealed slight hysteresis and corresponding repeatability of 0.006 in percent ODMR contrast. The observed fluorescence quenching and relatively slow response (ranging from several to tens of minutes) upon changes in oxygen concentration suggest that physisorption of gas molecules on the nanodiamond surfaces contributes to equilibration dynamics. The applicability of the nanodiamond-based oxygen quantum sensor was further demonstrated by detecting transient bursts of molecular oxygen generated by enzyme-catalyzed decomposition of hydrogen peroxide.
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All authors Nicholas A. Nunn, Antonin Marek, Alex I. Smirnov, Olga A. Shenderova, Marco D. Torelli

Materials Science

Fracture energy of 6H-SiC at the microscale: effects of testing geometry and notch preparation

Zhuoqi Lucas Li, Siyang Wang, Ao Li et al. (+5 more)

Micromechanical testing enables small-scale fracture energy measurements, but values depend strongly on geometry and specimen preparation. Here, the fracture energy of the single-crystal 6H-SiC {10-10} plane was measured using microscale double cantilever beam (DCB) and single cantilever beam (SCB) geometries. DCBs showed stable crack growth under displacement control and obtained 7.5 +- 0.3 J/m2. In contrast, SCBs notched by a Ga focused ion beam gave fracture energies over twice this value, indicating Ga implantation and near-notch residual stresses. Increasing the final notching current increased the measured fracture energy further. Although near-cryogenic notching limited ion-beam-induced damage, it did not reconcile SCB-derived values with DCB test results. Vacuum annealing substantially lowered the fracture energy and brought SCB results into close agreement with DCB measurements, whereas annealing in argon was less effective. Our findings highlight the importance of careful sample preparation and testing geometry selection for reliable fracture property measurement in ceramic materials.
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All authors Zhuoqi Lucas Li, Siyang Wang, Ao Li, James O. Douglas, Florian Bouville, Oriol Gavalda-Diaz, Katharina Tinka Marquardt, Finn Giuliani

Materials Science

RamanGPT: Bidirectional Mapping Between Crystal Structures and Raman Spectra with Graph Neural Networks and Generative Transformers

Frank M. Abel, Jaehyung Lee, Charles R. Campbell et al. (+1 more)

Raman spectroscopy is one of the most accessible vibrational probes in materials laboratories, but its forward problem (structure to spectrum) is bottlenecked by the cost of density functional perturbation theory, and its inverse problem (spectrum to structure) typically relies on retrieval against curated references. We introduce RamanGPT, a deep-learning framework that addresses both directions for crystalline inorganic materials. The forward model, an Atomistic Line Graph Neural Network (ALIGNN), is trained on the 5{,}099-material Computational Raman Database and predicts 200-bin spectra over 50-1000~cm$^{-1}$ with 42.5% having a cosine similarity greater than or equal to 0.354 suggesting qualitative features of the target spectrum. The model also shows some qualitative agreement with the approximate features and appearance of similar relative intensity of the modes to an experimental measurement of metallic 1T VSe$_{2}$, a system absent from the training set. The inverse model fine-tunes a large language model via Quantized Low-Rank Adaptation on Raman-plus-formula prompts, recovering lattice parameters with mean absolute errors of 1.14-2.16~Å and reduced-formula consistency of 86.8% on 508 held-out materials. A cosine-similarity matcher and an inverse$\rightarrow$relax$\rightarrow$forward consistency loop are deployed at https://atomgpt.org/raman.
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All authors Frank M. Abel, Jaehyung Lee, Charles R. Campbell, Kamal Choudhary

Materials Science

Demonstrating magnetic memory in iron-rhodium structures using a quantum diamond microscope

Kristine V. Ung, Gregory M. Stephen, Nicholas A. Blumenschein et al. (+7 more)

Iron-rhodium (FeRh) has a first-order phase transition near room temperature between antiferromagnetic (AFM) and ferromagnetic (FM) phases, making it a promising material for magnetic memory technologies like heat-assisted magnetic recording (HAMR). It has a comparatively sharper phase transition and lower writing temperature than alternative materials, implying less thermal engineering constraints and an increase in write/read head lifetime. Despite great effort, however, AFM-based magnetic memory using FeRh has not yet been realized. Here, we employ both wide-field and scanning nanoscale quantum diamond microscopes (QDMs) to image directly the magnetic field of a patterned FeRh thin film structure under ambient conditions, demonstrating a magnetic recording technique that is reliable and robust. We experimentally identify coupling between the Néel and magnetization vector directions; and also, that the magnetic orientation of the FM phase uniquely determines the Néel vector in the AFM phase, due to pinned uncompensated magnetic moments (UMMs) in the FeRh structure. Thus, the magnetic orientation is maintained when the system is cycled between AFM and FM phases, providing the foundation for a practical, AFM-based magnetic memory.
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All authors Kristine V. Ung, Gregory M. Stephen, Nicholas A. Blumenschein, Alexander J. Edwards, Samuel W. LaGasse, Steven P. Bennett, Aubrey T. Hanbicki, Ronald L. Walsworth, Adam L. Friedman, Paul V. Petruzzi

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

Mechanochemical Nano-Writing of an Atomically Thin Metal

Shuai Zhang, Yanyu Jia, Atanu Samanta et al. (+14 more)

Mechanical energy accelerates many physicochemical processes, including materials syntheses that are hard to produce with thermal energy alone. However, physical understanding connecting applied mechanical forces with internal stresses and ensuing reaction mechanisms is lacking. Here we demonstrate mechanical force-enabled synthesis and nanoscale patterning to metallize a two-dimensional (2D) material, producing an atomically-thin superconducting material. Localized force applied by atomic force microscope tips to van der Waals (vdW) encapsulated stacks of 2D bilayer MoTe2 and adjacent source Pd guides 2D Pd7MoTe2 growth with 50 nm lateral resolution. Force accelerates reaction kinetics exponentially per Eyring's stress-assisted thermal activation model, reducing synthesis temperatures from ~200 {\deg}C to near-room temperature. Finite element simulations, density functional theory, and ab-initio grand canonical Monte Carlo calculations show that tip-induced compression facilitates Pd chemisorption to tensile-strained MoTe2 that converts to uniform Pd7MoTe2. This demonstrates a new, generalizable paradigm for nanoscale synthesis of quantum materials, and high-precision engineering of superconductivity.
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All authors Shuai Zhang, Yanyu Jia, Atanu Samanta, Yutian Bao, Haosen Guan, Zhaoyi Joy Zheng, Guangming Cheng, Ting Liu, Cangyu Qu, Kenji Watanabe, Takashi Taniguchi, Nan Yao, Ashlie Martini, Leslie Schoop, Andrew M. Rappe, Sanfeng Wu, Robert W. Carpick

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

20 ps Non-Destructive Read and 1 ns Write Operations at <5 V in Ferroelectric HfO2/ZrO2 Non-Volatile Memories

Alexandre Baigol, Ruben Hamming-Green, Paul Uriarte Vicandi et al. (+8 more)

Achieving low-voltage, nanosecond multi-level programming and non-destructive read-out of ferroelectric non-volatile memories (NVM) is critical for analog in-memory computing architectures relying on ferroelectric capacitive devices (FeCap). We integrate HfO2/ZrO2 ferroelectric nanolayers concurrently in the BEOL of CMOS and on SiO2/Si, achieving nanosecond multilevel switching with programming voltages below 5 V. Partial ferroelectric switching enhances FeCap endurance above 1011 cycles, leading to MemCapacitance (MC) states with non-destructive read-out and 10-year retention. However, experiments reveal the collapse of the MC window for read frequencies above 1 MHz. To overcome this speed limit, we introduce a novel, non-destructive readout methodology. Using electrical pulses with widths down to 20 ps, below the RC time constant of the FeCaps, we enable measurement of the polarization-dependent leakage current, providing ultrafast and non-destructive read operations at only 14 fJ.
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All authors Alexandre Baigol, Ruben Hamming-Green, Paul Uriarte Vicandi, Jiajie Gao, Till Zellweger, Anwesha Panda, Alexandros Emboras, Miklós Csontos, Mathieu Luisier, Beatriz Noheda, Laura Bégon-Lours

Materials Science

Molecular neutron spectroscopy techniques applied to ceramics $\alpha$-SiC and $\beta$-Ga$_2$O$_3$

Adam J. Jackson, Svemir Rudić, Manh Duc Le et al. (+1 more)

Neutron spectroscopy is a powerful technique for determining the vibrational states of matter. Instruments with fixed geometry may measure inelastic scattering at a limited set of angles, producing a 1-D spectrum $S(\omega)$. Such measurements are usually simulated in a DOS-like semi-analytic incoherent approximation, well-established for study of bending/stretching modes in molecular crystals. In this work we empirically test the simulation method for two ceramics with industrial electronic applications that act as "worst-case" systems. The phonon scattering from $\alpha$-SiC and $\beta$-Ga$_2$O$_3$ is coherent, depends on momentum transfer $Q$ and sits in frequencies below the typical "fingerprint" range of molecular spectroscopy. Inelastic neutron-scattering measurements of powders were performed with two contrasting spectrometers at cryogenic and elevated temperatures, and simulations performed using a variety of density-functional approximations. We find that for 1-D powder spectra from a compact instrument, the approximate simulations are easily comparable with experimental spectra and give similar results to a more computationally-intensive numerical sampling of the coherent spectrum. Given the success with these systems, the approximate method appears to be suitable for modelling inelastic neutron scattering by harmonic phonons of almost any powder sample with this technique. When a $Q$-resolved instrument is used to collect the 2-D dynamical structure factor $S(Q,\omega)$, numerical averaging is still required to capture phonon features. Our simulations of inelastic scattering from $\alpha$-SiC in the 6H polytype using the PBEsol functional gave good agreement with the experiments. By contrast, the RSCAN functional gave the best agreement with the measured spectra of $\beta$-Ga$_2$O$_3$ and is recommended for future work on the lattice dynamics of this material.
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All authors Adam J. Jackson, Svemir Rudić, Manh Duc Le, Sanghamitra Mukhopadhyay

Materials Science

Reversible Superdense Ordering of Tetragonal Lithium in a Layered Material

Natalie L. Williams, Stephen D. Funni, Sihun Lee et al. (+14 more)

Understanding lithium (Li) ordering and dynamics is foundational in energy storage. X-ray based experimental methods do not simultaneously provide atomic structure information together with chemical composition and local bonding information for lithium in solids. Here we employ scanning transmission electron microscopy (STEM) and combine imaging, spectroscopy, and diffraction within a single experiment, to observe, in situ, an all-solid-state electrochemical cell. By integrating multimodal STEM with other complementary techniques, we report a complete mapping of lithium intercalation in a layered system, LaTe3. We identify three ordered phases of LixLaTe3 with x ranging from 1/3 to 3 with in-plane strain of up to 5%. At a very high lithium concentration of Li3LaTe3, we discover an unexpected three-layer, superdense lithium phase with tetragonal symmetry occupying the van der Waals gap. This represents a new Li phase that is reversible. Our multimodal approach thus enables complete tracking of lithium ordering and dynamics, important for next-generation energy storage applications.
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All authors Natalie L. Williams, Stephen D. Funni, Sihun Lee, Drake Niedzielski, Mingjia Fang, Josh Leeman, Ratnadwip Singha, Saif Siddique, Tyler Hendee, Shiyu Xu, Jeffrey Kaaret, Giovanni Sartorello, Nicole A. Benedek, Leslie M. Schoop, Lynden A. Archer, Tomás A. Arias, Judy J. Cha

Materials Science

Microscopic derivation of the microstretch theory for carbon nanotubes

Naoki Nishimura, Mamoru Matsuo and Takeo Kato

Twisted carbon nanotubes support phonons involving not only torsion, naturally associated with microrotation, but also radial breathing, which requires a scalar stretch degree of freedom. We derive an effective microstretch theory for these modes starting from nonlinear elasticity on a cylindrical surface. By linearizing the equation of motion around a uniformly twisted equilibrium configuration, we obtain the dynamical matrix for the twisting, longitudinal, and radial-breathing modes. This matrix coincides with that of a one-dimensional microstretch theory, and the corresponding elastic constants are expressed in terms of the Lamé constants, the nanotube radius, and the twist rate. The twist generates chiral couplings in the effective theory, which hybridize the three modes and open an anticrossing in the phonon dispersion. These results provide a microscopic basis for the microstretch description of phonons in twisted carbon nanotubes and clarify how structural chirality enters the effective couplings.
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Materials Science · Cross-listed from cond-mat.mes-hall

Epitaxial $\mathrm{Co_2MnSi}$ with intrinsic magnetocrystalline anisotropy as a route to bias-field-free nonlinear half-metal magnonics at the nanoscale

Anna Maria Friedel, Jaafar Ghanbaja, Björn Heinz et al. (+5 more)

Half-metallic Heusler compounds like $\mathrm{Co_2MnSi}$ allow to bridge magnonic and spintronic functionality for hybrid unconventional computing approaches with sought-after properties like 100% spin polarization and associated low Gilbert damping $\alpha\leq 10^{-3}$. However, the desirable material parameters are inherently tied to the crystal lattice with a particularly critical dependence on structural order in $\mathrm{Co_2MnSi}$. To date, the successful fabrication of nanoscale devices with robust structural integrity remains yet a challenge, and consequently the impact of the material parameters on the resulting nonlinear spin-wave dynamics remains largely unexplored. Here, we report on a study of linear and nonlinear spin-wave dynamics in transversally magnetized $\mathrm{Co_2MnSi}$ waveguides with impeccable crystalline ordering. We show that epitaxial, $\mathrm{L2}_1$-ordered $\mathrm{Co_2MnSi}$ exhibits an intrinsic cubic anisotropy with first- and second-order contributions, stabilizing a magnetization alignment along the crystal $\langle110\rangle$ directions. We confirm the implication of an unaffected crystal structure resulting in preserved magnetic properties in the patterned structures. Herein, the persistent magnetocrystalline anisotropy reshapes the spin-wave dispersion which yields a first-order nonlinear instability suppression range extending over several GHz - even for vanishing bias fields. Moreover, the intrinsic magnetocrystalline anisotropy can be exploited to counteract shape demagnetization for a stabilized low bias field operation in the favourable Damon-Eshbach geometry with high group velocities and decay lengths. Together with the proven half-metallicity and ultralow Gilbert damping, this research establishes $\mathrm{Co_2MnSi}$ as a robust, scalable platform towards bias-field-free nonlinear half-metal magnonics.
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All authors Anna Maria Friedel, Jaafar Ghanbaja, Björn Heinz, Moritz Bechberger, Sylvie Migot, Sébastien Petit-Watelot, Stéphane Andrieu, Philipp Pirro