Materials Science
Chemical Vapor Deposition Growth and Characterization of ReSe2
Jowon Onasanyab, Mourad Benamara, Kanagaraj Moorthi et al. (+3 more)
Two-dimensional (2D) flakes of ReSe2 structure were grown by chemical vapor deposition and investigated at room temperature using Raman, photoluminescence, and absorption spectroscopies. The Raman spectra revealed eighteen
phonon modes in the range of 100-300 cm-1 that were found in good agreement with the density functional theory (DFT) calculations. The thickness profiles of the ReSe2 flakes are in the range of 5-50 nm. The ReSe2
crystal structure and morphology were investigated using XRD, atomic force microscopy and scanning electron microscopy. The energy dispersion spectroscopy confirmed the 1:2 elemental composition. The absorption spectra were obtained for ReSe2 flakes and found to exhibit excitonic peaks in the spectral region of 885 - 942 nm. These peaks are used to define the band gap of the material. The DFT calculations predicted an indirect bandgap of 0.88 eV for the bulk structure, while a direct bandgap of 1.26 eV was predicted for the monolayer.
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All authors Jowon Onasanyab, Mourad Benamara, Kanagaraj Moorthi, H. O. H. Churchill, Bothina Hamad, M. O. Manasreh
Materials Science
Homogeneous Microwave Delivery for Quantum Sensing with Nitrogen-Vacancy Centers at High Pressures
Timothy A. Elmslie, Luca Basso, Adam Dodson et al. (+2 more)
Nitrogen vacancy (NV) centers have been demonstrated as a useful tool in high pressure environments. However, the geometry and small working area of the diamond anvil
cells (DACs) used to apply pressure present a challenge to effective delivery of microwave (mw) fields. We designed and characterized a novel slotted design for mw transmission to nitrogen-vacancy centers (NVs) in a diamond anvil
cell via zero-field and in-field optically detected
magnetic resonance (ODMR) measurements across pressures between 1 and 48 GPa. The mw fields experienced by NVs across the diamond culet was calculated from Rabi frequency and found to be higher and more uniform than those generated by an equivalent simple mw line, which will improve performance for wide-field, high-pressure measurements to probe spatial variations across samples under pressure.
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All authors Timothy A. Elmslie, Luca Basso, Adam Dodson, Jacob Henshaw, Andrew M. Mounce
Materials Science · Cross-listed from cond-mat.soft
Universal wrinkling dynamics of a sheet on viscous liquid
Ayrton Draux, Marco Rizzo, Dominic Vella et al. (+3 more)
We investigate the wrinkling dynamics of a thin elastic sheet that is indented or compressed while floating on a viscous
liquid. We show that the deformation speed controls the dynamics, leading to a wrinkle wavelength significantly smaller than that selected under quasistatic compression. Once active compression ceases, the wrinkles coarsen until their wavelength relaxes toward the
equilibrium value. We develop a theoretical model coupling Stokes flow in the
liquid to elastic bending of the sheet, which quantitatively predicts both the initial wavelength selection and its subsequent coarsening. We demonstrate that the same mechanism governs two dimensional and axisymmetric geometries, thereby extending classical static wavelength selection laws to dynamic situations. Although developed from controlled laboratory experiments, the model captures a generic viscous-elastic coupling and applies broadly to thin elastic films interacting with viscous environments, including the formation of surface wrinkles in pahoehoe lava flows.
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All authors Ayrton Draux, Marco Rizzo, Dominic Vella, Vincent Démery, Fabian Brau, Pascal Damman
Materials Science
Predictive autoencoder-transformer model of Cu oxidation state from EELS and XAS spectra
Brian Lee, Linna Qiao, Samuel Gleason et al. (+5 more)
X-ray absorption spectroscopy (XAS) and electron energy-loss spectroscopy (EELS) produce detailed information about oxidation state, bonding, and coordination, making them essential for quantitative studies of redox and structure in functional materials. However, high-throughput quantitative analysis of these spectra, especially for mixed valence materials, remains challenging as diverse experimental conditions introduce noise, misalignment, broadening of the spectral features. We address this challenge by training a machine learning model consisting of an autoencoder to standardize the spectra and a
transformer model to predict both Cu oxidation state and Bader charge directly from L-edge spectra. The model is trained on a large
dataset of FEFF-simulated spectra and evaluates model performance on both simulated and experimental data. The results of the machine learning model exhibit highly accurate prediction across the domains of simulated and experimental XAS as well as experimental EELS. These advances enable future quantitative analysis of Cu redox processes under in situ and operando conditions.
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All authors Brian Lee, Linna Qiao, Samuel Gleason, Guangwen Zhou, Xiaohui Qu, Judith Yang, Jim Ciston, Deyu Lu
Materials Science · Cross-listed from cond-mat.str-el
Visualization of Tunable Electronic Structure of Monolayer TaIrTe$_4$
Sandy Adhitia Ekahana, Aalok Tiwari, Souvik Sasmal et al. (+16 more)
Monolayer TaIrTe$_4$ is an ideal platform to explore the tunability of band
topology where charge doping converts the
quantum spin Hall insulator (QSHI) state into a dual QSHI state. However, experimental visualization of its band structure has been lacking despite its importance in interpreting this topological phase transition. Here we report the band structure of monolayer TaIrTe$_4$ using micro-focused angle-resolved photoemission spectroscopy ($\mu$ARPES). Observed dispersions agree with the Heyd-Scuseria-Ernzerhof (HSE) calculations, establishing the insulating ground state without strong electronic correlations. Furthermore, we show an electron-hole asymmetry in the doping response, where hole doping is readily induced by electrostatic gating, whereas electron doping via gating and alkali-metal deposition yields band renormalization instead of a rigid shift. Fractional-charge calculations demonstrate that added electrons shrink the band gap and drive band renormalization. Thus, our work identifies the microscopic mechanism by which induced charges reshape the band
topology of monolayer TaIrTe$_4$, beyond the rigid shift behavior.
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All authors Sandy Adhitia Ekahana, Aalok Tiwari, Souvik Sasmal, Zefeng Cai, Ravi Kumar Bandapelli, I-Hsuan Kao, Jian Tang, Chenbo Min, Tiema Qian, Kenji Watanabe, Takashi Taniguchi, Ni Ni, Qiong Ma, Chris Jozwiak, Eli Rotenberg, Aaron Bostwick, Simranjeet Singh, Noa Marom, Jyoti Katoch
Materials Science
Halide diffusion in mixed-halide perovskites and heterojunctions
Viren Tyagi, Mike Pols, Geert Brocks et al. (+1 more)
Migration of halide defects guides ion transport in metal halide perovskites and controls the kinetics of halide mixing and phase separation. We study the
diffusion of halide vacancies and interstitials in \ce{CsPb(I_{x}Br_{1-x})_{3}} and \ce{CsPbI_{3}}/\ce{CsPbBr_{3}} heterojunctions by molecular dynamics simulations using neural network potentials trained on density functional theory calculations. We observe enhanced
diffusion of both vacancies and interstitials in the mixed halide compounds compared to the single halide ones, as well as a difference in mobility between Br and I ions in the mixed compound.
Diffusion across heterojunctions is governed by the interface structure, where a Br-rich interface blocks migration of vacancies in particular, but an I-rich interface is permeable.
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All authors Viren Tyagi, Mike Pols, Geert Brocks, Shuxia Tao
Materials Science
Raman scattering fingerprints of the charge density wave state in one-dimensional NbTe$_4$
Natalia Zawadzka, Cem Sevik, Zahir Muhammad et al. (+4 more)
Charge-density waves (CDWs) are ordered
quantum states of conduction electrons accompanied by periodic
lattice distortions. Raman scattering (RS) spectroscopy is therefore well suited for probing CDW-induced structural modulations. We investigate the CDW state in quasi-one-dimensional NbTe$_4$ using RS spectroscopy. At $T$=5~K, the resonantly enhanced Raman spectrum exhibits 25
phonon modes. Polarization-dependent measurements reveal a strong coupling between
phonon-mode
symmetry and crystallographic
symmetry, with modes polarized parallel or perpendicular to the crystallographic $c$-axis, along which the one-dimensional structure is elongated. Temperature-dependent RS measurements identify a transition between commensurate and incommensurate CDW phases, accompanied by pronounced thermal hysteresis, with transition temperatures of approximately 45~K upon cooling and 90~K upon warming. The hysteresis width depends on the warming rate, indicating a finite nucleation rate of CDW domains and suggesting potential relevance for
memory-device applications.
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All authors Natalia Zawadzka, Cem Sevik, Zahir Muhammad, Zia Ur Rehman, Weisheng Zhao, Adam Babiński, Maciej R. Molas
Materials Science · Cross-listed from physics.chem-ph
The rise and fall of stretched bond errors: Extending the analysis of Perdew-Zunger self-interaction corrections of reaction barrier heights beyond the LSDA
Yashpal Singh, Juan E Peralta and Koblar Alan Jackson
Incorporating self-interaction corrections (SIC) significantly improves chemical reaction barrier height predictions made using density functional theory methods. We present a detailed, orbital-by-orbital analysis of these corrections for three semi-local density functional approximations (DFAs) situated on the three lowest rungs of the Jacob's Ladder of approximations. The analysis is based on
Fermi-Löwdin Orbital Self-Interaction Correction calculations performed at several steps along the reaction pathway from the reactants (R) to the transition state (TS) to the products (P) for four representative reactions selected from the BH76
benchmark set. For all three functionals, the major contribution to self-interaction corrections of the barrier heights can be traced to stretched bond orbitals that develop near the TS configuration. The magnitude of the ratio of the self-exchange-correlation energy to the self-Hartree energy (XC/H) for a given orbital is introduced as an indicator of one-electron self-interaction error. For the exact, but unknown density functional, XC/H = 1.0 for all orbitals, while for the practical DFAs studied here, XC/H spans a range of values. The largest values are obtained for stretched or strongly lobed orbitals. We show that significant differences in XC/H for corresponding orbitals in the R, TS, and P configurations can be used to identify the major contributors to the SIC of barrier heights and reaction energies. Based on such comparisons, we suggest that barrier height predictions made using the SCAN meta-generalized gradient approximation may have attained the best accuracy possible for a semi-local functional using the Perdew-Zunger SIC approach.
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Materials Science
An exciting approach to theoretical spectroscopy
Martí Raya-Moreno, Alexander Buccheri, Noah Alexy Dasch et al. (+27 more)
Theoretical spectroscopy, and more generally, electronic-structure theory, are powerful concepts for describing the complex many-body interactions in materials. They comprise a variety of methods that can capture all aspects, from ground-state properties to
lattice excitations to different types of light-matter interaction, including time-resolved variants. Modern electronic-structure codes implement either a few or several of these methods. Among them, exciting is an all-electron full-potential package that has a very rich portfolio of all levels of theory, with a particular focus on excitations. It implements the linearized augmented planewave plus local orbital (LAPW+LO) basis, which is known as the gold standard for solving the Kohn-Sham equations of density-functional theory (DFT). Based on this, it also offers
benchmark-quality results for a wide range of excited-state methods. In this review, we provide a comprehensive overview of the features implemented in exciting in recent years, accompanied by short summaries on the state of the art of the underlying methodologies. They comprise DFT and time-dependent DFT (TDDFT), density-functional perturbation theory (DFPT) for
phonons and electron-
phonon coupling, and many-body perturbation theory in terms of the $GW$ approach and the Bethe-Salpeter equation (BSE). Moreover, exciting can handle resonant inelastic x-ray scattering (RIXS), pump-probe spectroscopy as well as
exciton-
phonon coupling (EXPC). Finally, we cover workflows and a view on data and machine learning (ML). All aspects are demonstrated with examples for scientifically relevant materials.
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All authors Martí Raya-Moreno, Alexander Buccheri, Noah Alexy Dasch, Nasrin Farahani, Ignacio Gonzalez Oliva, Andris Gulans, Manoar Hossain, Hannah Kleine, Martin Kuban, Sven Lubeck, Benedikt Maurer, Pasquale Pavone, Fabian Peschel, Daria Popova-Gorelova, Lu Qiao, Elias Richter, Santiago Rigamonti, Ronaldo Rodrigues Pela, Maximilian Schebek, Kshitij Sinha, Daniel T. Speckhard, Jan Stutz, Sebastian Tillack, Dmitry Tumakov, Seokhyun Hong, Jānis Užulis, Mara Voiculescu, Cecilia Vona, Mao Yang, Claudia Draxl
Materials Science
Chemical Origin of Exciton Self-trapping in Cs$_3$Cu$_2$X$_5$ Cesium Copper Halides
Zijin Wu, Shuxia Tao and Geert Brocks
Copper halides Cs3Cu2X5 (X=Cl, Br, I) are promising materials for optoelectronic applications due to their high photoluminescence efficiency, stability, and large Stokes shifts. In this work, we uncover the chemical bonding origin of the Stokes shift in these materials using density functional theory calculations. Upon excitation, one [Cu2X5]3- anion undergoes sizeable local distortions, driven by Cu-X and Cu-Cu bond formation. These structural changes coincide with the formation of a self-trapped
exciton, where particularly the hole is strongly localized on one anion. Analysis of the electronic structure and bonding reveals reduced antibonding interactions and enhanced bonding character in the excited state, stabilizing the distorted geometry. Our results establish a direct link between orbital-specific hole localization and bond formation. It provides a fundamental understanding of the excitation mechanism in Cs3Cu2X5 and offers design principles to tune optical properties in 0D copper halides.
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Materials Science
Thermalization of Optically Excited Fermi Systems: Electron-Electron Collisions in Solid Metals
Stephanie Roden, Christopher Seibel, Tobias Held et al. (+3 more)
Ultrafast optical excitation of metals induces a non-
equilibrium energy distribution in the electronic system, with a characteristic step-structure determined by Pauli blocking. On a femtosecond timescale, electron-electron scattering drives the electrons towards a hot
Fermi distribution. In this work, we present a derivation of the full electron-electron Boltzmann collision integral within the random-k approximation. Building on this approach, we trace the temporal
evolution of the electron energy distribution towards
equilibrium, for an excited but strongly degenerate
Fermi system. Furthermore, we examine to which extent the resulting dynamics can be captured by the numerically simpler relaxation time approach, applying a constant and an energy-dependent relaxation time derived from
Fermi-
liquid theory. We find a better agreement with the latter, while specific features caused by the balance of scattering and reoccupation can only be captured with a full collision integral.
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All authors Stephanie Roden, Christopher Seibel, Tobias Held, Markus Uehlein, Sebastian T. Weber, Baerbel Rethfeld
Materials Science
Unexpected Anisotropic Mn-Sb Anti-site Distribution and Van der Waals Epitaxy of MnSb2Te4
Gustavo Chavez Ponce de Leon, Ahmad Dibajeh, Gert ten Brink et al. (+3 more)
Mn-Sb site mixing directly impacts both the
magnetic and topological properties of MnSb2Te4. This study reveals, unlike previously believed, that these anti-sites can be unevenly distributed within the
crystal. To that end, a polycrystalline sample was created with a two-step synthesis using MnTe and Sb2Te3 as precursors. DC-SQUID magnetometry was used to confirm its
magnetic properties. In addition, the use of High-Resolution Scanning Transmission Electron Microscopy combined with Energy-Dispersive X-ray Spectroscopy allowed us to identify the presence of an inversion-breaking asymmetry in the anti-site distribution. This reduced-
symmetry structure bears resemblance to the recently proposed class of Janus materials and thus warrants further exploration due to its potential for combining
topology and magnetism with other effects, such as non-linear optics and piezoelectricity. Finally, to further elucidate the interplay between site mixing, doping,
topology, and magnetism, a method for growing MnSb2Te4 thin films over amorphous SiOx using Sb2Te3 seeds is introduced. The successful Van der Waals epitaxy of MnSb2Te4 over Sb2Te3 seeds using Pulsed
Laser Deposition is confirmed using Scanning Transmission Electron Microscopy. This represents a crucial step in incorporating these materials into a Si-based architecture, which offers the possibility of controlling the
Fermi lever via gating.
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All authors Gustavo Chavez Ponce de Leon, Ahmad Dibajeh, Gert ten Brink, Majid Ahmadi, Bart Jan Kooi, George Palasantzas
Materials Science · Cross-listed from cond-mat.str-el
Three-dimensional topological insulator feature of ternary chalcogenide Ge2Bi2Te5
Shangjie Tian, Yuchong Zhang, Chenhao Liang et al. (+7 more)
The exploration of novel topological
insulators (TIs) beyond binary chalcogenides has been accelerated in pursuit of exotic
quantum states and device applications. Here, the layered ternary chalcogenide Ge2Bi2Te5 is identified as a three-dimensional TI. The bulk electronic structure of Ge2Bi2Te5 features a hole-type
Fermi surface at
Fermi level EF, which dominates the transport properties. Moreover, an unoccupied topological surface state with a Dirac point located at 290 meV above EF has been observed. Theoretical calculations confirm a bulk bandgap and a nontrivial Z2 topological invariant (000;1). The present study demonstrates that the material family of layered tetradymite-like ternary compounds is an important platform to explore exotic topological phenomena.
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All authors Shangjie Tian, Yuchong Zhang, Chenhao Liang, Yuqing Cao, Wenxin Lv, Xingyu Lv, Zhijun Wang, Tian Qian, Hechang Lei, Shouguo Wang
Materials Science
Growth of Large Crystals of Janus Phase RhSeCl Using Self-Selecting Vapour Growth
Anastasiia Lukovkina, Maria A. Herz, Xiaohanwen Lin et al. (+4 more)
In recent years, interest in 2D Janus materials has grown exponentially, particularly with regard to their applications in spintronics and optoelectronic devices. The defining feature of Janus materials is the ordered arrangement of different layer terminations - creating chemically distinct surfaces and an inherent out-of-plane polarity. Among the few known Janus materials, RhSeCl is particularly intriguing as a rare example of an intrinsic Janus compound. Owing to its exceptional chemical stability, RhSeCl offers a promising platform for exploring the physics related to the Janus-structure. However, synthesising large, high-quality
crystals of this compound remains a significant challenge. Here, we report a novel synthetic pathway for growing
crystals up to 6 mm in lateral size via a two-step self-selecting vapour growth reaction. We further present a comprehensive comparison of newly developed synthesis routes with all previously reported methods for RhSeCl. During these investigations, we identified a previously unreported
impurity that forms in specific growth pathways and demonstrate how it can be avoided to obtain phase-pure few- and monolayer flakes. We showcase the reproducibility of the process to obtain high-quality, large single-
crystals and flakes.
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All authors Anastasiia Lukovkina, Maria A. Herz, Xiaohanwen Lin, Volodymyr Multian, Alberto Morpurgo, Enrico Giannini, Fabian O. von Rohr
Materials Science
Cavity-Mediated Radiative Energy Transfer Enables Stable, Low-Threshold Lasing in Hybrid Quantum Dot-Nanoplatelet Supraparticles
Cristian Gonzalez, Yun Chang Choi, Gary Chen et al. (+5 more)
Colloidal
semiconductor nanocrystals are promising building blocks for optoelectronics due to their solution processability, spectral tunability, and ability to self-assemble into complex architectures. However, their use in lasing application remains limited by high working thresholds, rapid nonradiative losses from Auger recombination, and sensitivity to environmental conditions. Here, we report hybrid microscale supraparticles composed of core/shell CdSe/ZnS
quantum dots (QDs) and CdSe/CdxZn1-xS nanoplatelets (NPLs), which overcome these limitations through efficient, cavity-mediated energy funneling and coupling. Broadband absorbing QDs rapidly transfer excitation to narrow emitting NPLs, enabling stable whispering gallery mode lasing with a low threshold of 0.35 mJ/cm2. These supraparticles retain optical performance after prolonged exposure to air, water, and continuous irradiation, offering practical advantages for optoelectronic devices and advanced pigment technologies. Ultimately, our approach provides a versatile, programmable platform for optical amplification and tunable emission control within colloidal photonic architectures. Keywords
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All authors Cristian Gonzalez, Yun Chang Choi, Gary Chen, Jun Xu, Claire Yejin Kang, Emanuele Marino, Cherie R. Kagan, Christopher B. Murray
Materials Science
Controlled epitaxy of room-temperature quantum emitters in gallium nitride
Katie M. Eggleton, Joseph K. Cannon, Sam G. Bishop et al. (+5 more)
The ability to generate
quantum light at room temperature on a mature
semiconductor platform opens up new possibilities for
quantum technologies. Heteroepitaxial growth of gallium nitride on silicon substrates offers the opportunity to leverage existing expertise and wafer-scale manufacturing to integrate bright
quantum emitters in this material within cavities, diodes, and photonic
circuits. Until now, it has only been possible to grow GaN QEs at uncontrolled depths on sapphire substrates, which is disadvantageous for potential device architectures. Here, we report a method to produce GaN QEs by metal-organic vapor phase epitaxy at a controlled depth in the
crystal through the application of silane treatment and subsequent growth of 3D islands. We demonstrate this process on highly technologically relevant silicon substrates, producing room-temperature QEs with a high Debye Waller factor and strongly anti-bunched emission.
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All authors Katie M. Eggleton, Joseph K. Cannon, Sam G. Bishop, John P. Hadden, Chunyu Zhao, Menno J. Kappers, Rachel A. Oliver, Anthony J. Bennett
Materials Science · Cross-listed from physics.app-ph
In situ and operando laboratory X-ray absorption spectroscopy at high temperature and controlled gas atmosphere with a plug-flow fixed-bed cell
Sebastian Praetz, Emiliano Dal Molin, Delf Kober et al. (+10 more)
The capabilities of a plug-flow fixed-bed
cell for operando studies of heterogeneous catalysts are demonstrated using laboratory-based X-ray absorption spectroscopy (XAS) with a von Hamos spectrometer. The
cell operates at temperatures up to 1000 deg C and pressures up to 10 bar, equipped with three mass flow controllers and two infrared lamps for rapid heating under inert/reactive gas atmospheres. Proof-of-principle studies include in situ MnO oxidation in 5% Ni/MnO and operando Ni nanoparticle
evolution in 20-NiO/COK-12 (20.2% NiO on SiO2) during CO2 methanation before/after activation. Within 5-15 min per spectrum, oxidation state changes are resolved while catalytic activity is simultaneously quantified by online GC. Extended
datasets and methods are available in the ancillary file SI.pdf (Supplementary Information file). A shortened version of this work has been published as a Technical Note in Journal of Analytical Atomic Spectrometry (2026, 41, 1208-1211, DOI: 10.1039/D6JA00027D). This manuscript provides an extended version including additional
datasets, analysis, and methodological details beyond the published article.
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All authors Sebastian Praetz, Emiliano Dal Molin, Delf Kober, Marko Tesic, Christopher Schlesiger, Peter Kraus, Julian T. Müller, Jyothilakshmi Ravi Aswin, Daniel Grötzsch, Maged F. Bekheet, Albert Gili, Aleksander Gurlo, Birgit Kanngießer
Materials Science
Computational Design of Ductile Additively Manufactured Tungsten-Based Refractory Alloys
Kareem Abdelmaqsoud, Daniel Sinclair, Venkata Satya Surya Amaranth Karra et al. (+4 more)
Tungsten exhibits exceptional temperature and radiation resistance, making it well-suited for applications in extreme environments such as
nuclear fusion reactors. Additive manufacturing offers geometrical design freedom and rapid prototyping capabilities for these applications, provided the intrinsic brittleness and low printability of tungsten can be overcome. Designing tungsten
alloys with improved ductility, and thus printability in additive manufacturing, can be accelerated using a computationally derived performance predictor to screen out brittle compositions. Calculations of the Pugh ratio using density functional theory may serve this purpose, given its correlation with ductility. This process can be made more efficient through the use of machine learning interatomic potentials to accelerate density functional theory calculations. Here, we demonstrate that machine learning interatomic potentials can effectively identify optimal
alloy compositions in the W-Ta-Nb system along the melting point-Pugh ratio Pareto front. The trend in Pugh ratio as a function of tungsten fraction is explained in terms of the electronic density of states at the
Fermi level. Experimental validation reveals a strong correlation between the computed Pugh ratio and the observed crack fractions in additively manufactured
alloys. Notably, the two
alloys predicted to have the highest Pugh ratio values, W20Ta70Nb10 and W30Ta60Nb10, exhibit no intergranular microcracking in experiments.
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All authors Kareem Abdelmaqsoud, Daniel Sinclair, Venkata Satya Surya Amaranth Karra, S. Mohadeseh Taheri-Mousavi, Michael Widom, Bryan A. Webler, John R. Kitchin
Materials Science
DFT modelling of stacking faults in hexagonal and cubic GaN
Zijie Wang, Mazharul M. Islam and David R. Bowler
We have performed density functional theory (DFT) calculations to characterize the energetics, and the atomic and electronic structure, of stacking faults in GaN, both in the stable hexagonal wurtzite (wz) phase and in the metastable cubic zincblende (zb) phase. In wz GaN, SFs on the (0001) planes can be divided into three different intrinsic stacking faults (I1, I2, and I3) and oneextrinsic stacking fault (E). In zb GaN, SFs form along (111) directions, giving one type each of intrinsic, extrinsic and twin SFs. Based on the calculated formation energy, I1 is the most stable SF of wz GaN in agreement with experiment. For zb GaN, the intrinsic stacking fault is the most dominant planar defect. To characterize the effect of the stacking faults on the electronic structure of the material, we examined the band density. We found that the bands near the valence band maximum in wz GaN are localised on the Ga-polar side of the stacking fault (i.e. on the Ga side of the Ga-N bonds perpendicular to the SF), with the bands near the conduction band minimum more on the N-polar side, though somewhat delocalised. We found the opposite trend in zb GaN; this behaviour is caused by a redistribution of charge near the interface. We also show the band offsets for the stacking faults, finding that they are very sensitive to local conditions, but can all be described as type II interfaces, with the presence of a stacking fault reducing the gap locally.
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Materials Science
Impact ionization in narrow band gap CdHgTe quantum well with "resonant" band structure
V.Ya.Aleshkin, A.A.Dubinov and V.V.Rumyantsev
Impact ionization probabilities were calculated in a CdHgTe
quantum well, where the distance between electron subbands is close to the band gap energy. This band structure enables impact ionization with small momentum transfer for electrons in the second subband. The study demonstrates that such processes increase the impact ionization probability by approximately two orders of magnitude compared to the impact ionization probability for electrons in the first subband, for which transitions with small momentum changes are impossible. The probability of single impact ionization during the electron energy loss due to optical
phonon emission is estimated. Experimental methods for detecting impact ionization in this structure are discussed.
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Materials Science
Lattice dynamics and structural phase stability of group-IV elemental solids with the r$^2$SCAN functional
Adonis Haxhijaj, Stefan Riemelmoser and Alfredo Pasquarello
The strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) functional is a milestone achievement of electronic structure theory. Recently, a revised and restored form (r$^2$SCAN) has been suggested as a replacement for SCAN in high-throughput applications. Here, we assess the accuracy and reliability of the r$^2$SCAN meta-GGA functional for the group-IV elemental solids carbon (C), silicon (Si), germanium (Ge), and tin (Sn). We show that the r$^2$SCAN functional agrees closely with its parent functional SCAN for elastic constants, bulk
moduli, and
phonon dispersions, but the numerical stability of r$^2$SCAN is superior. Both meta-GGA functionals outperform standard GGA (Perdew-Burke-Ernzerhof) in terms of accuracy and approach the level of common hybrid functionals (Heyd-Scuseria-Ernzerhof). However, we find that r$^2$SCAN performs much worse than SCAN for the $\alpha\leftrightarrow \beta$ phase transition of both Ge and Sn, yielding larger phase energy differences and transition pressures.
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Materials Science
Mesoscale Modelling of Confined Split-Hopkinson Pressure Bar Tests on Concrete: Effects of Internal Damage and Strain Rates
Qingchen Liu and Yixiang Gan
The dynamic strength of concrete under complex loading conditions is a key consideration in the design and maintenance of infrastructures. To assess this mechanical property, Split Hopkinson Pressure Bar (SHPB) tests are typically adopted across a wide range of loading and confining conditions. In this study, mesoscale modelling based on the finite element method (FEM) is employed to simulate SHPB tests on three-phase concrete with realistic aggregate shape, in order to investigate the effects of loading ramp rate, internal friction, and confining pressure on the dynamic increase factor (DIF). Microscopic evidence to explain these effects is explored through analysing the distributions of the internal strain rate and local damage. As key results, increasing loading ramp rates, internal friction, and confining pressure can generally leads to higher DIF values. Only a higher loading ramp rate significantly amplifies the strain-rate effect on the DIF, as evidenced by pronounced increases in both internal strain rate and damage in the mortar and aggregate phases. In contrast, higher internal friction and confining pressure weaken the strain-rate effect on the DIF. Both can be attributed to the mortar phase, which shows a less pronounced increase in damage with increasing strain rate. This study enriches the understanding of the dynamic fracture of concrete toward complex loading scenarios.
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Materials Science · Cross-listed from cond-mat.supr-con
Majorana Zero Modes and Topological Nature in Bi2Ta3S6-family Superconductors
Yue Xie, Zhilong Yang, Ruihan Zhang et al. (+7 more)
In this work, we report that Bi2Ta3S6-family
superconductors exhibit nontrivial band
topology. They possess a natural
quantum-well structure consisting of alternating stacks of TaS2 and honeycomb Bi layers, which contribute superconducting and topological properties, respectively.
Symmetry-based indicators $(\mathbb{Z}_4;\mathbb{Z}_{2}\mathbb{Z}_{2}\mathbb{Z}_{2})=(2;000)$ reveal that the topological nature arises entirely from the Bi layers, which belong to a
quantum spin Hall phase characterized by a $p_x-p_y$ model on a honeycomb
lattice. The topological zigzag (ZZ) and armchair (AC) edge states are obtained. Using VASP2KP, the in-plane $g$ factors of these topological edge states are computed from the ab initio calculations: $g_{x/y}^{\mathrm{ZZ}}=2.07/1.60$ and $g_{x/y}^{\mathrm{AC}}=0.50/0.06$. The strong anisotropy of the edge-state $g$ factors allows us to explore Majorana zero modes in the Bi monolayer on a
superconductor, which can be obtained by exfoliation or molecular beam epitaxy. The relaxed structures of the Bi2Ta3Se6, Bi2Nb3S6 and Bi2Nb3Se6 are obtained. Their superconducting transition temperature $T_c$ are estimated based on the electron-
phonon coupling and the McMillan formula. Furthermore, using the experimental superconducting gap $\Delta$ and the computed $g$ factors, we obtain the phase diagram, which shows that the in-plane field $B_y>2.62\mathrm{ T}$ can generate corner Majorana zero modes in the Bi monolayer of the
superconductor Bi2Ta3S6. A similar paradigm also applies to the Bi2Ta3S6 bulk with the emergence of Majorana hinge states. These natural
quantum-well
superconductors therefore offer ideal platforms for exploring topological superconductivity and Majorana zero modes.
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All authors Yue Xie, Zhilong Yang, Ruihan Zhang, Sheng Zhang, Quansheng Wu, Gang Wang, Hongming Weng, Zhong Fang, Xi Dai, Zhijun Wang
Materials Science
Two-dimensional Intrinsic Janus Structures: Design Principle and Anomalous Nonlinear Optics
Yang Li, Chengzhi Wu, Xuelian Sun et al. (+5 more)
Two-dimensional Janus structures have garnered rapidly growing
attention across multidisciplinary fields. However, despite extensive theoretical and experimental efforts, a principle for designing intrinsic Janus materials remains elusive. Here, we propose a first-principles
alloy theory based on cluster expansion, incorporating a strong repulsive interaction of a cation-mediated anion-pair cluster and refined short-range cluster-cluster competitions, to unravel the formation mechanism of intrinsic Janus structures with a distorted 1T phase among numerous competing phases. Our theory not only explains why intrinsic Janus structures are accidentally observed in RhSeCl and BiTeI which are composed of alloyed elements from different groups, but also accurately predicts a wide range of 1T-like intrinsic Janus materials that are ready for synthesis. Intriguingly, as demonstrated in the case of RhSeCl, we reveal that intrinsic Janus materials can exhibit anomalous second-harmonic generation (SHG) with a distinct
quantum geometric effect, originating from strong
lattice and chemical-potential mirror asymmetry. Furthermore, a novel skin effect unexpectedly emerges in finite-thickness RhSeCl, accompanied by a hidden SHG effect within the bulk region. Our theory paves the way for the ab initio design of intrinsic Janus materials, significantly accelerating progress in Janus science.
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All authors Yang Li, Chengzhi Wu, Xuelian Sun, Liangting Ye, Yirui Lu, Hai-Qing Lin, Wenhui Duan, Bing Huang
Materials Science · Cross-listed from cond-mat.str-el
Spontaneous Anomalous Hall Effect at Room Temperature in Antiferromagnetic Material NbMnAs
Yuki Arai, Junichi Hayashi, Keiki Takeda et al. (+4 more)
Recent studies have shown that certain
antiferromagnetic (AFM) materials with the same
symmetry breaking as ferromagnets can generate sufficiently large
ferromagnetic (FM) responses. Here, we report that the new AFM material NbMnAs exhibits a large anomalous
Hall effect (AHE) at zero field and at room temperature, despite having only a small net magnetization. A polycrystalline sample of NbMnAs, likely close to stoichiometric composition, exhibited an AFM state with a small spontaneous magnetization of approximately $6 \times 10^{-3} \mu_{\rm B}$/Mn and the AHE below $T_{\rm N}=354\,{\rm K}$. In contrast, single
crystals of NbMnAs obtained by a flux method exhibited a deficiency at the As site, {which resulted} in a decrease in $T_{\rm N}$ and an increase in spontaneous magnetization. Although improvement of the single-
crystal growth is still required, our study reveals that NbMnAs is a novel material capable of exhibiting significant FM responses derived from antiferromagnetism at room temperature.
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All authors Yuki Arai, Junichi Hayashi, Keiki Takeda, Hideki Tou, Eiichi Matsuoka, Hitoshi Sugawara, Hisashi Kotegawa
Materials Science
Giant anomalous Hall effect in ultrathin Si/Fe bilayers
S. S. Das and M. Senthil Kumar
Anomalous
Hall effect studies on ultrathin Si(50Angstrom)/Fe(t_Fe)
bilayers were performed at 300 K.
Giant enhancements of about 60 times in saturation anomalous
Hall resistivity and 265 times in anomalous
Hall coefficient (R_s) were observed upon decreasing the Fe layer thickness t_Fe from 200 to 10 Angstrom. The R_s observed for t_Fe = 10 Angstrom is about three orders of magnitude larger than that of bulk Fe. The scaling law between R_s and longitudinal electrical resistivity (Rho) suggests that the side jump is the dominant mechanism of the anomalous
Hall effect. The observed largest
Hall sensitivity of 433 Ohm/T surpasses that of the semiconducting GaAs and InAs
Hall sensors already reported.
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Materials Science
Magnetization and anomalous Hall effect in SiO2/Fe/SiO2 trilayers
Sudhansu Sekhar Das and M. Senthil Kumar
SiO2/Fe/SiO2 sandwich structure films fabricated by sputtering were studied by varying the Fe layer thickness (t_Fe). The structural and microstructural studies on the samples showed that the Fe layer has grown in nanocrystalline form with (110) texture and that the two SiO2 layers are amorphous.
Magnetic measurements performed with the applied field in in-plane and perpendicular direction to the film plane confirmed that the samples are soft
ferromagnetic having strong in-plane
magnetic anisotropy. The temperature dependence of magnetization shows complex behavior with the coexistence of both
ferromagnetic and superparamagnetic properties. The transport properties of the samples as studied through
Hall effect measurements show anomalous
Hall effect (AHE). An enhancement of about 14 times in the saturation anomalous
Hall resistance (R_Ahs) was observed upon reducing the t_Fe from 300 to 50 Angstrom. The maximum value of R_Ahs = 2.3 Ohm observed for tFe = 50 Angstrom sample is about 4 orders of magnitude larger than that reported for bulk Fe. When compared with the single Fe film, a maximum increase of about 56% in the R_Ahs was observed in sandwiched Fe (50 Angstrom) film. Scaling law suggests that the R_s follows the longitudinal resistivity (Rho) as, R_s proportional to (Rho)^1.9, suggesting side jump as the dominant mechanism of the AHE. A maximum enhancement of about 156% in the sensitivity S was observed.
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Materials Science
Data-driven Prediction of Ionic Conductivity in Solid-State Electrolytes with Machine Learning and Large Language Models
Haewon Kim, Taekgi Lee, Seongeun Hong et al. (+2 more)
Solid-state electrolytes (SSEs) are attractive for next-generation lithium-ion batteries due to improved safety and stability but their low room-temperature ionic conductivity hinders practical application. Experimental synthesis and testing of new SSEs remain time-consuming and resource intensive. Machine learning (ML) offers an accelerated route for SSE discovery; however, composition-only models neglect structural factors important for ion transport while graph neural networks (GNNs) are challenged by the scarcity of structure-labeled conductivity data and the prevalence of crystallographic disorder in CIFs. Here, we train two complementary predictors on the same room-temperature, structure-labeled
dataset (n = 499). A gradient-boosted tree regressor (GBR) combining stoichiometric and
geometric descriptors achieves best performance (MAE = 0.543 in log(S cm-1)), and Shapley Additive exPlanations (SHAP) identifies probe-occupiable volume (POAV) and
lattice parameters as key correlations for conductivity. In parallel, we fine-tune large
language models (LLMs) using compact text
prompts derived from CIF metadata (formula with optional
symmetry and disorder tags), avoiding direct use of raw atomic coordinates. Notably, Llama-3.1-8B-Instruct achieves high accuracy (MAE = 0.657 in log(S cm-1)) using formula and
symmetry information, eliminating the need for numerical feature extraction from CIF files. Together, these results show that global
geometric descriptors improve tree-based predictions and enable interpretable structure-property analysis, while LLMs provide a competitive low-preprocessing alternative for rapid SSE screening.
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All authors Haewon Kim, Taekgi Lee, Seongeun Hong, Kyeong-Ho Kim, Yongchul G. Chung
Materials Science
Enhancement of anomalous Hall effect in Si/Fe multilayers
S. S. Das and M. Senthil Kumar
Anomalous
Hall effect studies were performed at 300 K on Si/Fe multilayers prepared by dc magnetron sputtering. About 60 times enhancement in the saturation
Hall resistance and 80 times enhancement in anomalous
Hall coefficient are obtained in [Si(50 angstrom)/Fe(tFe)]_20 multilayers when decreasing the Fe layer thickness from 100 Angstrom to 20 Angstrom. The largest anomalous
Hall coefficient (Rs) of 1.4 x 10^-7 Ohm m/T was found for t_Fe=20 Angstrom, which is about three orders of magnitude larger than that of pure Fe and Fe/Cr, Al/Fe, Cu/Fe, SiO2/FePt/SiO2 multilayers. The ordinary
Hall coefficient R_0 was about two orders of magnitude larger than that of pure Fe. The R_s was found to vary with the longitudinal electronic resistivity, Rho as R_s proportional to (Rho)^2.2, indicating the role of interfaces for the enhancement of the anomalous
Hall effect in the multilayers. An increase of
Hall sensitivity from 9 mOhm/T to 1.2 Ohm/T is observed on decreasing tFe from 100 Angstrom to 10 Angstrom. The high
Hall sensitivity obtained is about three orders of magnitude larger than that of Al/Fe and Cu/Fe multilayers, showing it as an emerging candidate for
Hall element for potential applications.
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Materials Science · Cross-listed from eess.SY
A monolithic fabrication platform for intrinsically stretchable polymer transistors and complementary circuits
Yujia Yuan, Chuanzhen Zhao, Margherita Ronchini et al. (+20 more)
Soft, stretchable organic field-effect transistors (OFETs) can provide powerful on-skin signal conditioning, but current fabrication methods are often material-specific: each new
polymer semiconductor (PSC) requires a tailored process. The challenge is even greater for complementary OFET
circuits, where two PSCs must be patterned sequentially, which often leads to device degradation. Here, we introduce a universal, monolithic photolithography process that enables high-yield, high-resolution stretchable complementary OFETs and
circuits. This approach is enabled by a process-design framework that includes (i) a direct, photopatternable, solvent-resistant, crosslinked dielectric/
semiconductor interface, (ii) broadly applicable crosslinked PSC blends that preserve high mobility, and (iii) a patterning strategy that provides simultaneous etch masking and encapsulation. Using this platform, we achieve record integration density for stretchable OTFTs (55,000 cm^-2), channel lengths down to 2 um, and low-voltage operation at 5 V. We demonstrate photopatterning across multiple PSC types and realize complementary
circuits, including 3 kHz stretchable ring oscillators, the first to exceed 1 kHz and representing more than a 60-fold increase in stage switching speed over the state of the art. Finally, we demonstrate the first stretchable complementary OTFT
neuron circuit, where the output frequency is modulated by the input current to mimic neuronal signal processing. This scalable approach can be readily extended to diverse high-performance stretchable materials, accelerating the development and manufacturing of skin-like electronics.
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All authors Yujia Yuan, Chuanzhen Zhao, Margherita Ronchini, Yuya Nishio, Donglai Zhong, Can Wu, Hyukmin Kweon, Zehao Sun, Rachael K. Mow, Yuran Shi, Lukas Michalek, Haotian Wu, Qianhe Liu, Weichen Wang, Yating Yao, Zelong Yin, Junyi Zhao, Zihan He, Ke Chen, Ruiheng Wu, Jiuyun Shi, Jian Pei, Zhenan Bao