Materials Science · Cross-listed from physics.optics
Temperature-dependent refractive index of AlGaAs for quantum-photonic devices near the bandgap
Moritz Langer, Sai Abhishikth Dhurjati, Martin Bauer et al. (+6 more)
We present an experimental method to determine the refractive index of $Al_{x}Ga_{1-x}As$ (x = 0.0 - 0.5) from 300 K to 4 K across the 500 - 1100 nm wavelength range. The values are extracted from spectroscopically observed microcavity resonances in thin $Al_{x}Ga_{1-x}As$ membranes embedded between fully and partially reflective gold mirrors. Refined Varshni and Paessler models are used to describe temperature-dependent bandgap shifts and material composition. By tracking resonance shifts and benchmarking against finite-difference time-domain simulations, we derive the dispersive optical response with high precision. This yields a quantitatively improved analytical expression for the refractive index of $Al_{x}Ga_{1-x}As$ matching the experimental results with a coefficient of determination as high as $R^2=0.993$, enabling accurate modeling near the band edge at cryogenic temperatures. The method is straightforward and broadly applicable to other
semiconductor systems, offering a valuable tool for the design of micro photonic devices such as
quantum light sources.
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All authors Moritz Langer, Sai Abhishikth Dhurjati, Martin Bauer, Yared Getahun Zena, Ahmad Rahimi, Riccardo Bassoli, Frank H. P. Fitzek, Oliver G. Schmidt, Caspar Hopfmann
Materials Science
Coupling between ferroelectric distortions and excitonic properties in PbTiO$_3$
Pietro Pacchioni, Lorenzo Varrassi and Cesare Franchini
PbTiO$_3$ is a ferroelectric perovskite
semiconductor with favourable electronic and optical properties, making it suitable for a wide range of applications, including photo-catalysis and (opto)electronic devices. Despite its relevance, an accurate ab-initio description of the optical absorption spectrum and of the impact of ferroelectric distortion on the excitonic properties is still lacking. We combine $G_0W_0$ and Bethe-Salpeter Equation calculations to investigate the electronic and optical properties of PbTiO$_3$, tracking the
evolution of its excitonic spectrum along the transition from the cubic paraelectric to the tetragonal ferroelectric phase. As the polar distortion increases, the first absorption peak of the cubic phase splits into two distinct features due to
symmetry breaking, which partially lifts the degeneracy of the underlying excitonic state. Crucially, the distortion further introduces an in-plane/out-of-plane anisotropy in the spectra and controls the energy separation between the resulting excitonic branches. These findings highlight the potential for tuning the optical absorption properties of PbTiO$_3$ via the application of an external electric field.
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Materials Science
Evaluation of carbon incorporation in sulfide thin films grown by hybrid pulsed laser deposition
Claire Wu, Mythili Surendran, Shin Muramoto et al. (+2 more)
Vapor-pressure-mismatched materials, such as transition metal chalcogenides, have emerged as key electronic, photonic, and
quantum materials. Hybrid pulsed
laser deposition (hPLD) has become a preferred method for epitaxial or textured growth of these materials; however, unintentional carbon (C) incorporation remains a persistent concern, particularly when using organic chalcogen precursors as safer alternatives to toxic hydrides. The mechanisms governing C incorporation and its impact on film growth and properties in hPLD remain poorly understood. Here, we investigate the influence of C-containing side products generated from organosulfur precursor pyrolysis on ZnS, BaTiS$_3$, and TiS$_2$ thin films grown by hPLD using tert-butyl disulfide (TBDS). Structural characterization via X-ray diffraction and atomic force microscopy, combined with secondary ion mass spectrometry, is used to systematically examine the effects of growth temperature and TBDS partial pressure on film morphology, crystallinity, and C incorporation. Optimal growth temperatures of 400{\deg}C, 500{\deg}C, and 700{\deg}C are identified for ZnS, TiS$_2$, and BaTiS$_3$, respectively. Growth above or below these temperatures leads to increased C incorporation at both the interface and within the film, correlating with degraded texture. In contrast, highly textured films exhibit minimal C content, comparable to films grown without TBDS. For TiS$_2$, C incorporation depends strongly on TBDS pressure, with 10$^{-1}$ Pa identified as the optimal pressure for minimizing contamination. At higher pressures, loss of preferential texture is observed, likely due to C graphitization poisoning the interface and bulk. These results provide new insight into process-induced C
impurities in hPLD-grown chalcogenide thin films and have important implications for sulfide-based thin film technologies.
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All authors Claire Wu, Mythili Surendran, Shin Muramoto, Alexander Grutter, Jayakanth Ravichandran
Materials Science · Cross-listed from cond-mat.str-el
Accurate prediction of macroscopic transport from microscopic imaging via critical fractals at the Mott transition
P.-Y. Chen, A. R. Rajapurohita, M. Alzate Banguero et al. (+7 more)
Vanadium dioxide (VO$_2$) exhibits hysteresis in resistance while undergoing a thermally driven
insulator-metal transition (IMT). Understanding the nonequilibrium effects in resistance is of great interest, as VO$_2$ is a strong candidate for
brain-inspired computing, which is more energy efficient for AI tasks compared to traditional computing. Accurate models of the connection between microscopic and macroscopic transport properties and microscopic imaging of VO$_2$ will allow us to better utilize VO$_2$ in future applications. However, predictions of macroscopic resistance of VO$_2$ that quantitatively match observations using spatially resolved data have not yet been achieved. Here, we demonstrate an accurate prediction of the macroscopic resistance of VO$_2$ throughout the entire temperature range of interest, by developing a multiscale resistor network model incorporating the assumption of fractal sub-pixel structure of the optical data, where the configuration of insulating and metallic domains within each pixel are drawn from the random field Ising model near criticality. This strongly indicates that the observed fractal, power law structure of metallic and insulating domains extends down to much smaller length scales than the current record for experimental resolution of this system, and that the two-dimensional random field Ising model near criticality is a suitable model for describing the metal and
insulator patches of VO$_2$ down to scales that approach the unit
cell.
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All authors P.-Y. Chen, A. R. Rajapurohita, M. Alzate Banguero, S. Basak, F. Simmons, P. Salev, L. Aigouy, Ivan. K. Schuller, A. Zimmers, E. W. Carlson
Materials Science
Local chemical order suppresses grain boundary migration under irradiation in CrCoNi
Ian Geiger, Penghui Cao and Timothy J. Rupert
Complex concentrated
alloys with intrinsic chemical heterogeneity are promising candidates for
nuclear applications, where local chemical order can strongly influence defect
evolution under irradiation. Grain boundaries also contribute to radiation damage mitigation by serving as defect sinks, yet this interaction can alter interfacial structure, typically leading to destabilization and grain growth. This study investigates how chemical ordering influences grain boundary migration and stability during successive radiation events in CrCoNi. Using atomistic simulations, bicrystals were equilibrated to induce segregation-enhanced chemical order, followed by prolonged irradiation at 1100 K. Our results show that grain boundaries in random CrCoNi begin to migrate after only a few collision cascades, whereas those in the ordered
alloy remain immobile until the chemical order is sufficiently disrupted. Single-cascade simulations reveal key mechanistic differences, where cascades near chemically ordered interfaces produce smaller damage volumes and reduced atomic displacement due to enhanced Frenkel pair combination within the cascade core. This limits both the residual defect population and the energetic driving force for interfacial rearrangement. Subsequent simulations of irradiated interfaces show that interstitial absorption induces a structural transition that modifies the segregation morphology at and near the grain boundary, demonstrating a dynamic coupling between ordering stability and defect
evolution. These findings offer new insights into the role of local chemical order on defect-interface interactions under extreme conditions and highlight pathways for designing radiation-tolerant materials for next-generation
nuclear systems.
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Materials Science
First-principles band alignment engineering in polar and nonpolar orientations for wurtzite AlN, GaN, and B$_x$Al$_{1-x}$N alloys
Cody L Milne and Arunima K Singh
Boron aluminum nitride (B$_x$Al$_{1-x}$N) is a promising material for next-generation electronic and optoelectronic devices due to its ultra-wide bandgap, high thermal stability, and compatibility with other III-nitride
semiconductors. Despite its potential, the band
alignments of B$_x$Al$_{1-x}$N remain largely unexplored, although this information is essential for device design. In this study, we compute the valence and conduction band
alignments of nonpolar ($a$-plane) and polar ($c$-plane) B$_x$Al$_{1-x}$N, and compare them with those of AlN and GaN. Using density functional theory, many-body perturbation theory, $GW_0$ method, and a novel passivation scheme, we find that they have near-zero valence band
alignments for low-$x$ B$_x$Al$_{1-x}$N/AlN, while higher compositions ($x > $0.333) exhibit type I or II band
alignments. The band
alignments also show a notable dependence on surface polarity and the tetrahedral distortion of the B$_x$Al$_{1-x}$N structures. Our computed offsets are in good agreement with available experimental data. Due to their low valence band
alignments and higher conduction band
alignments, the B$_x$Al$_{1-x}$N/AlN
heterostructures could be well suited for high-electron-mobility transistors and ultraviolet light-emitting diodes. The band
alignments of B$_x$Al$_{1-x}$N determined in this study provide essential design guidelines for integrating these ultra-wide bandgap
alloys into advanced
semiconductor technologies.
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Materials Science
On-chip high-order parametric downconversion in the excitonic Mott insulator Nb$_3$Cl$_8$ for programmable multiphoton entangled states
Dmitry Skachkov, Dirk R. Englund and Michael N. Leuenberger
Spontaneous parametric downconversion (SPDC) and four-wave mixing in $\chi^{(2)}$ and $\chi^{(3)}$ media underpin most entangled-
photon sources, but direct generation of higher-order entangled multiphoton states by $n$-th order parametric downconversion remains extremely challenging because conventional materials exhibit tiny high-order nonlinearities. Here we show that single-layer Nb$_3$Cl$_8$, an excitonic Mott
insulator on a breathing Kagome
lattice, supports exceptionally large nonlinear susceptibilities up to seventh order. Many-body GW–Bethe–Salpeter and time-dependent BSE / Kadanoff–Baym simulations yield resonant $\chi^{(2)}$–$\chi^{(7)}$ for monolayer Nb$_3$Cl$_8$, with $|\chi^{(4)}|$ and $|\chi^{(5)}|$ surpassing values in prototypical transition metal dichalcogenides by 5–9 orders of magnitude. We trace this enhancement to flat bands and strongly bound Frenkel
excitons with ferroelectrically aligned out-of-plane dipoles. Building on experimentally demonstrated 1$\times N$ integrated beam splitters with arbitrary power ratios, we propose an on-chip architecture where each output arm hosts an Nb$_3$Cl$_8$ patch, optionally gated by
graphene to tune the complex $n$-
photon amplitudes. Using the ab-initio $\chi^{(3)}$ and $\chi^{(4)}$ values, we predict that three-
photon GHZ$_3$ and four-
photon cluster-state sources in this platform can achieve $n$-
photon generation rates up to $\sim 10^8$ and $\sim 10^6$ times larger, respectively, than silica-fiber- and MoS$_2$-based implementations with comparable geometry. We derive the
quantum Hamiltonian and explicit $n$-
photon generation rates for this platform, and show how suitable interferometric networks enable electrically and spectrally tunable GHZ, $W$, and cluster states based on genuine high-order nonlinear processes in a 2D excitonic Mott
insulator.
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Materials Science · Cross-listed from physics.geo-ph
Granite sliding on granite: friction, wear rates, surface topography, and the scale-dependence of rate-state effects
Sergey V. Sukhomlinov, Martin H. Müser and B.N.J. Persson
We study tribological granite-granite contacts as a model for tectonic faulting, combining experiments, theory, and molecular dynamics simulations. The high friction in this system is not dominated by particulate wear or plowing, as frequently assumed, but by cold welding within plastically deformed asperity junctions. We base this conclusion on the observation that wear is repeatedly high after cleaning contacts but decreases as gouge accumulates, while friction shows the opposite trend. Moreover, adding water reduces wear by a factor of ten but barely decreases friction. Thermal and rate-dependent effects-central to most earthquake models-are negligible: friction remains unchanged between -40{\deg}C and 20{\deg}C, across abrupt velocity steps, and after hours of stationary contact. The absence of rate-state effects in our macroscopic samples is rationalized by the scale-dependence of pre-slip. The
evolution of surface topography shows that quartz grains become locally smooth, with height spectra isotropic for wavelength below 10 microns but anisotropic at longer wavelengths, similar to natural faults. The resulting gouge particles have the usual characteristic sizes near 100 nm. Molecular dynamics simulations of a rigid, amorphous silica tip sliding on {\alpha}-quartz reproduce not only similar friction coefficients near unity but also other experimentally observed features, including stress-introduced transitions to phases observed in post-mortem faults, as well as theoretical estimates of local flash temperatures. Additionally, they reveal a marked decrease of interfacial shear strength above 600{\deg}C.
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Materials Science · Cross-listed from cs.LG
Mofasa: A Step Change in Metal-Organic Framework Generation
Vaidotas Simkus, Anders Christensen, Steven Bennett et al. (+5 more)
Mofasa is an all-atom latent
diffusion model with state-of-the-art performance for generating Metal-Organic Frameworks (MOFs). These are highly porous crystalline materials used to harvest water from desert air, capture carbon dioxide, store toxic gases and catalyse chemical reactions. In recognition of their value, the development of MOFs recently received a Nobel Prize in Chemistry. In many ways, MOFs are well-suited for exploiting generative models in chemistry: they are rationally-designable materials with a large combinatorial design space and strong structure-property couplings. And yet, to date, a high performance generative model has been lacking. To fill this gap, we introduce Mofasa, a general-purpose latent
diffusion model that jointly samples positions, atom-types and
lattice vectors for systems as large as 500 atoms. Mofasa avoids handcrafted assembly
algorithms common in the literature, unlocking the simultaneous discovery of metal nodes, linkers and
topologies. To help the scientific community build on our work, we release MofasaDB, an annotated library of hundreds of thousands of sampled MOF structures, along with a user-friendly web interface for search and discovery: https://mofux.ai/ .
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All authors Vaidotas Simkus, Anders Christensen, Steven Bennett, Ian Johnson, Mark Neumann, James Gin, Jonathan Godwin, Benjamin Rhodes
Materials Science
Transition Metal Dichalcogenide 1T$'$-MoTe$_2$ Nanoscale Films as Spin Pumping Platforms
Emanuele Longo, Pinakapani Tummala, M. Belli et al. (+5 more)
Transition metal dichalcogenides (TMDs) have emerged as a promising class of materials for spintronics, with the aim of promoting efficient
spin-charge conversion (SCC) in TMD/ferromagnet (FM)-based devices. The MoTe$_2$ semimetal with distorted orthorhombic
crystal structure in the 1T$'$ phase has gathered particular
attention due to its high
spin-orbit coupling and reconfigurability as a type-II Weyl semimetal close to room temperature. Here, we report on the role of chemically grown 1T$'$-MoTe$_2$ thin films in inducing SCC in 1T$'$-MoTe$_2$/FM
heterostructures as measured at room temperature.
Ferromagnetic resonance (FMR) and electrically detected
spin-pumping FMR measurements performed on 1T$'$-MoTe$_2$/Co/Au and 1T$'$-MoTe$_2$/Au/Co/Au
heterostructures reveal a
spin-mixing conductance value of up to $\sim1.6 \times 10^{20}~\mathrm{m^{-2}}$ and a
spin Hall angle of $1.7\%$. These findings position MoTe$_2$ thin films as a competitive
spin-charge conversion option compared to other functional materials (e.g., heavy metals, topological
insulators), highlighting their potential for future applications in spintronic devices.
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All authors Emanuele Longo, Pinakapani Tummala, M. Belli, Alessio Lamperti, Christian Martella, Alessandro Molle, Marco Fanciulli, Roberto Mantovan
Materials Science
Reversible nanopore sealing and in situ iron oxide nanoparticle synthesis on thin silicon nitride membranes
Zehui Xia, Pia Bhatia, Celia Morral et al. (+6 more)
We report in-situ synthesis of iron
oxide particles inside silicon nitride nanopores via a chemical reaction, monitored by current readout. Nanopores were formed by electroporation on glass chips (diameters from 1.7 to 11.3 nm), transmission electron microscopy (TEM) drilling (diameters from 6.5 to 64.6 nm), or hydrofluoric acid (HF) etching (diameters from 12.6 to 36.2 nm) in 5 to 20 nm thick membranes. Nanopores seal on timescales from ~1 ms to ~3.6 s, across a range of sizes and concentrations. We show single and ~5-pore arrays, as fabricated, after sealing, and after cleaning and pore recovery. These results are independent of fabrication method. Energy dispersive X-ray spectroscopy (EDS), aberration-corrected scanning TEM (AC-STEM), and powder X-ray diffraction (XRD) verify the synthesis of mixed magnetite and maghemite iron
oxide. This work advances nanoparticle-nanopore chips for applications in biosensing, plasmonics and photonics when position and size control is required.
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All authors Zehui Xia, Pia Bhatia, Celia Morral, Brian DiPaolo, Iryna Golovina, Adriana Buvač-Drndić, Chih-Yuan Lin, David Niedzwiecki, Marija Drndić
Materials Science
Atomic-scale Origin of Interfacial Dzyaloshinskii–Moriya Interaction in Pt/Fe/Au
Emanuele Longo, Gianluca Gubbiotti, Matteo Belli et al. (+4 more)
Recent results show remarkable interfacial–Dzyaloshinskii–Moriya interaction (i-DMI) in
magnetic heterostructures composed of relatively thick Fe thin films ($\gg 1$ nm). To investigate its origin, we present a thorough
magnetic characterization of the SiO$_2$/${}^{57}\mathrm{Fe}$($t$)/Au and SiO$_2$/Pt/${}^{57}\mathrm{Fe}$($t$)/Au
heterostructures ($t = 1.6$ - $2.2$ nm). An i-DMI constant of $D_s^{\mathrm{Pt}} = 0.43\,\mathrm{mJ\,m^{-2}}$ is extracted for the Pt/Fe/Au system, as probed by wavevector-resolved Brillouin light scattering spectroscopy.
Ferromagnetic resonance and conversion electron Mössbauer spectroscopy indicate that significant surface anisotropy is present in Pt/Fe/Au, and that an interfacial Fe fraction ($\sim18$) exhibits tilted magnetization ($\sim25^\circ$ out of plane) and an enhanced hyperfine field, correlating with the stronger i-DMI.
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All authors Emanuele Longo, Gianluca Gubbiotti, Matteo Belli, Claudia Wiemer, Mario Alia, M. Fanciulli, Roberto Mantovan
Materials Science · Cross-listed from physics.optics
Effects of Zero-Point Motion in the High Harmonic Generation Spectrum of Solids
Aday Cárdenas, David N. Purschke, Graham G. Brown et al. (+3 more)
The interpretation of high-harmonic generation (HHG) in solids typically relies on phenomenological dephasing times far shorter than what is expected from microscopic scattering processes. Here we show that zero-point fluctuations associated with optical
phonons naturally suppress long-range electronic coherences and generate clean harmonic spectra without introducing ad-hoc decoherence parameters. Using a 1D
semiconductor composed of two distinct sites per unit
cell and realistic
phonon amplitudes, we demonstrate that random per-site optical-
phonon jitter reproduces the spectral sharpening typically attributed to ultrafast $T_2$ dephasing. In contrast, acoustic
phonons and local strain, whose distortions are correlated over nanometer scales, produce negligible spectral cleaning. We further show that such long-range site coherence leads to carrier-envelope-phase-dependent effects in the HHG spectrum driven by long pulses, but these effects collapse once optical-
phonon-induced decoherence is included. Our results (i) identify optical zero-point motion as a key mechanism governing coherence in solid-state HHG, (ii) demonstrate that it can be qualitatively modeled in periodic solids through site-distance-dependent dephasing, and (iii) suggest that CEP-resolved measurements can probe electronic coherence lengths and atomic fluctuations in crystalline materials.
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All authors Aday Cárdenas, David N. Purschke, Graham G. Brown, Pablo San-Jose, Rui E.F. Silva, Álvaro Jiménez-Galán
Materials Science · Cross-listed from physics.optics
Transient laser-induced periodic surface structures revealed by time-resolved EUV diffuse scattering
D. Ksenzov, F. Capotondi, A. A. Maznev et al. (+12 more)
The formation of permanent
laser-induced periodic surface structures (LIPSS) on solid surfaces under impulsive
laser irradiation above the damage threshold has been subject of extensive research. We demonstrate the formation of transient surface displacement patterns under femtosecond
laser irradiation at fluences well below this threshold. Time-resolved extreme ultraviolet scattering measurements reveal distinct reciprocal-space features similar to those observed for permanent LIPSS but dissipating on the hundreds-of-picoseconds time scale. We show that the transient surface displacement patterns responsible for these features are produced via thermal expansion by the spatial modulation of absorbed
laser intensity caused by scattering of the
laser radiation by surface roughness and present a model accounting for the experimental observations. We suggest that our experiment revealed a universal phenomenon that will be observed on any strongly absorbing material under ultrafast
laser irradiation.
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All authors D. Ksenzov, F. Capotondi, A. A. Maznev, F. Bencivenga, D. Engel, D. Fausti, L. Foglia, R. Gruber, N. Jaouen, M. Kläui, I. Nikolov, M. Pancaldi, E. Pedersoli, B. Pfau, C. Gutt
Materials Science · Cross-listed from cs.DB
LitMOF: An LLM Multi-Agent for Literature-Validated Metal-Organic Frameworks Database Correction and Expansion
Honghui Kim, Dohoon Kim and Jihan Kim
Metal-organic framework (MOF) databases have grown rapidly through experimental deposition and large-scale literature extraction, but recent analyses show that nearly half of their entries contain substantial structural errors. These inaccuracies propagate through high-throughput screening and machine-learning workflows, limiting the reliability of data-driven MOF discovery. Correcting such errors is exceptionally difficult because true repairs require integrating crystallographic files, synthesis descriptions, and contextual evidence scattered across the literature. Here we introduce LitMOF, a large
language model-driven multi-
agent framework that validates crystallographic information directly from the original literature and cross-validates it with database entries to repair structural errors. Applying LitMOF to the experimental MOF database (the CSD MOF Subset), we constructed LitMOF-DB, a curated set of 189,567 computation-ready structures, including the successful repair of 9,227 invalid entries, which accounts for 69.1% of the CSD-derived not-computation-ready MOFs in the latest CoRE MOF DB. Additionally, the system uncovered 8,771 experimentally reported MOFs absent from existing resources, substantially expanding the known experimental design space. Using direct air capture screening as a case study, we demonstrate that structural errors severely distort predicted adsorption energies and CO2/H2O selectivity, leading to systematic misranking of materials, false positives, and the omission of high-performance candidates. This work establishes a scalable pathway toward self-correcting scientific databases and a generalizable approach for LLM-driven curation in materials science.
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Materials Science
Revealing the tribological stress field by using deformation twins as probes
Antje Dollmann, Alexander Dyck, Claudius Klein et al. (+3 more)
Microstructural
evolution in metallic materials feedbacks with the loading conditions and influences the life time of parts and components. Therefore, the deformation mechanisms have to be fundamentally understood. Tribological loading causes a non-trivial, position-dependent, moving stress field. We present a systematic study on the influence of the complexity of the implemented material models on the calculated stress field. For the stress field validation, results of tribological experiments on single
crystals with the activation of deformation twins are used. The resolved shear stresses calculated with the stress field models have to be highest on the experimentally identified twin systems. From this combination of modelling and experiment, it clearly follows that a stress field model considering plasticity is required. The widely used Hamilton stress field for tribological loading is limited due to only considering elastic strains. Here, the predictive quality of the stress field is sensitive to the assumed yield strength, work hardening and plastic anisotropy. Certain stress field models are close to the experimental data, but none completely replicate them. These results highlight that the model type and parameters have to be carefully determined in order to be able to predict how a metallic material deforms due to a sliding load.
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All authors Antje Dollmann, Alexander Dyck, Claudius Klein, Alexander Kauffmann, Thomas Boehlke, Christian Greiner
Materials Science
Distinguish the Orientation of Sliding Ferroelectricity by Second-Harmonic Generation
Fengfeng Ye, Qiankun Li, Zhuocheng Lu et al. (+5 more)
As the emerging ferroelectric (FE) materials, the ultrathin two-dimensional (2D) sliding ferroelectrics without phase-matching bottleneck, usually exhibit the pronounced second harmonic generation (SHG) responses. Despite the structural polarity of sliding ferroelectrics can be precisely detected via SHG characterizations, distinguishing the orientations of sliding ferroelectricity based on SHG responses has rarely been realized, as SHG intensities for upward and downward polarization states are supposed to be same. In current work, combining computational simulations and experimental characterizations, the orientation of sliding ferroelectricity is demonstrated to be readily distinguishable via SHG responses in 2D SnP2S6 (SnP2Se6), a new sliding FE material. Specifically, owing to the unique
symmetry operation within FE-SnP2S6 (SnP2Se6), the intersection between ḩi}xxx and ḩi}yyy SHG susceptibility coefficients with opposite signs leads to the effective rotation of SHG polar directions upon switching of sliding ferroelectricity. Moreover, the remarkable dependence of SHG polar directions on the orientation of sliding ferroelectricity is further validated by experimental characterizations performed on SnP2S6
crystal in a single FE domain structural form. This work opens up the avenue for in-situ detecting the ferroelectricity orientation of 2D sliding ferroelectrics based on SHG nonlinear optical responses, and also demonstrates the controllable optical nonlinearly for new "slidetronics" applications.
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All authors Fengfeng Ye, Qiankun Li, Zhuocheng Lu, Xinfeng Chen, Yang Li, Hua Wang, Lu You, Gaoyang Gou
Materials Science
First-principles screening of materials with extreme effective masses
Szymon Błazucki, Junfeng Qiao, Aleksandr Poliukhin et al. (+1 more)
The effective mass of charge carriers is a fundamental descriptor of the electronic structure of materials, and can be used to assess performance in electronics applications, or to screen for thermoelectrics and transparent conductors. Here, we perform a high-throughput computational screening of approximately 20,000 experimentally known three-dimensional stoichiometric inorganics obtained from the Materials Cloud 3D structure database. By combining density-functional theory calculations and maximally localized Wannier functions, we are able to compute the full conductivity effective mass tensor for electrons and holes from the Boltzmann transport equation in the constant relaxation-time approximation. This approach captures the effects of band non-parabolicity, anisotropy, and valley multiplicity that would be neglected by standard
parabolic fittings. The screening identifies a curated set of candidates exhibiting extreme electronic properties, from ultra-low to ultra-large effective masses, these latter associated with flat-band physics. We validate the workflow by recovering established high-mobility
semiconductors and highlight promising novel candidates. Furthermore, we classify materials by their mass anisotropy and discuss the physical limits of defining a conductivity effective mass in narrow-gap regimes at room temperature. Importantly, the resulting
dataset provides a systematic roadmap to search for high-performance materials in novel chemical spaces.
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All authors Szymon Błazucki, Junfeng Qiao, Aleksandr Poliukhin, Nicola Marzari
Materials Science
Electric polarization driven by non-collinear spin alignment investigated by first principles calculations
Sergiy Mankovsky, Svitlana Polesya, Jan Minar et al. (+2 more)
We present an approach for first principles investigations on the
spin driven electric polarization in type II multiferroics. We propose a parametrization of the polarization with the parameters calculated using the Korringa-Kohn-Rostoker Green function (KKR-GF) formalism. Within this approach the induced electric polarization of a unit
cell is represented in terms of three-site parameters. Those antisymmetric with respect to
spin permutation are seen as an ab-initio based counter-part to the phenomenological parameters used within the inverse-Dzyaloshinskii-Moriya-interaction (DMI) model. Due to their relativistic origin, these parameters are responsible for the electric polarization induced in the presence of a non-collinear
spin alignment in materials with a centrosymmetric
crystal structure. Beyond to this, our approach gives direct access to the element- or site-resolved electric polarization. To demonstrate the capability of the approach, we consider several examples of the so-called type II multiferroics, for which the magneto-electric effect is observed either as a consequence of an applied
magnetic field (we use Cr$_2$O$_3$ as a prototype), or as a result of a phase transition to a
spin-spiral
magnetic state, as for instance in MnI$_2$, CuCrO$_2$ and AgCrO$_2$.
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All authors Sergiy Mankovsky, Svitlana Polesya, Jan Minar, Hongbin Zhang, Hubert Ebert
Materials Science
Origin of Bright Quantum Emissions with High Debye-Waller factor in Silicon Nitride
Shibu Meher, Manoj Dey and Abhishek Kumar Singh
Silicon nitride has emerged as a promising photonic platform for integrated single-
photon sources, yet the microscopic origin of the recently observed bright
quantum emissions remains unclear. Using hybrid density functional theory, we show that the negatively charged N$_\text{Si}$V$_\text{N}$ center (NV$^{-}$) in the C$_{1h}$ configuration exhibits a linearly polarized zero-
phonon line (ZPL) at 2.46 eV, with a radiative lifetime of 9.01 ns and a high Debye-Waller (DW) factor of 33%. We further find that the C$_{1h}$ configuration is prone to a pseudo-Jahn-Teller distortion, yielding two symmetrically equivalent defect structures that emit bright, linearly polarized ZPL at 1.80 eV with a lifetime of 10.17 ns and an increased DW factor of 41%. These nitrogen-vacancy-related defects explain the origins of visible
quantum emissions, paving the way for deterministic and monolithically integrated silicon-nitride
quantum photonics.
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Materials Science
Eu-assisted enhancement of photoresponse in MBE-grown CdO/Si photodetectors
Igor Perlikowski, Eunika Zielony, Abinash Adhikari et al. (+4 more)
Doping cadmium
oxide with rare earth (RE) elements is a way to control the band gap and enhance carrier concentration and mobility. This work presents how one of REs, europium, impacts performance of CdO/Si diode. The samples were grown using
plasma-assisted molecular beam epitaxy. Doping level was modified by changing the temperature of the effusion
cell with Eu and therefore flux of Eu particles. Different dopant concentrations were confirmed by secondary ion mass spectrometry. Atomic force microscopy images revealed a grain-like surface structure of the samples with grain size increasing after rapid thermal processing (RTP). Raman spectroscopy showed that introducing Eu changes vibrational properties of CdO through intraionic anharmonicity reduction. Kelvin probe method revealed upward band bending caused by oxygen adsorption during RTP. Electrical measurements confirmed that rectifying junctions were manufactured and that they are able to produce photocurrent in the spectral range of 450-1150 nm without external voltage bias. Introducing Eu into CdO was found to increase e.g. rectifying factor and responsivity. The results show that doping CdO with Eu is a way to enhance performance of the presented zero-power-consumption photodetectors, making it a promising material for future applications in optoelectronics.
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All authors Igor Perlikowski, Eunika Zielony, Abinash Adhikari, Rafał Jakieła, Sergij Chusnutdinow, Ewa Popko, Ewa Przeździecka
Materials Science
Defect-Limited Efficiency of Pnictogen Chalcohalide Solar Cells
Cibrán López, Seán R. Kavanagh, Pol Benítez et al. (+4 more)
Pnictogen chalcohalides (MChX) have recently emerged as promising nontoxic and environmentally friendly photovoltaic absorbers, combining strong light absorption coefficients with favorable low-temperature synthesis conditions. Despite these advantages and reported optimized morphologies, device efficiencies remain below 10%, far from their ideal radiative limit. To uncover the origin of these performance losses, we present a systematic and fully consistent first-principles investigation of the defect chemistry across the Bi-based chalcohalide family. Our results reveal a complex defect landscape dominated by chalcogen vacancies of low formation energy, which act as deep nonradiative recombination centers. Despite their moderate charge-carrier capture coefficients, the high
equilibrium concentrations of these defects reduce the theoretical maximum efficiencies by 6% in BiSeI and by 10% in BiSeBr. In contrast, sulfur vacancies in BiSI and BiSBr are comparatively benign, presenting smaller capture coefficients due to weaker electron-
phonon coupling. Interestingly, despite its huge nonradiative charge-carrier recombination rate, BiSeI presents the best conversion efficiency among all four compounds owing to its most suitable bandgap for outdoor photovoltaic applications. Our findings identify defect chemistry as a critical bottleneck in MChX
solar cells and proposes chalcogen-rich synthesis conditions and targeted anion substitutions as effective strategies for mitigation of detrimental vacancies.
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All authors Cibrán López, Seán R. Kavanagh, Pol Benítez, Edgardo Saucedo, Aron Walsh, David O. Scanlon, Claudio Cazorla
Materials Science · Cross-listed from cs.CV
QuantumCanvas: A Multimodal Benchmark for Visual Learning of Atomic Interactions
Can Polat, Erchin Serpedin, Mustafa Kurban et al. (+1 more)
Despite rapid advances in molecular and materials machine learning, most models still lack physical transferability: they fit correlations across whole molecules or
crystals rather than learning the
quantum interactions between atomic pairs. Yet bonding, charge redistribution, orbital hybridization, and electronic coupling all emerge from these two-body interactions that define local
quantum fields in many-body systems. We introduce QuantumCanvas, a large-scale
multimodal benchmark that treats two-body
quantum systems as foundational units of matter. The
dataset spans 2,850 element-element pairs, each annotated with 18 electronic, thermodynamic, and
geometric properties and paired with ten-channel image representations derived from l- and m-resolved orbital densities, angular field transforms, co-occupancy maps, and charge-density projections. These physically grounded images encode spatial, angular, and electrostatic
symmetries without explicit coordinates, providing an interpretable visual modality for
quantum learning. Benchmarking eight architectures across 18 targets, we report mean absolute errors of 0.201 eV on energy gap using GATv2, 0.265 eV on HOMO and 0.274 eV on LUMO using EGNN. For energy-related quantities, DimeNet attains 2.27 eV total-energy MAE and 0.132 eV repulsive-energy MAE, while a
multimodal fusion model achieves a 2.15 eV Mermin free-energy MAE. Pretraining on QuantumCanvas further improves convergence stability and generalization when fine-tuned on larger
datasets such as QM9, MD17, and CrysMTM. By unifying orbital physics with
vision-based representation learning, QuantumCanvas provides a principled and interpretable basis for learning transferable
quantum interactions through coupled visual and numerical modalities.
Dataset and model implementations are available at https://github.com/KurbanIntelligenceLab/QuantumCanvas.
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All authors Can Polat, Erchin Serpedin, Mustafa Kurban, Hasan Kurban
Materials Science
Optical refractive index measurements of AlGaAs at high temperature for fully automated molecular beam epitaxy growth of Bragg mirrors
Pierre Gadras, Léo Bourdon, Antoine Fées et al. (+3 more)
In-situ measurement is a key feature to better understand and precisely control the growth of complex structures, such as vertical-cavity surface-emitting
lasers. In this work, we are showing the precise measurement of optical indices of AlGaAs at 600 {\textdegree}C over a wide spectral range (450–1400 nm). To do so, in-situ spectral reflectance measurement is used, combined with ex-situ layer thickness and composition measurement by x-ray diffraction enabling for precise determination of the optical indices with an accuracy better than 1%. To validate our measurements, we realized the complete automation of the growth of a GaAs/AlAs 940 nm-DBR by molecular beam epitaxy, without the need to pre-calibrate
cells fluxes. The fabricated DBR shows a deviation of 0.2 nm of the stop-band central-wavelength compared to the targeted one. This approach holds significant interest for the III–V
semiconductor community and epitaxial growth techniques.
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All authors Pierre Gadras, Léo Bourdon, Antoine Fées, Karim Ben Saddik, Guilhem Almuneau, Alexandre Arnoult
Materials Science
Silver Alloyed Wide Bandgap (Ag,Cu)(In,Ga)S2 Thin Film Solar Cells With 15.5% Efficiency
Yucheng Hu, Ece Washbrook, Arivazhagan Valluvar Oli et al. (+14 more)
Sulfide chalcopyrite Cu(In,Ga)S2 (CIGS) is a wide bandgap
semiconductor suitable for the top
cell of a tandem
solar device. Here we demonstrate significant improvements in absorber quality by alloying with Ag to form (Ag,Cu)(In,Ga)S2 (ACIGS) absorbers. We report the Ag alloying effect on compositional, structural, and optoelectronic properties of absorbers. We demonstrate suppressed bulk recombination and improved carrier lifetime in ACIGS, as a result of improved grain size, porosity reduction and defect passivation. We also show that Ag alloying flattens the Ga gradient. Consideration of this impact of Ag will be necessary in future engineering of the Ga profile to maximize charge carrier collection and avoid interface recombination. Exploiting the beneficial effects of Ag alloying, we report a wide bandgap (1.58 eV) ACIGS
solar cell with a high power conversion efficiency of 15.5% and a large open-
circuit voltage (VOC) of 948 mV, improving on the reference pure CIGS
solar cell, with an 11.2% efficiency and an 821 mV VOC. Ag alloying is a useful route to further increase the efficiency of CIGS
solar cells and future tandem devices.
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All authors Yucheng Hu, Ece Washbrook, Arivazhagan Valluvar Oli, Andrea Griesi, Yurii P. Ivanov, Mariam Pelling, Simon M. Fairclough, Kulwinder Kaur, Michele Melchiorre, Adam Hultqvist, Tobias Törndahl, Wolfram Hempel, Wolfram Witte, Giorgio Divitini, Susanne Siebentritt, Rachel A. Oliver, Gunnar Kusch
Materials Science · Cross-listed from physics.optics
Effects of thermal annealing and film thickness on the structural and optical properties of indium-tin-oxide thin films
Ding Xu, Wen Zhou, Yuxin Du et al. (+3 more)
Indium-tin
oxide (ITO) is a crucial functional layer for the optoelectronic applications, such as non-volatile color display thin films based on the ITO/phase-change material (PCM)/ITO/reflective metal multilayer structures on a silicon substrate. In addition to non-volatile color tuning by PCMs, thermally induced crystallization may alter the optical properties of ITO layers as well. But the potential change in color of the ITO layers is not considered so far. In this work, we investigate the structural and optical properties of ITO thin films via X-ray diffraction, spectroscopic ellipsometry and ultraviolet-visible spectrophotometry measurements. After thermal annealing at 250 {\deg}C, the ITO thin films of 15-100 nm get crystallized with strong changes in refractive index n and extinction coefficient k in the visible light range. However, for the 5-nm ITO thin film, crystallization is only observed after thermal annealing at 350 {\deg}C and the change in color is limited upon phase transition. We provide a colormap of the ITO/platinum/silicon structure in terms of the annealing temperature (150-350 {\deg}C) and ITO film thickness (5-100 nm). Our work suggests that the intrinsic change in colors of ITO layers should also be considered for the PCM-based reconfigurable display application.
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All authors Ding Xu, Wen Zhou, Yuxin Du, Junying Zhang, Wei Zhang, Jiangjing Wang
Materials Science
An Investigation of Thermal Properties of Cu-Au Janus Nanoparticles
Mehmet Akif Cebeci, Hatice Zor Oguz, Sevgi Ozdemir Kart et al. (+1 more)
In this paper, the thermal and structural properties of Cu-Au (Copper-Gold) Janus nanoparticles with a diameter of 5 nm are investigated by using molecular dynamics (MD) simulations within the interactions defined by the many-body embedded atom model (EAM). A set of nanoparticle models has been constructed, with varying Cu and Au ratios. MD method is carried out to calculate the melting temperature, heat capacity, radial distribution function (RDF), Lindemann index, mean square displacement (MSD), and
diffusion coefficients of these models. The findings demonstrate that nanoparticles rich in Cu exhibit a higher melting temperature and more defined phase transitions. In contrast, structures rich in gold exhibited reduced melting temperatures and showed surface-initiated melting behaviours. MD study highlights that the thermal stability and atomic mobility of Cu-Au Janus nanoparticles depend on the composition ratio and the dispersion of materials.
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All authors Mehmet Akif Cebeci, Hatice Zor Oguz, Sevgi Ozdemir Kart, Hasan Huseyin Kart
Materials Science
Predicting cement microstructure and mechanical properties in hydrating cement paste with a Phase-Field model
Alexandre Sac-Morane, Katerina Ioannidou, Manolis Veveakis et al. (+1 more)
Predicting the evolving microstructure of hydrating cement is essential for understanding and modeling its mechanical property development. Physics-based continuum approaches offer a rigorous framework for capturing the thermodynamics of dissolution and precipitation processes at the microstructural scale. In this work, we present an adapted Phase-Field (PF) model for cement hydration that resolves key physical inconsistencies in existing PF formulations by introducing a revised free-energy potential and distinct
equilibrium constants for clinker dissolution and hydrate precipitation. The resulting PF framework reproduces microstructural
evolution, yielding realistic porosity levels and continuous phase boundaries in close agreement with experimental observations. The predicted hydrated microstructures are subsequently used in a computational homogenization scheme to evaluate the elastic response of the material. The PF-derived mechanical properties show good agreement with experimental trends, supporting the ability of the proposed framework to consistently link hydration chemistry, microstructure formation, and the resulting mechanical response.
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All authors Alexandre Sac-Morane, Katerina Ioannidou, Manolis Veveakis, Hadrien Rattez
Materials Science
Extraordinary cation-replace-cation antisite defect predominate in Bi2SeO5
Chen-Min Dai, Feifan Bian, Yafeng Zhang et al. (+4 more)
As a newly identified single-crystalline van der Waals dielectric with a high dielectric constant, Bi2SeO5 plays a pivotal role in advancing 2D electronic devices. In this work, we systematically investigate the defect properties of Bi2SeO5 using first-principles calculations based on a hybrid functional. Although Bi2SeO5 is a chemically ternary compound, each constituent element occupies several crystallographically nonequivalent sites, rendering its defect chemistry highly complex. Due to the anomalous +4 cationic valence state of Se, the defect formation energies of same main group anion antisite defects (SeO and OSe) are prohibitively high, and their concentrations can therefore be neglected. In contrast, the extraordinary cation-cation antisite defects BiSe and SeBi emerge as the dominant defects. The pronounced variability in the formation energies of the six types of VO defects demonstrates that identical defect types located on nonequivalent atomic sites can exhibit markedly different properties. Under O-rich and Se/Bi-poor conditions, Bi2SeO5 shows relatively robust p-type behavior. Conversely, under O-poor and Se/Bi-rich conditions, or at intermediate O, Se, and Bi partial pressures, Bi2SeO5 behaves as an intrinsic
semiconductor or displays very weak n-type conductivity due to strong donor-acceptor compensation. This study provides theoretical insights to guide the design and development of high-performance Bi2SeO5-based electronic devices.
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All authors Chen-Min Dai, Feifan Bian, Yafeng Zhang, Jiaqi Chen, Zenghua Cai, Menglin Huang, Chunlan Ma
Materials Science
Competing Lattice and Defect Dynamics Govern Terahertz-Induced Ferroelectricity in Quantum Paraelectric SrTiO$_3$
L. Cheng, K. Hu, S. Yang et al. (+3 more)
Intense terahertz (THz) pulses induce transient inversion-
symmetry breaking in
quantum paraelectric SrTiO$_3$, yet the underlying mechanism remains controversial. Using fields up to $\sim$1.1 MV/cm, we reveal spatially inhomogeneous THz-field-induced second harmonic generation (TFISH) governed by competing
lattice and defect dynamics. Short-lived coherent antiferrodistortive (AFD) modes suppress dipole correlations within $\sim$5 ps, while heavily damped soft/AFD modes and a defect-induced low-frequency mode ($\sim$0.1-0.3 THz) jointly prevent long-range ferroelectric coherence in oxygen-vacancy-rich regions. Collective modes manifested by oscillatory TFISH components exhibit softening followed by hardening below a critical temperature $T^*\simeq$28 K, confirming transient ferroelectric order where defects are sparse. These results reconcile conflicting interpretations, establish defect-mediated competition as a central regulator of light-induced ferroelectricity, and open routes to ultrafast control of
quantum materials.
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All authors L. Cheng, K. Hu, S. Yang, Yan Liang, Jiandi Zhang, J. Qi