Peer Revenue Now accepting positions

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Wednesday 31 December

Materials Science

Learning and retrieval for warm-starting charge-self-consistent DFT+DMFT

Rishi Rao and Li Zhu

Charge-self-consistent (CSC) DFT+DMFT delivers quantitative correlated-electron physics one configuration at a time, making ensemble sampling dependent on reliable warm starts for its expensive fixed-point iteration. Here we compare retrieval from the most similar converged structure with an E(3)-equivariant model that predicts a physics-structured self-energy and Fermi level. Because the full CSC loop refines both initializations, every production result remains a converged DFT+DMFT solution. Across metallic Fe, correlated FeO, and Mott-insulating NiO, learning reduces the typical iterations to sustained convergence from 8 to 3, 8 to 3, and 6 to 1. Retrieval matches this median speed when a dense same-state archive is available, but several poor transplants reveal that structural similarity does not predict transplant quality. In a pre-registered volume window excluded from training and donor pools, learning retains its speed, whereas retrieval starts $3.4\times$ farther from the fixed point and approaches cold-start cost. Either initialization can select a distinct near-degenerate branch on a rugged CSC landscape. Applied end to end, the workflow generates over one thousand correlated energy and force labels for iron at Earth's-core conditions and trains an equivariant interatomic potential. Solid–liquid coexistence with 9216 atoms gives $T_m = 6225 \pm 42\,\mathrm{K}_{\mathrm{stat}}$ at 330~GPa, consistent with recent experiments. A 50-configuration DFT+DMFT audit resolves the potential's energy calibration but does not justify a corrected melting temperature, because four-atom cells cannot realize a liquid. The resulting regime map favors retrieval within dense coverage, amortized learning at and beyond its boundary, and solver refinement throughout.
Read the full abstract

Materials Science

Best Practices for Modelling Electrides

Lee A. Burton

Materials in which electrons occupy interstitial sites as anions are called electrides and exhibit unusual dimensionality-dependent electronic behavior. These properties make electrides attractive for catalysis, transparent conductors, and emergent quantum phenomena, yet their theoretical treatment remains challenging. In conventional materials, the ground-state atomic structure dictates the electronic configuration, whereas in electrides the electronic structure can instead govern the atomic arrangement. Here, the performance of commonly used exchange-correlation functionals is evaluated for representative one-, two-, and three-dimensional electrides. The results show that higher-cost approaches do not necessarily perform better across all cases, while standard methods capture the qualitative electride character and many key energetic and structural trends with surprising reliability. This behavior, likely arising from fortuitous error cancellation, supports the reliability of legacy studies in the field and the viability of efficient high-throughput exploration using low-cost methods. Overall, the findings support a tiered computational strategy for electride modelling, integrating system-specific heuristics with efficient first-principles screening. This approach balances computational feasibility with physical fidelity and underscores the continuing leadership of theory in the predictive discovery of electride materials across dimensionalities.
Read the full abstract

Materials Science

Microscopic Insights to the Ultralow Thermal Conductivity of Monolayer 1T-SnTe2

Kemal Aziz, John E. Ekpe, Augustine O. Okekeoma et al. (+8 more)

Two-dimensional (2D) metallic systems with intrinsically low lattice thermal conductivity are rare, yet they are of great interest for next-generation energy and electronic technologies. Here, we present a comprehensive first-principles investigation of monolayer tin telluride (SnTe2) in its 1T (CdI2-type, P3m1) structure. Our calculations establish its energetic and dynamical stability, confirmed by large cohesive (10.9 eV/atom) and formation (-4.06 eV/atom) energies and a phonon spectrum free of imaginary modes. The electronic band structure reveals metallicity arising from strong Sn-Te p orbital hybridization. Most importantly, phonon dispersion analysis uncovers a microscopic origin for the ultralow lattice thermal conductivity: the heavy mass of Te atoms, weak Sn-Te bonding, and flat acoustic branches that yield exceptionally low and anisotropic group velocities (~5.0 x 10^3 m/s), together with the absence of a phonon bandgap that enhances Umklapp scattering. These features converge to suppress phonon-mediated heat transport. Complementary calculations of the optical dielectric response and joint density of states reveal pronounced interband transitions and a plasmonic resonance near 4.84 eV, suggesting additional optoelectronic opportunities. These findings establish monolayer SnTe2 as a 2D material whose vibrational softness naturally enforces ultralow lattice thermal conductivity, underscoring its potential for thermoelectric applications.
Read the full abstract

All authors Kemal Aziz, John E. Ekpe, Augustine O. Okekeoma, Stanley O. Ebuwa, Sylvester M. Mbam, Shedrack Ani, Malachy N. Asogwa, Richard A. Mangluhut, Anthony C. Iloanya, Fabian I. Ezema, Chinedu E. Ekuma

Materials Science

Metallic solid-state hydrogen storage crystals achieved through chemical precompression under ambient conditions

Baiqiang Liu, Chenxi Wan, Rui Liu et al. (+3 more)

Improving hydrogen storage density is essential for reducing the extreme conditions required in applications such as nuclear fusion. However, the recognition of metallic hydrogen as the "Holy Grail" of high-pressure science highlights the difficulty of high-density hydrogen aggregation. Here, we report a solid-state crystal H9@C20 formed by embedding hydrogen atoms into C20 fullerene cages and utilizing chemical precompression, which remains stable under ambient pressure and temperature conditions and exhibits metallic properties. This precompression effect is reflected in the formation of C-H bonds within the cage and C-C bonds between cages, resulting in the transformation of all C atoms from sp2 to sp3 hybridization with inward and outward distortions, while promoting delocalized multicenter bonding within the H9 aggregate. In particular, the hydrogen density inside the C20 cage exceeds that of solid hydrogen, achieving a uniform discrete distribution with H9 as monomers. Further study reveals that filling hydrogen molecules into voids between H9@C20 primitive cells can increase hydrogen content while maintaining structural stability, forming a solid-gas mixed hydrogen storage crystal. Our findings provide a basis for developing high-density hydrogen storage materials under ambient conditions.
Read the full abstract

All authors Baiqiang Liu, Chenxi Wan, Rui Liu, Zhen Gong, Jia Fan, Zhigang Wang

Materials Science

SSCHA-based evolutionary crystal structure prediction at finite temperatures with account for quantum nuclear motion

Daniil Poletaev and Artem R. Oganov

Reliable crystal structure prediction (CSP) at finite temperatures, including quantum anharmonic effects, remains challenging but is particularly important for systems containing light atoms such as superconducting hydrides. Here, we integrate machine-learned interatomic potentials (MLIPs) with the stochastic self-consistent harmonic approximation (SSCHA) to enable evolutionary CSP on the quantum anharmonic free-energy landscape. Using LaH10 as a test case, we compare three approaches: (i) active-learning MLIPs (AL-MLIPs) trained on the fly, (ii) universal MLIPs (uMLIPs), and (iii) temperature-dependent effective potentials (TDEPs) trained on SSCHA ensemble data. AL-MLIPs correctly predict the cubic Fm-3m phase but require thermodynamic perturbation theory corrections for consistent results. The foundation uMLIP Mattersim-5m enables SSCHA-based CSP without per-structure training, but fine-tuning is required for higher accuracy. Temperature-dependent effective potentials trained on SSCHA data enable accurate and very efficient CSP for large unit cells on the quantum anharmonic free-energy landscape. We demonstrate that quantum anharmonicity simplifies the free-energy landscape and is essential for the correct energy ranking of LaH10 structures.
Read the full abstract

Materials Science

Upscaling from ab initio atomistic simulations to electrode scale: The case of manganese hexacyanoferrate, a cathode material for Na-ion batteries

Yuan-Chi Yang, Eric Woillez, Quentin Jacquet et al. (+1 more)

We present a generalizable scale-bridging computational framework that enables predictive modeling of insertion-type electrode materials from atomistic to device scales. Applied to sodium manganese hexacyanoferrate, a promising cathode material for grid-scale sodium-ion batteries, our methodology employs an active-learning strategy to train a Moment Tensor Potential through iterative hybrid grand-canonical Monte Carlo–molecular dynamics sampling, robustly capturing configuration spaces at all sodiation levels. The resulting machine learning interatomic potential accurately reproduces experimental properties including volume expansion, operating voltage, and sodium concentration-dependent structural transformations, while revealing a four-order-of-magnitude difference in sodium diffusivity between the rhombohedral (sodium-rich) and tetragonal (sodium-poor) phases at 300 K. We directly compute all critical parameters – temperature- and concentration-dependent diffusivities, interfacial and strain energies, and complete free-energy landscapes – to feed them into pseudo-2D phase-field simulations that predict phase-boundary propagation and rate-dependent performances across electrode length scales. This multiscale workflow establishes a blueprint for rational computational design of next-generation insertion-type materials, such as battery electrode materials, demonstrating how atomistic insights can be systematically translated into continuum-scale predictions.
Read the full abstract

All authors Yuan-Chi Yang, Eric Woillez, Quentin Jacquet, Ambroise van Roekeghem

Materials Science

Temperature dependence of the spontaneous magnetization of Ni2MnGa and other ferromagnets. The superellipse equation

A. Perevertov

The temperature dependence of the spontaneous magnetization of Ni2MnGa and other ferromagnets can be described in reduced coordinates by the superellipse equation using a single dimensionless parameter. This critical exponent parameter equals 2.4 for Ni2MnGa, 2.7 for nickel and cobalt, 3 for iron and 2.05 for gadolinium. Because reduced magnetization and reduced temperature enter the equation symmetrically, the MS(T) dependence can be measured only in the low-temperature range, from 0 to 0.5TC. The magnetization curve from 0.5TC to TC can then be obtained by interchanging reduced magnetization and temperature in the superellipse equation. In this way, the experimentally challenging task of measuring spontaneous magnetization near TC is avoided, as the behavior near TC is effectively determined from measurements performed near T = 0. The MS(T) dependence in a whole temperature range is fully determined by two parameters - the Curie temperature, TC and the critical exponent, n .
Read the full abstract

Materials Science

Essential Principles and Practices in X-ray Photoelectron Spectroscopy

Jan Čechal

X-ray photoelectron spectroscopy (XPS) is a widely used technique for chemical analysis of solid surfaces, sensitive to the chemical environments of atoms via core-level binding energy shifts. While modern instruments allow experimental data to be acquired with ease, their evaluation and interpretation remain challenging for newcomers to the field, as a profound knowledge of the method is required for correct analysis. Here we present a concise yet comprehensive overview of the fundamental principles and methodologies of XPS, covering photoemission processes, chemical shifts, charge referencing, peak fitting, and quantification strategies. This overview aims to bridge the gap between data collection and reliable analysis, providing essential knowledge for correct interpretation. By clarifying key concepts and common practices, this work supports improved accuracy in surface chemical characterization using XPS.
Read the full abstract

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

Modulation of quantum geometry and its coupling to pseudo-electric field by dynamic strain

Surat Layek, Mahesh A. Hingankar, Ayshi Mukherjee et al. (+11 more)

Two-dimensional materials are a fertile ground for exploring quantum geometric phenomena, with Berry curvature and its first moment, the Berry curvature dipole, playing a central role in their electronic response. These geometric properties influence electronic transport and result in the anomalous and nonlinear Hall effects, and are typically controlled using static electric fields or strain. However, the possibility of modulating quantum geometric quantities in real-time remains unexplored. Here, we demonstrate the dynamic modulation of Berry curvature and its moments, as well as the generation of a pseudo-electric field using time-dependent strain. By placing heterostructures on a membrane, we introduce oscillatory strain together with an in-plane AC electric field and measure Hall signals that are modulated at linear combinations of the frequencies of strain and electric field. Our measurements reveal modulation of Berry curvature and its first moment. Notably, we provide direct experimental evidence of pseudo-electric field that results in an unusual dynamic strain-induced Hall response. This approach opens up a new pathway for controlling quantum geometry on demand, moving beyond conventional static perturbations. The pseudo-electric field provides a framework for external electric field-free anomalous Hall response and opens new avenues for probing the topological properties.
Read the full abstract

All authors Surat Layek, Mahesh A. Hingankar, Ayshi Mukherjee, Atasi Chakraborty, Digambar A. Jangade, Anil Kumar, L. D. Varma Sangani, Amit Basu, R Bhuvaneswari, Kenji Watanabe, Takashi Taniguchi, Amit Agarwal, Umesh V. Waghmare, Mandar M. Deshmukh

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

Observing unconventional superconductivity via kinetic inductance in Weyl semimetal MoTe$_2$

Mary Kreidel, Julian Ingham, Xuanjing Chu et al. (+10 more)

Identifying the pairing symmetry of unconventional superconductors plays an essential role in the ongoing quest to understand correlated electronic matter. A long-standing approach is to study the temperature dependence of the London penetration depth $\lambda$ for evidence of nodal points where the superconducting gap vanishes. However, experimental reports can be ambiguous due to the requisite low-temperature resolution, and the similarity in signatures of nodal quasiparticles and impurity states. Here we study the pairing symmetry of Weyl semimetal $T_d$-MoTe$_2$, where previous measurements of $\lambda$ have yielded conflicting results. We utilize a novel technique based on a microwave resontor to measure the kinetic inductance of MoTe$_2$, which is directly related to $\lambda$. The high precision of this technique allows us to observe power-law temperature dependence of $\lambda$, and to measure the anomalous nonlinear Meissner effect – the current dependence of $\lambda$ arising from nodal quasiparticles. Together, these measurements provide smoking gun signatures of nodal superconductivity.
Read the full abstract

All authors Mary Kreidel, Julian Ingham, Xuanjing Chu, Jesse Balgley, Ted S. Chung, Abhinandan Antony, Nishchhal Verma, Luke N. Holtzman, Katayun Barmak, Raquel Queiroz, James Hone, Robert M. Westervelt, Kin Chung Fong

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

Disentangle Intertwined Interactions in Correlated Charge Density Wave with Magnetic Impurities

J. W. Park, H. Kim and H. W. Yeom

Magnetic impurities in strongly correlated electronic systems serve as sensitive probes to a wide range of many-body quantum phenomena. Broken symmetries in such a system can lead to inequivalent lattice sites, and magnetic impurities may interact selectively with particular orbitals or sublattices. However, the microscopic mechanisms behind such site-specific interactions have been poorly understood. Here, we explore the behavior of individual Fe adatoms on a cluster-Mott charge-density-wave (CDW) system of 1T-TaS2 utilizing scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT). Our measurements uncover pronounced site-dependent electronic states of CDW clusters with Fe adatoms, indicating distinct local coupling to cluster-Mott states. DFT calculations identify three distinct types of interactions; hybridization with localized correlated electrons, distorting the CDW cluster, and charge transfer. In particular, the hybridization of Fe 3d and half-filled Ta 5dz2 orbitals suppresses the Mott insulating state for an adatom at the center of a CDW cluster. While the results underscore a crucial role of the direct orbital hybridization and the limitation of the prevailing single-site Kondo impurity model, they suggest the possibility of controlling entangled interactions separately in a cluster Mott insulator.
Read the full abstract

Materials Science

Vapor-solid-solid growth of single-walled carbon nanotubes

Daniel Hedman

Single-walled carbon nanotubes (SWCNTs) are promising for nanoscale electronics and photonics, but practical deployment requires chirality control. Most catalytic chemical vapor deposition (CCVD) growth of SWCNTs proceeds on liquid metal nanoparticles via a vapor-liquid-solid (VLS) mechanism and yields broad chirality distributions, whereas improved selectivity has been reported for high-melting-point crystalline catalysts, suggesting vapor-solid-solid (VSS) growth. However, the atomistic mechanism and kinetic of VSS SWCNT growth remain unclear. Here it is shown, using machine-learning interatomic potential-driven molecular dynamics on rhenium nanoparticles, that VSS growth is diffusion-limited and governed by facet-dependent surface carbon transport coupled to carbon-driven facet reconfiguration without catalyst melting. Surface diffusion is up to $\sim 50\times$ slower than carbon diffusion in liquid iron, imposing a strict upper bound on sustainable carbon supply and producing a narrow growth window: insufficient transport drives carbon accumulation and multiple nucleation, whereas higher temperatures favor graphitic encapsulation. In contrast to defect-free VLS growth, defects persist, indicating slow defect healing, and equilibrium simulations reveal suppressed edge configurational entropy with stabilization of zigzag-rich, Klein-decorated edges. Together, these results establish facet evolution and surface diffusion as joint regulators of diffusion-limited VSS growth and motivate stringent control of temperature and carbon supply.
Read the full abstract

Materials Science

Matter with apparent and hidden spin physics

Jia-Xin Xiong, Xiuwen Zhang, Lin-Ding Yuan et al. (+1 more)

Materials with interesting physical properties are often designed based on our understanding of the target physical effects. The physical properties can be either explicitly observed ("apparent") or concealed by the perceived symmetry ("hidden") but still exist. Both are enabled by specific symmetries and induced by certain physical interactions. Using the underlying approach of condensed matter theory of real materials (rather than schematic model Hamiltonians), we discuss apparent and hidden physics in real materials focusing on the properties of spin splitting and spin polarization. Depending on the enabling symmetries and underlying physical interactions, we classify spin effects into four categories with each having two subtypes; representative materials are pointed out. We then discuss the electric tunability and switch of apparent and hidden spin splitting and polarization in antiferromagnets. Finally, we extend "hidden effects" to views that are farsighted in the sense of resolving the correct atomistic and reciprocal symmetry and replaced by the incorrect higher symmetry. This framework could guide and enable systematic discovery of such intriguing effects.
Read the full abstract

All authors Jia-Xin Xiong, Xiuwen Zhang, Lin-Ding Yuan, Alex Zunger

Materials Science

From Berry curvature to quantum metric: a new era of quantum geometry metrology for Bloch electrons in solids

Bohm-Jung Yang

For decades, “geometry" in band theory has largely meant Berry phase and Berry curvature-quantities that reshape semiclassical dynamics and underpin modern topological matter. Yet the full geometric content of a Bloch band is richer and encoded in the quantum geometric tensor (QGT), whose imaginary part is the Berry curvature and whose real part is the quantum metric. Here, we briefly review the recent progress in direct experimental access to the QGT in real crystalline solids using the polarization- and spin-resolved angle-resolved photoemission spectroscopy (ARPES). The extraction of the QGT in momentum space was successfully addressed by two different approaches: One is by introducing quasi-QGT that faithfully represents the QGT and is directly measurable by ARPES. The other is through pseudospin tomography in a material with simple low energy band structure, which successfully retrieved all matrix components of the quantum metric. We discuss the physical meaning of these two recent progresses, their implication/limitation, and open directions.
Read the full abstract

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

Imaging nanoscale photocarrier traps in solar water-splitting catalysts

Levi D. Palmer, Wonseok Lee, Pushp Raj Prasad et al. (+12 more)

Defects trap photocarriers and hinder solar water splitting. The nanoscale photocarrier transport, trapping, and recombination mechanisms are usually inferred from ensemble-averaged measurements and remain elusive. Because an individual high-performing nanoparticle photocatalyst may outperform the ensemble average, design rules that would otherwise enhance catalytic efficiency remain unclear. Here, we introduce photomodulated electron energy-loss spectroscopy (EELS) in an optically coupled scanning transmission electron microscope (STEM) to map photocarrier localization. Using rhodium-doped strontium titanate (SrTiO3:Rh) solar water-splitting nanoparticles, we directly image the carrier densities concentrated at oxygen-vacancy surface trap states. This is achieved by separating photothermal heating from photocarrier populations through experimental and computational analyses of low-loss spectra. Photomodulated STEM-EELS enables angstrom-scale imaging of defect-induced photocarrier traps and their impact on photocatalytic efficiency.
Read the full abstract

All authors Levi D. Palmer, Wonseok Lee, Pushp Raj Prasad, Bradley W. Layne, Han-Hsuan Wu, Zejie Chen, Jianguo Wen, Yuzi Liu, Xiaoqing Pan, A. Alec Talin, Akihiko Kudo, Shane Ardo, Joseph P. Patterson, Thomas E. Gage, Scott K. Cushing

Tuesday 30 December

Materials Science

Fluoride doping into SiO2-MgO-CaO bioactive glass nanoparticles: bioactivity, biodegradation and biocompatibility assessments

N. Esmati, T. Khodaei, E. Salahinejad et al. (+1 more)

In this research, for the first time, the structure, bioactivity, biodegradation and biocompatibility of SiO2-MgO-CaO glasses doped with different levels of fluoride were studied. The glassy powder samples were synthesized by a coprecipitation method followed by calcination at 500 C, where amorphicity and fluoride incorporation were verified by X-ray diffraction and Raman spectroscopy, respectively. The in vitro biomineralization and biodegradation of the samples were also investigated by electron microscopy, Raman spectroscopy and inductively coupled plasma optical emission spectrometry. These assessments revealed that there is an optimum level of fluoride doping to meet the highest bioactivity. Remarkably, the same level of incorporation presented the foremost biocompatibility with respect to osteoblast-like MG-63 human cells, as realized by the MTT assay and cell attachment studies.
Read the full abstract

All authors N. Esmati, T. Khodaei, E. Salahinejad, E. Sharifi

Materials Science · Cross-listed from physics.optics

Exploring Spectral Singularities and Topological Lasers in PT-Symmetric Weyl Semimetals

Arda Sevinc, Rama Alassadi and Mustafa Sarisaman

This paper investigates the unique properties of PT-symmetric Topological Weyl Semimetals (TWS) within the framework of non-Hermitian physics, focusing on their potential for generating topological lasers. By exploring the role of spectral singularities and their relationship to exceptional points, we examine how these materials, characterized by Weyl nodes and topologically protected surface states, can support novel optical phenomena such as unidirectional propagation and enhanced lasing. Through a theoretical model based on the transfer matrix approach, we reveal how the interplay between the PT symmetry and the axion term introduces new dynamics, leading to 12 distinct topological laser configurations. The study also investigates the impact of the $\theta$-term on spectral singularities, showing how it quantizes the system's gain values and influences the topological properties of the lasers. By applying our model to the TaAs material, a known Weyl semimetal, we uncover previously unreported effects, demonstrating the potential of PT-symmetric TWS materials for advanced optoelectronic applications. We show that the axion-induced cyclotron-like Hall current in a PT-symmetric TWS medium, revealing its topological characteristics and distinct flow patterns in the gain and loss regions, which serve as indicators of the system's topological symmetry. Our findings open new avenues for the development of robust, tunable, and efficient topological lasers with applications in quantum information processing and beyond.
Read the full abstract

Materials Science

Connecting strain rate dependence of fcc metals to dislocation avalanche signatures

M. Aissaoui, C. Kahloun, O.U. Salman et al. (+1 more)

Strain rate sensitivity is a key feature of material deformation, whose importance is growing both because miniaturized components experience higher effective rates and because small scale simulations increasingly probe such conditions. As a dynamical characteristic, strain rate dependence is shown to be intimately connected to dislocation avalanches, which are a fundamental mechanism of dislocation dynamics. Using carefully designed, state of the art dislocation dynamics simulations in the intermediate range strain rate from 5 to 1000, we show that increasing strain rate promotes the activation of a growing number of stronger sites. The dislocation microstructure progressively rearranges into configurations with shorter segments. Dislocation avalanches become larger through the superposition of simultaneous events and because stronger obstacles are required to arrest them. As a result, the avalanche statistics are strongly affected by strain rate, with a reduced power law regime and an increasing power law exponent. Larger avalanches, in turn, lead to an enhanced dislocation storage rate. Contribution from collinear systems to avalanches and cross slip activity decreases, altering the fraction of screw dislocations and the resulting microstructure. These results provide an original mesoscopic picture of rate sensitivity in this strain rate range and offer a mechanistic interpretation of existing observations and findings from experiments and simulations.
Read the full abstract

All authors M. Aissaoui, C. Kahloun, O.U. Salman, S. Queyreau

Materials Science

Wafer-Scale Integration of Piezo- and Ferroelectric Al0.64Sc0.36N Thin Films by Reactive Sputtering

Sanjay Nayak, Venkata Raveendra Nallagatla, Ravindra Singh Bisht et al. (+19 more)

Large-area deposition of Aluminium-Scandium-Nitride (Al1-xScxN) thin films with higher Sc content (x) remains challenging due to issues such as abnormal orientation growth, stress control, and the undesired crystal phase. These anomalies across the wafer hinder the development of high scandium-content AlScN films, which are critical for microelectromechanical systems applications. In this study, we report the sputter deposition of Al0.64Sc0.36N thin films from a 300 mm Al0.64Sc0.36 alloy target on 200 mm Si(100) wafers, achieving an exceptionally high deposition rate of 8.7 {\mu}m/h with less than 1% AOGs and controllable stress tuning. Comprehensive microstructural and electrical characterizations confirm the superior growth of high-quality Al0.64Sc0.36N films with exceptional wafer-average piezoelectric coefficients (d33,f =15.62 pm/V and e31,f = -2.9 C/m2) owing to low point defects density and grain mosaicity. This was accomplished through the implementation of an optimized seed layer and a refined electrode integration strategy, along with optimal process conditions. The wafer yield and device failure rates are analysed and correlated with the average stress of the films and their stress profiles along the diameter. The resulting films show excellent uniformity in structural, compositional, and piezoelectric properties across the entire 200 mm wafer, underscoring their strong potential for next-generation MEMS applications.
Read the full abstract

All authors Sanjay Nayak, Venkata Raveendra Nallagatla, Ravindra Singh Bisht, Dmytro Solonenko, Demian Henzen, Washim Reza Ali, Carla Maria Lazzari, Robert JW Frost, Andrea Serafini, Davide Codegoni, Amalia Balsamo, Rossana Scaldaferri, Elaheh Allahyari, Anirban Ghosh, Martin Kratzer, Andrea Picco, Sonia Costantini, Andrea Rusconi, Mohssen Moridi, Humberto Campanella, Marco Deluca, Annalisa De Pastina

Materials Science · Cross-listed from physics.optics

Achieving high-performance polarization-independent nonreciprocal thermal radiation with pattern-free heterostructures

Bach Do, Bardia Nabavi, Sina Jafari Ghalekohneh et al. (+3 more)

Many advanced energy harvesting technologies rely on advanced control of thermal emission. Recently, it has been shown that the emissivity and absorptivity of thermal emitters can be controlled independently in nonreciprocal emitters. While significant progress has been made in engineering these nonreciprocal thermal emitters, realizing a highly efficient, pattern-free emitter capable of supporting dual-polarization nonreciprocal emission remains a challenging task. Existing solutions are largely based on metamaterials and exhibit polarization-dependent behavior. This work proposes pattern-free multilayer heterostructures combining magneto-optical and magnetic Weyl semimetal materials and systematically evaluates their nonreciprocal emission performance for p- and s-polarized waves. The findings show that omnidirectional polarization-independent nonreciprocity can be achieved utilizing multilayer structures with different magnetization directions that do not follow simple vector summation. To further enhance the performance, Pareto optimization is employed to tune the key design parameters, enabling the maximization of nonreciprocal thermal emission in a given wavelength range. This approach offers a versatile strategy for designing high-performance thermal emitters tailored for multi-objective optical functionalities.
Read the full abstract

All authors Bach Do, Bardia Nabavi, Sina Jafari Ghalekohneh, Taiwo Adebiyi, Bo Zhao, Ruda Zhang

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

Evidence of Spin-Valley Coupling in Dirac Material BaMnBi2 Probed by Quantum Hall Effect and Nonlinear Hall Effect

Subin Mali, Yingdong Guan, Lujin Min et al. (+2 more)

Valleytronics is a rapidly advancing field that explores the use of the valley degree of freedom in electronic systems to encode and process information. It relies on electronic states with spin valley locking, first predicted and observed in monolayer transition metal dichalcogenides such as MoS2. However, very few bulk materials have been reported to host spin valley locked electronic states. In this work, we present experimental evidence for a predicted, unique spin valley locked electronic state generated by Bi zigzag chains in the layered compound BaMnBi2. We observe remarkable quantum transport properties in this material, including a stacked quantum Hall effect (QHE) and a nonlinear Hall effect (NLHE). From the analysis of the QHE, we identify a spin valley degeneracy of four, while the NLHE provides supporting evidence for the anticipated valley contrasted Berry curvature, a typical signature of a spin valley locked state. This spin valley locked state contrasts with that observed in the sister compound BaMnSb2, where the degeneracy is two. This difference arises from significant variations in their orthorhombic crystal structures and spin orbit coupling. These findings establish a new platform for exploring coupled spin valley physics in bulk materials and highlight its potential for valleytronic device applications.
Read the full abstract

All authors Subin Mali, Yingdong Guan, Lujin Min, David Graf, Zhiqiang Mao

Materials Science

"X-ray Coulomb Counting" to understand electrochemical systems

Chuntian Cao and Hans-Georg Steinrück

Electrochemical systems are important for a sustainable and defossilized energy system of the future. While accurate and precise, the corresponding electrochemical measurements, in which many reactions may occur simultaneously, often do not contain enough information to understand the underlying mechanism and processes. This information, however, is crucial towards rational materials and devices as well as process development and for inventing innovative concepts. In this perspective, we introduce explicitly the concept of "X-ray Coulomb Counting" in which X-ray methods are used to quantify on an absolute scale how much charge is transferred into which reactions during the electrochemical measurements. This allows to interpret the electrochemical measurements in detail and obtain the desired phenomenological and mechanistic understanding. We show a few recent examples from the Li-ion battery literature in which the concept of X-ray Coulomb Counting was employed to obtain foundational understanding.
Read the full abstract

Materials Science · Cross-listed from physics.optics

From Disorder to Function: Entropy-Engineered Broadband Photonics with Ion-Transport-Stabilized Spectral Fidelity

Yuxiang Xin, Chen-Xin Yu, Jianru Wang et al. (+14 more)

The high-entropy halide-perovskite field has expanded rapidly, yet a key gap remains: configurational entropy is not yet a reliable, designable lever to co-deliver expanded photonic functionality and operational robustness with a composition-transferable mechanistic basis. Here we develop entropy-engineered rare-earth halide double-perovskite single crystals, Cs2Na(Sb, RE)Cl6 (RE3+ = Sc3+, Er3+, Yb3+, Tm3+), that simultaneously expand near-infrared (NIR) functionality and establish a mechanistic stability rule. Near-equiatomic B(III)-site alloying yields a single-phase high-entropy solid solution (Delta_Sconfig about 1.6R). Sb3+ serves as a sensitizer that unifies excitation and cooperatively activates multiple lanthanide channels, transforming the parent single-mode response into a broadband NIR output (~850-1600 nm) with three spectrally orthogonal fingerprint bands at 996, 1220, and 1540 nm. This tri-peak, self-referenced output enables redundancy-based ratiometric solvent identification and quantitative mixture sensing with reduced susceptibility to intensity drift. Accelerated aging under humidity and oxygen shows improved phase and emission stability versus single-component analogues. DFT and molecular dynamics attribute the robustness to strongly suppressed RE$^{3+}$/Cl$^-$ self-diffusion despite comparable H$_2$O/O$_2$ adsorption, kinetically impeding ion-migration-assisted reconstruction and degradation. Integration into a phosphor-converted LED delivers spectrally stable, broadband NIR illumination, establishing entropy engineering as a practical handle to couple expanded photonic functionality with mechanistically accountable durability in metal-halide photonics.
Read the full abstract

All authors Yuxiang Xin, Chen-Xin Yu, Jianru Wang, Jianbo Jin, Minliang Lai, Yinan Wang, Shuwen Yan, Gu-wen Chen, Liang Fan, Xiachu Xiao, Yutao Yang, Luying Li, Han Wang, Zhi-Pan Liu, Jiang Tang, Li-Ming Yang, Zhuolei Zhang

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

Geometry induced net spin polarization of $d$-wave altermagnets

Abhiram Soori

Altermagnets exhibit spin-split electronic bandstructures despite having zero net magnetization, making them attractive for field-free spintronic applications. In this work, we show that a finite rectangular altermagnetic sample can acquire a net spin polarization purely due to its geometry. This effect arises from the interplay between the anisotropic, spin-resolved Fermi contours of an altermagnet, the discrete sampling of momentum space and unequal sample dimensions. By explicitly counting occupied states, we demonstrate that rectangular samples with $L_x \neq L_y$ host a finite spin polarization, which vanishes in the symmetric limit $L_x=L_y$ and in the thermodynamic limit. We further show that this geometry-induced spin polarization can be directly probed in transport measurements. In the tunneling regime, the charge and the spin conductances exhibit characteristic patterns as a function of sample dimensions, faithfully reflecting the underlying spin polarization. In addition, transport across ferromagnet–altermagnet–ferromagnet junctions reveals an asymmetric magnetoresistance with respect to reversal of the Zeeman field, providing an independent transport signature of the finite spin polarization. Our results establish geometry as an effective control parameter for spin polarization in altermagnets and suggest a viable route for exploiting finite-size effects in mesoscopic altermagnetic spintronic devices.
Read the full abstract

Materials Science

Tritium accumulation and ozone decontamination of tungsten and beryllium

Dominic Batzler, Robin Größle, Philipp Haag et al. (+5 more)

Tritium adsorption on surfaces creates a variety of issues, ranging from the fields of fusion applications to small and large-scale laboratory experiments using tritium. The extent to which tritium accumulates on surfaces is generally material-dependent and must be determined through experiments. Additionally, this surface contamination necessitates the implementation of appropriate decontamination procedures, preferably in-situ. A suitable method could be exposure to ozone during UV irradiation. However, it is currently not known if both components are necessary for the decontamination. At Tritium Laboratory Karlsruhe, both questions on contamination and decontamination can be addressed using a single experimental setup. With this, it is possible to expose solid samples to gaseous tritium to measure the temporal activity evolution. Furthermore, the system can be filled with dry air, and dry air containing ozone to explore their decontamination effect. Both measurement modes were applied to beryllium and tungsten samples, which were chosen for their relevance in fusion. The beryllium surface was observed to accumulate tritium more than four times faster than tungsten when exposed to gaseous tritium. Concerning the decontamination, without simultaneous UV irradiation, exposure to ozone did not have any distinct effect on the surface activity compared to simply using dry air. This leads to the conclusion that UV illumination of the surfaces is required to achieve a significant decontamination factor.
Read the full abstract

All authors Dominic Batzler, Robin Größle, Philipp Haag, Elizabeth Paine, Marco Röllig, Marie-Christine Schäfer, Marius Schaufelberger, Kerstin Trost

Materials Science

High-Performance KV$_3$Sb$_5$/WSe$_2$ van der Waals Photodetectors

Yang Yang, Shaofeng Rao, Yuxuan Hou et al. (+7 more)

Kagome metals AV$_3$Sb$_5$ (A = K, Rb, Cs) have recently emerged as a promising platform for exploring correlated and topological quantum states, yet their potential for optoelectronic applications remains largely unexplored. Here, we report high-performance photodetectors based on van der Waals KV$_3$Sb$_5$/WSe$_2$ heterojunctions. A high-quality Schottky interface readily forms between KV$_3$Sb$_5$ and WSe$_2$, enabling efficient separation and transport of photoinduced carriers. Under 520 nm illumination, the device achieves an open-circuit voltage up to 0.6 V, a responsivity of 809 mA/W, and a fast response time of 18.3 us. This work demonstrates the promising optoelectronic applications of Kagome metals and highlights the potential of KV$_3$Sb$_5$-based van der Waals heterostructures for high-performance photodetection.
Read the full abstract

All authors Yang Yang, Shaofeng Rao, Yuxuan Hou, Jiabo Liu, Deng Hu, Yufei Guo, Jianzhou Zhao, Hechen Ren, Zhiwei Wang, Fan Yang

Materials Science

Increased Covalence and V-center mediated Dark Fenton-Like Reactions in V-doped TiO2: Mechanisms of Enhanced Charge-Transfer

Manju Kumari, Dilip Sasmal, Suresh Chandra Baral et al. (+5 more)

Tuning the valence state and electronic structure of catalytically active sites is crucial for improving Fenton and Fenton-like reactions, which rely on the efficient activation of the H2O2 molecule. Pure TiO2, however, has inadequate activity towards the H2O2 activation and is often constrained by the intrinsic electronic limitations of pristine TiO2. Herein, a rational approach has been demonstrated to improve the Fenton-like catalytic performance of TiO2 through multivalent vanadium (V) doping. A comprehensive characterization using X-Ray Diffraction (XRD), Raman spectroscopy, UV-Vis spectroscopy, X-Ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR), and Density functional theory (DFT) reveals that V incorporation substantially alters the electronic structure of TiO2. The DFT results, supported by experimental data, indicate that V doping enhances Ti-O covalence and introduces mid-gap states, resulting in a reduced band gap and improved charge transfer. XPS confirms the coexistence of multiple oxidation states of V, which serve as active centres for activating H2O2 and generating OH radicals. As a result, V-doped TiO2 exhibits significantly enhanced dark-catalytic activity in degrading the organic dye Rhodamine B (RhB). Overall, this study provides fundamental insights into multivalent-cation-induced valence state and electronic structure modulation in TiO2, offering a promising strategy for designing high-performance catalysts via defect engineering for sustainable environmental remediation.
Read the full abstract

All authors Manju Kumari, Dilip Sasmal, Suresh Chandra Baral, Maneesha P, Poonam Singh, Abdelkrim Mekki, Khalil Harrabi, Somaditya Sen

Materials Science

Extending the Growth Temperature-N Concentration Regime Through Pd Doping in Fe4N Thin Films

Rohit Kumar Meena, Akhil Tayal, Andrei Gloskovskii et al. (+1 more)

Fe4N is a well-known anti-perovskite compound exhibiting high magnetization, high chemical stability, low coercivity, high Curie temperature, and high spin-polarization ratio. Therefore, it is a viable candidate for applications in spintronic and magnetic storage devices. However, the Fe4N phase is formed in a narrow substrate temperature (Ts)-N concentration (Nc) regime in the phase diagram of Fe-N. It has been observed that a slight N deficiency will lead to impurity of alpha-Fe, and some N efficiency would result in epsilon-Fe3N phase. Through this work, it has been demonstrated that the doping of Pd can be suitably utilized to extend the Ts-Nc regime for the growth of Fe4N thin films. EXAFS analysis indicate that Pd atoms are substituting corner Fe atoms. Magnetization measurements reveal that the saturation magnetization reduces nominally with Pd doping up to 13 at.%. Therefore, it is foreseen that Pd doping is effective in extending the Fe4N phase formation regime without a significant impact on its structural, electronic, and magnetic properties.
Read the full abstract

All authors Rohit Kumar Meena, Akhil Tayal, Andrei Gloskovskii, Mukul Gupta

Materials Science

Soft x-rays with Orbital Angular Momentum for resonant scattering experiments at the SOLEIL synchrotron

Pietro Carrara, Franck Fortuna, Renaud Delaunay et al. (+15 more)

The paper presents a comprehensive description of a new setup implemented and commissioned at the SEXTANTS beamline of the SOLEIL synchrotron for absorption and scattering experiments with x-ray beams carrying an orbital angular momentum, also known as twisted x-ray beams. Two alternative methods have been implemented, based on the use of either spiral zone plates or fork gratings devices, and we show how they can be used for both defining and assessing the orbital angular momentum of an x-ray beam. We show also how multiple devices can be used in sequence to define an integer arithmetic of the orbital angular momentum of the final x-ray beam. Finally, we report the results of the first resonant scattering pilot experiments in transmission and reflection mode, intended to assess the feasibility of future users measurements. The availability of twisted soft x-rays complements the range of experimental techniques in elastic, resonant and coherent scattering available at the SEXTANTS beamline of the SOLEIL synchrotron.
Read the full abstract

All authors Pietro Carrara, Franck Fortuna, Renaud Delaunay, Joan Vila-Comamala, Benedikt Rösner, Christian David, Stefania Pizzini, Clément Fourniols, Laurent Vila, Matteo Pancaldi, Carlo Spezzani, Flavio Capotondi, Pierre Nonnon, Mauro Fanciulli, Thierry Ruchon, Nicolas Jaouen, Horia Popescu, Maurizio Sacchi

Materials Science

Topological spin textures in an antiferromagnetic monolayer

Felix Zahner, Tim Drevelow, Roberto Lo Conte et al. (+3 more)

Topological spin structures such as magnetic skyrmions are of fundamental interest and promising for various types of applications in spintronics. Skyrmions have been predicted to emerge also in antiferromagnetic materials where they exhibit superior transport properties. They were experimentally revealed in synthetic antiferromagnets, however, still remain elusive in intrinsic antiferromagnets. Here, we demonstrate the stabilization of topological spin structures in an antiferromagnetic monolayer. Using spin-polarized scanning tunneling microscopy, we observe an antiferromagnetic spin spiral in the Mn monolayer and a collinear antiferromagnetic state in the Mn double-layer on Ta(110). Near the boundary to the double-layer half-skyrmions form in the monolayer as revealed in combination with first-principles calculations and micromagnetic simulations. Our work shows how the topological state in antiferromagnetic material systems can be controlled by the configuration within a lateral heterostructure, resulting in trivial non-coplanar states or antiferromagnetic skyrmions.
Read the full abstract

All authors Felix Zahner, Tim Drevelow, Roberto Lo Conte, Roland Wiesendanger, Stefan Heinze, Kirsten von Bergmann