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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Wednesday 17 June

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

Evidence for Multiband Superconductivity in 2H-NbSeS

K. Yadav, M. Lamba K. Bhattacharya, M. Majumder et al. (+1 more)

The nature of superconductivity in 2H-NbSe2 has generated sustained debate in the recent past. While angle resolved photoemission spectroscopy data have been interpreted as evidence for multiband superconductivity, the data from scanning tunneling microscope experiments relate to strongly anisotropic single-band superconductivity. In the later case, the charge density wave (CDW) order mimics the multigap character. Because the CDW reconstructs the Fermi surface and modifies the superconducting gap distribution, disentangling intrinsic multiband pairing from CDW-related effects is challenging. To address this issue, we investigate single-crystalline 2H-NbSeS, a mixed-chalcogen analogue of 2H-NbSe2 in which random Se/S substitution suppresses long-range CDW order while preserving the layered crystal structure P63/mmc. The material becomes superconducting below 6.0 K with moderate magnetic anisotropy. The upper critical field exhibits a pronounced upward curvature that cannot be described within a single-band framework but is well captured by a dirty-limit two-band model with a large diffusivity ratio. This indicates strong band-dependent scattering. The in-plane upper critical field exceeds the weak-coupling Pauli limit. Measurements of the lower critical field, superfluid density, and electronic specific heat are consistent with an interpretation of a fully gapped superconducting state with two nodeless gaps of different magnitudes.
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All authors K. Yadav, M. Lamba K. Bhattacharya, M. Majumder, S. Patnaik

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

Room-Temperature Calcium Intercalation into Graphite Catalyzed by Sodium

Akira Iyo, Shigeyuki Ishida, Hiroshi Eisaki et al. (+2 more)

Calcium (Ca) insertion into graphite (C) has been considered to require elevated temperatures, and its occurrence at room temperature (RT) has been regarded as highly unlikely. Here, we demonstrate that sodium (Na) catalysis enables the formation of superconducting CaC$_6$ even at RT. In mixtures of Ca, Na, and graphite, the gradual development of superconducting diamagnetism and the emergence of X-ray diffraction peaks confirm the formation of CaC$_6$ during storage at RT. The superconducting transition temperature increases with storage time, and the amount of CaC$_6$ scales proportionally to the square root of storage time. These findings provide new insights into the mechanism of superconductivity and Na-catalyzed formation of CaC$_6$, and highlight the potential of this RT intercalation process for practical applications such as electrode materials in Ca-ion batteries.
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All authors Akira Iyo, Shigeyuki Ishida, Hiroshi Eisaki, Hiraku Ogino, Kenji Kawashima

Materials Science

Projected altermagnetism by symmetry reduction at surfaces and in thin films

Sopheak Sorn, Charanpreet Singh, Lukasz Plucinski et al. (+3 more)

Altermagnets are a newly identified class of magnetic materials that combine vanishing net magnetization within the unit cell with spin-split electronic states. Their theoretical description relies on symmetry properties of the bulk band structure. Surfaces and thin films, however, inherently break these symmetries. Here, we investigate the consequences of such symmetry reduction for the electronic structure of bulk altermagnets near the surface and of thin films. When the surface coincides with a symmetry plane of the bulk altermagnetic order, the resulting two-dimensional Brillouin zone exhibits spin-degenerate bands, corresponding to conventional antiferromagnetic behavior. In all other cases, the symmetry of the altermagnetic order is reduced, leading to modified spin splitting. Remarkably, we discover a thin-film geometry of a $g$-wave altermagnet with a particular surface orientation that enables a $d$-wave spin splitting, which is commonly accompanied by the spin-splitter effect, suggesting the functionalization of non-$d$-wave altermagnets by surfaces. Our findings demonstrate that symmetry breaking at surfaces and in thin films fundamentally reshapes altermagnetic spin textures, providing a tunable platform for controlling spin-dependent electronic phenomena.
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All authors Sopheak Sorn, Charanpreet Singh, Lukasz Plucinski, Gustav Bihlmayer, Yuriy Mokrousov, Wulf Wulfhekel

Materials Science

Spin-orbit coupling renormalization of the natural optical activity of Pb5Ge3O11 from first-principles

Asier Zabalo, Massimiliano Stengel and Eric Bousquet

We present a first-principles study of the natural optical activity of the gyroelectric Pb$_5$Ge$_3$O$_{11}$ crystal, explicitly accounting for spin-orbit coupling (SOC) effects. We derive a new analytical expression for the gyration coefficients within the recent framework of long-wavelength density-functional perturbation theory [Phys. Rev. Lett. 131, 086902 (2023)], which significantly improves computational efficiency by reducing the number of required response functions and includes spin-orbit coupling effects. We use this implementation to investigate the evolution of Pb$_5$Ge$_3$O$_{11}$'s optical rotation across the ferroelectric double-well, from the paraelectric $P\bar{6}$ phase to the ferroelectric $P3$ phase. Our results demonstrate that, in addition to the substantial renormalization of the double-well energy, spin-orbit coupling contributions play an equally crucial role in the natural optical activity, largely through purely electronic contributions, while SOC-induced structural relaxation effects are minor.
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Materials Science

Self-Aligned Metallic-Semiconducting Phosphorus Nanoarrays Driven by Facet Engineering

M. Bassotti, M. Tallarida, J. Dai et al. (+10 more)

Two-dimensional (2D) materials often require specific substrate terminations for epitaxial stabilization, yet the search for suitable templates has largely focused on low-index metal surfaces, which may not provide the optimal conditions for the growth of new phases. Here, we show that crystal-facet engineering on curved Cu surfaces enables the stabilization, within a single preparation step, of two distinct 2D phosphorus phases with different electronic properties. Hexagonal blue phosphorene forms on Cu(111) terraces, whereas a previously unreported skewed-square phosphorus phase is stabilized on Cu(513) facets. By combining complementary microscopy and spectroscopy techniques with theoretical calculations, we determine the structural and electronic properties of this new phase, which displays semiconducting character, in contrast to the metallic behavior of blue phosphorene. The coexistence of these two competing phases gives rise to a metal-to-semiconducting transition of the 2D phosphorus layer over the substrate. Locally, the competition between the two phases gives rise to self-aligned nanoarrays of alternating metallic and semiconducting phosphorus terraces. These results establish crystal-facet engineering as a practical route for discovering and stabilizing emergent 2D material phases on high-index substrates, while also enabling the engineering of nanostructures with tailored electronic properties through a simple and scalable growth process.
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All authors M. Bassotti, M. Tallarida, J. Dai, S. Salaverria, P. Angulo-Portugal, L. Fernandez, A. El-Sayed, J.E. Ortega, A.A. Makarova, Dimas G. de Oteyza, D.Yu. Usachov, A. Verdini, F. Schiller

Materials Science

First-Principles Study of Novel Lead-Free Double Perovskite e̱ta}2SnGeX6 (e̱ta} = K, Rb; X = Cl, Br, I) for thermomechanical, optoelectronic and outstanding thermoelectric applications

Jubair Hossan Abir, Tauhidur Rahman, S.S.B. Pallab et al. (+3 more)

In this study, the structural, mechanical, electronic, optical, and thermoelectric properties of the novel lead-free halide double perovskite series beta2SnGeX6 (beta = K, Rb; X = Cl, Br, I) are systematically investigated using density functional theory (DFT). Calculated formation energies, Tolerance factors, and octahedral factors confirm that all six compounds exhibit robust thermodynamic stability within a highly symmetric cubic geometry. Mechanical analysis derived from elastic parameters characterizes the entire series as fundamentally ductile, ensuring high processing elasticity and resistance to micro-cracking during device manufacturing. Electronic band structures reveal direct bandgaps showing exceptional composition-dependent tunability from 1.44 eV down to 0.64 eV via progressive halogen substitution. The wide gap chloride variations are optimized for single-junction photovoltaic absorbers, while the narrower-gap bromide and iodide analogs show immense promise for tandem solar architectures and near-infrared photodetectors. Thermoelectrically, heavy constituent atoms introduce strong lattice anharmonicity and intense high-temperature Umklapp phonon scattering, significantly suppressing lattice thermal conductivity. Combined with low carrier effective masses that optimize electrical transport, the iodide compounds achieve higher power factors and outstanding dimensionless figures of merit (ZT = 2.4 for K2SnGeI6 at 1000 K). Ultimately, these lead-free double perovskite family emerges as an environmentally benign and versatile platform for next-generation green optoelectronics and solid-state waste-heat recovery.
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All authors Jubair Hossan Abir, Tauhidur Rahman, S.S.B. Pallab, Md. Sharear Aman, R. S. Islam, S. H. Naqib

Materials Science

Solution gate control of shallow silicon vacancy charge states in diamond

Charlie Pattinson, Daniel J. McCloskey, Nikolai Dontschuk et al. (+3 more)

Silicon-vacancy (SiV) centers in diamond combine near-infrared emission with solid-state robustness, but their performance hinges on isolating favorable defect charge states. We demonstrate static and dynamic control of ultra-shallow (<15 nm) SiV ensembles in type IIa diamond. By combining low-energy ion implantation with tailored oxygen and hydrogen terminations, we map regimes that maximise the fluorescent SiV- population over dark charge states. We then realize reversible SiV- to SiV0 conversion using aqueous electrolytic gating with sub-200 mV biases and low optical powers. Our results enable low-power electrical control of SiV ensembles for integrated quantum photonics and biologically compatible voltage imaging in the near-infrared.
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All authors Charlie Pattinson, Daniel J. McCloskey, Nikolai Dontschuk, Brett C. Johnson, Alexander A. Wood, David Simpson

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

Polarized neutron scattering as a probe for vortex-type spin correlations in iron oxide multicore assemblies

Venus Rai, Ivan Titov, Elizabeth M. Jefremovas et al. (+11 more)

We report an experimental investigation of the magnetic microstructure of iron oxide multicore assemblies by means of polarized small-angle neutron scattering (SANS). Guided by a recently developed analytical theory for vortex-state magnetic nanoparticles, we provide a quantitative comparison between the measured and calculated cross sections, revealing signatures that are consistent with vortex-type magnetization configurations at low applied magnetic fields. In particular, the field evolution and the characteristic isotropic ring-type feature of the spin-flip scattering intensity at intermediate momentum transfers are in line with the formation of flux-closure states. The latter are stabilized by the interplay of exchange, Zeeman, and magnetostatic energies. The methodology allows for a statistically significant characterization of vortex states in densely packed nanoparticle systems, thereby complementing surface-sensitive techniques that are commonly limited to the observation of spin structures in individual particles.
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All authors Venus Rai, Ivan Titov, Elizabeth M. Jefremovas, Štefan Liščák, Sivarenjini Shan, Nina-Juliane Steinke, Jonathan Leliaert, Álvaro Gallo-Córdova, María P. Morales, Davide Peddis, Pierfrancesco Maltoni, Luis Fernández Barquín, Andreas Michels, Michael P. Adams

Materials Science

Role of Local Structural Variation in X-ray Photoelectron Spectrum of Silicon Oxide Interfaces

Mikael Santonen, Sari Granroth, Johanna Laaksonen et al. (+2 more)

We show that the broad X-ray photoelectron lines of silicon oxide on silicon arise from a continuous statistical distribution of core-level binding energies. Statistical simulations spanning compositions from Si to SiO$_2$ reproduce the full extent of this broadening, reaching 5 eV for SiO$_{1.0}$ , in quantitative agreement with 0.23 nm layer-resolved spectra reconstructed from Ar$^+$ sputtering data. This continuous distribution blurs distinct spectral fingerprints of local structural motifs, thereby challenging conventional chemical state assignment in oxide X-ray photoelectron spectra.
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All authors Mikael Santonen, Sari Granroth, Johanna Laaksonen, Pekka Laukkanen, Johannes Niskanen

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

$d$-wave altermagnetism revealed by resonant inelastic X-ray scattering

Guangkai Zhang, Yuehong Li, Xubin Ye et al. (+16 more)

Altermagnetism defines a third fundamental class of collinear magnetic order, featuring compensated magnetic moments with antiparallel spin alignment, yet lifted Kramers degeneracy without the need for relativistic spin-orbit coupling. Its ability to host spin-polarized electronic bands and unconventional chiral magnons makes it a promising platform for functional materials. However, experimental verification has proven challenging; while circular dichroism in resonant inelastic X-ray scattering (RIXS) has been suggested as a signature of chiral magnons, it remains controversial whether this effect is an intrinsic property of altermagnetism or an artifact of experimental geometry. In this work, we resolve this debate and provide unambiguous experimental evidence of $d$-wave altermagnetism in the strongly correlated Lieb-lattice magnet La$_2$O$_3$Mn$_2$Se$_2$. The RIXS spectra exhibit a $d$-wave-symmetry circular dichroism in the magnetic excitations that vanishes in the paramagnetic phase. Through RIXS-operator symmetry analysis and exact-diagonalization calculations, we prove that the observed dichroism is a direct consequence of altermagnetic symmetry constraints, independent of magnon branch splitting. Our results provide definitive evidence for the experimental realization of $d$-wave altermagnetism in La$_2$O$_3$Mn$_2$Se$_2$ and establish circularly polarized RIXS as a highly symmetry-sensitive spectroscopic framework for detecting magnetic phases that evade conventional probes.
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All authors Guangkai Zhang, Yuehong Li, Xubin Ye, Vincent C. Morano, Sze Tung Li, Jaewon Choi, Rebecca Scatena, Shuai Tang, Maocai Pi, Mengqi Ye, Mirian Garcia-Fernandez, Alessandro Bombardi, Xiaomei Qin, Zhao Pan, Daniel G. Mazzone, Qisi Wang, Yi Lu, Yao Shen, Youwen Long

Materials Science · Cross-listed from cs.LG

Robust and Interpretable Adaptation of Equivariant Materials Foundation Models via Sparsity-promoting Fine-tuning

Youngwoo Cho, Seunghoon Yi, Wooil Yang et al. (+6 more)

Pre-trained materials foundation models, or machine learning interatomic potentials, leverage general physicochemical knowledge to effectively approximate potential energy surfaces. However, they often require domain-specific calibration due to physicochemical diversity as well as mismatches between practical computational settings and those used in constructing the pre-training data. To address this, we propose a sparsity-promoting fine-tuning method that selectively updates model parameters by exploiting the structural properties of E(3)-equivariant materials foundation models. On energy and force prediction tasks across molecular and crystalline benchmarks, our method matches or surpasses full fine-tuning and equivariant low-rank adaptation while updating only $\sim$3~% of parameters, and in some cases as little as $\sim$0.5~%. Beyond energy and force calibration, we further demonstrate task generalizability by applying our method to magnetic moment prediction and magnetism-aware total energy modeling. Finally, analysis of sparsity patterns reveals physically interpretable signatures, such as enhanced $d$-orbital contributions in transition metal systems. Overall, our results establish sparsity-promoting fine-tuning as a flexible and interpretable method for domain specialization of equivariant materials foundation models.
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All authors Youngwoo Cho, Seunghoon Yi, Wooil Yang, Sungmo Kang, Young-woo Son, Jaegul Choo, Joonseok Lee, Soo Kyung Kim, Hongkee Yoon

Materials Science

Strain induced magnetic phase transition and anomalous transport phenomena in RuO$_2$ and MnF$_2$

Xiuxian Yang, Zhangqi Wu, Xiangju Wang et al. (+6 more)

Collinear antiferromagnets with broken time-reversal symmetry have emerged as a fertile platform for spintronics. Using a general tight-binding model and first-principles calculations, we show that strain engineering provides a simple route to control magnetic phase transition and activate transverse responses in representative altermagnets RuO$_2$ and MnF$_2$. For pristine RuO$_2$ and MnF$_2$ with Néel vector $\mathbf{n}\parallel$ [001], symmetry constrains the off-diagonal elements of the Hall conductivity tensor to vanish, thereby forbidding anomalous transport and magneto-optical responses. Shear strain applied along the $ac$ direction preserves the spin symmetry relating the two spin-opposite magnetic sublattices and therefore maintains the altermagnetic phase. By contrast, shear strain applied along the $ab$ direction breaks this spin symmetry and drives a transition from an altermagnetic phase to a partially compensated ferrimagnetic phase in metallic RuO$_2$ and to a fully compensated ferrimagnetic phase in semiconducting MnF$_2$. In addition, the lowered symmetry enables finite anomalous Hall, anomalous Nernst, and anomalous thermal Hall conductivities, as well as magneto-optical rotation angles, which are prohibited in the pristine systems. These responses exhibit a clear strain dependence and become progressively stronger as the strain amplitude increases. Our results establish strain engineering as an effective route to manipulate magnetic phases and functional responses in unconventional antiferromagnets, thereby expanding opportunities for antiferromagnetic spintronics and magneto-optical applications.
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All authors Xiuxian Yang, Zhangqi Wu, Xiangju Wang, Shifeng Qian, Ping Yang, Xiaodong Zhou, Jian Hao, Wanxiang Feng, Yinwei Li

Tuesday 16 June

Materials Science · Cross-listed from cs.CE

datascribe_api: Enabling Data-Driven Materials Discovery with DataScribe

Doğuhan Sar{\i}türk, Raymundo Arróyave and Vahid Attari

datascribe_api is a Python library and command-line interface (CLI) that gives researchers programmatic access to DataScribe Cloud, an AI-native platform for materials design and discovery. DataScribe integrates two data services: user-managed scientific data tables, where research groups store experimental measurements, simulation outputs, and derived features; and curated materials science databases from the Materials Project, AFLOW, and OQMD. datascribe_api exposes both through a single, typed Python interface, so researchers can retrieve, filter, and analyze data without writing custom HTTP code. The library handles authentication, connection management, and transient network errors automatically. It exposes nine query endpoints as ordinary Python method calls. Filter conditions use standard Python comparison syntax and are passed as a list, keeping query logic readable without format-specific boilerplate. Pydantic models validate all API responses at parse time, so schema mismatches surface as exceptions rather than silent wrong values. Each result collection converts to a pandas DataFrame in a single call, so retrieved data is directly available for machine learning and statistical analysis. Every materials search result carries a provenance field identifying its source database, satisfying FAIR traceability requirements. The library includes a CLI that exposes all nine endpoints as subcommands, using Typer for argument parsing and Rich for terminal output. Every subcommand supports machine-readable JSON output for shell pipelines and LLM agents. Pre-built wheels for Python 3.11 and later are published on PyPI under the GPLv3 license for Linux, macOS, and Windows.
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Materials Science · Cross-listed from cond-mat.mes-hall

Field-like Perturbation Enabled Six-state Readout in Triaxial $\alpha$-$\mathrm{Fe}_{2}\mathrm{O}_{3}$|Pt Bi-layers

Aditya A. Wagh, Shwetha G. Bhat, Krishna Jha et al. (+2 more)

Canted antiferromagnet $\alpha$-$\mathrm{Fe}_{2}\mathrm{O}_{3}$|Pt bilayers offer a platform for multistate memory, but spin Hall magnetoresistance (SMR) readout cannot distinguish states separated by $180^{\circ}$, limiting detection to three states. We show that a field-like perturbation lifts the degeneracy of opposite states in $\alpha$-$\mathrm{Fe}_{2}\mathrm{O}_{3}$, enabling the resolution of six states in the SMR signal. We introduce a dual-modulation SMR method to mitigate thermal drifts and enable reliable readout. Computations of first- and second-harmonic SMR reveal the role of exchange, anisotropy and field-like perturbations in resolving the states.
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All authors Aditya A. Wagh, Shwetha G. Bhat, Krishna Jha, Aiswarya Sukumaran, P. S. Anil Kumar

Materials Science

Chemical Vapor Deposition of Ni-doped Iron Germanium Telluride Nanosheets

Matthew Metcalf, Jesse Martinez, Armella Mushfique et al. (+4 more)

Iron germanium telluride (FGT; FemGenTe2) compounds have attracted significant interest due to their layered van der Waals structure, relatively high Curie temperature, and tunable magnetic properties. Chemical vapor deposition (CVD) is a particularly promising synthesis route owing to its simplicity, low cost, potential for scalability, and widespread adoption in the semiconductor industry, yet it has not been used previously to synthesize FGT with dopants. Here, we report CVD synthesis of both undoped and Ni-doped FGT nanosheets on SiO2/Si substrates. By adjusting precursor molar ratios, we synthesized Ni-doped FGT with multiple Fe concentrations and a 4% Ni-to-Fe ratio. X-ray photoelectron spectroscopy depth profiling further demonstrates that Ni is present in the bulk of the crystals. This straightforward, low-cost, and CMOS-compatible approach demonstrates a route to Ni-doped FGT nanosheets, establishing a foundation for future characterization of Ni-doped FGT and its potential integration into spintronic devices.
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All authors Matthew Metcalf, Jesse Martinez, Armella Mushfique, Alexander Riou, Lutfun Nahar, Bamidele Onipede, Hui Cai

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

Magnon-dislon hybridization in magnetic insulators

Carlos Saji, Nicolas Vidal-Silva and Roberto E. Troncoso

Spin dynamics in ordered magnets with topological lattice defects is investigated. Using fracton–elasticity duality, we develop an effective field theory of magnons coupled to quantized lattice dislocations (dislons) in magnetic insulators. Within this framework, an elastic gauge field mediates a nonlocal interaction between dislocations and magnetization gradients. The resulting magnetoelastic coupling gives rise to coherent magnon-dislon hybridization whose properties are dictated by dislocation topology. Screw dislocations exhibit helicity-selective hybridization and symmetry-protected dark dislon sectors, while edge dislocations generate anisotropic hybrid excitations with finite spin-precession ellipticity through the glide constraint. Our results establish dislocations as dynamical topological defects with directly observable polarization fingerprints in magnon spectra, and reveal magnon-dislon hybridization as a new route to control spin dynamics.
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Materials Science

Hydration-controlled twist forms a moiré glass in charge-frustrated layered silicates

Juhyeok Lee, Piotr Zarzycki, Colin Ophus et al. (+5 more)

Twisting layered materials produces moiré superlattices, but prescribed twist angles are usually obtained by demanding assembly procedures. Here we show that montmorillonite, an abundant swelling clay, forms tunable moiré superlattices naturally. Focal-series high-resolution transmission electron microscopy, geometric phase analysis, and molecular dynamics simulation reveal that its apparent rotational disorder is biased toward low-angle misorientations inherited from discrete hydration states. Multilayer stacks preferentially adopt twists near 1-2{\deg}, 4{\deg}, and 10{\deg}, producing long-wavelength moirés without long-range rotational order. We define this kinetically trapped state as a moiré glass, distinct from featureless turbostratic stacking. Simulations indicate that lattice-charge disorder stabilizes the angular preferences, whereas charge ordering promotes random stacking. Hydration screens interlayer interactions and lubricates twist, while dehydration arrests the resulting configurations in discrete steps. These results establish dynamic hydration as a macroscopic handle for programming twist in layered matter.
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All authors Juhyeok Lee, Piotr Zarzycki, Colin Ophus, Jim Ciston, Benjamin Gilbert, Jillian F. Banfield, Mary C. Scott, Michael L. Whittaker

Materials Science

Magnetotransport Measurements on Isolated Polycrystalline Grains of Type-II Silicon Clathrate

Sam Saiter, Joseph P. Briggs, Yinan Liu et al. (+5 more)

The first low-temperature electronic transport characterization of individual polycrystalline grains of type-II silicon clathrate (Na$_x$Si$_{136}$, $x \ll 1$), isolated using microfabrication techniques, is reported. Structural characterization via Raman spectroscopy confirms that the isolated grains are largely devoid of amorphous silicon (a-Si). Temperature-dependent resistivity reveals multiple conduction regimes, including thermally activated freeze-out behavior and a transition to low-activation-energy transport at cryogenic temperatures, consistent with hopping conduction mechanisms. Hall measurements from 290 K to 3.5 K yield carrier concentration and mobility trends that correlate with the extracted activation energies, verifying $n$-type conduction. Additionally, gate-dependent conductivity measurements demonstrate electrostatic tunability at room temperature. Collectively, these results establish the magnetotransport parameters of single, isolated grains of type-II silicon clathrate and demonstrate the potential of this material for future quantum and optoelectronic devices.
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All authors Sam Saiter, Joseph P. Briggs, Yinan Liu, Audrey Faricy, Gavin Sher, Carolyn A. Koh, Reuben T. Collins, Meenakshi Singh

Materials Science

akaitools: A Python package for parsing and analyzing AkaiKKR electronic structure calculations

Doğuhan Sar{\i}türk and Raymundo Arróyave

The Korringa-Kohn-Rostoker (KKR) Green's function method is a first-principles electronic structure approach well suited to substitutionally disordered alloys through the Coherent Potential Approximation (CPA). AkaiKKR is a widely used implementation, known for efficient treatment of metallic systems and their magnetic properties. Its output, however, is unstructured plain text with no programmatic interface, leaving data extraction entirely to the user and making systematic or high-throughput studies impractical. akaitools is a Python package that parses AkaiKKR output files into structured, type-annotated Python objects. The package covers three output types: self-consistent field (SCF) results, which capture convergence history and per-atom electronic and magnetic properties; spin-resolved, orbital projected density of states for each CPA component; and Bloch spectral functions on a user-defined k-point path. Results come back as immutable dataclasses backed by NumPy arrays. Energy quantities are available in both Rydbergs and electronvolts, and results can be exported to Pandas DataFrames. A built-in plotting module produces Matplotlib figures for DOS curves and SCF convergence. A command-line interface provides file summaries and JSON export without any Python scripting. The package also includes a programmatic input file generator, so full calculation pipelines from input preparation to output analysis can be run in Python.
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Materials Science · Cross-listed from physics.ins-det

Diffuse scattering of neutrons in a wave resonator

E.D. Kolupaev, V.D. Zhaketov and Yu.V. Nikitenko

In fundamental experiments with neutrons, the neutron flux and the neutron storage time in the measuring setup are of primary importance. These quantities can be increased by using a storage device for neutrons generated by a pulsed source. In a storage device with material walls, both parameters are determined by the probabilities of neutron absorption and diffuse scattering upon reflection from the storage walls, as well as by the neutron decay probability. This work considers a neutron measurement method and presents the results of an experimental determination of the probability of diffuse neutron scattering in a wave resonator.
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Materials Science

Anisotropic Short-Range Order Modulates Ferroelectric Switching in Wurtzite ScAlN Alloys

Shunda Chen, Xianchao Dong, Xiaochen Jin et al. (+1 more)

Ferroelectric switching in wurtzite alloys is typically understood in terms of composition, strain, defects, and interfaces, while local chemical order is often neglected or treated as a secondary perturbation. Here we show that short-range order (SRO) is a previously overlooked microscopic variable that substantially influences the intrinsic switching barrier. Using first-principles canonical sampling, we find that wurtzite ScAlN develops a robust, highly anisotropic SRO that challenges the conventional random-alloy picture. This ordering suppresses in-plane Sc–N–Sc motifs while enhancing columnar mixed-cation chains along the polar $c$ axis, reflecting the symmetry-distinct polar and basal directions of the wurtzite lattice and reorganizing its polar connectivity. Relative to random-alloy structures, SRO systematically increases the intrinsic switching barrier across a broad composition range. Motif-resolved analysis further identifies the population of columnar Sc–N–Al–N–Sc motifs as the primary structural descriptor underlying switching-barrier variations among configurations with different local order. These results establish anisotropic SRO as an independent degree of freedom for tuning ferroelectric switching. More broadly, they reveal how local chemical order can couple to the symmetry-distinct directions of a polar semiconductor lattice to modify functional behavior. Our findings lay a foundation for SRO engineering as a route to tailoring switching barriers without changing alloy composition.
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All authors Shunda Chen, Xianchao Dong, Xiaochen Jin, Tianshu Li

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

High-temperature ferromagnetism and antiferromagnetism in monolayer \ce{CrTe2}: Roles of strong spin-lattice coupling and charge doping

Anupama S and Mukul Kabir

The interplay of structural, electronic, and magnetic degrees of freedom governs phase stability and critical temperatures in two-dimensional magnets. Controlling this coupling is essential for advancing fundamental understanding and spintronic applications. Combining first-principles calculations with Heisenberg Monte Carlo simulations, we reveal a rich magnetic phase diagram governed by the interplay of lattice strain and carrier density. These results provide a unified framework that reconciles diverse experimental reports on epitaxial layers and predicts a novel double-stripe antiferromagnetic phase, further stabilized by electron doping. Moreover, structural and electronic perturbations enable room-temperature ferromagnetism and antiferromagnetism. This magnetic evolution arises from competing, highly tunable direct and ligand-mediated exchange interactions in the presence of Ruderman-Kittel-Kasuya-Yosida coupling. By disentangling their individual contributions, we elucidate the underlying microscopic mechanisms, which transcends the conventional conduction electron picture. Finally, we quantify the colossal magnetoelastic response and identify zone-folded Raman modes that serve as unique experimental fingerprints for phase identification. Together, these results establish \ce{CrTe2} as a versatile platform for two-dimensional spintronics, where magnetic order and transition temperatures are tailorable via structural and electrical engineering.
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Materials Science

Double quantum spin Hall phase in bilayer ZrTe$_5$

Chao Chen Ye, Gábor Kalla, Jianting Ye et al. (+1 more)

Quantum spin Hall insulators (QSH) are topological materials that host helical edge states protected against backscattering, making them ideal candidates for dissipationless spin transport. Within the conventional $\mathbb{Z}_2$ classification, only phases with an odd number of edge state pairs ($\mathbb{Z}_2 = 1$) are topologically nontrivial, whereas even-channel systems ($\mathbb{Z}_2 = 0$) lie beyond this framework but can host robust edge transport characterized by a spin Chern number. Experimentally accessible realizations of such phases remain rare, particularly in systems with sizeable band gaps. Here, we show that bilayer ZrTe$_5$ realizes a double quantum spin Hall phase in its energetically most stable structure. Using first principles calculations, we demonstrate that uniaxial strain drives a transition from this phase to a conventional single pair QSH phase with $\mathbb{Z}_2 = 1$. The double QSH phase hosts two pairs of helical edge states, resulting in enhanced edge conductance and a quantized spin Hall response that remains robust over an energy window of up to $\sim$100 meV. These results establish bilayer ZrTe$_5$ as a tunable platform connecting conventional and double QSH phases within a single material. More broadly, they demonstrate that untwisted van der Waals bilayers can host topological phases beyond the conventional $\mathbb{Z}_2$ classification.
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All authors Chao Chen Ye, Gábor Kalla, Jianting Ye, Jagoda Sławińska

Materials Science

Impact of dynamic electrostatic disorder on hole mobility in rubrene: a nonadiabatic molecular dynamics investigation

Jan Elsner, Samuele Giannini and Jochen Blumberger

High-mobility organic molecular crystals such as rubrene are important materials for organic electronics, yet a quantitatively predictive description of their charge transport properties remains challenging. Direct mixed quantum-classical nonadiabatic molecular dynamics simulations provide a promising route by explicitly propagating the charge carrier wavefunction, without assuming a specific transport mechanism. However, previous large-scale simulations of apolar molecular crystals have commonly neglected dynamic electrostatic disorder, since evaluation of electrostatic interactions is computationally demanding and the approximation appears plausible for apolar systems. Here, we use the damped shifted-force (DSF) real-space electrostatic summation method, combined with an efficient addition-subtraction scheme, to include dynamic electrostatic disorder in fragment orbital-based surface hopping (FOB-SH) simulations of room-temperature hole transport in rubrene. We find that electrostatic interactions increase the reorganization energy for (hypothetical) nearest neighbour hopping by 29 and 39 meV along the a and b-directions, respectively, relative to a baseline value of 152 meV obtained without electrostatics. In FOB-SH simulations, electrostatic interactions lead to increased site energy disorder, reducing the spatial extent of the hole wavefunction, as measured by a decrease in the inverse participation ratio from 13 to 9, and lowering the predicted mobility along the high-mobility direction from $35$ to $21~\mathrm{cm^2 V^{-1}s^{-1}}$, in close agreement with experiment.
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Materials Science

Tunable Electronic and Transport Properties of Biphenylene via Fluorination and Disorder

Lucas Soares Sousa, Felipe Crasto de Lima and Roberto Hiroki Miwa

Biphenylene (BPN) network is a newly synthesized 2D carbon allotrope hosting anisotropic Dirac electronic states. Here, we investigate how fluorination and correlated chemical disorder modify the electronic structure and charge transport of fluorinated biphenylene (F/BPN) using density functional theory, Wannier-based tight-biding Hamiltonian, and quantum transport simulations. We show that fluorination reshapes the transport response of BPN, producing concentration-dependent anisotropic conduction regimes. For pristine and ordered fluorinated systems, we identified the emergence of negative differential resistance (NDR) and a bias-induced inversion of the preferred transport direction, from armchair to zigzag and vice versa. In contrast, disorder suppresses the NDR, driving the system toward an approximately Ohmic transport regime. At high fluorine coverage, we further observed a nonmonotonic dependence of the armchair current on adatom concentration, which we attribute to the formation of correlated quasi-linear fluor conformation that promote armchair-oriented C-$\pi$ transport channels while simultaneously suppressing transport along the zigzag direction. Our results demonstrate that correlated fluorination can be used as an active mechanism to engineer electronic transport.
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Materials Science · Cross-listed from cond-mat.mes-hall

Highly nonlinear Moiré exciton and trion polaritons

Arnab Barman Ray, Trevor Ollis, Fei Cheng et al. (+3 more)

Moiré multi-layers of transition metal dichalcogenides have been shown to exhibit optical responses that are endowed with a richness that is absent in single monolayers. Much of this can be attributed to the Moiré superlattice that modulates the electronic landscape of these heterostructures. Strongly coupled layer-hybridized excitons in $\text{MoSe}_2 / \text{WS}_2$ heterobilayers have been shown to exhibit enhanced optical nonlinearities. In this work we strongly couple layer hybridized excitons and trions in n-doped $\text{MoSe}_2 / \text{WS}_2$ heterobilayers inside an optical microcavity. We find that the additional Lindhard screening from dopant electrons and the formation of trions result in a strikingly non-monotonic nonlinear response. The absence of electron capture in the Moiré superlattice plays a crucial role, promising very large second-order nonlinearities. In this work, trion polaritons manifest as high velocity hot polaritons, reaching nominal diffusion lengths approaching 100 microns.
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All authors Arnab Barman Ray, Trevor Ollis, Fei Cheng, Adam L. Freidman, Aubrey T. Hanbicki, Anthony Nickolas Vamivakas

Materials Science

Coupled spin dynamics in epitaxial trilayer heterostructures of ferrimagnetic garnet

A. Del Giacco, M.J. Gross, O. Wojewoda et al. (+9 more)

The magnetization dynamics of an all-garnet trilayer consisting of Y3Fe5O12/Y3Fe3Al2O12/Y3Fe5O12 (YIG/YIAG/YIG) is analysed. The two magnetic YIG layers, separated by a 4 nm thick paramagnetic YIAG layer, are coupled via dipolar interactions leading to the formation of hybrid magnon modes distinct from the modes found in a single YIG layer. The YIAG exchange-decouples the YIG layers while enabling lattice coherence, maintaining the low damping of the YIG. Both ferromagnetic resonance and micro-Brillouin light scattering measurements were used to characterize the sample and its hybrid dynamics, which showed excellent agreement with an analytical reciprocal space model of spin-wave dynamics and with micromagnetic modeling of a dipolarly coupled magnetic heterostructure.
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All authors A. Del Giacco, M.J. Gross, O. Wojewoda, L. Menna, T. Grossmark, P. Lauer, V. Levati, S. Kurdi, E. Albisetti, D. Petti, M. Urbanek, C.A. Ross

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

Theory of clusterization in orbitally degenerate transition-metal compounds driven by lattice instabilities

Soshun Ozaki, Kota Mitsumoto and Chisa Hotta

We derive an effective orbital-lattice model with quantum $S=1$ degrees of freedom for transition-metal compounds, providing a microscopic understanding of cluster formation driven by the cooperative interplay of spin, orbital, and lattice degrees of freedom. Motivated by the trimerized phases observed in LiVS$_2$ and LiVO$_2$, we consider a triangular-lattice three-orbital system with two electrons per site occupying the threefold-degenerate $t_{2g}$ manifold. Starting from a multiorbital Kanamori-Hubbard Hamiltonian, we project the low-energy sector onto the local $S=1$ triplet manifold, in which two electrons occupy different orbitals according to Hund's coupling. The resulting effective model exhibits exchange networks whose geometry is determined by the orbital configuration. However, the orbital-driven exchange interactions alone do not stabilize the experimentally observed trimer phase. We find that by incorporating ionic lattice displacements that modulate transfer integrals and induce bond-dependent exchange couplings on shortened and elongated bonds, the phase competition is qualitatively altered, leading to the robust stabilization of a trimerized ground state within a fully quantum-mechanical framework. We further show that a simplified orbital-lattice model, in which the spin-exchange energy is replaced by effective bond energies, faithfully reproduces the essential ground-state properties of the microscopic model. This reduced description enables large-scale finite-temperature simulations and reveals a rich sequence of thermal phase transitions, including first-order, second-order, and Kosterlitz-Thouless transitions into distinct spin-, orbital-, and lattice-ordered phases.
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Materials Science

Revisiting quantum effects on dislocation glide in bcc metals from DFT calculations and machine-learning potentials

Arnaud Allera, Lisa Ventelon, Mihai-Cosmin Marinica et al. (+2 more)

Quantum zero-point effects have been long proposed to explain a well-known discrepancy between the low-temperature flow stresses of body-centered cubic metals and corresponding atomistic models of plastic flow. Previous investigations on quantum effects relied on empirical interatomic potentials, which poorly reproduce dislocation energy landscapes compared to density functional theory (DFT) calculations. Here, we revisit this problem using DFT and machine-learning interatomic potentials (MLIPs). We show that while quantum effects do contribute to dislocation glide at low temperature, their magnitude is much lower than previously reported, and insufficient to reconcile atomistic predictions with experiments. Our results thus reopen a long-standing question and challenge for predictive atomistic modeling, on a fundamental property of crystals.
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All authors Arnaud Allera, Lisa Ventelon, Mihai-Cosmin Marinica, David Rodney, Laurent Proville

Materials Science

Hydrogen s-electrons as the origin of crystal magnetism beyond spin-orbit coupling

Baiqiang Liu, Zhen Gong, Rui Liu et al. (+3 more)

Magnetism has long been attributed to localized d, f, and even p electrons with strong correlations, whereas s electrons exemplified by hydrogen are reactive and tend to have their spins quenched, making s-electron-derived magnetism and long-range ordered magnetic crystals seem unattainable. Here we report a low-Z ferromagnetic crystal H13@(BN)12 using first-principles calculations, where thirteen hydrogen atoms are encapsulated within a (BN)12 cage and magnetism originates from the 1s electron of the central hydrogen atom. The crystal remains stable under ambient pressure owing to chemical precompression. Notably, the central hydrogen atom retains a magnetic moment of 1 {\mu}B, with long-range magnetic order established through multicenter bonding within the H13 aggregate and the intercell B-B network, while the zero orbital angular momentum of s electrons renders spin-orbit coupling (SOC) negligible as expected. Electronic structure analyses reveal that the large cavity and central negative electrostatic potential of the (BN)12 cage localize the hydrogen 1s electron, preventing spin quenching. Interestingly, under 16 GPa compression, the system transforms into a nonmagnetic metallic state driven by delocalized electrons of the central hydrogen atom. This study opens a pathway for constructing s-electron-driven magnetic materials and lays the foundation for developing low-energy consumption magnetic devices without SOC.
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All authors Baiqiang Liu, Zhen Gong, Rui Liu, Siyang Liu, Yue Feng, Zhigang Wang