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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Tuesday 9 June

Materials Science

Layer-parity-dependent interfacial coupling in Nb$_3$Cl$_8$/graphene van der Waals heterostructures

Hansheng Xu, Yuchen Gao, Xinyue Huang et al. (+8 more)

Strongly correlated two-dimensional systems provide compelling platforms for investigating exotic quantum phenomena. Niobium chloride (Nb$_3$Cl$_8$), a single-band Mott insulator, exhibits a remarkable out-of-plane polarization in its topmost layer that oscillates with layer parity, manifesting as an odd-even effect. Using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM), this layer-parity-dependent polarization can be effectively characterized through surface morphology and potential mapping, enabling the unambiguous identification of different surface phases. We then fabricated dual-gate Hall devices by coupling different surface phases of Nb$_3$Cl$_8$ with monolayer graphene to investigate how the topmost-layer out-of-plane polarization influences interfacial coupling and the resulting transport behavior. Our results reveal significant phase-dependent variations in charge transfer, carrier densities, and hybridization gaps (25.2 meV for Phase 1 and 30.0 meV for Phase 2). Density functional theory calculations corroborate these experimental findings, showing that distinct out-of-plane polarizations in the topmost layer lead to different orbital overlaps and interfacial coupling strengths. These findings highlight the critical importance of surface polarization and orbital orientation in engineering the properties of strongly correlated van der Waals heterostructures.
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All authors Hansheng Xu, Yuchen Gao, Xinyue Huang, Weihanzhang Guo, Zhijie Ma, Ziqi Liu, Pinfan Gu, Kenji Watanabe, Takashi Taniguchi, Youguo Shi, Yu Ye

Materials Science

Ultra-Soft Ferrimagnetism in a High-Entropy Spinel Oxide Driven by Site-Selective Cation Disorder

Neha Sharma, AmritPal, Nikita Sharma et al. (+6 more)

High-entropy materials are complex, multifunctional materials that have reshaped the design of advanced functional materials. Their chemically diverse compositions enable access to a broader compositional space than conventional solid solutions, while simultaneously posing significant challenges for fundamental structure property understanding. In this study, we introduce a new highentropy spinel oxide with an exceptionally low coercivity of 1.8 Oe at room temperature, among the lowest reported for bulk spinel oxides, and a high electrical resistivity (1560 ohm-cm). Neutron powder diffraction (NPD) and magnetic measurements reveal long-range collinear ferrimagnetic ordering (k = 0,0,0) with a transition temperature at 420 K. This rare combination of ultra-soft magnetic behavior, robust ferrimagnetic ordering well above room temperature, and high resistivity highlights its strong potential as an advanced soft-magnetic oxide for low-loss, high-frequency applications. Furthermore, X-ray absorption spectroscopy (XAS), Mossbauer spectroscopy, and NPD analyses were combined to determine the cation distribution and site selectivity across the tetrahedral and octahedral sites of the complex structure.
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All authors Neha Sharma, AmritPal, Nikita Sharma, Mathieu Duttine, Denis Pelloquin, S. D. Kaushik, Sanjoy Mahatha, Olivier Toulemonde, Sourav Marik

Materials Science · Cross-listed from hep-th

Chiral Plasma under Strong Magnetic Fields: A Holographic Analysis of Transport Phenomena

Michael Lublinsky and Hadas Tzarfati

Chiral plasma appears in several areas of physics, historically starting from primordial plasma in the early Universe, then in quark-gluon plasma produced in heavy ion collisions, and, more recently, in Dirac and Weyl semimetals. The major signature of the plasma is the non-conservation of the axial current due to the chiral anomaly and the emergence of new, anomaly-induced transport phenomena. In this paper, we study the plasma exposed to arbitrarily strong constant magnetic and weak electric fields. Employing all-order gradient resummation, we write down constitutive relations for electric and axial currents parameterized by thirteen momentum- and magnetic- field-dependent transport coefficient functions. The latter are computed utilizing a theoretical lab for a realistic plasma, namely a holographic $U(1)_V \times U(1)_A$ Maxwell–Chern–Simons theory in Schwarzschild–AdS$_5$, in the probe limit. As an application, we revisit the phenomena of negative magnetoresistance and chiral magnetic waves, beyond the naive hydrodynamic limit.
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Materials Science

Extending Field Limits in Nanoscale Magnetic Imaging with Metamaterial-inspired Magnetic Flux Concentrators

A. Barrera, E. Fourneau, T. Pirottin et al. (+14 more)

Many nanoscale magnetic imaging techniques are constrained by the maximum magnetic field that can be applied during measurements, due to geometrical limitations or interactions with the probe or the detected signal (e.g., electrons). Here, it is demonstrated that sample-integrated metamaterial-inspired magnetic flux concentrators (MFCs) locally amplify magnetic fields, allowing observation of magnetization processes beyond instrumental limits. Micrometer-sized MFCs fabricated directly on the samples are tested in photoemission electron microscopy experiments employing X-ray magnetic circular dichroism as magnetic contrast mechanism. At low applied fields, substantial amplification factors enable observation of magnetization reversal in a chain of magnetite nanoparticles synthesized by magnetotactic bacteria at an applied field of 8 mT, substantially smaller than the 50 mT predicted by simulations in absence of MFCs. At higher fields, the field enhancement extends the accessible field range by a factor of five, enabling for the first time, imaging of the field-dependent magnetic domain structure evolution of an isolated giant magnetofossil. Finally, we show how MFC geometry and material parameters can be tuned to optimize performance considering sample and experimental constraints, providing a tunable and broadly applicable strategy for extending the accessible field range in a wide variety of nanoscale magnetic imaging techniques.
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All authors A. Barrera, E. Fourneau, T. Pirottin, L. Marcano, R. Abrudan, R. Huang, Ll. Balcells, I. Orue, M.L. Fdez-Gubieda, D. Villanueva, A.G. Gubieda, L. Chang, B. Vanderheyden, R.J. Harrison, A.V. Silhanek, A. Palau, S. Valencia

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

Dichotomous electronic system in a bilayer Ni$^{1+}$ nickelate

Young-Joon Song, K.-W. Lee and W. E. Pickett

"Infinite layer" nickelates (ILNs) ${\cal R}$NiO$_2$ (${\cal R}$=rare earth), having empty apical O sites, become superconducting upon hole doping, stimulating research into the related sequence Nd$_{n+1}$Ni$^{+p}_n$O$_{2n+2}$, formal charge state $p$=1+$\frac{1}{n}$, $n$=2,3,4,...., with the $n$=5 member being found to be superconducting. The two layer system La$_3$Ni$_2$O$_{7-\delta}$, with $\delta$=0,$\frac{1}{2}$,1 ($p$=2.5,2,1.5) approaches the peak in the nickelate superconducting dome but shows no superconductivity. Newly reported La$_3$Ni$_2$O$_5$F reaches the Ni$^{1+}$ goal while, as we show, introducing a partially occupied electron band $E^*$, based on an interstitial density that extends over the three open "apical" layers and leads to a single cylindrical electron Fermi surface giving self-doping. The commonly inert Ni $d_{xz},d_{yz}$ orbitals partner with interstitial $E^*$ to provide an incipient non-analytic Dirac point, with the critical point being reachable by pressure or further F insertion. The $E^*$ electron cylinder and the conventional Ni $dp\sigma$ hole carriers combine to provide a two-fluid dichotomy of hole and electron quasiparticles, affecting normal state properties that should verify the dichotomous aspect of transport.
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Materials Science

Optical-like interference control polar-phonons dispersions in 2D materials

Benoit Van Troeye and Geoffrey Pourtois

It has been argued that the polar phonon modes of two-dimensional (2D) materials should show a linear dependence close to the Brillouin zone center due to the reduced problem dimensionality compared to a three-dimensional crystal, leading to a vanishing LO-TO splitting. Revisiting this question using a mirror-charge framework derived from classical electrostatics, we show that it is not always true: with perfectly-reflective dielectric interfaces, it is possible to recover a LO-TO splitting, or an equivalent phenomenon for the out-of-plane modes. Effectively, the dispersion of polar phonon modes is governed by optical-like constructive and destructive interferences of the source potential with its reflection at the dielectric interfaces. This work highlights the critical role of dielectric boundary conditions to understand phonon-related properties in 2D materials.
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Materials Science · Cross-listed from eess.IV

Unsupervised Deep Learning for Limited-Angle STEM-EDX Tomography – Application to 3D Chemical Analysis of Phase-Change Memory Devices

Daniel del Pozo Bueno, Serge Brosset, Theo Monniez et al. (+3 more)

Energy Dispersive X-ray (EDX) tomography in Scanning Transmission Electron Microscopy (STEM) enables 3D compositional and elemental mapping at the nanoscale, but its use is limited by restricted tilt ranges and low-dose conditions required to avoid beam damage. Limited-angle acquisition introduces missing-wedge artefacts such as elongation and anisotropic resolution, while noisy low-dose data further degrade reconstruction quality and quantitative reliability. Here, we introduce an unsupervised deep learning framework based on Deep Image Prior with total variation regularization (DIP-TV) for limited-angle STEM-EDX tomography. We extend it to a multi-channel formulation (DIPm-TV) that jointly reconstructs multiple elemental maps by exploiting spatial correlations. Using a synthetic 3-channel phantom, we show that the method compensates for severe missing-wedge artefacts corresponding to approximately $100^\circ$ of missing angular range under moderate noise, outperforming simultaneous iterative reconstruction technique and compressed sensing approaches. We apply the method to 3D chemical analysis of Ge-Sb-Te (GST) memory devices in virgin (as-fabricated) and SET (crystalline) operational states. Samples were prepared as cross-sectional focused ion beam lamellae and acquired under a limited-angle tilt range from $-40^\circ$ to $+40^\circ$ with $5^\circ$ steps and a dose of $2.0\times10^5$ $e^-/Ang^2$. The multi-channel approach enables voxel-by-voxel elemental reconstruction using only EDX signals without external structural priors such as high-angle annular dark-field imaging. The reconstructed volumes show near-isotropic spatial resolution and reveal compositional heterogeneities associated with device operation. This approach enables 3D chemical characterization in experimentally accessible sample geometries where conventional methods fail due to severe angular limitations.
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All authors Daniel del Pozo Bueno, Serge Brosset, Theo Monniez, Gabriele Navarro, Philippe Ciuciu, Zineb Saghi

Materials Science

Probing Spin Configurations in Exchange-Coupled Magnetic Bilayers with Orthogonal Anisotropies via Anomalous Hall and Nernst Effects

Sebin Jung, Hiroki Koizumi, Hiroaki Sukegawa et al. (+1 more)

When two ferromagnetic thin films with different magnetic easy axes are coupled via the exchange interaction, the magnetization process becomes nontrivial. In this paper, we demonstrate that three-dimensional magnetization information in such a bilayer system can be accessed electrically by combining measurements of the anomalous Hall effect (AHE) and anomalous Nernst effect (ANE). Specifically, we investigate a CoFe$_2$O$_4$(001)/Fe bilayer, where the insulating nature of CoFe$_2$O$_4$ ensures that these transport measurements selectively probe only the conductive Fe layer. By combining the AHE and ANE results and comparing them with a simple micromagnetic simulation, we probe the magnetic configuration of antiferromagnetically coupled Fe layer and suggest the emergence of a twisted magnetic structure near the interface.
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All authors Sebin Jung, Hiroki Koizumi, Hiroaki Sukegawa, Hideto Yanagihara

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

SANS and magnetometry study of the magnetic phase diagram of the B20 helimagnet FeRhSi

E. V. Altynbaev, A. V. Guseva, D. O. Skanchenko et al. (+5 more)

This manuscript reports the first direct neutron-scattering evidence for long-period helimagnetism in the newly identified 4d-substituted B20 compound Fe0.5Rh0.5Si. By combining SANS with low-field magnetometry, we establish the magnetic modulation, construct a field-temperature phase diagram, and identify a candidate A-phase region supported by an independent structural signature. The work is important beyond this single compound because it expands the family of chiral B20 helimagnets into Rh-substituted materials, where spin-orbit coupling, disorder, and Dzyaloshinskii-Moriya interactions can be tuned. It will interest researchers in chiral magnetism, topological spin textures, magnetic neutron scattering, and quantum materials, and provides a foundation for future studies of emergent magnetic phases and topology-driven phenomena in chemically tuned chiral magnets.
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All authors E. V. Altynbaev, A. V. Guseva, D. O. Skanchenko, V. N. Krasnorussky, A. V. Bokov, D. A. Salamatin, V. A. Sidorov, A. V. Tsvyashchenko

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

Electrical Spectroscopy of Intervalley Relaxation in WSe$_2$ Transistors

Katsunori Wakabayashi

We show that the transconductance of multilayer WSe$_2$ field-effect transistors serves as a direct electrical spectrometer of the intervalley relaxation time $\tau_{\rm iv}$, previously accessible only by ultrafast optical techniques. Extending an equilibrium valley-thermodynamics framework with a single relaxation equation for the $\Gamma$-valley carrier fraction $f_\Gamma(t)$, we predict three signatures: (i)~a Lorentzian transconductance $g_m(\omega)=g_{m,0}+g_{m,v}^0/(1+i\omega\tau_{\rm iv})$, whose imaginary part peaks at $\omega_c=\tau_{\rm iv}^{-1}$ with opposite signs for bilayer and trilayer; (ii)~a two-stage current transient after a gate step, exhibiting bilayer overshoot or trilayer undershoot; and (iii)~sweep-rate-proportional hysteresis whose gate-voltage profile and the layer-dependent transconductance sign reversal distinguish valley from trap-induced dynamics. All three signatures provide quantitative electrical access to $\tau_{\rm iv}$ with standard radio-frequency (rf) and direct-current (dc) instrumentation.
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Materials Science · Cross-listed from cond-mat.str-el

Improved selector behavior in ultrathin chromium-doped V$_2$O$_3$ films

Johannes Mohr, Tyler Hennen, Yudi Wang et al. (+6 more)

Devices based on the negative differential resistance effect in chromium doped V$_2$O$_3$ are considered to be promising as selector elements for use in emerging memory technologies, as well as for neuromorphic applications. It is shown by electrical measurements, that the switching effect is maintained for very thin films down to 5 nm, and even improved properties such as a low leakage current and an abrupt transition are observed. For these thicknesses, the behavior of crystalline and amorphous films becomes very similar; most strikingly, a forming step is required in both. Transmission electron microscopy reveals this to be likely due to a thin amorphous layer that forms at the interface to the TiN electrode. Elemental mapping further shows a complex distribution of the chromium dopants, as well as a diffusion of Ti into the layer from the electrode, which might be responsible for the improved properties.
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All authors Johannes Mohr, Tyler Hennen, Yudi Wang, Xiaoyu Xu, Loc Vinh, Dirk J. Wouters, Rainer Waser, Joyeeta Nag, Daniel Bedau

Materials Science

Neural electron backscatter diffraction

I-Tzu Huang and Marat I. Latypov

At the mesoscale, the state of a material is described by continuous fields. In polycrystals, crystallographic orientation and defect content vary continuously within grains, and grain boundaries trace continuous curves. Like other spatially resolved characterization methods, electron backscatter diffraction (EBSD) records this continuum on a discrete grid. Every subsequent analysis inherits the grid, whether it is classical Hough indexing or pattern-based machine learning. We introduce neural EBSD, which treats a scan as a continuous and differentiable field of Kikuchi diffraction intensity over specimen and detector coordinates. Two formulations are explored: a joint network over all four coordinates, and a factorized representation that combines continuous specimen-domain coefficient fields with learned detector-domain basis patterns. The factorized formulation exhibits higher accuracy: for recrystallized and additively manufactured Ni-base superalloys, it reconstructs 900,000 Kikuchi patterns per map with mean errors below 1% of the maximum intensity, while reducing data storage nearly 750-fold relative to the raw patterns. Since the learned field is continuous, patterns can be queried at any specimen position. Trained only on a quarter of the scan points, the model recovers withheld patterns whose indexed orientations fall within 4 deg. of reference at 97% of positions in the recrystallized alloy. Analytical spatial derivatives of the differentiable representation provide a diffraction gradient that localizes grain boundaries continuously, free of indexing, disorientation thresholds, and staircase artifacts. The gradient field also exposes intragranular heterogeneity, including dislocation-cell substructure in the as-built alloy.
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Materials Science · Cross-listed from cond-mat.supr-con

Vortex pinning of Ba$_{0.62}$K$_{0.38}$BiO$_3$ investigated by magneto-optical Kerr-effect and magnetization measurements

Soichiro Yamane, Sota Nakamura, Atsutoshi Ikeda et al. (+8 more)

Vortex pinning plays a crucial role in determining properties of type-II superconductors. For example, it governs the irreversible magnetic response as well as dissipation caused by vortex motion. Here, we study vortex pinning in the three-dimensional oxide superconductor Ba1-xKxBiO3 using ultra-high-resolution magneto-optical Kerr effect (MOKE) and detailed magnetization measurements. We find that the zero-field MOKE signal in the superconducting state exhibits a pronounced magnetic-history dependence. This behavior closely resembles the remanent magnetization caused by trapped vortices. Furthermore, we demonstrate that the observed evolution of the MOKE signals is well described by Bean's critical-state model for trapped vortices. Our results establish MOKE as a viable optical and mesoscopic probe of vortex pinning in type-II superconductors, providing a new complementary approach to investigate mixed-state phenomena. We also find that the training-field dependence of the MOKE is linear near zero training field, without any anomalies indicative of spontaneous time-reversal-symmetry breaking in an unconventional superconducting state. Our study defines a clear protocol to distinguish vortex-induced MOKE responses from those associated with a time-reversal-symmetry broken superconducting order parameter.
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All authors Soichiro Yamane, Sota Nakamura, Atsutoshi Ikeda, Dayu Zhai, Siddarth Gorregattu, Xing He, Sudarshan Sharma, Yipeng Cai, Yasutomo J. Uemura, Martin Greven, Shingo Yonezawa

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

Filamentary Transport and Thermoelectric Effects in Mushroom Phase Change Memory Cells

Md Samzid Bin Hafiz, Helena Silva and Ali Gokirmak

We performed a 2D finite-element electrothermal computational study of thermoelectric effects and filamentary electronic transport in Ge$_2$Sb$_2$Te$_5$ mushroom phase change memory cells during Reset and Set operations, accounting for spatial activation energy variations in amorphous Ge$_2$Sb$_2$Te$_5$ and phase-change dynamics. Reset operations with current going from the top electrode to the narrow 4 nm bottom electrode require $\sim$3x less energy and power, and $\sim$2x lower current to achieve the same Reset resistance, compared to the opposite polarity, due to thermoelectric effects. Filamentary conduction, electrical breakdown, thermal runaway, and local crystallization of amorphous Ge$_2$Sb$_2$Te$_5$ depend on current polarity and thermal boundary conditions, and determine the location, shape, and volume of the programming region, which may be significantly smaller than the semi-cylindrical mushroom region. The programming volume does not scale with contact dimensions larger than 10 nm. Larger contact areas introduce increased device-to-device and cycle-to-cycle variability due to filamentary conduction but are expected to lead to higher reliability and endurance.
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Monday 8 June

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

The Sustainability Paradox of Biodegradable Packaging: A Life Cycle Perspective on Chitosan-Based Food Packaging

Maria Cosic, Milena Cosic, Amy Kim et al. (+9 more)

Chitosan-based nanomaterials are being increasingly explored as sustainable alternatives to petroleum-derived food packaging, yet their environmental performance across the full life cycle remains insufficiently understood. This review critically evaluates these systems from a life cycle perspective and examines how material origin, processing pathways, functional performance, and end-of-life behavior collectively influence sustainability outcomes. Beginning with chitin extraction from crustacean waste, key processing steps, including demineralization, deproteinization, and nanoparticle synthesis, are assessed in terms of chemical intensity, energy demand, and associated emissions. Manufacturing routes, including solvent-based and green synthesis approaches, are compared with those of conventional plastics to identify relative environmental burdens. The use phase is analyzed with respect to antimicrobial functionality, shelf life extension, and potential reductions in food waste. End-of-life pathways, including biodegradation and composting, are evaluated alongside uncertainties related to degradation behavior and nanoparticle fate. By synthesizing these stagewise interactions, this review highlights critical trade-offs that are often overlooked in sustainability narratives and examines whether chitosan-based nanomaterials provide net environmental benefits in food packaging applications.
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All authors Maria Cosic, Milena Cosic, Amy Kim, Siddhartha Pahari, Grace Wu, Rayna Zhou, Trisha Daftari, Shaily Gupta, Reyna Michelle Suneel, Srinivasan Latha, Rashi Sharma, Utkarsh Chadha

Materials Science

Robust AI-Driven Discovery of Electronic Metal Phosphide Semiconductors

Benhao Zhu, Muhammad Faizan, Zewei Li et al. (+4 more)

Metal phosphides have diverse bonding motifs and coordination environments, making them promising for optoelectronic and thermoelectric applications, but their chemical space remains underexplored. Here we report an AI-driven high-throughput discovery workflow that combines generative materials design, machine-learning interatomic potentials, and targeted density functional theory (DFT) calculations. ICSD-derived Wyckoff-site substitution and MatterGen-based conditional structure generation are used to expand the candidate space beyond existing phosphide databases. A domain-finetuned DPA3 machine-learning potential then enables efficient prescreening of thermodynamic and dynamical stability before DFT validation. This workflow identifies 3,574 previously unreported stable phosphide structures, including 196 semiconductors with HSE06 band gaps of 0-3.0 eV. By screening these new semiconductors together with experimentally known phosphide semiconductors, we identify 30 promising optoelectronic candidates and 26 promising thermoelectric candidates, including seven newly discovered optoelectronic materials and eight newly discovered thermoelectric materials. These results provide a candidate pool for experimental synthesis and show that combining generative AI with machine-learning interatomic potentials can accelerate the discovery of functional semiconductor materials.
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All authors Benhao Zhu, Muhammad Faizan, Zewei Li, Wenshuo Li, Feifei Ren, Jiahao Xie, Lijun Zhang

Materials Science

Finite-temperature Fe K-edge X-ray absorption simulations reveal local structural dynamics of an iron(II) photosensitizer in solution and the crystalline phase

Patrick Müller, Lorena Fritsch, Matthias Bauer et al. (+1 more)

Interpreting metal K-edge spectra of flexible photosensitizers requires a structural model that separates electronic signatures from thermal motion, solvent disorder, and crystal-packing effects. We combine Fe K-edge X-ray absorption measurements with second-generation Car–Parrinello ab initio molecular dynamics and all-electron Gaussian and augmented-plane-wave simulations for an iron(II) N-heterocyclic carbene photosensitizer in acetonitrile solution and in the crystalline phase. Ensemble-averaged spectra reproduce the main near-edge features in both environments and preserve the experimentally observed similarity of the first Fe coordination shell upon dissolution. Comparison with radial distributions extracted from extended fine-structure measurements validates the Fe–N and Fe–C coordination shells sampled by the trajectories, while element-resolved pair distributions explain why higher-shell experimental contrast is rapidly lost. The same dynamical ensembles reveal a broad out-of-plane distribution of the terpyridine nitrogen atom and a nearly octahedral distribution of the Fe-centered coordination planes. The results show that finite-temperature X-ray absorption simulations can provide a compact structural-dynamics picture of molecular transition metal photosensitizers by linking local spectra, solvent-phase ligand motion, and medium-range structural disorder within one trajectory-based description.
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All authors Patrick Müller, Lorena Fritsch, Matthias Bauer, Thomas D. Kühne

Materials Science

Graphlet Histogram Representation Database of Inorganic Crystals

Aaditya Panigrahi, Yanjun Liu, Omri Lesser et al. (+2 more)

Machine learning models for materials property prediction increasingly rely on representations learned end-to-end from large density-functional-theory databases, limiting their applicability when only scarce experimental data are available. Domain-knowledge-driven representations precomputed from crystal structures alone offer a data-efficient, interpretable alternative, but existing approaches capture at most composition or bonding connectivity and discard local structural geometry. Here, we present Graphlet-MP, a database of graphlet histogram representations for 149,082 inorganic crystals from the Materials Project (MP). Seventy-nine distributions describe each material over three hierarchical graphlet orders: atomic sites, bonded pairs, and bond-angle triplets, extracted via screened Voronoi tessellation from the crystallographic information file. We provide a complete technical specification of the representation, an Earth Mover's Distance metric for comparing materials in this space, and the full precomputed database. An accompanying open-source codebase enables users to generate graphlet histograms for arbitrary crystal structures, including experimentally determined ones, and to extend the database to new materials or target properties.
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All authors Aaditya Panigrahi, Yanjun Liu, Omri Lesser, Krishnanand Mallayya, Eun-Ah Kim

Materials Science

Pressure-Driven Structural Phase Competition and Functional Response in Layered LiInP2S6

Xiaochi Xie, Pegah Mohammadi and Sobhit Singh

Understanding how hydrostatic pressure modifies interlayer interactions and competing ionic configurations is essential for controlling the emergent functional properties of layered quantum materials. Here, using first-principles density-functional theory calculations, we investigate the pressure-dependent structural, mechanical, electronic, and optical properties of three competing LiInP2S6 polymorphs: the monoclinic C2/c phase and the trigonal P-31c phase in both in-layer and in-gap configurations. Our results reveal a pressure-induced structural phase transition from the monoclinic ground-state C2/c phase to a trigonal P-31c in-layer phase at ~0.38 GPa, driven by enhanced interlayer coupling and anisotropic lattice compression. In contrast, the trigonal P-31c in-gap phase remains energetically unfavorable due to its stronger interlayer ionic interactions and reduced compressibility. All phases remain mechanically stable under compression (0-26 GPa) and exhibit enhanced mechanical rigidity, elastic wave velocities, and Debye temperatures with increasing pressure. Remarkably, the electronic and optical properties within each phase remain highly robust under pressure, with only moderate changes in the band gap and optical absorption edge (UV-Visible range) under pressure; however, substantial modifications emerge across the pressure-induced structural phase transition. These findings establish LiInP2S6 as a pressure sensitive ionic-vdW material in which subtle changes in interlayer interactions govern structural stability and functional properties.
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Materials Science

Synthesis and Characterization of Atomically-Sharp Superconductor-Dielectric Interface

Nathan Sitaraman, Zhaslan Baraissov, Alexis Grassl et al. (+4 more)

Modification of superconductor-dielectric interfaces is known to strongly impact coherence times of superconducting quantum devices. This relationship is thought to arise from differences in the concentration of "two-level system" defects in the disordered dielectrics and superconductor-dielectric interfaces; these defects couple to electromagnetic modes in the device and cause dissipation. Zirconium oxide barrier layers on niobium have emerged as a promising pathway to low-loss interfaces in recent years, evidently due to the crystalline nature of these layers in comparison to the amorphous niobium native oxide. We explain the unique ability of zirconium oxide to form a crystalline layer, to maintain a sharp interface with metallic niobium, and to prevent niobium oxide re-growth in terms of the chemical properties of ZrO$_2$ and the Nb-Zr-O ternary system. We demonstrate a new method to grow air-stable zirconium oxide layers on niobium with a higher level of crystallinity and a sharper oxide-metal interface than previously shown, and provide the first comprehensive microscopic analysis of ZrO$_2$ capping layer properties. These developments pave the way toward vital performance advances in superconducting quantum devices.
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All authors Nathan Sitaraman, Zhaslan Baraissov, Alexis Grassl, Hongbin Yang, Daniel Tong, David Muller, Matthias Liepe

Materials Science

Predicting Defect States: A Quick Screening Protocol for Substitutional Point Defect Engineering

Hyosik Kang and Lukas Muechler

Point defects in crystalline materials play a central role in determining electronic, optical, and magnetic properties. However, systematic exploration of defect configurations remains computationally expensive because large supercell calculations are required to approximate isolated defects under periodic boundary conditions. We present a unit-cell-based tight-binding protocol that enables rapid pre-screening of substitutional defects. The protocol extracts Wannier tight-binding Hamiltonians from small, fully relaxed unit cells of the host and defect-like systems, replicates the host Hamiltonian to construct a supercell model, and introduces the defect by modifying only the on-site energies at the substitution site while leaving the hopping parameters unchanged. We validate the protocol across three diverse systems: isostructural substitutional defects in transition-metal dichalcogenides (M$_\mathrm{Mo}$ MoS$_2$, M = Ce, Zr, Nb, Tc, and Ru), symmetry-breaking carbon substitutions in hexagonal boron nitride (C$_\mathrm{B}$C$_\mathrm{N}$ h-BN), and nitrogen-vacancy (NV$^-$) centers in diamond. These case studies span two-dimensional and three-dimensional hosts, simple substitutions, and substitution-vacancy complexes. In all cases, the protocol successfully captures the number of in-gap states, their degeneracies, and their shallow or deep character relative to host band edges, despite some quantitative deviations in absolute energy positions. We further identify limitations for vacancies of highly electronegative atoms and for charge-state or spin-polarization effects, both of which involve self-consistent charge redistribution not captured by the protocol.
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Materials Science

Dominant in-plane anomalous Hall effect in a monoclinic room-temperature ferromagnet

Guoxin Zheng, Arjyama Bordoloi, Mingjun Fan et al. (+6 more)

Ferromagnetic metals are characterized by enhanced dissipationless transverse transport responses via the anomalous Hall effect, offering a route towards magnetic sensing and spintronic readout functionalities. In most ferromagnets, the anomalous Hall current is constrained to lie in the plane perpendicular to the magnetization (or applied magnetic field). Recently, it has been recognized that selected symmetries can also permit a Hall response in a traditionally forbidden configuration, where the Hall current lies in the same plane as the magnetization, realizing an in-plane anomalous Hall effect. Reported realizations of this effect, however, are typically much weaker than the conventional Hall response in the same material. Here, through engineering specific crystallographic mirror symmetry-breaking, we realize a strongly enhanced in-plane anomalous Hall response in monoclinic Cr3Te4 with room-temperature ferromagnetism. Remarkably, the in-plane anomalous Hall signal exceeds the out-of-plane response by a factor of five, with which we demonstrate a unique in-plane field and current sensing functionality. Combined with density functional theory calculations, our results establish low-crystalline-symmetry ferromagnets with near-Fermi-level Weyl points as a practical platform for symmetry-engineered Hall responses, and point to a route towards room-temperature, geometry-flexible sensing devices.
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All authors Guoxin Zheng, Arjyama Bordoloi, Mingjun Fan, Shunsuke Kitou, Hiraku Saito, Taro Nakajima, Sobhit Singh, Takashi Kurumaji, Linda Ye

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

Fabry-Perot Interference, g-factor Anisotropy, and Gate-Tunable Quantum dot in Chiral Tellurium Nanowires

Suresh Ghimire, Mohammad Hafijur Rahaman, Nathan Tanner Sawyers et al. (+8 more)

Chiral materials with strong spin-orbit coupling offer a unique platform for exploring the interplay between topology, chirality, and quantum transport yet the quantum coherent regime in elemental tellurium nanostructures remains largely unexplored. Here we demonstrate phase-coherent quasi-ballistic transport, anisotropic Zeeman spectroscopy, and gate-tunable quantum dot formation in hydrothermally grown t-tellurium nanowires. Single nanowire field-effect transistors exhibit p-type transport with hole mobilities rising from approx. 80 cm2 V-1 s-1 at 210 K to approx. 190 cm2 V-1 s-1 at 1 K, consistent with a crossover from phonon-limited to Coulomb scattering dominated regimes near 50 K. Notably, devices segregate into two distinct regimes based on their room temperature two-terminal resistance : low-resistance devices (< 30 kOhm) exhibit Fabry-Perot interference, whereas high resistance devices (> 30 kOhm) display Coulomb-blockade behavior revealing a two-terminal resistance-driven transition between quasi-ballistic and strongly localized transport regimes. Zeeman spectroscopy in in-plane and out-of-plane magnetic fields yields highly anisotropic Lande g-factors (an in-plane gparallel = 1.18 and an out-of-plane gperp = 18.41) and directly resolves a spin-orbit energy gap DeltaSO = 0.864 meV from an avoided crossing. These results establish chiral tellurium nanowires as a versatile platform for gate-defined spin qubits exploiting large, tunable g-factors and for hybrid tellurium-superconductor architectures targeting Majorana zero modes in an elemental vdW system.
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All authors Suresh Ghimire, Mohammad Hafijur Rahaman, Nathan Tanner Sawyers, Madan Mohan Bhandari, Gokul Acharya, Syed Zulfiqar Hussain Shah, Iris Nandhakumar, Pawan Kumar, Zainul Aabdin Khan, Hugh O. H. Churchill, Dharmraj Kotekar-Patil

Materials Science

Anatomy of fast current-induced skyrmion motion in synthetic antiferromagnets

W. C. Chen, H. X. Yang and X. F. Zhang

The high mobility of current-driven skyrmions in synthetic antiferromagnets (SAFs) is widely explained by the macroscopic suppression of the skyrmion Hall effect through gyrotropic force compensation. This established view, however, overlooks a concurrent and significant reduction in the Gilbert damping parameter {\alpha}, a key factor in the Thiele equation governing skyrmion velocity. Here, we show that this damping attenuation originates from a reconfigured magnon-electron scattering landscape. Using a microscopic s-d model, we demonstrate that the strong antiferromagnetic interlayer Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange coupling in SAFs increases the magnonic gap of skyrmion collective modes, thereby suppressing the thermal magnon population and, consequently, the magnon-electron scattering rate that dominates damping in metallic ferromagnets. Our work establishes a dual-mechanism framework to fully explain the superior kinetics of SAF skyrmions: the macroscopic topological effect rectifies the motion direction, while the microscopic dissipation mechanism reduces the drag. This synergy enables high-speed and efficient motion, providing a fundamental elucidation of the enhanced mobility reported in recent studies such as the work by Pham et al. [Science 384, 307-312 (2024)].
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Materials Science

Bi-S network origin of cation-disorder stability and dispersive band edges in AgBiS2

Han-Pu Liang, Songyuan Geng, Heng Kang et al. (+9 more)

Cation-disordered AgBiS2 is a promising lead-free optoelectronic material, but both its ordered structure and the microscopic origin of its favorable electronic properties remain debated. Theory has proposed a mixed-coordination tendency with tetrahedral AgS4 and octahedral BiS6 units, whereas experiments mainly report octahedrally coordinated ordered and cation-disordered phases, together with local cation off-centering. Here, we combine a machine-learning interatomic potential with a deep-learning Hamiltonian to resolve the coupled structural and electronic evolution of AgBiS2 at large length scales. We identify the three-dimensional Bi-S network as the central structural motif governing both disorder stability and band-edge electronic states. At weak disorder, Ag/Bi exchange competes with the off-centering tendency of the Ag sublattice, producing strongly distorted local environments and convoluted diffraction signatures that hinder the identification of the ordered phase. With increasing disorder, BiS6-like units connect into a continuous Bi-S network, which stabilizes the rocksalt-like disordered phase. Despite strong cation disorder, AgBiS2 retains clear semiconductor-like band dispersion and develops a direct band gap. The connected Bi:p-S:p states supported by the Bi-S network preserve a dispersive conduction-band edge and a small electron effective mass. In contrast, mobile Ag disrupts the long-range periodicity of Ag-S bonding, leading to strongly localized valence states. These results clarify the structural controversy in ordered AgBiS2 and establish a unified physical picture of disorder stability and optoelectronic response in nonisovalent semiconductor alloys.
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All authors Han-Pu Liang, Songyuan Geng, Heng Kang, Chen Qiu, Xiao-Ping Yao, Qing'an Li, Bozhao Zhang, Lechuan Sun, Yuxuan Chen, Shan Zhang, Su-Huai Wei, Peng-Fei Guan

Materials Science

Crystallography of periodic nanotextures in a strained Mott insulator

Benjamin Z. Gregory, Yorick A. Birkhölzer, Noah Schnitzer et al. (+9 more)

Here we investigate stripes of alternating structural phases spontaneously forming in epitaxially strained $Ca_2RuO_4$ thin films below the metal-insulator transition. Using large-volume X-ray reciprocal-space mapping, we show that satellite-pattern intensities across 24 symmetry-inequivalent Bragg reflections collapse onto a single parameter-free curve. The collapse identifies a coherent martensitic laminate of few-nm-wide domains separated by ${012}$ interfaces, with displacements along $\left\langle01\bar{2}\right\rangle$. Satellite-extinction analysis demonstrates that both coexisting phases retain the bulk orthorhombic space group despite the pseudocubic $LaAlO_3$ substrate, biaxial epitaxial strain, and intrinsic strain at the interfaces. Classical invariant-plane-strain crystallography thus governs the nanoscale domain geometry of a Mott insulator with intertwined magnetic, electronic, and lattice order.
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All authors Benjamin Z. Gregory, Yorick A. Birkhölzer, Noah Schnitzer, Ziming Shao, Jeff Hodgson, Suchismita Sarker, Jacob P. Ruff, Berit H. Goodge, David A. Muller, Kyle M. Shen, Darrell G. Schlom, Andrej Singer

Materials Science

Ab initio parametrization of distributed polarizable force fields

Felix Post, Jean-Philip Filling, Toulik Maitra et al. (+3 more)

Polarizable force fields offer superior transferability and accuracy compared to classical force fields, enabling access to electronic response properties such as refractive index and electronic density of states. Here, we demonstrate two key improvements that significantly enhance their accuracy: (1) assigning atomic polarizability to individual atoms rather than atom types, and (2) employing atomic polarizability tensors instead of scalar values. These modifications extend the applicability of polarizable force fields to cations, anions, and excited states, while also providing more accurate descriptions of neutral molecules. We propose a first-principles-based parameterization procedure for atomic polarizability tensors and scalars, validated on a set of small organic molecules with conjugated building blocks. To overcome the computational cost of ab initio calculations, we train a message-passing graph neural network to predict polarizability parameters, enabling efficient and scalable parameterization. Crucially, this approach imposes no additional computational cost during simulations and provides a clear diagnostic criterion for identifying cases where polarizable force field models fail to accurately describe molecular polarizability.
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All authors Felix Post, Jean-Philip Filling, Toulik Maitra, Falk May, Michael Wand, Denis Andrienko

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

Evolution of terahertz third harmonic response across rare-earth nickelate phase-diagram

Gulloo Lal Prajapati, Igor Ilyakov, Alexey Ponomaryov et al. (+8 more)

High harmonic generation (HHG) is a sensitive probe for investigating electronic structures and dynamics of materials and a source for attosecond pulses. In particular, HHG with terahertz (THz) light can enable probing of nonlinear responses in correlated materials arising from low-energy many-body interactions. However, THz HHG studies have so far largely focused on topological materials and superconductors, leaving out other potential material systems which could also become efficient THz HHG sources. Here, we report THz third harmonic generation (THG) in rare-earth nickelates – a prototype material for exploring the Mott insulator-metal transition and related technological applications. We find that the THG amplitude is highly sensitive to the strengths of electronic and magnetic phases of nickelates. In films with sharp phase-transitions, the local maximum and minimum in the temperature-dependent THG amplitude coincide with insulator-metal and magnetic transition temperatures, respectively. While in films with weaker transitions, these features shift toward lower temperatures or even monotonous THG enhancement is observed down to low temperatures. We developed a generalized theory for THz harmonic generation in negative charge-transfer insulators and outlined strategies to enhance the THz nonlinearities further. Our study broadens the scope of THz HHG studies and related applications to strongly correlated materials.
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All authors Gulloo Lal Prajapati, Igor Ilyakov, Alexey Ponomaryov, Atiqa Arshad, Sanjeev Kumar, Jayaprakash Sahoo, Dhanvir Singh Rana, Abdelrahman Azab, Friedemann Queisser, Ralf Schützhold, Jan-Christoph Deinert

Materials Science

Lattice genome: representation and analysis of heterogeneous crystalline microstructures

Jiayang Wang, Mathieu Calvat, J.C. Stinville et al. (+1 more)

Inspired by the concept of a generalized materials genome, we introduce the notions of lattice gene and lattice genome for crystalline materials. A lattice gene is a compact representation of the local crystalline structure obtained by encoding the Kikuchi diffraction patterns with a variational autoencoder. We show that this representation satisfies key criteria for a materials gene: compactness, experimental accessibility, existence of a distance metric reflecting structural similarity, and sufficient information content for reconstructing the original diffraction patterns. The lattice genome is the spatially resolved collection of lattice genes across a representative area mapped by electron backscatter diffraction (EBSD), which captures mesoscale heterogeneity that ultimately controls properties. We demonstrate three applications of the lattice genome: (i) latent component maps that visualize grain-scale and intra-grain heterogeneities, (ii) domain segmentation based on distance and angle metrics in the latent space, and (iii) kernel and domain latent vector spreads that quantify intragranular heterogeneity as high-dimensional analogs of kernel average misorientation and grain orientation spread. All three tools are validated on microstructures of additively manufactured and wrought Ni-base superalloys in as-built and recrystallized conditions.
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All authors Jiayang Wang, Mathieu Calvat, J.C. Stinville, Marat I. Latypov

Materials Science

k-Means Clustering in Fingerprint-Based Configuration Selection for Fitting Interatomic Potentials

Miroslav Lebeda, Jan Drahokoupil, Ludvík Löbel et al. (+1 more)

In this study, we present a method for selecting an arbitrary number of distinct configurations from a larger data set by applying k-means clustering to atomistic configuration fingerprints based on the CrystalNN model and radial distribution function (RDF). This approach improves the accuracy of fitting classical molecular dynamics interatomic potentials to density functional theory (DFT) data for both energies and forces while requiring fewer configurations than random selection. We demonstrate this improvement by fitting an embedded-atom method (EAM) potential for titanium, using various configurational sizes from an initial set of 1800 configurations. The k-means clustering consistently achieves better precision and lower standard deviations for a smaller number of configurations than random selection. The results also suggest that only about 30 configurations are sufficient to obtain an EAM model that describes well the full set of 1800 configurations in terms of energies and forces. Additionally, t-distributed stochastic neighbor embedding (t-SNE) method was used to reduce the configuration fingerprints into 2D space, and it revealed an overlap between two configuration subsets with and without Ti vacancy, indicating similar atomic environments. This similarity is captured by k-means clustering but not by random selection. Furthermore, when the overlapping configurations with vacancies were excluded from the k-means algorithm and used only as a test set, their energy and force predictions showed similar precision to those when they were included. This indicates that the overlapping configurations in the 2D t-SNE space indeed imply potential information redundancy among the atomistic configurations.
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All authors Miroslav Lebeda, Jan Drahokoupil, Ludvík Löbel, Petr Vlčák