Materials Science · Cross-listed from cond-mat.mes-hall
Deep-UV bleaching of charge disorder in encapsulated graphene
Daniil Domaretskiy, Ned Hayward, Van Huy Nguyen et al. (+11 more)
Disorder masks much of the rich physics in two-dimensional electronic systems, with charged
impurities often the limiting factor. In
graphene, progress in reducing disorder has largely stagnated since boron nitride encapsulation was introduced a decade ago. Here we show that a brief deep-UV exposure enhances the electronic quality of encapsulated
graphene - typically by two orders of magnitude - by neutralizing charged
impurities within boron nitride. Following illumination, standard
graphene devices exhibit numerous evendenominator fractional
quantum Hall states, including non-Abelian candidates, and frequently reveal hidden superlattice minibands. Even macroscopically inhomogeneous devices, seemingly unusable for transport studies, recover after deep-UV illumination and display Landau quantization in millitesla fields. This finding provides a straightforward route to exceptional-quality
graphene, enabling further exploration of interaction-driven, topological and other
quantum phenomena.
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All authors Daniil Domaretskiy, Ned Hayward, Van Huy Nguyen, Simone Benaglia, Kornelia Indykiewicz, Hadrien Vignaud, Jing Zhang, Kenji Watanabe, Takashi Taniguchi, V. I. Fal'ko, Laura Fumagalli, L. A. Ponomarenko, I. V. Grigorieva, A. K. Geim
Materials Science · Cross-listed from physics.chem-ph
Gap edge eigenpairs from density matrix purification using moments of the Dirac distribution
Lionel Alexandre Truflandier
In this work, we propose a simple method to resolve the eigenstates located at the band gap edges of an electronic eigenspectrum using only the quasi-purified one-particle density
matrix as input. The theoretical framework relies on the decomposition of the occupation number variance into a particle and a hole moment. These moments, when purified using power narrowing iterations, allow us to isolate the highest occupied and lowest unoccupied single-state projectors, \colp{giving ready access} to the corresponding eigenpairs. We demonstrate that when degeneracy is encountered, power narrowing remains able to deliver relevant mixed states. From a
benchmark of selected molecules, we show that the method is robust and efficient since it requires from four to sixteen
matrix-
matrix multiplications in the worst case. The possibility of reducing the computational cost using the Lanczos subspace approach is discussed. The
algorithm simplicity of power narrowing makes it very easy to implement in electronic structure codes or libraries already featuring
Fermi operator expansion or density
matrix purification.
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Materials Science · Cross-listed from cond-mat.mes-hall
Angular anisotropy landscape of vortex ensembles in polarized small-angle neutron scattering
Michael P. Adams, Elizabeth M. Jefremovas and Andreas Michels
We present a
symmetry-resolved classification of two-dimensional
spin-flip small-angle
neutron scattering (SANS) patterns arising from dilute ensembles of spherical nanoparticles hosting
magnetic vortex states. Based on a linear
vortex ansatz with an axially symmetric distribution of
vortex axes and the corresponding analytical expression for the orientationally averaged
spin-flip SANS cross section, we show that the angular scattering patterns organize into four distinct
symmetry regimes: a four-fold anisotropy corresponding to coherent field-aligned magnetization, vertical and horizontal two-fold anisotropies associated with aligned and isotropically distributed
vortex ensembles, and an isotropic ring-like condition separating the two two-fold regimes. The corresponding
symmetry boundaries are obtained analytically and define a compact
symmetry landscape in the parameter space of
vortex amplitude and
vortex-axis distribution width. Comparison with a nonlinear
vortex profile shows that these
symmetry regions are robust with respect to the detailed radial structure of the
vortex core. The angular anisotropies are therefore governed primarily by rotational
symmetry and by the statistical distribution of
vortex axes, providing a compact and model-transparent classification framework of experimental polarized SANS data.
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Materials Science · Cross-listed from physics.chem-ph
Short-lived memory in multidimensional spectra encodes full signal evolution
Thomas Sayer, Ethan H. Fink, Zachary R. Wiethorn et al. (+9 more)
Ultrafast multidimensional spectroscopies are powerful tools that can access charge and energy flow in complex materials, shifting chemical kinetics, and even many-body interactions in correlated matter. However, current implementations typically involve complex apparatuses and long averaging times. As a result, these methods have been limited to detailed mechanistic investigations of a few samples, precluding the broad characterization of molecular systems and/or the optimization of material ones. For example, converging the statistical noise in 2D spectra becomes exponentially expensive with increasing waiting times, and extended
laser exposure heightens the probability of sample degradation. We address this fundamental challenge by developing a new technique, the spectral generalized master equation (GME), that enables one to employ short-waiting time 2D spectra to determine the full
evolution of 2D spectra over arbitrary waiting times with high temporal resolution. In addition to reducing the cost of experiments by multiple orders of magnitude, our approach accurately removes statistical noise, reducing the need for time averaging, while circumventing the increasing convergence costs with longer waiting times. We provide a rigorous theoretical footing for the spectral GME and demonstrate its applicability on theoretically generated and experimentally measured 2D electronic and 2D infrared spectra. We anticipate that this advance has the potential to enable the investigation of systems that are too delicate for study with current multidimensional spectroscopies and accelerate the progress of 2D spectroscopy-based microscopies that can offer highly resolved excitation dynamics with spatial resolution over heterogeneous environments.
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All authors Thomas Sayer, Ethan H. Fink, Zachary R. Wiethorn, Devin R. Williams, Anthony J. Dominic III, Luke Guerrieri, Yi Ji, Veronica Policht, Jennifer Ogilvie, Gabriela Schlau-Cohen, Amber Krummel, Andrés Montoya-Castillo
Materials Science · Cross-listed from cs.LG
AMShortcut: An Inference- and Training-Efficient Inverse Design Model for Amorphous Materials
Yan Lin, Jonas A. Finkler, Tao Du et al. (+2 more)
Amorphous materials are solids that lack long-range atomic order but possess complex short- and medium-range order. Unlike crystalline materials that can be described by unit
cells containing few up to hundreds of atoms, amorphous materials require larger simulation
cells with at least hundreds or often thousands of atoms. Inverse design of amorphous materials with probabilistic generative models aims to generate the atomic positions and elements of amorphous materials given a set of desired properties. It has emerged as a promising approach for facilitating the application of amorphous materials in domains such as energy storage and thermal management. In this paper, we introduce AMShortcut, an inference- and training-efficient probabilistic generative model for amorphous materials. AMShortcut enables accurate inference of diverse short- and medium-range structures in amorphous materials with only a few sampling steps, mitigating the need for an excessive number of sampling steps that hinders inference efficiency. AMShortcut can be trained once with all relevant properties and perform inference conditioned on arbitrary combinations of desired properties, mitigating the need for training one model for each combination. Experiments on three amorphous materials
datasets with diverse structures and properties demonstrate that AMShortcut achieves its design goals.
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All authors Yan Lin, Jonas A. Finkler, Tao Du, Jilin Hu, Morten M. Smedskjaer
Materials Science
Superlinear Temperature-Dependent Resistivity and Structural Phase Transition in BaNi$_2$P$_4$
E. H. Krenkel, M. A. Tanatar, E. I. Timmons et al. (+13 more)
The mechanism of anomalous superlinear temperature-dependent resistivity, $\rho (T)$, in the metallic unconventional clathrate BaNi$_2$P$_4$ was studied by examining its
evolution with artificial disorder induced by low-temperature ($\sim$ 20 K) 2.5 MeV electron irradiation. We find a dominant effect of the tetragonal-orthorhombic transition at $T_s$ ($ \sim$373 to 378 K, depending on heat cycle rate and direction) on $\rho (T)$, with standard metallic $T-$linear resistivity above the transition and anomalous behavior in the orthorhombic phase below. The transition is accompanied by the formation of structural domains and a notable (about 4~K) hysteresis in the magnetization and resistivity measurements, clearly showing its first order character. Matthiessen rule is obeyed both above and below the transition, suggesting negligible changes in the electronic structure. This conclusion is supported by the smooth
evolution of the
Hall effect through the transition. The
Hall number is in good agreement with band structure calculations both above and below the transition. The transition temperature is notably suppressed with electron irradiation. Raman scattering at temperatures above room temperature find softening of local Ba vibration mode in the orthorhombic phase on approaching the transition. $^{31}P$ NMR line splits in the orthorhombic phase, suggesting a partial shift of the Ba atom from the central position in the cage. We suggest that local Ba rattling leads to enhanced residual contribution to resistivity in the high temperature tetragonal phase, the decay of which is responsible for the anomalous temperature-dependent resistivity in the orthorhombic phase.
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All authors E. H. Krenkel, M. A. Tanatar, E. I. Timmons, S. L. Bud'ko, P. C. Canfield, Qing-Ping Ding, Y. Furukawa, Lin-Lin Wang, M. Konczykowski, R. Grasset, J. L. Niedziela, O. Delaire, G. Viswanathan, J. Wang, K. Kovnir, R. Prozorov
Materials Science · Cross-listed from eess.SY
RHINO-MAG: Recursive H-Field Inference based on Observed Magnetic Flux Density under Dynamic Excitation
Hendrik Vater, Oliver Schweins, Lukas Hölsch et al. (+3 more)
Driven by the MagNet Challenge 2025 (MC2), increased research interest is directed towards modeling transient
magnetic fields within ferrite materials. An accurate time-resolved and temperature-aware H-field prediction is essential for optimizing
magnetic components in applications with quasi-stationary / non-stationary excitation waveforms. Within the scope of this investigation, a selection of model architectures with varying degrees of physically motivated structure is compared. Based on a Pareto investigation, a rather black-box gated recurrent unit (GRU) model structure with a graceful initialization setup is found to offer the most attractive model size vs. model accuracy trade-off in the small-model regime, while the examined physics-inspired models performed worse. For a GRU-based model architecture with only 325 parameters (trained separately per material), an average sequence relative error of 8.02 % and an average normalized energy relative error of 1.07 % across five different materials are achieved on unseen test data. With this excellent parameter efficiency, the proposed model won the first place in the performance category of the MC2.
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All authors Hendrik Vater, Oliver Schweins, Lukas Hölsch, Wilhelm Kirchgässner, Till Piepenbrock, Oliver Wallscheid
Materials Science
On the flash temperature in sliding contacts
M. H. Müser and B. N. J. Persson
The temperature increase in the contact regions between solids in sliding contact can easily reach several hundred Kelvin and thereby dramatically affect friction and wear. The classical theories by Jaeger, Archard, and Greenwood, commonly used to estimate flash temperature, ignore the multiscale nature of real surfaces and instead approximate the frictional heat sources with circular or square shapes. Here, we present an analytical theory for the flash temperature valid for randomly rough surfaces with roughness across arbitrarily many decades in length scale. The theory extends established methods for stress correlation functions and peak stresses to temperature. Numerical results for rubber sliding on concrete, and granite on granite, are presented as illustrations. We show that classical theories for flash temperature fail severely for surfaces with multiscale roughness.
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Materials Science
Phase-Singularity Control of Topological Acoustic Spin Textures
Huaijin Ma, Te Liu, Jiachen Sheng et al. (+6 more)
Acoustic
spin textures provide a degree of freedom for programmable topological field states, yet a unified framework for constructing and classifying higher-order textures in open-air acoustics remains lacking. Here we introduce polygonal standing-wave interference as a framework connecting discrete
symmetry, angular phase encoding, phase singularities,
chiral time-averaged energy flux, and acoustic
spin. By controlling the number and relative phases of the standing-wave channels, we experimentally realize D4 meron/anti-meron
lattice, D6 double-skyrmion superlattice, and D8 acoustic-
spin quasicrystal composed of four meron/anti-meron sublattices. Finite polygonal fields are normalized angular discretizations of continuous standing-wave spectra. Under the m=2 phase encoding, the D6 and D8 fields reproduce the local q=+2 core of a second-order Bessel
vortex while retaining distinct long-range order through their discrete interference channels. At fixed m increasing N under normalized angular sampling yields the continuous Bessel limit. These results establish phase encoding, pairwise interference, reciprocal-space composition, and angular discretization as a unified design principle for programmable topological acoustic
spin textures.
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All authors Huaijin Ma, Te Liu, Jiachen Sheng, Xiaochang Pan, Wenwei Qian, Xiangyu Chen, Kaiyuan Cao, Jinpeng Yang, Jian Wang
Materials Science
Thermal Conductivity and Temperature-Induced Band Gap Renormalization in Crystalline and Amorphous Ga$_2$O$_3$
Rustam Arabov, Jiaxuan Li, Xiaotong Chen et al. (+2 more)
The
lattice thermal conductivity (LTC) and electron-
phonon interactions in crystalline and amorphous gallium
oxide are herein determined by coupling a machine-learned interatomic potential, namely the moment tensor potential (MTP) model, to first-principles calculations. Crystalline $\beta$-Ga$_2$O$_3$ exhibits a substantial band gap renormalization (BGR) of $\sim$0.45 eV at 700 K, with $\sim$0.2 eV caused by zero-point BGR. The computed temperature dependence of BGR induced by classical
nuclear motion in $\beta$-Ga$_2$O$_3$ is stronger than that in amorphous Ga$_2$O$_3$, with the difference in BGR reaching $\sim$0.18 eV at 900 K. Thermal transport calculations reveal that the LTC of amorphous Ga$_2$O$_3$ remains near $0.9$ W$\cdot$ m$^{-1}$$\cdot$K$^{-1}$ for temperatures between 300 K and 700 K, which is approximately an order of magnitude lower than that of crystalline $\beta$-Ga$_2$O$_3$. Overall, the presented framework provides a computationally tractable and reliable route for predicting properties of
semiconductors (both crystalline and amorphous) under operating conditions relevant to microelectronics and optoelectronics.
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All authors Rustam Arabov, Jiaxuan Li, Xiaotong Chen, Nikita Rybin, Alexander Shapeev
Materials Science
Fe-site-resolved anisotropy energies in Nd$_2$Fe$_{14}$B for atomistic spin dynamics
Veronica T. C. Lai and Christopher E. Patrick
Nd-Fe-B magnets are the most widely used high performance magnets in the world today, and remain the subject of both experimental and computational research aimed at understanding and optimizing them. Atomistic
spin dynamics (ASD) is one technique which has been used in recent years to provide insight into
magnetic properties relevant to coercivity, such as domain wall width. Although it is relatively clear how to model magnetocrystalline anisotropy arising from rare-earth atoms in these simulations, the contribution from the transition metal Fe is less obvious, due to the itinerant nature of the magnetism. Here, we examine previous treatments of Fe anisotropy in ASD simulations and identify a discrepancy with previously-published first-principles studies. We derive two models which correct this discrepancy, one based on single-ion theory and the other on anisotropic exchange, and test their performance by comparing to first-principles torque calculations on Y$_2$Fe$_{14}$B. The torque calculations show a contribution which cannot be explained by the single-ion model but arises naturally from (antisymmetric) anisotropic exchange. We propose practical strategies to model Fe anisotropy in future ASD simulations, including a simplified (mean-field) description of anisotropic exchange, which may have applications beyond R$_2$Fe$_{14}$B to the wider class of itinerant
magnetic materials.
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Materials Science
Continuous three-dimensional imaging of nanoscale dynamics by in situ electron tomography
Timothy M. Craig, Adrien Moncomble, Ajinkya A. Kadu et al. (+4 more)
Visualizing nanoscale transformations in three dimensions (3D) is essential for understanding materials
evolution under operating conditions, yet dynamic electron
tomography remains limited by slow tilt series acquisition and by reconstruction methods that assume static specimens. These constraints prevent continuous 3D imaging of evolving structures and require electron doses that can alter the specimens and their dynamics. Here, we demonstrate a framework for dynamic electron
tomography that combines continuous tilting with a self-supervised deep-learning reconstruction strategy. Our approach incorporates the temporal aspect into the electron
tomography reconstruction process to recover 3D volumes at arbitrary time points from a single tilt series. We validate the method using simulations and demonstrate its merit in experimental studies of heat-induced transformations, including morphological
evolution of Au nanostars and alloying in Au@Ag nanocubes. Our results establish a practical framework for dynamic, dose-efficient electron
tomography, enabling in situ 3D investigation of nanomaterial transformations as well as the characterization of beam-sensitive structures.
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All authors Timothy M. Craig, Adrien Moncomble, Ajinkya A. Kadu, Gail A. Vinnacombe-Willson, Luis M. Liz-Marzán, Robin Girod, Sara Bals
Materials Science
Unquenched orbital angular momentum as the origin of spin inertia
Tarek Moussa, Darpa Narayan Basu, Ritwik Mondal et al. (+1 more)
The recent proposal and observation of
spin inertia, and the consequent high-frequency
spin nutation mode, have raised key questions for our understanding of magnetization dynamics, especially considering its high relevance for
magnetic memories and ultrafast switching. Notwithstanding recent progress, a clear identification of
spin inertia's physical origin thereby offering predictive power remains to be accomplished. Here, discussing general principles for identifying this physical origin, we examine unquenched orbital angular momentum (OAM) finding it to be a key candidate, despite its typically small value. Treating OAM and
spin within a two-sublattice model, we derive the equivalent single-sublattice framework for magnetization dynamics making appropriate approximations. The latter naturally manifests the
spin inertia term and parameter, which are otherwise introduced phenomenologically. The inertia parameter evaluated within our model is found to be in good agreement with its experimentally observed value in cobalt. We further delineate key experimental signatures that could verify or rule out the unquenched OAM as the origin of the observed high-frequency mode, and avoid a spurious optical mode in a two-sublattice ferromagnet from being identified as nutation. Our analysis offers a potential link between the recently emerged fields of orbitronics and
spin inertia, thereby motivating investigations at their intersection.
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All authors Tarek Moussa, Darpa Narayan Basu, Ritwik Mondal, Akashdeep Kamra
Materials Science
Plasmon Engineering in Intercalated 2H-TaS$_2$
Luigi Camerano, Laura Martella, Lorenzo Battaglia et al. (+8 more)
Plasmons in low dimensional materials provide a powerful platform for nanoscale control of light matter interactions, yet strategies to tailor their coherence and dissipation remain limited. Here, we demonstrate that transition metal intercalation offers a fundamentally distinct route to engineer plasmonic response in layered materials. By combining high-resolution core-level photoemission spectroscopy with first-principles calculations, we show that Fe and Co intercalation in 2H-TaS2 does not act as conventional electron doping, but instead reshapes the low energy electronic structure through orbital hybridization and structural reconstruction. This process introduces a dense continuum of low energy excitations that efficiently damp and ultimately suppress the plasmon mode. First principle calculations of the energy loss function reveal a transition from a well defined collective excitation to an overdamped response, signaling the breakdown of coherent charge dynamics. Our results establish intercalation as a chemically controlled pathway to tune plasmon losses and dielectric response in
quantum van der Waals materials, providing a new design principle for plasmonic and optoelectronic functionalities at the nanoscale.
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All authors Luigi Camerano, Laura Martella, Lorenzo Battaglia, Federico Giannessi, Filippo Camilli, Luca Lozzi, Polina M. Sheverdyaeva, Paolo Moras, Luca Ottaviano, Gianni Profeta, Federico Bisti
Materials Science
Decoding Dopant-Induced Electronic Modulation in Graphene via Region-Resolved Machine Learning of XANES
Yinan Wang, Arpita Varadwaj, Teruyasu Mizoguchi et al. (+1 more)
Revealing how heteroatom doping alters the local electronic structure of
graphene is crucial for understanding and controlling its functional properties. In this study, we combine density functional theory (DFT) and machine learning (ML) to interpret how boron (B) and nitrogen (N) dopants influence the local electronic environments of
graphene. A
dataset of 415 DFT-simulated XANES spectra from 91 distinct configurations was analyzed using a region-specific approach by decomposing each spectrum into pi*, sigma*, and post-edge regions. Random forest models trained on these spectral segments identified the pi* region as the most informative for predicting key local electronic descriptors, particularly the Bader charge and mean dopant-carbon bond length. The Bader charge quantifies dopant-induced charge redistribution and local bonding polarity, directly reflecting the degree of electronic perturbation introduced by heteroatom substitution. The enhanced predictive power of the pi* region arises from its strong coupling to the perturbed pi-electron network, which captures these charge-transfer and hybridization effects more effectively than sigma* or post-edge regions. These findings establish Bader charge as a robust and physically meaningful descriptor for quantifying dopant-induced electronic modulation and demonstrate that region-resolved ML analysis of XANES spectra provides a powerful pathway to uncover structure-property relationships in doped
graphene and related materials.
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All authors Yinan Wang, Arpita Varadwaj, Teruyasu Mizoguchi, Masato Kotsugi
Materials Science · Cross-listed from gr-qc
Mexican Burrowing Toads as gravitational wave detectors
Frederic V. Hessman and Christian Jooss
It is generally assumed that gravitational waves are extremely difficult to detect. However, we show that the call of the Mexican Burrowing Toad has an amazing resemblance to
cosmic gravitational wave signals due to the merging of
neutron stars and/or black holes. It is known that toads exhibit magnetoreception - the ability to detect
magnetic fields - and that
magnetic fields thus subtly affect ion channel activities in toad
neurons. We speculate that gravitational strains produce
phonons and
magnons in a
ferromagnetic substance embedded in the nervous system of the toads and that these coherent signals are exponentially amplified by a Raman
laser mechanism to the point where they can be detected. The fine tuning necessary for this mechanism to work would help to explain why this species of toad show this remarkable ability and others do not. We analyze the sound of a pond full of Mexican Burrowing Toads in the hopes of detecting slight phase shifts in their calls due to a gravitational wave event. No effect was found and the the LIGO/VIRGO consortia have not reported an event during the recording, illustrating the power of this approach. We suggest the massive use of these toads would be an inexpensive way to support the operation of optical interferometric gravitational wave detector facilities.
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Materials Science
Machine Learning Assisted Reconstruction of Local Electronic Structure of Non-Uniformly Strained MoS2
Soumyadip Hazra, Sraboni Dey, Arijit Kayal et al. (+3 more)
Wrinkles and nanobubbles are an integral and often unavoidable part of integrating 2D van der Waals
semiconductors into actual device architectures. Despite their ubiquitous nature, quantitative correlation between such spatially non-uniform strain and modifications to the local electronic structure remains challenging. Here, density functional theory is combined with a recurrent neural network to reconstruct the local electronic structure of monolayer MoS2 from strain maps derived from atomic force microscopy (AFM) topography and Raman spectral maps. The analysis reveals that biaxial bending induced strain is significantly more effective than both uniaxial bending or in-plane strain in modifying electronic and dielectric properties. A ~ 0.35% strain induced by biaxial bending results in ~ 22% reduction in band gap and ~ 7% increase in dielectric constant, compared to a ~ 5% reduction in band gap and ~ 1% increase in dielectric constant under comparable uniaxial bending. The modified band structure reveals band edge states that concentrate charge in regions of high
curvature or strain. While conductive AFM measurements indicate increased local conductance (carrier density) at wrinkles and nanobubbles, the spatial band gap maps predicted by the model are validated against experimental photoluminescence peak energy maps. The results indicate that strained features like wrinkles and nanobubbles commonly present in real devices influence the band gap, carrier distribution, and dielectric response, which favourably affects electrical transport in such systems. The framework developed here can be readily extended to other 2D materials and
heterostructures, offering a computationally efficient route for studying and exploiting strain effects.
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All authors Soumyadip Hazra, Sraboni Dey, Arijit Kayal, Narendra Shah, Renjith Nadarajan, Joy Mitra
Materials Science
Atomically Reconfigurable Single-Molecule Optoelectronics
Atif Ghafoor, Santeri Neuvonen, Thinh Tran et al. (+6 more)
Deterministic control of excitonic properties is key to advancing nanoscale optoelectronic and
quantum technologies and to understanding diverse physical, optical, chemical, and biological phenomena. At the molecular scale, these properties can be tuned through chemical modification, local-environment influence or charge-state manipulation. Yet, direct control of a molecule's transition dipole moment and its resulting light emission via atomic-scale structural modification has remained elusive. Here, using scanning tunnelling microscopy-induced luminescence, we show that a single structural parameter-the vertical displacement of the central metal atom in a planar phthalocyanine molecule on a decoupling layer-enables active tuning of the transition dipole, allowing either suppression or enhancement of emission. Exploiting this control, we realized a tunable homodimer switchable among three optical states: non-emissive, single-molecule-like emissive, and coupled states exhibiting subradiant and superradiant modes, directly revealing intermolecular dipole-dipole coupling. We further demonstrate a heterodimer in which resonant energy transfer can be turned on or off simply by controlling the acceptor's transition dipole moment. These findings not only establish atomic-scale displacement as a general strategy for optical molecular switching, but also demonstrate the reconfigurable engineering of excitonic interactions within molecular assemblies.
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All authors Atif Ghafoor, Santeri Neuvonen, Thinh Tran, Oscar Moreno Segura, Yitao Sun, Yaroslav Pavlyukh, Riku Tuovinen, Jose L. Lado, Shawulienu Kezilebieke
Materials Science
Quantum anomalous Hall effect in monolayer transition-metal trihalides
Thi Phuong Thao Nguyen and Kunihiko Yamauchi
We present systematic first-principles results for the electronic and
magnetic properties of two-dimensional transition-metal trihalide monolayers MX3 (M = V, Cr, Mn, Fe, Ni, Pd; X = F, Cl, Br, I), focusing on their potential to host the
quantum anomalous
Hall effect. In particular, MnF3 and PdF3 exhibit a
spin-polarized Dirac cone at the K point,
spin-orbit coupling opens a sizable gap with a nonzero Chern number. Nanoribbon slab calculations reveal gap-crossing
chiral edge states, establishing the nontrivial topological character. Beyond these case studies, our systematic screening clarifies general trends across the MX3 family and provides insight into how electronic configuration and
spin-orbit coupling cooperate to produce
magnetic and topological phases in two-dimensional magnets.
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Materials Science
Long-range interaction effects on the phase transition, mechanical effect, and electric field response of BaTiO3 by machine learning potentials
Po-Yen Chen and Teruyasu Mizoguchi
Bulk materials are governed by both short-range and long-range interactions, both of which are naturally captured in conventional density functional theory (DFT) calculations through Ewald summation of electrostatic contributions. In contrast, machine learning potentials (MLPs) typically rely on local atomic environment descriptors, and long-range interactions are often neglected. Such approximations may introduce systematic energetic errors and lead to inaccuracies in predicted material properties. To systematically investigate the impact of long-range interactions in ferroelectric BaTiO3 within the framework of MLPs, we developed a long-range MACELES model and compared its performance with the previously reported BaTiO3 MACE model across four key properties (
phonon dispersion, phase transition behavior, mechanical response, and ferroelectric properties including dielectric constants). We find that qualitative behaviors, including phase transitions, stress-induced polarization switching, and polarization-electric field hysteresis, are consistently reproduced by both models. In contrast, quantitative properties such as transition temperatures, elastic constants, and dielectric constants exhibit systematic improvements in MACELES model, highlighting the importance of incorporating long-range electrostatics for accurately describing the structural and dielectric responses of BaTiO3. These results suggest that while long-range interactions play a role in improving quantitative accuracy, their omission does not significantly alter the qualitative ferroelectric behavior of BaTiO3.
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Materials Science
Phonon Signatures of Near-Room-Temperature Phase Transition in Quasi-One-Dimensional Bi4I4 Topological van der Waals Material
Nidhish Thiruthukkal Puthenveettil, Topojit Debnath, Clayton Mantz et al. (+7 more)
The quasi-one-dimensional material Bi4I4 hosts two crystallographically similar polymorphs that realize distinct topological insulating phases separated by a first-order structural transition near room temperature. This transition occurs without a change in space group, arising instead from a subtle rearrangement of chain stacking registry. Polarization-resolved Raman spectroscopy directly resolves this structural-topological phase transition through abrupt, hysteretic modifications of the
phonon spectrum. Angle-dependent measurements establish the
symmetry of the dominant Raman-active modes and require a complex Raman tensor formalism to account for absorption-induced phase effects. Across the transition, selected
phonon modes exhibit discontinuous, reversible shifts in frequency, linewidth, and relative intensity despite the absence of a space-group change. Density functional theory calculations reproduce the direction of the observed
phonon renormalizations and confirm their sensitivity to stacking-dependent force constants. These results demonstrate that polarization-resolved Raman spectroscopy can detect subtle stacking-driven structural rearrangements that underlie topological band character, even when global crystallographic
symmetry remains unchanged. The obtained results provide valuable insights into the interplay among
lattice dynamics, structural distortions, and topological properties in this class of low-dimensional materials, with strong potential for unique functionalities.
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All authors Nidhish Thiruthukkal Puthenveettil, Topojit Debnath, Clayton Mantz, Zahra Ebrahim Nataj, Jordan Teeter, Md. Shafayat Hossain, Fariborz Kargar, Tina T. Salguero, Roger K. Lake, Alexander A. Balandin
Materials Science
Role of surface states and band modulations in ultrathin ruthenium interconnects
Gyungho Maeng, Subeen Lim, Mi Gyoung Lee et al. (+3 more)
Mitigating the RC delay from transistor miniaturization is essential for next-generation devices, driving a focus on interconnect electrical performance. Current copper-based interconnects face a critical challenge, that their resistivity sharply increases at the nanometer-scale due to surface and grain boundary scattering. Therefore, there is a pressing need for techniques that reduce resistance in ultrathin metal films. In this study, we employ the density functional theory to investigate how the intrinsic electronic structure of thin films impacts conductivity as a function of thickness. Notably, our analysis of ruthenium slab structures shows that surface states significantly influence thickness-dependent resistivity. It reveals that
vacuum-terminated Ru slab exhibits decreasing resistivity with the decrease in thickness, whereas oxygen-terminated Ru slab shows the opposite trend. This difference is fundamentally attributed to the presence or absence of surface states, highlighting the importance of surface engineering in optimizing interconnect performance.
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All authors Gyungho Maeng, Subeen Lim, Mi Gyoung Lee, Bonggeun Shong, Kyeongjae Cho, Yeonghun Lee
Materials Science
Robust Flat Magnetoresistivity in D0$_3$-Fe$_3$Ga Driven by Chiral Anomaly
Ruoqi Wang, Xinyang Li, Bo Zhao et al. (+11 more)
Topologically non-trivial nodes emerging from flat-band crossings not only enhance unconventional topological responses but also play a fundamental role in exploring correlation-driven topological physics. Here, we report the exceptionally robust
chiral-anomaly-dominated transport in D0_3-Fe_3Ga. First, we observe a combination of positive and negative magnetoresistance, ideal planar longitudinal magnetoresistance (PLMR), and the planar
Hall effect (PHE). Second, ultra-low-temperature resistivity exhibits pronounced non-
Fermi-
liquid (NFL) behavior, accompanied by the emergence of
giant intrinsic anomalous
Hall conductivity (AHC), in excellent agreement with our DFT calculations, which confirm the existence of tilted Weyl points arising from crossings of nearly three-dimensional (3D) flat bands. Most remarkably, we detect an exceptionally robust flat magnetoresistance (flat-MR) that persists without decay up to 33 T. This set of phenomena provides strong evidence that the
Fermi level intersects the flattened Weyl crossings, offering confirmation of a topological flat-band semimetal. D0_3-Fe_3Ga presents a promising
magnetic platform for
quantum device innovations.
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All authors Ruoqi Wang, Xinyang Li, Bo Zhao, Haofu Wen, Xin Gu, Shijun Yuan, Langsheng Ling, Chuanying Xi, Ze Wang, Kunquan Hong, Liang Ma, Ke Xia, Taishi Chen, Jinlan Wang