Materials Science
Correlations Between the Dielectric Properties, Domain Structure Morphology and Phase State of Bi1-xSmxFeO3 Nanoparticles
Oleksandr S. Pylypchuk, Vladyslav O. Kolupaiev, Victor V. Vainberg et al. (+5 more)
Nanoscale multiferroics are basic model objects for studying polar,
magnetic and magnetoelectric properties and mutual couplings. Bismuth-samarium ferrite (Bi1-xSmxFeO3) is a model orthoferrite, whose polar,
magnetic and magnetoelectric properties have been studied for the bulk and thin film samples. The properties of Bi1-xSmxFeO3 nanoparticles have been much less studied, despite the nanoparticles can be used in a wide range of applications, such as energy storage,
magnetic hyperthermia and advanced nanoelectronics. In this work we performed experimental measurements and analysis of the temperature dependence of the Bi1-xSmxFeO3 nanopowders dielectric properties. Calculations of the ferro-ionic coupling influence on the dielectric properties, domain structure morphology and phase states are performed in the framework of the Ginzburg-Landau-Devonshire-Stephenson-Highland approach. Theoretical results explain the main trends of experimentally observed temperature dependences of the effective dielectric permittivity, which allows us to understand the correlations between the temperature behavior of dielectric properties, domain structure morphology and phase state of Bi1-xSmxFeO3 nanoparticles.
Read the full abstract ▾
All authors Oleksandr S. Pylypchuk, Vladyslav O. Kolupaiev, Victor V. Vainberg, Vladimir N. Poroshin, Ihor V. Fesych, Lesya D. Demchenko, Eugene A. Eliseev, Anna N. Morozovska
Materials Science · Cross-listed from physics.ins-det
Detective Quantum Efficiency of the Timepix4 Hybrid Pixel Detector and its Application to Parallel-Beam Diffraction
Zhiyuan Ding, Nina Dimova, Jonathan S. Barnard et al. (+6 more)
The detective
quantum efficiency (DQE) and normalised noise power spectrum (NNPS) of the Timepix4 hybrid pixel detector in event-driven mode in TEM have been measured at 100 kV and 200 kV. In a raw data readout mode, the zero-frequency DQE exceeds 0.9 at both 100 kV and 200 kV. At the Nyquist frequency, the DQE remains above 0.2 at 100 kV but drops close to zero at 200 kV. Initial parallel-beam diffraction data from a polycrystalline gold nanoparticle sample is reported which shows that at 200 kV Timepix4 can detect weak diffracted information beyond a 75 mrad half-angle.
Read the full abstract ▾
All authors Zhiyuan Ding, Nina Dimova, Jonathan S. Barnard, Giulio Crevatin, Liam O'Ryan, Richard Plackett, Daniela Bortoletto, Angus I. Kirkland, Marcus Gallagher-Jones
Materials Science
Adsorption-Controlled Epitaxy and Twin Control of $\gamma$-GaSe on GaAs (111)B
Joshua Eickhoff, Wendy L. Sarney, Sina Najmaei et al. (+2 more)
The III-Se layered
semiconductors, including InSe and GaSe, are promising optoelectronic materials due to their relatively high electron mobilities at room temperature, nonlinear optical responses, ferroelectricity, self-passivated van der Waals surfaces, and ability to
alloy and synthesize
heterostructures for bandgap engineering. Adsorption control is a widely utilized strategy for controlling the stoichiometry and phase formation of these materials; however, the bounds of the adsorption-controlled growth window for GaSe have not been systematically established. Additionally, challenges with control over polytype and twinning remain. Here, we use molecular beam epitaxy to experimentally map the adsorption-controlled growth window of GaSe films on vicinal GaAs (111)B substrates. The observed phase boundaries show qualitative agreement with Ellingham diagram predictions. All films crystallize in the $\gamma$ ($R3m$) polytype. Increasing growth and annealing temperature leads to decreased mosaicity measured by x-ray rocking curve and smoother surfaces measured by atomic force microscopy, at the expense of a transition from singly oriented $\gamma$ to twinned $\gamma$ with $60\degree$ rotated domains.
Read the full abstract ▾
All authors Joshua Eickhoff, Wendy L. Sarney, Sina Najmaei, Daniel A. Rhodes, Jason Kawasaki
Materials Science
AIMD-L: An automated laboratory for high-throughput characterization of structural materials for extreme environments
Todd C. Hufnagel, Pranav Addepalli, Anuruddha Bhattacharjee et al. (+14 more)
Rapid developments in artificial intelligence and machine learning as applied to materials science are creating an urgent need for experimental data, which can be provided by high-throughput and autonomous laboratories. To date most demonstrations of such laboratories have focused on functional materials, with less
attention paid to structural materials. We present here the Artificial Intelligence in Materials Design Laboratory (AIMD-L), an automated, high-throughput facility for characterizing the microstructure and properties of structural metals and ceramics, with an emphasis on materials in extreme environments. AIMD-L has two custom instruments for characterization of structural materials: HELIX for shock studies of materials, and MAXIMA for X-ray diffraction and X-ray fluorescence spectroscopy. Specifically designed for high-throughput studies, HELIX and MAXIMA are each capable of collecting data at rates two to three orders of magnitude faster than conventional systems. A third experimental station, SPHINX, is a commercial nanoindenter modified for integration into the automated workflow of AIMD-L. A user (which may be human or an AI
agent) directs the experiments to be carried out by means of a centralized control program. The experimental stations are linked by a conveyance that moves samples around the lab, with a
robot at each station for sample transfer in/out of the instrument. The experimental stations also communicate with a common data layer that streams data autonomously from each instrument to a data portal, where their arrival triggers automated workflows for data reduction and analysis. The processed data are immediately available to the human operator or agentic AI, forming a closed loop for rapid decision-making and experimental control.
Read the full abstract ▾
All authors Todd C. Hufnagel, Pranav Addepalli, Anuruddha Bhattacharjee, Rohit Berlia, Jaafar El-Awady, David Elbert, Lori Graham-Brady, Axel Krieger, Harichandana Neralla, T. Joseph Nkansah-Mahaney, Mostafa M. Omar, Hyun Sang Park, K.T. Ramesh, Matthew Shaeffer, Eric Walker, Piyush Wanchoo, Timothy P. Weihs
Materials Science
Bridging the lab-to-fab gap in non-fullerene organic solar cells via gravure printing
Svitlana Taranenko, Chen Wang, David Holzner et al. (+10 more)
Organic
solar cells have reached record efficiencies with non-fullerene acceptors, yet their translation to industrial printing remains a critical bottleneck. Here we report the highest efficiency achieved for a fully roll-to-roll-compatible gravure-printed non-fullerene organic
solar cell. High-performance blends are typically optimised under laboratory coating conditions, while roll-to-roll manufacturing imposes fundamentally different constraints on ink stability, drying dynamics, and multilayer integration. Whether these constraints intrinsically limit device physics has remained unresolved. Here, we demonstrate a gravure-printed PM6:Y12
solar cell architecture using commercially available materials and establish a quantitative framework that disentangles optical, recombination, and transport losses in printed devices. We find that favourable bulk morphology and
exciton harvesting can be preserved under gravure printing and non-halogenated solvents. The dominant efficiency penalties arise instead from optical interference within the printed layer stack and slow charge transport. Our results demonstrate that the performance gap between laboratory and printed
solar cells is originating from device architecture rather than the intrinsic physics of modern non-fullerene systems, providing a mechanistic roadmap for roll-to-roll manufacturing of non-fullerene
solar cells.
Read the full abstract ▾
All authors Svitlana Taranenko, Chen Wang, David Holzner, Robert Eland, Christopher Wöpke, Toni Seiler, Alexander Ehm, Fabio Le Piane, Roderick C. I. Mackenzie, Dietrich R. T. Zahn, Carsten Deibel, Arved Carl Hübler, Maria Saladina
Materials Science · Cross-listed from cond-mat.supr-con
Quasiparticle spectroscopy in tantalum films with different Ta/sapphire interfaces
Bicky S. Moirangthem, Kamal R. Joshi, Anthony P. Mcfadden et al. (+8 more)
One of the crucial aspects of current research in
quantum information science is the identification and control of loss mechanisms in superconducting
circuits. Although microwave measurements directly quantify device performance, additional techniques that probe quasiparticle excitations in superconducting films are needed to understand the microscopic mechanisms underlying dissipation and decoherence. Here, we present results from quasiparticle spectroscopy of Ta/sapphire films by measuring the Meissner-state
magnetic susceptibility using a precision frequency-domain resonator specifically designed for thin films. We find direct evidence for additional low-energy excitations in samples with lower internal quality factors. These excitations are consistent with deep subgap states due to two-level systems, Yu-Shiba-Rusinov states near the gap edge, and perhaps other pair-breaking mechanisms. The developed non-destructive frequency-domain quasiparticle spectroscopy is a valuable addition to the
quantum materials toolbox.
Read the full abstract ▾
All authors Bicky S. Moirangthem, Kamal R. Joshi, Anthony P. Mcfadden, Jin-Su Oh, Amlan Datta, Makariy A. Tanatar, Florent Lecocq, Raymond W. Simmonds, Lin Zhou, Matthew J. Kramer, Ruslan Prozorov
Materials Science · Cross-listed from physics.chem-ph
From Accurate Quantum Chemistry to Converged Thermodynamics for Ion Pairing in Solution
Niamh O'Neill, Benjamin X. Shi, William C. Witt et al. (+6 more)
Quantitative prediction of thermodynamic properties in solution is essential for translating atomistic simulations into reliable chemical insight. As an exemplar system, the behaviour of CaCO$_3$ in water has been widely studied to understand its mineralization in seawater, with potential implications for carbon-capture strategies. However, making accurate computational predictions has been a long-standing challenge, requiring both highly accurate electronic structure methods and extensive statistical sampling. Here, we combine advances in machine learning and electronic structure theory to fully resolve the ion pairing free energy of CaCO$_3$ with explicit solvation. We show that achieving quantitative agreement with experiment requires going beyond the standard density functional theory up to the "gold-standard" coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. We generate a set of systematically improvable models, enabling reliable insights into the initial association mechanism of Ca and CO$_3$ ions prior to nucleation while fully quantifying enthalpic and entropic effects. Our results demonstrate that CCSD(T)-level thermodynamic predictions of complex aqueous systems can now be routinely achieved.
Read the full abstract ▾
All authors Niamh O'Neill, Benjamin X. Shi, William C. Witt, Blake I. Armstrong, William J. Baldwin, Paolo Raiteri, Christoph Schran, Angelos Michaelides, Julian D. Gale
Materials Science
Patterns of load, elastic energy and damage in network models of architected composite materials
Christian Greff, Leon Pyka, Michael Zaiser et al. (+1 more)
We investigate the role of architected thin films in the interfacial failure properties of bi-layer composites. Our results show that, while graded structures can be used to prescribe failure at the interface, they do not offer significant advantages in terms of fracture toughness. Hierarchically patterned layers can localize failure at the interface and simultaneously enhance interface toughness, by enforcing a buffer region where elastic energy is dissipated in the form of diffuse damage, so that no stress concentration can drive crack growth. To analyze these mechanisms, the associated patterns of local load redistribution and the soft deformation modes, we develop a network formalism that brings together concepts of discrete differential geometry and spectral graph theory.
Read the full abstract ▾
All authors Christian Greff, Leon Pyka, Michael Zaiser, Paolo Moretti
Materials Science
Effect of Exchange-Correlation Functionals on Schottky Barriers at Si/Metal Interfaces
Viviana Dovale-Farelo and Kamal Choudhary
Accurate prediction of Schottky barrier heights (SBHs) at metal-
semiconductor (M-SC) interfaces is essential for understanding and optimizing charge injection in electronic and optoelectronic devices. However, first-principles calculations of SBHs remain challenging due to the combined difficulties of
semiconductor bandgap underestimation, metal
Fermi level placement,
lattice-mismatch, relative
geometric alignment and electrostatic potential
alignment across heterogeneous interfaces. In this work, we present a systematic and physically grounded assessment of computational strategies for SBH prediction using Si(111)/Metal (Al, Cu, Ag, Au) interfaces as representative test cases. We evaluate multiple exchange-correlation (XC) treatments, in combination with three distinct bulk reference protocols: relaxed bulk, relaxed bulk with
spin-orbit coupling, and strained bulk references consistent with the interface geometry. By benchmarking against experimental data, we demonstrate that structural and electrostatic consistency between interface and bulk reference calculations is the dominant factor governing SBH accuracy. We show that mixed hybrid-semilocal approaches combined with strained reference protocols yield uniformly positive and significantly improved SBHs, achieving near-experimental accuracy while maintaining a favorable balance between computational cost and predictive performance. Our results establish a clear and transferable methodology for reliable Schottky barrier prediction and provide practical guidance for large-scale screening and interface engineering.
Read the full abstract ▾
Materials Science · Cross-listed from cs.LG
A recipe for scalable attention-based MLIPs: unlocking long-range accuracy with all-to-all node attention
Eric Qu, Brandon M. Wood, Aditi S. Krishnapriyan et al. (+1 more)
Machine-learning interatomic potentials (MLIPs) have advanced rapidly, with many top models relying on strong physics-based inductive biases. However, as models scale to larger systems like biomolecules and electrolytes, they struggle to accurately capture long-range (LR) interactions, leading current approaches to rely on explicit physics-based terms or components. In this work, we propose AllScAIP, a straightforward,
attention-based, and energy-conserving MLIP model that scales to O(100 million) training samples. It addresses the long-range challenge using an all-to-all node
attention component that is data-driven. Extensive ablations reveal that in low-data/small-model regimes, inductive biases improve sample efficiency. However, as data and model size scale, these benefits diminish or even reverse, while all-to-all
attention remains critical for capturing LR interactions. Our model achieves state-of-the-art energy/force accuracy on molecular systems, as well as a number of physics-based evaluations (OMol25), while being competitive on materials (OMat24) and catalysts (OC20). Furthermore, it enables stable, long-timescale MD simulations that accurately recover experimental observables, including density and heat of vaporization predictions.
Read the full abstract ▾
All authors Eric Qu, Brandon M. Wood, Aditi S. Krishnapriyan, Zachary W. Ulissi
Materials Science · Cross-listed from cond-mat.mes-hall
Nanoscale Electronic Phase Separation Driven by Fe-site Ordering in Fe\textsubscript{5-x}GeTe\textsubscript{2}
Shreyashi Sinha, Ayan Jana, Suchanda Mondal et al. (+3 more)
Understanding how local structural order governs electronic correlations is essential for revealing the microscopic mechanism underlying emergent behavior in two-dimensional magnets. In the layered van der Waals ferromagnet Fe\textsubscript{5-x}GeTe\textsubscript{2}, intrinsic Fe-site disorder provides a natural platform to probe this interplay. Here, we establish a direct atomic scale correlation between Fe-site ordering and local electronic structure by combining high-resolution scanning tunneling microscopy with density functional theory calculations. Scanning tunneling microscopy resolves two coexisting surface phases, a $\sqrt{3} \times \sqrt{3}$ superstructure associated with ordered Fe(1) configurations and an undistorted $1 \times 1$ hexagonal Te
lattice in Fe(1)-deficient regions. Spatially resolved spectroscopy shows that the $\sqrt{3}$-ordered domains exhibit metallic behavior, whereas Fe(1) vacant areas display a suppressed density of states(DOS) near the
Fermi level, indicative of pseudogapped electronic states. The nanoscale coexistence of these distinct electronic responses provides direct evidence of electronic phase separation driven by Fe-site ordering. First-principles calculations reveal that
symmetry allowed hybridization between Fe 3d and Te 5p orbitals reconstructs the low-energy electronic structure, giving rise to the contrasting tunneling signatures of ordered and disordered phases. Bias-dependent local DOS simulations reproduce the experimentally observed contrast
evolution and reveal that hybridization induced out of plane orbital character governs the spatial modulation of tunneling conductance. These results provide a microscopic framework linking atomic-scale structural order to nanoscale electronic inhomogeneity in van der Waals magnets.
Read the full abstract ▾
All authors Shreyashi Sinha, Ayan Jana, Suchanda Mondal, Ravi Prakash Singh, Manoranjan Kumar, Sujit Manna
Materials Science
Deterministic Electrical Switching in Altermagnets via Surface Antisymmetry Groups
K. D. Belashchenko
A surface antisymmetry group framework is developed to establish design rules for deterministic electrical switching of the Néel vector in a film of a collinear bipartite antiferromagnet. In centrosymmetric altermagnets, where current-induced
spin-orbit torques vanish in the bulk, staggered effective fields can nevertheless exist as a macroscopic interfacial response, whose allowed tensor form is determined by the surface antisymmetry point group for the given surface orientation. Separately, the structure of the
spin conductivity tensor determines which surface orientations allow transverse
spin current generation via the nonrelativistic
spin-splitter effect. Taken together, these
symmetry-enforced properties establish which surface orientations of $d$-wave altermagnets can serve as deterministically switchable
spin current sources in
spin-torque
heterostructures. Because the design rules are based solely on the surface antisymmetry point group, the
symmetry-allowed staggered effective fields are robust against averaging over
equilibrium surface roughness.
Read the full abstract ▾
Materials Science
Epitaxial stabilization of magnetic GdAuSb/LaAuSb superlattices
Patrick J. Strohbeen, Soohyun Im, Tamalika Samanta et al. (+7 more)
We report the epitaxial stabilization of GdAuSb films and GdAuSb/LaAuSb superlattices via molecular beam epitaxy on (0001)-oriented Al$_{2}$O$_{3}$ substrates. GdAuSb crystallize in the Au-Au dimerized YPtAs structure type (space group $P6_{3}/mmc$), the same structure as the Dirac semimetal LaAuSb. Angle-resolved photoemission spectroscopy (ARPES) measurements show similar near $E_F$ bandstructures for GdAuSb and LaAuSb, plus a rigid band shift for GdAuSb towards more hole-like behavior and core-like Gd $4f$ states $\sim 9$~eV below the
Fermi energy. LaAuSb/GdAuSb superlattices exhibit sharp superlattice fringes by X-ray diffraction and atomically-precise interfaces by scanning transmission electron microscopy. Superlattices display two transitions in temperature-dependent resistvity, compared to a single Néel temperature for thick GdAuSb films. Superlattices of $Ln$AuSb materials ($Ln=$ rare earth) with atomically abrupt interfaces offer a new epitaxial platform for control of
magnetic and topological order via tunable intralayer exchange and reduced dimensionality.
Read the full abstract ▾
All authors Patrick J. Strohbeen, Soohyun Im, Tamalika Samanta, Zachary LaDuca, Dongxue Du, Estiaque H. Shourov, Jessica L. McChesney, Fanny Rodolakis, Paul M. Voyles, Jason K. Kawasaki
Materials Science · Cross-listed from cond-mat.mes-hall
Altermagnets Enable Gate-Switchable Helical and Chiral Topological Transport with Spin-Valley-Momentum-Locked Dual Protection
Xianzhang Chen, Jiayong Zhang, Bowen Hao et al. (+5 more)
We establish a unified,
symmetry-driven framework that combines the alternating
spin splitting of altermagnets with valley
topology to realize and electrically interconvert helical and
chiral topological phases within a single material platform. We first demonstrate a
magnetic analogue of the
quantum spin Hall effect in altermagnets, hosting helical
spin-valley-momentum-locked (SVML) edge states characterized by a composite
spin-valley Chern number Csv = 2. Large-scale
quantum transport simulations show these SVML edge states exhibit fully quantized
spin conductance robust against nonmagnetic and long-range
magnetic disorder, reflecting their dual topological protection, while remaining vulnerable to short-range
magnetic disorder. Exploiting that the counterpropagating SVML modes are linked by
crystal rotation
symmetry, we introduce a gate-tunable sublattice-staggered potential that selectively gaps one valley and converts the helical state into a
chiral quantum anomalous
Hall phase with Csv = 1, robust against all disorder types. Reversing the potential switches the transmitted
spin-valley polarization. Our first-principles calculations identify monolayer V2STeO and VO families as realistic platforms supporting both helical and
chiral topological phases and their electrical switching. These results establish altermagnets as electrically programmable platforms for robust topological devices across charge,
spin, and valley.
Read the full abstract ▾
All authors Xianzhang Chen, Jiayong Zhang, Bowen Hao, Jiahui Qian, Ziye Zhu, Igor Zutic, Zhenyu Zhang, Tong Zhou
Materials Science · Cross-listed from cond-mat.mes-hall
Linearly Polarized Light-Induced Anomalous Hall Effect and Topological Phase Transitions in an Altermagnetic Topological Insulator
Yichen Liu, Tongshuai Zhu and Haijun Zhang
A recently identified class of collinear
magnetic order, characterized by vanishing net magnetization yet unconventional
spin splitting, known as altermagnets (AMs), has attracted significant research interest. Controlling the unconventional
spin splitting and the associated band
topology in AMs offers opportunities for realizing novel
spin and topological transport phenomena. In this work, using Floquet engineering with periodically driven linearly polarized light (LPL), we explore light-induced control of an AM topological
insulator. Remarkably, we find that AMs and conventional antiferromagnets (AFMs) exhibit distinct responses under LPL irradiation. Specifically, since LPL breaks neither time-reversal ($\mathcal{T}$)
symmetry nor parity-time-reversal ($\mathcal{PT}$)
symmetry, it is incapable of generating
spin splitting or inducing an anomalous
Hall effect (AHE) in conventional AFMs. In contrast, AMs intrinsically lack both $\mathcal{T}$ and $\mathcal{PT}$
symmetries. Their
spin-up and
spin-down bands are related by the combined
symmetry of time reversal $\mathcal{T}$ and a
crystal rotation. We show that LPL readily breaks these
symmetries, thereby triggering a finite AHE exclusively in AMs. Furthermore, LPL can drive the AM topological
insulator into a fully
spin-polarized Chern insulating phase. Our findings not only provide a robust experimental scheme to distinguish AMs from conventional AFMs, but also establish a promising pathway toward dissipationless spintronic applications.
Read the full abstract ▾
Materials Science
Structural Commonalities in Amorphous Elemental Materials
I. Rodríguez, R. M. Valladares, A. Valladares et al. (+5 more)
In the In recent times, the research community has explored diverse structures and novel fabrication methods for amorphous solids. This work investigates structural trends among different classes of amorphous materials to identify universal commonalities and fundamental differences. It is found that amorphous
semiconductors exhibit similar Pair Distribution Functions (PDFs), characteristic of their underlying network-forming nature. On the other hand, amorphous metallic systems also display internally consistent PDF profiles, but different from those of the semiconducting materials. A comparative analysis of short-range and medium-range order reveals that while
semiconductor structures feature a well-isolated first peak, with a zero-intensity region between the first and second peaks, metallic systems maintain a significant non-zero value between the first and second peaks. Furthermore, the second peak in metallic systems is bimodal, featuring a distinct elephant-like profile. Amorphous semi-metals display a still different profile, and the PDFs for Bi, for example, are similar to those for As and Sb. To deepen this structural comparison, we have incorporated amorphous Plane Angle Distributions (PADs), providing a more complete perspective on the local geometry. We introduce a renormalization approach that uses the positions of the first peaks in the PDFs to quantify these structural coincidences and discuss the implications.
Read the full abstract ▾
All authors I. Rodríguez, R. M. Valladares, A. Valladares, D. Hinojosa-Romero, F. B. Quiroga, S. Calderón-Alba, R. S. Vilchis-Peyret, A. A. Valladares
Materials Science
Revisiting the symmetry and optical phonons of altermagnetic $\alpha$-MnTe
Ece Uykur, Marcos V. Gonçalves-Faria, Sahana Rößler et al. (+5 more)
Using infrared (IR) and Raman spectroscopies combined with high-resolution x-ray diffraction, we address several controversial aspects of altermagnetic $\alpha$-MnTe. We show that mechanical stress applied to
crystals of this material causes a drastic broadening of Bragg peaks that conceals signatures of additional phases present in the sample. Indeed, spatially resolved Raman spectroscopy reveals that the modes around 175 cm$^{-1}$ often reported in $\alpha$-MnTe are not reproducible across different positions and samples and originate from the secondary phase of MnTe$_2$. By combining spectroscopic probes with ab initio calculations, we establish the IR-active optical
phonon of $\alpha$-MnTe around 155 cm$^{-1}$ ($E_{1u}$) and the Raman-active optical
phonon around 100 cm$^{-1}$ ($E_{2g}$) at room temperature. Two intense Raman modes around 120 and 140 cm$^{-1}$ are shown to be intrinsic, even though they can not be assigned to $\Gamma$-point optical
phonons. These modes couple to
magnetic order in $\alpha$-MnTe and also to the transient reflectivity resulting in coherent oscillations. Both 6-fold rotation
symmetry and inversion
symmetry are preserved in $\alpha$-MnTe within our experimental resolution.
Read the full abstract ▾
All authors Ece Uykur, Marcos V. Gonçalves-Faria, Sahana Rößler, Victoria A. Ginga, Marcus Schmidt, Stephan Winnerl, Manfred Helm, Alexander A. Tsirlin
Materials Science
Real-time exciton dynamics in two-dimensional materials under ultrashort laser pulses
Dmitry Tumakov and Daria Popova-Gorelova
The optical response of two-dimensional materials is often significantly impacted by excitonic effects due to the reduced screening of attractive Coulomb interactions in low-dimensional systems. Accurate modeling of
exciton formation and real-time dynamics is essential to understanding their ultrafast optical properties. In this study, we theoretically investigate the
exciton dynamics in a two-dimensional hexagonal boron nitride (h-BN) and a germanium sulfide (GeS) monolayers exposed to an ultrashort
laser pulse. We analyze the system's response to the external field in one- and two-
photon excitation regimes. For our calculations, we combine a state-of-the-art ab initio approach to study
exciton dynamics with a highly precise numerical scheme. We incorporate electron-hole interactions through a non-local self-energy operator derived from the many-body perturbation theory (MBPT) within the time-dependent adiabatic $GW$ (TD-a$GW$) approximation. We implement this approach using the full-electron LAPW+lo method in the all-electron exciting package. Our results elucidate the role of many-body effects in shaping ultrafast excitonic processes in two-dimensional materials, contributing to the fundamental understanding necessary for optoelectronic and photonic applications.
Read the full abstract ▾
Materials Science
Giant orbital magnetoresistance in the antiferromagnet CoO driven by dynamic orbital angular momentum interaction
Christin Schmitt, Sachin Krishnia, Edgar Galindez-Ruales et al. (+12 more)
Recent predictions of orders of magnitude larger orbital current effects compared to
spin currents have attracted significant interest. However, the full potential of
giant orbital currents remains to be fully harnessed, since so far, the orbital currents need to be converted into
spin currents before they can interact with the static magnetization that is dominated by
spin angular momentum in conventional magnets. By using a magnet dominated by orbital angular momentum, we demonstrate a more than fifty-fold enhancement in orbital
Hall magnetoresistance in CoO/Cu*, compared to conventional CoO/Pt. This is found to be driven by a unique interaction between dynamic orbital angular momentum from surface oxidized Cu* (i.e., the orbital current) and the static orbital angular momentum which constitutes the
magnetic moments in the
antiferromagnetic insulator CoO. A distinctive scattering mechanism for orbital currents at the CoO interface leads to a sign reversal in orbital magnetoresistance in CoO/Cu* compared to CoO/Pt. Our results show how by using orbital angular momentum-dominated materials such as CoO, we can harness the benefits of
giant orbital currents that have not been possible using conventional
spin-dominated magnets, for orbitronics-based devices, offering unprecedented energy efficiency for operations of antiferromagnets that combine ultimate stability with THz dynamics.
Read the full abstract ▾
All authors Christin Schmitt, Sachin Krishnia, Edgar Galindez-Ruales, Luca Micus, Takashi Kikkawa, Hiroki Arisawa, Marjana Lezaic, Duc Tran, Timo Kuschel, Jairo Sinova, Eiji Saitoh, Gerhard Jakob, Olena Gomonay, Yuriy Mokrousov, Mathias Kläui
Materials Science
Understanding the anisotropic response of $\beta$-Ga$_2$O$_3$ to ion implantation
Duarte Magalhães Esteves, Ru He, Sérgio Magalhães et al. (+8 more)
While $\beta$-Ga$_2$O$_3$ is considered a promising wide bandgap
semiconductor, the impact of ion-induced defect formation and anisotropic elasticity remains poorly understood. Here, we combine a simulation and experiment X-ray diffraction (XRD) study of the strain-stress dynamics induced by ion implantation into $\beta$-Ga$_2$O$_3$ single-
crystals with different surface orientations. The strain accumulation in the out-of-plane direction is observed by XRD to occur in an anisotropic manner, with compressive strain along the [010] direction and tensile strain along the directions perpendicular to (100) and (001). An anisotropic stress/strain accumulation model is proposed and probed via Molecular Dynamics (MD), showing an excellent agreement with the experiments. For higher damage levels, pole figures obtained both experimentally and by MD via a novel reciprocal-space projection method reveal an orientation-independent $\beta$-to-$\gamma$ phase transition, with a fixed crystallographic relationship between the polymorphs. By exploring the strain-stress dynamics in anisotropic systems, this work establishes a method to directly compare macroscale diffraction experiments and atomistic simulations and opens a new path to engineer the properties of such systems utilizing their anisotropic response to ion implantation/irradiation.
Read the full abstract ▾
All authors Duarte Magalhães Esteves, Ru He, Sérgio Magalhães, Miguel Carvalho Sequeira, Ângelo Rafael Granadeiro da Costa, Julia Zanoni, Joana Rodrigues, Teresa Monteiro, Flyura Djurabekova, Katharina Lorenz, Marco Peres
Materials Science
Unlocking extreme doping and strain in epitaxial monocrystalline silicon
Léonard Desvignes, Dominique Débarre, Ludovic Largeau et al. (+8 more)
Hyperdoping, overcoming the solubility limit of dopants in a crystalline
semiconductor, is a fertile method for the enhancement of the electrical, structural and optical devices' performances and for the exploration of exotic phases such as superconductivity. We demonstrate an unprecedented control on the dopant concentration and
lattice deformation via nanosecond
laser doping in epitaxial boron doped silicon, achieving record carrier concentrations (8 at.%) and
lattice deformations (3 %). Probing the microscopical hyperdoping limitations, we show that the relevant mechanisms are caught by a simple combinatorial model, which quantitatively explains both the experimental carrier concentration and
lattice deformation
evolution. First principle calculations complete and support such simple model. Indeed, at the high doping levels now attainable, the maximum carrier concentration is inherently limited by the probability of two or three substitutional dopants occupying neighboring
lattice sites, forming partially inactive complexes that we detail. This description is valid in the case of perfect layers with no crystallographic defects and a fully substitutional dopant occupation, highlighting the quality of the epitaxial layers realized.
Read the full abstract ▾
All authors Léonard Desvignes, Dominique Débarre, Ludovic Largeau, Géraldine Hallais, Gilles Patriarche, Giacomo Priante, Eric Ngo, Olivia Mauguin, Alberto Debernardi, Bernard Sermage, Francesca Chiodi
Materials Science · Cross-listed from physics.comp-ph
Frustrated supermolecules: the high-pressure phases of crystalline methane
Marcin Kirsz, Miguel Martinez-Canales, Ayobami D. Daramola et al. (+3 more)
Methane is the simplest hydrocarbon, yet it exhibits an extraordinarily complicated series of
crystal phases. Notably, the non-plastic phases have large unit
cells with nearly, but not quite cubic
symmetry. Furthermore, although non-polar molecules interact very weakly, their reorganisation across phase transitions is very sluggish. Here, we demonstrate that these complex structures can be understood as simple packing of near-spherical supermolecular clusters of methane molecules: the departure from cubic
symmetry arising from the non-spherical nature of the molecules. We use molecular dynamics based on density functional theory calculations to simulate the finite-temperature
crystal structures of methane, finding that the complex Phase A is based around a 13-molecule regular icosahedron, with 8 additional molecules forming the 21-molecule unit
cell. Similarly, Phase B is based on a body-centred cubic bcc packing of 17-molecule Z16 polyhedra, with the remaining 12 molecules per
cell in tetrahedral interstices. We demonstrate that the favored intermolecular separation depends sensitively on molecular orientation, leading to hindered rotation and suppressed
entropy. The structures are determined by a trade-off between efficient packing and
entropy.
Read the full abstract ▾
All authors Marcin Kirsz, Miguel Martinez-Canales, Ayobami D. Daramola, John S. Loveday, Ciprian G. Pruteanu, Graeme J Ackland
Materials Science
Spin Inertia as a Source of Topological Magnons: Chiral Edge States from Coupled Precession and Nutation
Subhadip Ghosh, Mikhail Cherkasskii, Ritwik Mondal et al. (+2 more)
Spin inertia has been demonstrated to give rise to high-frequency nutational excitations beyond the conventional low-frequency precessional modes. Here, we demonstrate that the hybridization between precessional and nutational
magnons may give rise to topological phenomena in the
spin-wave spectrum. This hybridization requires the presence of interactions breaking angular-momentum conservation, such as the pseudodipolar interaction. We show on the example of a honeycomb ferromagnet how topological gaps open between the precessional and nutational bands that host
chiral edge states in slab geometries. Our work establishes a theoretical foundation for exploring inertial
spin dynamics as a new route to engineer topological phases in
magnetic materials.
Read the full abstract ▾
All authors Subhadip Ghosh, Mikhail Cherkasskii, Ritwik Mondal, Alexander Mook, Levente Rózsa
Materials Science
Tracing the film structure of an organic semiconductor with photoemission orbital tomography
Monja Stettner, Siegfried Kaidisch, Andrey V. Matetskiy et al. (+7 more)
Photoemission orbital
tomography (POT) is a powerful tool for investigating the orbitals and electronic band structure of oriented layers of organic molecules. In many cases, POT allows conclusions to be drawn regarding the
geometric structure, but so far it has been mainly applied to (sub)monolayers and rarely to
bilayers, raising the question of whether POT can also provide structure information for thicker films. Here, we use POT to analyze the band dispersion in up to eight layers of $\alpha$-sexithiophene (6T) adsorbed on Cu(110)-p($2\times1$)O. This linear oligomer turns out to be a textbook example that exemplifies the concepts of intra- and intermolecular band dispersion in molecules. Moreover, the rich band and orbital structure information available from POT for this system enables us to trace subtle changes in the
crystal structure as a function of layer thickness. Specifically, we find that the periodicity of an intermolecular band changes with film thickness, revealing an increase of the intralayer distance between the molecules with the number of layers. At the same time, the momentum distribution of photoemission from the highest occupied molecular orbital of 6T discloses a decrease of the molecular tilt angle. Following the
evolution of tilt angle and
lattice constant with layer thickness, we observe – purely based on electronic structure data – that the surface-templated monolayer structure relaxes into the structure of bulk 6T
crystals. The experimental findings agree well with the results of density functional theory calculations.
Read the full abstract ▾
All authors Monja Stettner, Siegfried Kaidisch, Andrey V. Matetskiy, Eric Fackelman, Serguei Soubatch, Christian Kumpf, François C. Bocquet, Michael G. Ramsey, Peter Puschnig, F. Stefan Tautz
Materials Science · Cross-listed from physics.optics
Long-range mid-infrared energy transfer mediated by hyperbolic phonon polaritons
Gonzalo Álvarez-Pérez, Simone De Liberato and Huatian Hu
We provide a framework to theoretically describe long-range energy transfer in single and twisted two-dimensional
hyperbolic slabs. We demonstrate that
phonon polaritons (PhPs,
quantum superpositions of
photons and
lattice vibrations in polar dielectrics) can mediate and enhance room-temperature energy transfer at ranges far exceeding those of conventional mid-infrared (MIR) platforms, and with extreme directionality. This is because the dipole-dipole interaction potential energy diverges along the asymptotes of the real-space
hyperbolic opening angle. Our findings allow us to extend classical and
quantum interactions between dipoles, typically strictly confined to the near-field, beyond several free-space MIR wavelengths. We use $\alpha$-MoO$_3$ as a representative material, but this mechanism is not limited to the MIR: it is general to anisotropic media across the whole electromagnetic spectrum.
Read the full abstract ▾
Materials Science
Validation of constant mean free path and relaxation time approximations for metal resistivity: explicit treatment of electron-phonon interactions
Subeen Lim, Yumi Kim, Gyungho Maeng et al. (+1 more)
The figure of merit $\rho \lambda$ the product of resistivity and mean free path (MFP) evaluated from first-principles calculations, is widely adopted to screen promising interconnect metals with high electrical conductivity at ultranarrow dimensions. However, the $\rho \lambda$ has been calculated without addressing the validity of the assumption that the MFP is independent of the wavevector $\mathbf{k}$. Here, we assess the validity of the constant MFP approximation, by estimating the $\mathbf{k}$-dependent MFPs for (an)isotropic elemental metals, with explicit treatment of electron-
phonon interactions. Additionally, we verify the validity of the constant relaxation time approximation (CRTA) for resistivity calculations. We show that both the constant MFP approximation and CRTA are reasonable even for highly anisotropic
Fermi surfaces. Our results support the practical use of those approximations in transport studies, where explicit electron-
phonon calculations are not feasible.
Read the full abstract ▾
All authors Subeen Lim, Yumi Kim, Gyungho Maeng, Yeonghun Lee
Materials Science
Electric field switching of chiral phonons
Michael Grimes, Clifford J. Allington, Hiroki Ueda et al. (+8 more)
Lattice vibrations carrying angular momentum, known as
chiral phonons, have emerged as a promising route to control and understand complex material properties, yet their deterministic manipulation remains largely unexplored. Here we demonstrate electric-field switching of
phonon angular momentum in the technologically relevant ferroelectric BaTiO3. Using circularly dichroic resonant inelastic X-ray scattering (CD-RIXS) at the oxygen K edge, we directly probe the
phonon angular momentum and compare the measured dichroism with first-principles predictions of
phonon-mode chirality. We find excellent agreement, revealing a momentum-dependent circular-dichroism contrast that exhibits a reversible gyroelectric effect, stable for at least 15 hours. Our results establish a robust mechanism for non-volatile control of
chiral phonons and point towards new opportunities for
phonon-based information and energy technologies.
Read the full abstract ▾
All authors Michael Grimes, Clifford J. Allington, Hiroki Ueda, Carl P. Romao, Kurt Kummer, Puneet Kaur, Li-Shu Wang, Yao-Wen Chang, Jan-Chi Yang, Shih-Wen Huang, Urs Staub
Materials Science
Long-Lived Interlayer Excitons and Type-II Band Alignment in Janus MoTe2/CrSBr van der Waals Heterostructures
Mohammad Ali Mohebpour, Peter C Sherrell, Catherine Stampfl et al. (+2 more)
Identifying two-dimensional
heterostructures with exceptional electronic and optical properties remains an active area of research in advanced optoelectronics. Here, we present a comprehensive first-principles investigation of the electronic, optical, and excitonic properties of a MoTe2/CrSBr van der Waals
heterostructure using density functional theory combined with fully relativistic GW and Bethe-Salpeter equation calculations. The close
lattice matching between the two monolayers enables the formation of stable heterobilayers with two inequivalent interfaces (Te-S and Te-Br) arising from the Janus nature of CrSBr. Both interfaces are dynamically and thermally stable and exhibit type-II band
alignment with a direct quasiparticle gap, promoting efficient spatial separation of electrons and holes. The
heterostructure hosts interlayer
excitons with lifetimes 18-45 ps significantly longer than those of the intralayer
excitons in the isolated MoTe2, 3.6 ps, and CrSBr, 8.1 ps, monolayers. Moreover, the optical gap,
exciton binding energy, and
exciton lifetime of the
heterostructure are strongly modulated by the built-in electric field associated with the Janus layer. These results establish the MoTe2/CrSBr
heterostructure as a versatile platform for engineering long-lived interlayer
excitons and highlight its potential for next-generation optoelectronic and light-harvesting applications.
Read the full abstract ▾
All authors Mohammad Ali Mohebpour, Peter C Sherrell, Catherine Stampfl, Carmine Autieri, Meysam Bagheri Tagani
Materials Science
Spectra-Scope : A toolkit for automated and interpretable characterization of material properties from spectral data
Amalya C. Johnson, Chris Fajardo, Leena Sansguiri et al. (+2 more)
Spectroscopy is a central pillar of materials characterization, providing useful information on properties like structure, composition, or excited state dynamics of a system. However, many spectroscopic techniques present challenges in the development of interpretable, performant, and reliable supervised learning models due to the wide range of possible nonlinear correlations that can exist between the signal and the response variable (target) of interest. Here, we present Spectra-Scope, an open-source AutoML framework for automatic characterization of material properties from spectroscopy data using interpretable machine learning (ML) models. The software is implemented in Python and a no-code web application. It comprises tools for data preprocessing, nonlinear feature extraction, machine learning model training, and feature selection. Users can easily train different types of simple, interpretable ML models on a set of feature transformations quickly and with modest computational resources. In this work, we outline the methods of Spectra-Scope and its effectiveness across diverse
datasets, with applications to materials and agricultural spectroscopy data. We show that Spectra-Scope can reproduce performance of comparable models in the literature, and highlight how our emphasis on interpretability can be used to rationalize the behavior of individual models and understand the physical processes behind spectral features.
Read the full abstract ▾
All authors Amalya C. Johnson, Chris Fajardo, Leena Sansguiri, Weike Ye, Steven B. Torrisi
Materials Science
Riemannian geometric classification and emergent phenomena of magnetic textures
Koki Shinada and Naoto Nagaosa
We propose a new classification of
magnetic textures from the viewpoint of differential geometry.
Magnetic textures are conventionally classified into collinear, coplanar, and noncoplanar magnets. These classes are typically characterized by the vector
spin chirality (VSC) and the scalar
spin chirality (SSC), which indicate noncollinearity and noncoplanarity, respectively. However, this conventional classification is incomplete: in particular, noncoplanar textures cannot be fully characterized by the SSC alone, as exemplified by conical magnets. To refine this classification, we analyze the curves and surfaces traced by
spins in real space using differential geometry and introduce two novel scalar
spin chiralities that properly characterize noncoplanarity: the geodesic scalar
spin chirality and the torsional scalar
spin chirality. These quantities are directly connected to differential geometry: the former reflects the geodesic
curvature while the latter is related to the torsion. Based on these chiralities, we identify three distinct classes of noncoplanar
magnetic textures. Furthermore, analogous to the roles of the VSC and the conventional SSC in emergent electrodynamics, the geodesic SSC gives rise to novel emergent phenomena. By constructing a semiclassical theory including nonadiabatic effects and higher-order spatial gradients of
magnetic textures, we demonstrate that the geodesic SSC induces an emergent band asymmetry, leading to nonreciprocal responses as a
quantum geometric effect. This mechanism is a purely orbital effect, requiring no
spin-orbit coupling, and the resulting discussion runs in parallel with the conventional picture of the topological
Hall effect driven by the SSC. The
geometric viewpoint developed here will provide broad new insights into classification,
quantum geometry, emergent electrodynamics, and a wider variety of emergent phenomena.
Read the full abstract ▾