Materials Science
Effective-Hamiltonian reconstruction through Bloch-wave interferometry in bulk GaAs driven by strong THz fields
Qile Wu, Seamus D. O Hara, Joseph B. Costello et al. (+3 more)
Reconstructing effective
Hamiltonians of condensed matter systems directly from experimental data is challenging because of the intricate relationship between
Hamiltonian parameters and observables. Here, we reconstruct an effective three-band electron-hole (e-h)
Hamiltonian in bulk GaAs based on high-order sideband generation (HSG) induced by quasi-continuous NIR and THz
lasers. We perform polarimetry of high-order sidebands while varying the wavelength and polarization of the NIR
laser, as well as the strength of the THz field. An analytic model is derived to incorporate the effects of both dephasing and
quantum fluctuations around the semiclassical e-h recollision pathways. Surprisingly, the contribution of
quantum fluctuations to the decay of sideband intensity with increasing sideband order is comparable to the contribution of dephasing. We simultaneously and unambiguously determine through Bloch-wave interferometry the effective
Hamiltonian parameter that determines the e-h reduced masses, the bandgap of GaAs, and two dephasing constants associated with two e-h species. We demonstrate that full
Hamiltonian reconstruction can be achieved by combining HSG measurements with absorbance spectroscopy. Unexpectedly, we find that the extracted bandgap of GaAs is about 10 meV larger than the value inferred from previous absorbance measurements.
Quantum-kinetic analysis suggests that, in the HSG experiments, the e-h energy may be renormalized through Fröhlich interaction that is modulated by the strong THz fields. We also show that the energy threshold for optical-
phonon emission can be suppressed by applying a strong THz field, leading to nearly constant dephasing rates.
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All authors Qile Wu, Seamus D. O Hara, Joseph B. Costello, Loren N. Pfeiffer, Ken W. West, Mark S. Sherwin
Materials Science · Cross-listed from cond-mat.supr-con
Superconductor discovery in the emerging paradigm of Materials Informatics
Huan Tran, Hieu-Chi Dam, Christopher Kuenneth et al. (+2 more)
The last two decades have witnessed a tremendous number of computational predictions of hydride-based (
phonon-mediated)
superconductors, mostly at extremely high pressures, i.e., hundreds of GPa. These discoveries were heavily driven by Migdal-Éliashberg theory (and its first-principles computational implementations) for electron-
phonon interactions, the key concept of
phonon-mediated superconductivity. Dozens of predictions were experimentally synthesized and characterized, triggering not only enormous excitement in the community but also some debates. In this Article, we review the computational-driven discoveries and the recent developments in the field from various essential aspects, including the theoretical, computational, and, specifically, artificial intelligence (AI)/machine learning (ML) based approaches emerging within the paradigm of materials informatics. While challenges and critical gaps can be found in all of these approaches, AI/ML efforts specifically remain in its infant stage for good reasons. However, opportunities exist when these approaches can be further developed and integrated in concerted efforts, in which AI/ML approaches could play more important roles.
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All authors Huan Tran, Hieu-Chi Dam, Christopher Kuenneth, Tuoc N. Vu, Hiori Kino
Materials Science
Revisiting and Accelerating the Basin Hopping Algorithm for Lennard-Jones Clusters: Adaptive and Parallel Implementation in Python
Oliver Carmona, Peter Ludwig Rodríguez-Kessler, Sebastián Salazar-Colores et al. (+1 more)
We present an adaptive and parallel implementation of the Basin Hopping (BH)
algorithm for the global optimization of atomic clusters interacting via the Lennard-Jones (LJ) potential. The method integrates local energy minimization with adaptive step-size Monte Carlo moves and simultaneous evaluation of multiple trial structures, enabling efficient exploration of complex potential energy landscapes while maintaining a balance between exploration and refinement. Parallel evaluation of candidate structures significantly reduces wall-clock time, achieving nearly linear speedup for up to eight concurrent local minimizations. This framework provides a practical and scalable strategy to accelerate Basin Hopping searches, directly extendable to ab initio calculations such as density functional theory (DFT) on high-performance computing architectures.
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All authors Oliver Carmona, Peter Ludwig Rodríguez-Kessler, Sebastián Salazar-Colores, Alvaro Muñoz-Castro
Materials Science · Cross-listed from cs.CV
Generative Image Restoration and Super-Resolution using Physics-Informed Synthetic Data for Scanning Tunneling Microscopy
Nikola L. Kolev, Tommaso Rodani, Neil J. Curson et al. (+2 more)
Scanning tunnelling microscopy (STM) enables atomic-resolution imaging and atom manipulation, but its utility is often limited by tip degradation and slow serial data acquisition. Fabrication adds another layer of complexity since the tip is often subjected to large voltages, which may alter the shape of its apex, requiring it to be conditioned. Here, we propose a machine learning (ML) approach for image repair and super-resolution to alleviate both challenges. Using a
dataset of only 36 pristine experimental images of Si(001):H, we demonstrate that a physics-informed synthetic data generation pipeline can be used to train several state-of-the-art flow-matching and
diffusion models. Quantitative evaluation with metrics such as the CLIP Maximum Mean Discrepancy (CMMD) score and structural similarity demonstrates that our models are able to effectively restore images and offer a two- to fourfold reduction in image acquisition time by accurately reconstructing images from sparsely sampled data. Our framework has the potential to significantly increase STM experimental throughput by offering a route to reducing the frequency of tip-conditioning procedures and to enhancing frame rates in existing high-speed STM systems.
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All authors Nikola L. Kolev, Tommaso Rodani, Neil J. Curson, Taylor J.Z. Stock, Alberto Cazzaniga
Materials Science
Liquid anomalies and Fragility of Supercooled Antimony
Flavio Giuliani, Francesco Guidarelli Mattioli, Yuhan Chen et al. (+5 more)
Phase-change materials (PCMs) based on group IV, V, and VI elements, such as Ge, Sb, and Te, exhibit distinctive
liquid-state features, including thermodynamic anomalies and unusual dynamical properties, which are believed to play a key role in their fast and reversible crystallization behavior. Antimony (Sb), a monoatomic PCM with ultrafast switching capabilities, stands out as the only elemental member of this group for which the properties of the
liquid and supercooled states have so far remained unknown. In this work, we use large-scale molecular dynamics simulations with a neural network potential trained on first-principles data to investigate the
liquid, supercooled, and amorphous phases of Sb across a broad pressure-temperature range. We uncover clear signatures of anomalous behavior, including a density maximum and non-monotonic thermodynamic response functions, and introduce a novel octahedral order parameter that captures the structural
evolution of the
liquid. Moreover, extrapolation of the viscosity to the glass transition, based on configurational and excess
entropies, indicates that Sb is a highly fragile material. Our results present a compelling new case for the connection between the
liquid-state properties of phase-change materials and their unique ability to combine high amorphous-phase stability with ultrafast crystallization.
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All authors Flavio Giuliani, Francesco Guidarelli Mattioli, Yuhan Chen, Daniele Dragoni, Marco Bernasconi, John Russo, Lilia Boeri, Riccardo Mazzarello
Materials Science
Evaluation of Structural Properties and Defect Energetics in Al$_x$Ga$_{1-x}$N Alloys
Farshid Reza, Beihan Chen and Miaomiao Jin
Al$_x$Ga$_{1-x}$N
alloys are essential for high-performance optoelectronic and power devices, yet the role of composition on defect energetics remains underexplored, largely due to the limitations of first-principles methods in modeling disordered
alloys. To address this, we employ a machine learning interatomic potential (MLIP) to investigate the structural and defect-related physical properties in Al$_x$Ga$_{1-x}$N. The MLIP is first validated by reproducing the equation of state,
lattice constants, and elastic constants of the binary endpoints, GaN and AlN, as well as known defect formation and migration energies from density functional theory and empirical potentials. We then apply the MLIP to evaluate elastic constants of AlGaN
alloys, which reveals a non-linear relation with alloying effect. Our results reveal that nitrogen Frenkel pair formation energies and the migration barriers for nitrogen point defects are highly sensitive to the local chemical environment and migration path. In contrast, Ga and Al vacancy migration energies remain relatively insensitive to
alloy composition, whereas their interstitial migration energies exhibit stronger compositional dependence. These results provide quantitative insight into how alloying influences defect energetics in AlGaN, informing defect engineering strategies for improved material performance.
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Materials Science · Cross-listed from cond-mat.supr-con
Nonadiabatic and anharmonic effects in high-pressure H3S and D3S superconductors
Shashi B. Mishra and Elena R. Margine
Superconductivity in compressed H3S arises from the interplay between high-frequency
phonons and a pronounced van Hove singularity near the
Fermi level. Using first-principles calculations, we investigate the superconducting properties of H3S and D3S at 160 and 200 GPa, explicitly incorporating anharmonic
lattice dynamics and first-order vertex corrections to electron-
phonon (e-ph) interactions, thereby going beyond the Migdal approximation underlying conventional Migdal-Eliashberg theory. We find that both anharmonicity and nonadiabatic vertex corrections suppress the effective e-ph coupling and reduce the superconducting critical temperature (Tc). Calculations performed within the energy-dependent full-bandwidth Eliashberg formalism, including both anharmonic and vertex effects, yield Tc values in close agreement with experimental measurements for D3S at both pressures and for H3S at 200 GPa.
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Materials Science
Mutual enhancement of altermagnetism and ferroelectricity
Chi Sun and Jacob Linder
We consider theoretically the possibility of coexisting ferroelectric and metallic altermagnetic order, which has recently been predicted in insulating and semiconducting systems via ab initio calculations. Solving self-consistently a mean-field Hubbard model, accounting also for the energy cost of distorting the
lattice to produce an electric polarization, our results show that metallic altermagnetism and ferroelectricity suppress or enhance each other depending on the doping level of the system. Close to half-filling, the system can lower its energy by becoming altermagnetic, but at the expense of losing the electric polarization. Away from half-filling, the coexistence of ferroelectricity and altermagnetism is much more robust toward an increase in the energy cost associated with the deformation of the
lattice. Therefore, our results suggest that filling fractions corresponding to doping relatively far away from half-filling constitute the most promising regime to look for coexistent ferroelectricity and metallic altermagnetism with mutual enhancement. Moreover, we propose a way to electrically tune altermagnetism between nodal and nodeless phases as well as achieving coexistence of a nodal and nodeless phase for the two
spin species.
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Materials Science
Insights into the adhesion and delamination strength of carbon films on metals by high-throughput ab initio calculations
Elisa Damiani, Margherita Marsili and Maria Clelia Righi
Diamond and diamond-like carbon (DLC) coatings are widely employed for their exceptional mechanical, thermal and chemical properties, but their industrial application is often limited by weak adhesion to metallic substrates. In this work, we employ a high-throughput ab initio approach to systematically investigate the adhesion of diamond/metal interfaces, combining a set of technologically relevant metals (Al, Ag, Au, Cr, Cu, Fe, Ir, Mg, Mo, Pt, Rh, Ti, V, W, Zn) with the C(111), C(111)-2x1 (Pandey reconstructed), C(110), C(100) surfaces, that are most common in diamond and are representative of different types of bonds present in DLC. Thanks to our automated and accurate computational protocol for interface construction and characterization, databases are populated and relevant trends are identified on the effect of surface graphitization, ability to form carbides and metal reactivity on carbon film adhesion and delamination strength. Beyond capturing trends, our workflow yields predictive insights. Indeed, we found that adhesion energy scales with the
geometric mean of the constituent surface energies, providing a simple descriptor for rapid screening; while comparing the work of separation with the metal's cohesive energy anticipates the fracture location under tensile loading. A novel method based on the radial distribution function g(r) analysis is introduced to identify when contact with a metal drives rehybridization of surface carbon from sp2 to sp3, the structural signature of improved resistance to delamination. These structural changes are mirrored by an electronic rearrangement at the interface, quantified by a charge-redistribution descriptor that strongly correlates with adhesion.
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Materials Science
Crystallization Behavior of ZBLAN Glass Under Combined Thermal and Vibrational Effects: Part I – Experimental Investigation
Ayush Subedi, Anthony Torres, Jeff Ganley et al. (+1 more)
ZBLAN glass is a promising material for infrared optical fibers due to its wide transmission window and low theoretical attenuation. However, its strong tendency to crystallize during processing limits optical performance. While microgravity environments have been shown to suppress crystallization, the role of mechanical vibration under normal
gravity conditions remains poorly understood. This study systematically investigates the influence of vibration on the crystallization behavior of ZBLAN using a controlled heating and vibration apparatus. Samples were subjected to varied thermal and vibrational conditions, and their crystallization onset and morphological
evolution were examined through optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). Results show that vibration reduces the crystallization onset temperature, indicating enhanced atomic mobility and nucleation kinetics. Progressive morphological transitions from needle-like to bow-tie and feather-like
crystals were observed with increasing temperature and vibration intensity. Surface roughness analysis corroborates these findings, revealing a significant increase in nanoscale roughness in crystallized regions. Although brief exposure duration and partial thermal decoupling introduced variability among samples, the overall results confirm that vibration acts as a direct facilitator of nucleation rather than a purely thermal effect. This work provides new insight into vibration-induced crystallization in fluoride glasses and establishes the experimental foundation for follow-up modeling and apparatus optimization studies under terrestrial and microgravity conditions.
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All authors Ayush Subedi, Anthony Torres, Jeff Ganley, Ujjwal Dhakal
Materials Science
Intrinsic emittance properties of an Fe-doped Beta-Ga2O3(010) photocathode: Ultracold electron emission at 300K and the polaron self-energy
Louis A. Angeloni, Ir-Jene Shan, J.H. Leach et al. (+1 more)
Measurements of the spectral emission properties of an iron-doped a beta-Ga2O3(010) photocathode at 300 K reveal the presence of an ultracold contribution to the total electron beam emission with a 6 meV mean transverse energy (MTE) in the 3.5-4.4 eV
photon energy range (282-354 nm). This extreme sub-thermal photoemission signal is consistent with direct emission of electrons photoexcited from the Fe dopant states into the low effective mass and positive electron affinity primary conduction band, and it is superimposed on a stronger signal with a larger MTE associated with an (optical)
phonon-mediated momentum resonant Franck-Condon (FC) emission process from a thermally populated and negative electron affinity upper conduction band. For
photon energies above 4.5 eV, a transition from a long to a short transport regime is forced by an absorption depth reduction to below 100 nm and both MTE signals exhibit spectral trends consistent with
phonon-mediated FC emission if the polaron formation self-energy is included in the temperature of the initial thermalized photoexcited electron distribution.
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All authors Louis A. Angeloni, Ir-Jene Shan, J.H. Leach, W. Andreas Schroeder
Materials Science
Dual quantum locking: Dynamic coupling of hydrogen and water sublattices in hydrogen filled ice
Loan Renaud, Tomasz Poreba, Simone Di Cataldo et al. (+7 more)
Hydrogen hydrates (HH) are a unique class of materials composed of hydrogen molecules confined within crystalline water frameworks. Among their multiple phases, the filled ice structures, particularly the cubic C2 phase, exhibit exceptionally strong host-guest interactions due to ultra-short H2-H2O distances and a 1:1 stoichiometry leading to two interpenetrated identical diamond-like sublattices, one comprised of water molecules, the other of hydrogen molecules. At high pressures,
nuclear quantum effects involving both hydrogen molecules and the water
lattice become dominant, giving rise to a dual-
lattice quantum system. In this work, we explore the sequence of pressure- and temperature-driven phase transitions in HH, focusing on the interplay between molecular rotation, orientational ordering,
lattice symmetry breaking and hydrogen bond symmetrization. Using a combination of computational modeling based on classical and path-integral molecular dynamics,
quantum embedding, and high pressure experiments, including Raman spectroscopy and synchrotron X-ray diffraction at low temperatures and high pressures, we identify signatures of
quantum-induced ordering and structural transformations in the C2 phase. Our findings reveal that orientational ordering in HH occurs at much lower pressures than in solid hydrogen, by inducing structural changes in the water network and enhancing the coupling of water and hydrogen dynamics. This work provides new insights into the
quantum behavior of hydrogen under extreme mechanochemical confinement and establishes hydrogen-filled ices as a promising platform for the design of hydrogen-rich
quantum materials.
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All authors Loan Renaud, Tomasz Poreba, Simone Di Cataldo, Alasdair Nicholls, Léon Andriambariarijaona, Maria Rescigno, Richard Gaal, Michele Casula, A. Marco Saitta, Livia Eleonora Bove
Materials Science · Cross-listed from eess.SY
Over 3 kV and Ultra-Low leakage Vertical (011) e̱ta}-Ga2O3 Power Diodes with Engineered Schottky Contact and High-permittivity Dielectric Field Plate
Emerson J. Hollar and Esmat Farzana
We report over 3 kV breakdown voltage and ultra-low leakage (011) e̱ta}-Ga2O3 power devices utilizing Schottky barrier engineering and high-permittivity (ąppa}) dielectric (ZrO2) field plate. The (011) orientation of e̱ta}-Ga2O3 enabled low background doping and thick drift layers which are promising to support kV-class vertical e̱ta}-Ga2O3 power switches. The Schottky barrier engineering was performed with a composite Pt cap/PtOx/Pt (1.5 nm) anode contact to take advantage of the enhanced reverse blocking capabilities enabled by PtOx while allowing low turn-on voltage by the interfacing thin Pt layer. We also performed a systematic study using a co-processed Pt/(011) e̱ta}-Ga2O3 Schottky barrier diodes (SBDs) on the same wafer. The bare SBDs revealed a breakdown voltage of ~1.5 kV, while the field-plate Pt/(011) e̱ta}-Ga2O3 SBDs achieved an increased breakdown voltage of 2.75 kV owing to the edge field management. Further enhancement of the breakdown voltage was achieved by tunneling leakage management using composite Pt cap/PtOx/Pt (1.5 nm) Schottky contacts that ultimately enabled breakdown voltage of 3.7 kV for the field-plate diodes. Remarkably, the Pt cap/PtOx/Pt (1.5 nm) Schottky contacts maintained similar turn-on voltage as the Pt/(011) e̱ta}-Ga2O3 SBDs. The combination of efficient tunneling leakage management by composite Pt cap/PtOx/Pt (1.5 nm) contacts with similar turn-on voltage, edge field reduction by high-ąppa} dielectric ZrO2 field plate, as well as the advantageous material properties offered by (011) e̱ta}-Ga2O3 demonstrate a promising strategy for developing ultra-low leakage and multi-kV class vertical (011) e̱ta}-Ga2O3 power devices.
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Materials Science
Spin-dependent anisotropic electron-phonon coupling in KTaO$_3$
Giulia Venditti, Francesco Macheda, Paolo Barone et al. (+2 more)
KTaO$_3$ (KTO) is an incipient ferroelectric, characterized by a softening of the lowest transverse optical (TO) mode with decreasing temperature. Cooper pairing in the recently discovered KTO-based
heterostructures has been proposed to be mediated by the soft TO mode. Here we study the electron coupling to the zone-center odd-parity modes of bulk KTO by means of relativistic Density Functional Perturbation Theory (DFPT). The coupling to the soft TO mode is by far the largest, with comparable contributions from both intraband and interband processes. Remarkably, we find that for this mode,
spin-non-conserving
matrix elements are particularly relevant. We develop a three-band microscopic model with
spin-orbit coupled $t_{2g}$ orbitals that reproduces the main features of the ab initio results. For the highest energy band, the coupling can be understood as a "dynamical" isotropic Rashba effect. In contrast, for the two lowest bands, the Rashba-like coupling becomes strongly anisotropic. The DFPT protocol implemented here enables the calculation of the full electron-
phonon coupling
matrix projected onto any mode of interest, and it is easily applicable to other systems.
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All authors Giulia Venditti, Francesco Macheda, Paolo Barone, José Lorenzana, Maria N. Gastiasoro
Materials Science
Combined ab initio and experimental study of phosphorus-based anti-wear additives interacting with iron and iron oxide
Francesca Benini, Paolo Restuccia, Sophie Loehlé et al. (+2 more)
The performance of phosphorus-based lubricant additives is governed by their adsorption, stability, and reactivity at the metal interface. In this study, we investigate the adsorption behavior and tribochemical stability of three additives: Octyl Acid Phosphate (OAP), Dibutyl Hydrogen Phosphite (DBHP), and Amine Neutralized Acid Phosphate (ANAP). These additives are studied on iron and hematite surfaces using both ab initio calculations and experimental analyses on steel. Simulations revealed that ANAP exhibited the strongest adsorption on iron, followed by DBHP, while OAP showed weaker interactions, though its chemisorption was enhanced on hematite via hydrogen loss. Under tribological conditions, the DBHP phosphite dissociated more readily than the other two phosphates molecules due to its lower phosphorus coordination, as confirmed by bond order analysis. Quartz
crystal microbalance (QCM) measurements indicated significant differences in adsorption behavior across temperatures, with DBHP forming stable deposits, while ANAP exhibited poor retention, in agreement with ab initio molecular dynamics simulations. X-ray photoelectron spectroscopy (XPS) confirmed DBHP's strong chemisorption and molecular dissociation, leading to increased phosphorus deposition. OAP, despite forming a phosphorus-based layer, caused a reduction in Fe
oxide, consistent with its hydrogen release mechanism observed in simulations. These findings highlight the critical role of molecular structure and oxidation state in tribofilm formation and stability. Understanding these interactions at the atomic level provides valuable insights for designing high-performance lubricant additives for extreme operating conditions.
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All authors Francesca Benini, Paolo Restuccia, Sophie Loehlé, Quentin Arnoux, Maria Clelia Righi
Materials Science · Cross-listed from quant-ph
Second-order Stark shifts exceeding 10$\,$GHz in electrically contacted SiV$^-$ centers in diamond
Manuel Rieger, Nori N. Chavira Leal, Rubek Poudel et al. (+7 more)
Negatively charged silicon vacancy centers (SiV$^-$) in diamond exhibit excellent
spin coherence and optical properties, making them promising candidates for
quantum technologies. However, the strain-induced inhomogeneous distribution of optical transition frequencies poses a challenge for scalability. We demonstrate electrical tuning of the SiV$^-$ center zero-
phonon lines using in-plane contacts to apply moderate electric fields up to 45$\,$MV/m. The second-order Stark shift exceeds 10$\,$GHz, which is of the same order of magnitude as the 15$\,$GHz inhomogeneous distribution of SiV$^-$ observed in emitters embedded in optical nanostructures such as photonic
crystal nanocavities. Analysis of individual SiV$^-$ centers shows significant variation in polarizabilities between defects indicating that the polarizability strongly depends on local parameters like strain. The observed polarizabilities are 3-25 times larger than those of tin vacancy centers, which we attribute to valence band resonances that delocalize the $e_u$ wavefunctions. Photoluminescence excitation measurements reveal that optical linewidths increase moderately with applied electric field strength. Our results demonstrate that large electrical Stark shifts can overcome the inhomogeneous distribution of transition frequencies, representing a significant step toward scalable SiV$^-$-based
quantum technologies such as
quantum repeaters.
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All authors Manuel Rieger, Nori N. Chavira Leal, Rubek Poudel, Tobias Waldmann, Lina M. Todenhagen, Stefan Kresta, Viviana Villafane, Martin S. Brandt, Kai Müller, Jonathan J. Finley
Materials Science
Finite-Temperature Ferroelectric Phase Transitions from Machine-Learned Force Fields
Kristoffer Eggestad, Ida C. Skogvoll, Øystein Gullbrekken et al. (+2 more)
Simulating finite temperature phase transitions from first-principles is computationally challenging. Recently, molecular dynamics (MD) simulations using machine-learned force fields (MLFFs) have opened a new avenue for finite-temperature calculations with near-first-principles accuracy. Here we use MLFFs, generated using on-the-fly training, to investigate structural phase transitions in four of the most well-studied ferroelectric
oxides; BaTiO$_3$, PbTiO$_3$, LiNbO$_3$ and BiFeO$_3$. Only using the 0 K ground state structure as input for the training, the resulting MLFFs can qualitatively predict all the main structural phases and phase transitions, while the quantitative results are sensitive to the choice of exchange correlation functional with PBEsol found to be more robust than LDA and r$^2$SCAN. MD simulations also reproduce the experimentally observed order-disorder character of Ti displacements in BaTiO$_3$, the abrupt first order transitions of BiFeO$_3$ and PbTiO$_3$, and the mixed order-disorder and displacive character of the ferroelectric transition in LiNbO$_3$. Finally, we discuss the potential and limitations of using MLFFs for simulating ferroelectric phase transitions.
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All authors Kristoffer Eggestad, Ida C. Skogvoll, Øystein Gullbrekken, Benjamin A. D. Williamson, Sverre M. Selbach
Materials Science · Cross-listed from cond-mat.mes-hall
Effects of interlayer Dzyaloshinskii-Moriya interaction on the shape and dynamics of magnetic twin-skyrmions
Tim Matthies, Levente Rózsa, Roland Wiesendanger et al. (+1 more)
Magnetic skyrmions have been proposed as promising candidates for storing information due to their high stability and easy manipulation by
spin-polarized currents. Here, we study how these properties are influenced by the interlayer Dzyaloshinskii–Moriya interaction (IL-DMI), which stabilizes twin-skyrmions in
magnetic bilayers. We find that the
spin configuration of the twin-skyrmion adapts to the direction of the IL-DMI by elongating or changing the helicities in the two layers. Driving the skyrmions by
spin-polarized currents in the current-perpendicular-to-plane configuration, we observe significant changes either in the skyrmion velocity or in the skyrmion
Hall angle depending on the current polarization. These findings unravel further prospects for skyrmion manipulation enabled by the IL-DMI.
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All authors Tim Matthies, Levente Rózsa, Roland Wiesendanger, Elena Y. Vedmedenko
Materials Science
The Microscopic Nature of Orbital Disorder in LaMnO$_{3}$
Bodoo Batnaran, Andrew L. Goodwin, Michael A. Hayward et al. (+1 more)
We present a revised atomistic picture of the order-disorder transition in the archetypal orbital-ordered perovskite material, LaMnO$_{3}$. Our study uses machine-learning-driven molecular-dynamics simulations which describe the temperature
evolution of pair distribution functions in close agreement with experiment. We find the orbital-disordered phase in LaMnO$_{3}$ to comprise a mixture of differing structural distortions with and without inversion
symmetry, implying a mixture of different orbital arrangements. These distortions are highly dynamic with an estimated lifetime of $\sim 40$ fs at 1,000 K, and their fluctuations converge with the timescales of conventional thermal motion in the high-$T$ phase - indicating that the electronic instability responsible for static Jahn-Teller distortions at low temperature instead drives
phonon anharmonicity at high temperatures. Beyond LaMnO$_{3}$, our work opens an avenue for studying a wider range of correlated materials.
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All authors Bodoo Batnaran, Andrew L. Goodwin, Michael A. Hayward, Volker L. Deringer
Materials Science · Cross-listed from cond-mat.soft
Self-organization, Memory and Learning: From Driven Disordered Systems to Living Matter
Muhittin Mungan, Eric Clement, Damien Vandembroucq et al. (+1 more)
Disordered systems subject to a fluctuating environment can self-organize into a complex history-dependent response, retaining a
memory of the driving. In sheared amorphous solids, self-organization is established by the emergence of a persistent system of mechanical instabilities that can repeatedly be triggered by the driving, leading to a state of high mechanical reversibility. As a result of self-organization, the response of the system becomes correlated with the dynamics of its environment, which can be viewed as a sensing mechanism of the system's environment. Such phenomena emerge across a wide variety of soft matter systems, suggesting that they are generic and hence may depend very little on the underlying specifics. We review self-organization in driven amorphous solids, concluding with a discussion of what self-organization in driven disordered systems can teach us about how simple organisms sense and adapt to their changing environments.
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All authors Muhittin Mungan, Eric Clement, Damien Vandembroucq, Srikanth Sastry
Materials Science
Terahertz Time-Domain Spectroscopy and Density Functional Theory Analysis of Low-Frequency Vibrational Modes of a Benzoxazolium-Coumarin Donor-pi-Acceptor Chromophore
Sidhanta Sahu, Phalguna Krishna Das Vana, Anupama Chauhan et al. (+5 more)
To elucidate low-frequency vibrational modes, we investigate a benzoxazolium–coumarin (BCO+) donor-pi-acceptor derivative using transmission terahertz time-domain spectroscopy (THz-TDS). The retrieved complex refractive index reveals distinct modes at 0.62, 0.85, 1.30, 1.81, and 2.07 THz. Gas-phase density functional theory (DFT) agrees well with these features and enables assignment of specific intramolecular motions. Together, THz-TDS and DFT identify the characteristic low-frequency modes of BCO+ and suggest their connection to intramolecular charge transfer-relevant
nuclear motions, highlighting that THz-TDS can serve as a sensitive probe of vibrational signatures in donor-pi-acceptor systems.
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All authors Sidhanta Sahu, Phalguna Krishna Das Vana, Anupama Chauhan, Poulami Ghosh, Vijay Sai Krishna Cheerala, Sanyam, C. N. Sundaresan, N. Kamaraju
Materials Science
Colloidal quasi-2D Cs2AgBiBr6 double perovskite nanosheets: synthesis and application as high-performance photodetectors
Pannan I. Kyesmen, Eugen Klein, Brindhu Malani S et al. (+2 more)
The search for non-toxic lead-free halide perovskites that can compete with the lead-based counterparts has led to the emergence of double perovskites as potential candidates. Among many options, Cs2AgBiBr6 stands out as one of the most suitable eco-friendly materials for numerous optoelectronic applications. In this study, quasi-2D Cs2AgBiBr6 nanosheets (NSs) were prepared via the low-temperature injection colloidal synthesis and used to fabricate high-performance photodetectors in a transport-layer-free architecture. The reaction temperature and ligands played vital roles in the structural purity, shape, and size of the synthesized Cs2AgBiBr6 NSs. The fabricated NSs disclosed lateral sizes of up to 1.4 um and are only a few nanometers thick. The high-performance photodetectors fabricated using the Cs2AgBiBr6 NSs yielded a high detectivity (D) of 1.15*10^12 Jones, responsivity (R) of 121 mA/W, a notable on/off ratio of 2.39*10^4, and a fast rise and decay time of 857 and 829 us, respectively. The device demonstrates remarkable stability. Basically, it sustains its entire photocurrent after storage in ambient conditions for 80 days. This work showcases a pathway for the colloidal synthesis of quasi-2D Cs2AgBiBr6 lead-free double perovskite NSs with suitable properties for high-performance photodetection and other optoelectronic applications.
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All authors Pannan I. Kyesmen, Eugen Klein, Brindhu Malani S, Rostyslav Lesyuk, Christian Klinke
Materials Science
Two Orders of Magnitude Enhancement in Oxide Ion Conductivity in Cu2P2O7 via Vanadium Substitution: A Pathway Toward SOFC Electrolytes
Bibhas Ghanta, Kuldeep Singh Chikara, Uttam Kumar Goutam et al. (+2 more)
In the quest of green energy, Solid
Oxide Fuel
Cells (SOFC) have drawn considerable
attention for chemical-to-electric energy conversion. In the present paper, we report an enhancement of ionic conductivity in Cu2P2-xVxO7 by vanadium substitution. The electrical (dc and ac conductivity, diffusivity, hopping rate, electric modulus and dielectric properties) and
crystal structural properties of Cu2P2-xVxO7 (x = 0, 0.4, 0.6, 0.8 and 1) are investigated by impedance spectroscopy and
neutron diffraction, respectively. X-ray photoelectron spectroscopy (XPS) study confirms the presence of Cu2+, P5+and V5+ mono-valence states. The dc conductivity results reveal a two orders of magnitude enhancement of ionic conductivity from ~3.81x10-5 S cm-1 for x =0 to ~2.08x10-3 S cm-1 for x =1 at 993 K, revealing a possible application in SOFCs. DC transport number studies reveal that the total conductivity is dominated by ionic conduction (> 95%). In addition, the diffusivity and hopping rate of
oxide ions increase with increasing x. Besides, ac conductivity, electric modulus and dielectric properties have been investigated to illustrate the microscopic conduction mechanism. The derived results suggest that the mechanism for ionic conduction is the correlated barrier hopping (CBH) process. The soft-bond valence sum (BVS) analysis of the
neutron diffraction patterns reveals the three-dimensional (3D)
oxide ion conduction pathways within the
crystal structure. The present study provides a pathway to enhance the ionic conductivity, as well as understanding of microscopic conduction mechanism, ionic conduction pathways and the role of
crystal structure on the ionic conduction.
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All authors Bibhas Ghanta, Kuldeep Singh Chikara, Uttam Kumar Goutam, Anup Kumar Bera, Seikh Mohammad Yusuf
Materials Science
Advanced structural characterization of single-walled carbon nanotubes with 4D-STEM
Antonin Louiset, Daniel Förster, Vincent Jourdain et al. (+5 more)
Single wall carbon nanotubes (SWCNT) exhibit remarkable optical and electrical properties making them one of the most promising materials for next generation electronic and optoelectronic devices. Their electronic properties strongly depend on their chirality, i.e., their structural configuration, as well as on the presence and nature of atomic defects. Currently, the lack of versatile and efficient structural characterization techniques limits SWCNT applications. Here, we report how four-dimensional scanning transmission electron microscopy (4D-STEM) can address critical challenges in SWCNT structural analysis. Using modern fast pixelated electron detectors, we were able to acquire rapidly a large number of low noise electron diffraction patterns of SWCNTs. The resulting 4D-STEM data allow to precisely determine the local chirality of multiple nanotubes at once, with limited electron dose (down to 1750 e-/Å^2) and nanometric spatial resolution (down to 3.1 nm). We also show how this approach enables to track the chirality along a single nanotube, while giving access to the strain distribution. Then, we report how 4D-STEM data enable to reconstruct high-resolution images with electron ptychography. With this second approach, structural information can be obtained with atomic scale spatial resolution allowing atomic defect imaging. Finally, we investigate how multi-slice electron ptychography could provide even further insight on nanotube defect structures thanks to its close to 3D imaging capabilities at atomic resolution.
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All authors Antonin Louiset, Daniel Förster, Vincent Jourdain, Saïd Tahir, Nicola Vigano, Jean-Luc Rouvière, Christophe Bichara, Hanako Okuno
Materials Science · Cross-listed from cond-mat.mes-hall
Strain Engineering of Correlated Charge-Ordered Phases in 1T-TaS2
Rafael Luque Merino, Felix Carrascoso, Eudomar Henríquez-Guerra et al. (+3 more)
Strain engineering is a powerful strategy for controlling the structural and electronic properties of two-dimensional materials, particularly in systems hosting charge density wave (CDW) order. In this work, we apply uniaxial tensile and compressive strain to thin 1T-TaS2 flakes using a flexible, device-compatible platform, and systematically investigate the strain-dependent behavior of the nearly commensurate (NC) to incommensurate (IC) CDW phase transition. This transition is driven by Joule heating at room temperature. Electrical transport measurements reveal that both the switching threshold voltage and the resistance of the NC-CDW phase exhibit clear, reversible strain dependence. Furthermore, we identify a quadratic dependence between the strain-induced resistance change and the threshold voltage, confirming that piezoresistive modulation governs the strain-tunability of the phase transition. We demonstrate a room-temperature, electrically-readout strain and displacement sensor with threshold-like response in a programmable window. These results highlight the potential of 1T-TaS2 for on-chip sensing of strain and displacement.
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All authors Rafael Luque Merino, Felix Carrascoso, Eudomar Henríquez-Guerra, M. Reyes Calvo, Riccardo Frisenda, Andres Castellanos-Gomez
Materials Science · Cross-listed from cond-mat.str-el
Monte Carlo study on critical exponents of the classical Heisenberg model in ferromagnetic icosahedral quasicrystal
Shinji Watanabe, Tsunetomo Yamada, Hiroyuki Takakura et al. (+1 more)
Quasicrystals (QCs) lack three-dimensional periodicity of atomic arrangement but possess long-range structural order, which are distinct from periodic
crystals and random systems. Here, we show how the
ferromagnetic (FM) order arises in the icosahedral QC (i-QC) on the basis of the Monte Carlo simulation of the Heisenberg model on the Yb
lattice of Cd$_{5.7}$Yb composed of regular icosahedrons. By finite-size scaling of the Monte Carlo data, we identified the critical exponents of the magnetization,
magnetic susceptibility, and
spin correlation length, $\beta=0.508(30)$, $\gamma=1.361(59)$, and $\nu=0.792(17)$, respectively. We confirmed that our data satisfy the hyperscaling relation and estimated the other critical exponents $\alpha=-0.376(51)$, $\delta=3.68(23)$, and $\eta=0.282(65)$. These results show a new universality class inherent in the i-QC, which is different from those in periodic magnets and
spin glasses. In the i-QC, each Yb site at vertices of the regular icosahedrons is classified into 8 classes with respect to the coordination numbers of the nearest-neighbor and next-nearest-neighbor bonds. We revealed the FM-transition mechanism by showing that the difference in the local environment of each site is governed by cooperative
evolution of
spin correlations upon cooling, giving rise to the critical phenomena.
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All authors Shinji Watanabe, Tsunetomo Yamada, Hiroyuki Takakura, Nobuhisa Fujita
Materials Science
A Geometric Pathway for Tuning Ferroelectric Properties via Polar State Reconfiguration
Hao-Cheng Thong, Bo Wu, Fan Hu et al. (+7 more)
We report the discovery of a
geometric pathway for tuning ferroelectric properties through thermally driven reconfiguration between coexisting polar states in Li-substituted NaNbO3. Using first-principles density functional theory calculation and 7Li solid-state
nuclear magnetic resonance spectroscopy measurement, we reveal that Li substitution creates two distinct polar configurations whose transformation under annealing enhances the Curie temperature and induces piezoelectric hardening. Our findings establish a geometrically-driven polar state reconfiguration mechanism, providing a general design principle for ferroics whereby macroscopic functional properties can be engineered via
lattice geometry.
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All authors Hao-Cheng Thong, Bo Wu, Fan Hu, Pedro B. Groszewicz, Chen-Bo-Wen Li, Jun Chen, Mao-Hua Zhang, Dragan Damjanovic, Ben Xu, Ke Wang