Search results for "Materials Science | Hot Paper"
showing 10 items of 1457 documents
Coarse-graining collective skyrmion dynamics in confined geometries
2023
Magnetic skyrmions are magnetic quasi-particles with enhanced stability and different manipulation mechanisms using external fields and currents making them promising candidates for future applications for instance in neuromorphic computing. Recently, several measurements and simulations have shown that thermally activated skyrmions in confined geometries, as they are necessary for device applications, arrange themselves predominantly based on commensurability effects. In this simulational study, based on the Thiele model, we investigate the enhanced dynamics and degenerate non-equilibrium steady state of a system in which the intrinsic skyrmion-skyrmion and skyrmion-boundary interaction co…
New Approach to Determine the Quality of Graphene
2017
The reduction of graphene oxide is one of the most facile methods to fabricate a large amount of graphene and the reduction rate of graphene oxide is related with the quality of synthesized graphene for its possible application. The reduction rate is usually determined by using various spectroscopy measurements such as Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Here we propose that the magnetic data can be used as a means of determining the quality of graphene oxide (GO) and reduced graphene oxide (RGO) by the investigation of close relation between magnetic moment and chemical bonding state. Our experimental findings and previous theo…
Spinorial formulation of the GW-BSE equations and spin properties of excitons in 2D Transition Metal Dichalcogenides
2021
In many paradigmatic materials, like Transition Metal Dichalcogenides, the role played by the spin degrees of freedom is as important as the one played by the electron-electron interaction. Thus an accurate treatment of the two effects and of their interaction is necessary for an accurate and predictive study of the optical and electronic properties of these materials. Despite the GW-BSE approach correctly accounts for electronic correlations the spin-orbit coupling effect is often neglected or treated perturbatively. Recently spinorial formulations of GW-BSE have become available in different flavours in material-science codes. Still an accurate validation and comparison of different appro…
Curvature in graphene nanoribbons generates temporally and spatially focused electric currents
2015
Today graphene nanoribbons and other graphene-based nanostructures can be synthesized with atomic precision. But while investigations have concentrated on straight graphene ribbons of fixed crystal orientation, ribbons with intrinsic curvature have remained mainly unexplored. Here, we investigate electronic transport in intrinsically curved graphene nanoribbons coupled to straight leads, using two computational approaches. Stationary approach shows that while the straight leads govern the conductance gap, the presence of curvature blurs the gap and reduces on-off ratio. An advanced time-dependent approach shows that behind the fa\c{c}ade of calm stationary transport the currents run violent…
Long-term stability of phase-separated Half-Heusler compounds
2015
Half-Heusler (HH) compounds have shown high Figure of merits up to 1.5. The key to these high thermoelectric efficiencies is an intrinsic phase separation, which occurs in multicomponent Half-Heusler compounds and leads to an significantly reduction of the thermal conductivity. For commercial applications, compatible n- and p-type materials are essential and their thermal stability under operating conditions, e.g. for an automotive up to 873 K, needs to be guaranteed. For the first time, the long-term stability of n- and p-type HH materials is proved. We investigated HH materials based on the Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both compounds exhibit a …
Including atomic vibrations in XANES calculations: polarization-dependent damping of the fine structure at the Cu K edge of (creat)$_{2}$CuCl$_{4}$
2016
Atomic vibrations are usually not taken into account when analyzing x-ray absorption near edge structure (XANES) spectra. One of the reasons is that including the vibrations in a formally exact way is quite complicated while the effect of vibrations is supposed to be small in the XANES region. By analyzing polarized Cu K edge x-ray absorption spectra of creatinium tetrachlorocuprate [(creat)$_{2}$CuCl$_{4}$], we demonstrate that a technically simple method, consisting in calculating the XANES via the same formula as for static systems but with a modified free-electron propagator which accounts for fluctuations of interatomic distances, may substantially help in understanding XANES of some l…
Interplay between local structure and electronic properties on CuO under pressure
2020
The electronic and local structural properties of CuO under pressure have been investigated by means of X-ray absorption spectroscopy (XAS) at Cu K edge and ab-initio calculations, up to 17 GPa. The crystal structure of CuO consists of Cu motifs within CuO$_4$ square planar units and two elongated apical Cu-O bonds. The CuO$_4$ square planar units are stable in the studied pressure range, with Cu-O distances that are approximately constant up to 5 GPa, and then decrease slightly up to 17 GPa. In contrast, the elongated Cu-O apical distances decrease continuously with pressure in the studied range. An anomalous increase of the mean square relative displacement (EXAFS Debye Waller, \sigma$^2$…
The high-pressure high-temperature phase diagram of calcium fluoride from classical atomistic simulations
2013
We study the phase diagram of calcium fluoride (CaF2) under pressure using classical molecular dynamic simulations performed with a simple pairwise interatomic potential of the Born-Mayer-Huggings form. Our results obtained under conditions 0 < P < 20 GPa and 0 < T < 4000 K reveal a rich variety of multi-phase boundaries involving different crystal, superionic and liquid phases, for all which we provide an accurate parametrization. Interestingly, we predict the existence of three special triple points (i.e. solid-solid-superionic, solid-superionic-superionic and superionic-superionic-liquid coexisting states) within a narrow and experimentally accessible thermodynamic range of 6…
Fabrication and characterization of semiconducting half Heusler YPtSb thin films
2012
The semiconducting half Heusler compound YPtSb was predicted theoretically to be capable of changing into topological insulator under proper strain. In this work, p type semiconducting half-Heusler YPtSb thin films were prepared by magnetron co-sputtering method from a specially designed target for the first time. Textured structure with (111) plane paralleling with (001) of MgO substrate was observed when YPtSb thin films were grown on MgO (100) substrate at 600{\deg}C.Electrical measurements show that the resistivity of YPtSb films decreases with increasing temperature, indicating a semiconductor-like behavior. The carrier density is as high as 1.15 X 10^21 cm-3 at 300 K. The band gap of …
Effect of confinement and Coulomb interactions on the electronic structure of (111) LaAlO$_3$/SrTiO$_3$ interface
2023
A tight binding supercell approach is used for the calculation of the electronic structure of the (111) LaAlO$_3$/SrTiO$_3$ interface. The confinement potential at the interface is evaluated solving a discrete Poisson equation by means of an iterative method. In addition to the effect of the confinement, local Hubbard electron-electron terms are included at mean-field level within a fully self-consistent procedure. The calculation carefully describes how the two-dimensional electron gas arises from the quantum confinement of electrons near the interface due to band bending potential. The resulting electronic sub-bands and Fermi surfaces show full agreement with the electronic structure dete…