4,345 research outputs found
Effects of Strain on Electronic Properties of Graphene
We present first-principles calculations of electronic properties of graphene
under uniaxial and isotropic strains, respectively. The semi-metallic nature is
shown to persist up to a very large uniaxial strain of 30% except a very narrow
strain range where a tiny energy gap opens. As the uniaxial strain increases
along a certain direction, the Fermi velocity parallel to it decreases quickly
and vanishes eventually, whereas the Fermi velocity perpendicular to it
increases by as much as 25%. Thus, the low energy properties with small
uniaxial strains can be described by the generalized Weyl's equation while
massless and massive electrons coexist with large ones. The work function is
also predicted to increase substantially as both the uniaxial and isotropic
strain increases. Hence, the homogeneous strain in graphene can be regarded as
the effective electronic scalar potential.Comment: 4 pages, 6 figures; Published versio
Beyond domain-specific expertise: Neural signatures of face and spatial working memory in Baduk (Go game) experts
Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer
Magnetic skyrmions have fast evolved from a novelty, as a realization of
topologically protected structure with particle-like character, into a
promising platform for new types of magnetic storage. Significant engineering
progress was achieved with the synthesis of compounds hosting room-temperature
skyrmions in magnetic heterostructures, with the interfacial
Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation.
Here we report findings of ultrathin skyrmion formation in a few layers of
SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer.
Measurement of the topological Hall effect (THE) reveals a robust stability of
skyrmions in this platform, judging from the high value of the critical field
1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as
much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up
to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film
proves the rumpling of the Ru-O plane to be the source of inversion symmetry
breaking and DMI. First-principles calculations based on the structure obtained
from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the
main source of skyrmion robustness. These features promise a few-layer SRO to
be an important new platform for skyrmionics, without the necessity of
introducing the capping layer to boost the spin-orbit coupling strength
artificially.Comment: Supplementary Information available upon reques
Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer
Magnetic skyrmions have fast evolved from a novelty, as a realization of
topologically protected structure with particle-like character, into a
promising platform for new types of magnetic storage. Significant engineering
progress was achieved with the synthesis of compounds hosting room-temperature
skyrmions in magnetic heterostructures, with the interfacial
Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation.
Here we report findings of ultrathin skyrmion formation in a few layers of
SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer.
Measurement of the topological Hall effect (THE) reveals a robust stability of
skyrmions in this platform, judging from the high value of the critical field
1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as
much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up
to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film
proves the rumpling of the Ru-O plane to be the source of inversion symmetry
breaking and DMI. First-principles calculations based on the structure obtained
from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the
main source of skyrmion robustness. These features promise a few-layer SRO to
be an important new platform for skyrmionics, without the necessity of
introducing the capping layer to boost the spin-orbit coupling strength
artificially.Comment: Supplementary Information available upon reques
Study of vacancy ordering and the boson peak in metastable cubic Ge-Sb-Te using machine learning potentials
The mechanism of the vacancy ordering in metastable cubic Ge-Sb-Te (c-GST)
that underlies the ultrafast phase-change dynamics and prominent thermoelectric
properties remains elusive. Achieving a comprehensive understanding of the
vacancy-ordering process at an atomic level is challenging because of enormous
computational demands required to simulate disordered structures on large
temporal and spatial scales. In this study, we investigate the vacancy ordering
in c-GST by performing large-scale molecular dynamics simulations using machine
learning potentials. The initial c-GST structure with randomly distributed
vacancies rearranges to develop a semi-ordered cubic structure with layer-like
ordered vacancies after annealing at 700~K for 100~ns. The vacancy ordering
significantly affects the lattice dynamical properties of c-GST. In the initial
structure with fully disordered vacancies, we observe a boson peak, usually
associated with amorphous solids, that consists of localized modes at
0.575~THz. As vacancies become ordered, the boson peak disappears and the
Debye-Waller thermal \textit{B} factor of Te decreases substantially. This
finding indicates that the c-GST undergoes a transition from amorphous-like to
crystalline-like solid state by thermal annealing in low-frequency dynamics.Comment: 8 pages, 1 Table of Contents figure, 7 main figures, Supplemental
Materia
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