594 research outputs found
Spin-helical Dirac states in graphene induced by polar-substrate surfaces with giant spin-orbit interaction: a new platform for spintronics
Spintronics, or spin electronics, is aimed at efficient control and
manipulation of spin degrees of freedom in electron systems. To comply with
demands of nowaday spintronics, the studies of electron systems hosting giant
spin-orbit-split electron states have become one of the most important
directions providing us with a basis for desirable spintronics devices. In
construction of such devices, it is also tempting to involve graphene, which
has attracted great attention because of its unique and remarkable electronic
properties and was recognized as a viable replacement for silicon in
electronics. In this case, a challenging goal is to make graphene Dirac states
spin-polarized. Here, we report on absolutely new promising pathway to create
spin-polarized Dirac states based on coupling of graphene and polar-substrate
surface states with giant Rashba-type spin-splitting. We demonstrate how the
spin-helical Dirac states are formed in graphene deposited on the surface of
BiTeCl. This coupling induces spin separation of the originally spin-degenerate
graphene states and results in fully helical in-plane spin polarization of the
Dirac electrons.Comment: 5 pages, 3 figure
The role of surface plasmons in the decay of image-potential states on silver surfaces
The combined effect of single-particle and collective surface excitations in
the decay of image-potential states on Ag surfaces is investigated, and the
origin of the long-standing discrepancy between experimental measurements and
previous theoretical predictions for the lifetime of these states is
elucidated. Although surface-plasmon excitation had been expected to reduce the
image-state lifetime, we demonstrate that the subtle combination of the spatial
variation of s-d polarization in Ag and the characteristic non-locality of
many-electron interactions near the surface yields surprisingly long
image-state lifetimes, in agreement with experiment.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let
Ultrafast electron dynamics in metals
During the last decade, significant progress has been achieved in the rapidly
growing field of the dynamics of {\it hot} carriers in metals. Here we present
an overview of the recent achievements in the theoretical understanding of
electron dynamics in metals, and focus on the theoretical description of the
inelastic lifetime of excited hot electrons. We outline theoretical
formulations of the hot-electron lifetime that is originated in the inelastic
scattering of the excited {\it quasiparticle} with occupied states below the
Fermi level of the solid. {\it First-principles} many-body calculations are
reviewed. Related work and future directions are also addressed.Comment: 17 pages, two columns, 13 figures, to appear in ChemPhysChe
Ideal two-dimensional electron systems with a giant Rashba-type spin splitting in real materials: surfaces of bismuth tellurohalides
Spintronics is aimed at active controlling and manipulating the spin degrees
of freedom in semiconductor devices. A promising way to achieve this goal is to
make use of the tunable Rashba effect that relies on the spin-orbit interaction
(SOI) in a two-dimensional (2D) electron system immersed in an
inversion-asymmetric environment. The SOI induced spin-splitting of the
2D-electron state provides a basis for many theoretically proposed spintronic
devices. However, the lack of semiconductors with large Rashba effect hinders
realization of these devices in actual practice. Here we report on a giant
Rashba-type spin splitting in 2D electron systems which reside at
tellurium-terminated surfaces of bismuth tellurohalides. Among these
semiconductors, BiTeCl stands out for its isotropic metallic surface-state band
with the Gamma-point energy lying deep inside the bulk band gap. The giant
spin-splitting of this band ensures a substantial spin asymmetry of the
inelastic mean free path of quasiparticles with different spin orientations.Comment: 12 pages, 5 figure
Non-Dirac topological surface states in (SnTe)(BiTe)
A new type of topological spin-helical surface states was discovered in
layered van der Waals bonded (SnTe)(BiTe) compounds
which comprise two covalently bonded band inverted subsystems, SnTe and
BiTe, within a building block. This novel topological states
demonstrate non-Dirac dispersion within the band gap. The dispersion of the
surface state has two linear sections of different slope with shoulder feature
between them. Such a dispersion of the topological surface state enables
effective switch of the velocity of topological carriers by means of applying
an external electric field
Surface-state electron dynamics in noble metals
Theoretical investigations of surface-state electron dynamics in noble metals
are reported. The dynamically screened interaction is computed, within
many-body theory, by going beyond a free-electron description of the metal
surface. Calculations of the inelastic linewidth of Shockley surface-state
electrons and holes in these materials are also presented. While the linewidth
of excited holes at the surface-state band edge () is
dominated by a two-dimensional decay channel, within the surface-state band
itself, our calculations indicate that major contributions to the
electron-electron interaction of surface-state electrons above the Fermi level
come from the underlying bulk electrons.Comment: 17 pages, 7 figures, to appear in Prog. Surf. Sc
Electron-phonon relaxation and excited electron distribution in gallium nitride
We develop a theory of energy relaxation in semiconductors and insulators
highly excited by the long-acting external irradiation. We derive the equation
for the non-equilibrium distribution function of excited electrons. The
solution for this function breaks up into the sum of two contributions. The
low-energy contribution is concentrated in a narrow range near the bottom of
the conduction band. It has the typical form of a Fermi distribution with an
effective temperature and chemical potential. The effective temperature and
chemical potential in this low-energy term are determined by the intensity of
carriers' generation, the speed of electron-phonon relaxation, rates of
inter-band recombination and electron capture on the defects. In addition,
there is a substantial high-energy correction. This high-energy 'tail' covers
largely the conduction band. The shape of the high-energy 'tail' strongly
depends on the rate of electron-phonon relaxation but does not depend on the
rates of recombination and trapping. We apply the theory to the calculation of
a non-equilibrium distribution of electrons in irradiated GaN. Probabilities of
optical excitations from the valence to conduction band and electron-phonon
coupling probabilities in GaN were calculated by the density functional
perturbation theory. Our calculation of both parts of distribution function in
gallium nitride shows that when the speed of electron-phonon scattering is
comparable with the rate of recombination and trapping then the contribution of
the non-Fermi 'tail' is comparable with that of the low-energy Fermi-like
component. So the high-energy contribution can affect essentially the charge
transport in the irradiated and highly doped semiconductors.Comment: 15 pages, 6 figure
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