680 research outputs found
Quantum transport in a curved one-dimensional quantum wire with spin-orbit interactions
The one-dimensional effective Hamiltonian for a planar curvilinear quantum
wire with arbitrary shape is proposed in the presence of the Rashba spin-orbit
interaction. Single electron propagation through a device of two straight lines
conjugated with an arc has been investigated and the analytic expressions of
the reflection and transmission probabilities have been derived. The effects of
the device geometry and the spin-orbit coupling strength on the
reflection and transmission probabilities and the conductance are investigated
in the case of spin polarized electron incidence. We find that no spin-flip
exists in the reflection of the first junction. The reflection probabilities
are mainly influenced by the arc angle and the radius, while the transmission
probabilities are affected by both spin-orbit coupling and the device geometry.
The probabilities and the conductance take the general behavior of oscillation
versus the device geometry parameters and . Especially the electron
transportation varies periodically versus the arc angle . We also
investigate the relationship between the conductance and the electron energy,
and find that electron resonant transmission occurs for certain energy.
Finally, the electron transmission for the incoming electron with arbitrary
state is considered. For the outgoing electron, the polarization ratio is
obtained and the effects of the incoming electron state are discussed. We find
that the outgoing electron state can be spin polarization and reveal the
polarized conditions.Comment: 7 pages, 8 figure
Theory of spin-orbit coupling in bilayer graphene
Theory of spin-orbit coupling in bilayer graphene is presented. The
electronic band structure of the AB bilayer in the presence of spin-orbit
coupling and a transverse electric field is calculated from first-principles
using the linearized augmented plane wave method implemented in the WIEN2k
code. The first-principles results around the K points are fitted to a
tight-binding model. The main conclusion is that the spin-orbit effects in
bilayer graphene derive essentially from the single-layer spin-orbit coupling
which comes almost solely from the d orbitals. The intrinsic spin-orbit
splitting (anticrossing) around the K points is about 24\mu eV for the
low-energy valence and conduction bands, which are closest to the Fermi level,
similarly as in the single layer graphene. An applied transverse electric field
breaks space inversion symmetry and leads to an extrinsic (also called
Bychkov-Rashba) spin-orbit splitting. This splitting is usually linearly
proportional to the electric field. The peculiarity of graphene bilayer is that
the low-energy bands remain split by 24\mu eV independently of the applied
external field. The electric field, instead, opens a semiconducting band gap
separating these low-energy bands. The remaining two high-energy bands are
spin-split in proportion to the electric field; the proportionality coefficient
is given by the second intrinsic spin-orbit coupling, whose value is 20\mu eV.
All the band-structure effects and their spin splittings can be explained by
our tight-binding model, in which the spin-orbit Hamiltonian is derived from
symmetry considerations. The magnitudes of intra- and interlayer
couplings---their values are similar to the single-layer graphene ones---are
determined by fitting to first-principles results.Comment: 16 pages, 13 figures, 5 tables, typos corrected, published versio
Suppression of the Persistent Spin Hall Current by Defect Scattering
We study the linear response spin Hall conductivity of a two-dimensional
electron gas (2DEG) in the presence of the Rashba spin orbit interaction in the
diffusive transport regime. When defect scattering is modeled by isotropic
short-range potential scatterers the spin Hall conductivity vanishes due to the
vertex correction. A non-vanishing spin Hall effect may be recovered for
dominantly forward defect scattering.Comment: Submitted to The Physical Review
Least action principle for envelope functions in abrupt heterostructures
We apply the envelope function approach to abrupt heterostructures starting
with the least action principle for the microscopic wave function. The
interface is treated nonperturbatively, and our approach is applicable to
mismatched heterostructure. We obtain the interface connection rules for the
multiband envelope function and the short-range interface terms which consist
of two physically distinct contributions. The first one depends only on the
structure of the interface, and the second one is completely determined by the
bulk parameters. We discover new structure inversion asymmetry terms and new
magnetic energy terms important in spintronic applications.Comment: 4 pages, 1 figur
Spin Hall Effect and Spin Orbit coupling in Ballistic Nanojunctions
We propose a new scheme of spin filtering based on nanometric crossjunctions
in the presence of Spin Orbit interaction, employing ballistic nanojunctions
patterned in a two-dimensional electron gas. We demonstrate that the flow of a
longitudinal unpolarized current through a ballistic X junction patterned in a
two-dimensional electron gas with Spin Orbit coupling (SOC) induces a spin
accumulation which has opposite signs for the two lateral probes. This spin
accumulation, corresponding to a transverse pure spin current flowing in the
junction, is the main observable signature of the spin Hall effect in such
nanostructures.
We benchmark the effects of two different kinds of Spin Orbit interactions.
The first one (-SOC) is due to the interface electric field that
confines electrons to a two-dimensional layer, whereas the second one
(-SOC) corresponds to the interaction generated by a lateral confining
potential.Comment: 6 pages, 3 figure
Topological defects and Goldstone excitations in domain walls between ferromagnetic quantum Hall effect liquids
It is shown that the low-energy spectrum of a ferromagnetic quantum Hall
effect liquid in a system with a multi-domain structure generated by an
inhomogeneous bare Zeeman splitting is formed by excitations
localized at the walls between domains. For a step-like , the
domain wall spectrum includes a spin-wave with a linear dispersion and a small
gap due to spin-orbit coupling, and a low-energy topological defects. The
latter are charged and may dominate in the transport under conditions that the
percolation through the network of domain walls is provided.Comment: 4 pages, 1 fi
Rashba coupling in quantum dots: exact solution
We present an analytic solution to the problem of the Rashba spin-orbit
coupling in semiconductor quantum dots. We calculate the exact energy spectrum,
wave-functions, and spin--flip relaxation times. We discuss various effects
inaccessible via perturbation theory. In particular, we find that the effective
gyromagnetic ratio is strongly suppressed by the spin-orbit coupling. The
spin-flip relaxation rate has a maximum as a function of the spin-orbit
coupling and is therefore suppressed in both the weak- and strong coupling
limits.Comment: 5 pages, 4 figs, reference adde
Linear response theory of interacting topological insulators
Chiral surface states in topological insulators are robust against
interactions, non-magnetic disorder and localization, yet topology does not
yield protection in transport. This work presents a theory of interacting
topological insulators in an external electric field, starting from the quantum
Liouville equation for the many-body density matrix. Out of equilibrium,
topological insulators acquire a current-induced spin polarization.
Electron-electron interactions renormalize the non-equilibrium spin
polarization and charge conductivity, and disorder in turn enhances this
renormalization by a factor of two. Topological insulator phenomenology remains
intact in the presence of interactions out of equilibrium, and an exact
correspondence exists between the mathematical frameworks necessary for the
understanding of the interacting and non-interacting problems.Comment: 9 pages, 1 figur
Radioactivity and Electron Acceleration in Supernova Remnants
We argue that the decays of radioactive nuclei related to Ti and
Ni ejected during supernova explosions can provide a vast pool of mildly
relativistic positrons and electrons which are further accelerated to
ultrarelativistic energies by reverse and forward shocks. This interesting link
between two independent processes - the radioactivity and the particle
acceleration - can be a clue for solution of the well known theoretical problem
of electron injection in supernova remnants. In the case of the brightest radio
source Cas A, we demonstrate that the radioactivity can supply adequate number
of energetic electrons and positrons for interpretation of observational data
provided that they are stochastically pre-accelerated in the upstream regions
of the forward and reverse shocks.Comment: 6 pages, 1 figure, revised version accepted to Phys.Rev.
Spin-orbit-enhanced Wigner localization in quantum dots
We investigate quantum dots with Rashba spin-orbit coupling in the
strongly-correlated regime. We show that the presence of the Rashba interaction
enhances the Wigner localization in these systems, making it achievable for
higher densities than those at which it is observed in Rashba-free quantum
dots. Recurring shapes in the pair-correlated densities of the yrast spectrum,
which might be associated with rotational and vibrational modes, are also
reported.Comment: 5 pages, 4 figure
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