1,078 research outputs found

### Mechanism of half-frequency electric dipole spin resonance in double quantum dots: Effect of nonlinear charge dynamics inside the singlet manifold

Electron dynamics in quantum dots manifests itself in spin-flip spectra
through electric dipole spin resonance (EDSR). Near a neutrality point
separating two different singlet charged states of a double quantum dot, charge
dynamics inside a $2\times2$ singlet manifold can be described by a
1/2-pseudospin. In this region, charge dynamics is highly nonlinear and
strongly influenced by flopping its soft pseudospin mode. As a result, the
responses to external driving include first and second harmonics of the driving
frequency and their Raman satellites shifted by the pseudospin frequency. In
EDSR spectra of a spin-orbit couplet doublet dot, they manifest themselves as
charge satellites of spin-flip transitions. The theory describes gross features
of the anomalous half-frequency EDSR in spin blockade spectra [Laird et al.,
Semicond. Sci. Techol. {\bf 24}, 064004 (2009)].Comment: One figure, one equation, comments adde

### Renormalization of spin-orbit coupling in quantum dots due to Zeeman interaction

We derive analitycally a partial diagonalization of the Hamiltonian
representing a quantum dot including spin-orbit interaction and Zeeman energy
on an equal footing. It is shown that the interplay between these two terms
results in a renormalization of the spin-orbit intensity. The relation between
this feature and experimental observations on conductance fluctuations is
discussed, finding a good agreement between the model predictions and the
experimental behavior.Comment: 4 pages, no figures. To appear in Phys. Rev. B (Brief Report) (2004

### Quantum nanostructures in strongly spin-orbit coupled two-dimensional systems

Recent progress in experimental studies of low-dimensional systems with
strong spin-orbit coupling poses a question on the effect of this coupling on
the energy spectrum of electrons in semiconductor nanostructures. It is shown
in the paper that this effect is profound in the strong coupling limit. In
circular quantum dots a soft mode develops, in strongly elongated dots electron
spin becomes protected from the effects of the environment, and the lower
branch of the energy spectrum of quantum wires becomes nearly flat in a wide
region of the momentum space.Comment: 5 pages, 1 figur

### Spin-resolved scattering through spin-orbit nanostructures in graphene

We address the problem of spin-resolved scattering through spin-orbit
nanostructures in graphene, i.e., regions of inhomogeneous spin-orbit coupling
on the nanometer scale. We discuss the phenomenon of spin-double refraction and
its consequences on the spin polarization. Specifically, we study the
transmission properties of a single and a double interface between a normal
region and a region with finite spin-orbit coupling, and analyze the
polarization properties of these systems. Moreover, for the case of a single
interface, we determine the spectrum of edge states localized at the boundary
between the two regions and study their properties

### Interplay of spin-orbit coupling and Zeeman splitting in the absorption lineshape of 2D fermions

We suggest that electron spin resonance (ESR) experiment can be used as a
probe of spinon excitations of hypothetical spin-liquid state of frustrated
antiferromagnet in the presence of asymmetric Dzyaloshinskii-Moriya (DM)
interaction. We describe assumptions under which the ESR response is reduced to
the response of 2D electron gas with Rashba spin-orbit coupling. Unlike
previous treatments, the spin-orbit coupling, \Delta_{SO}, is not assumed small
compared to the Zeeman splitting, \Delta_Z. We demonstrate that ESR response
diverges at the edges of the absorption spectrum for ac magnetic field
perpendicular to the static field. At the compensation point,
\Delta_{SO}\approx \Delta_Z, the broad absorption spectrum exhibits features
that evolve with temperature, T, even when T is comparable to the Fermi energy.Comment: 11 pages, 6 figure

### Evanescent states in 2D electron systems with spin-orbit interaction and spin-dependent transmission through a barrier

We find that the total spectrum of electron states in a bounded 2D electron
gas with spin-orbit interaction contains two types of evanescent states lying
in different energy ranges. The first-type states fill in a gap, which opens in
the band of propagating spin-splitted states if tangential momentum is nonzero.
They are described by a pure imaginary wavevector. The states of second type
lie in the forbidden band. They are described by a complex wavevector. These
states give rise to unusual features of the electron transmission through a
lateral potential barrier with spin-orbit interaction, such as an oscillatory
dependence of the tunneling coefficient on the barrier width and electron
energy. But of most interest is the spin polarization of an unpolarized
incident electron flow. Particularly, the transmitted electron current acquires
spin polarization even if the distribution function of incident electrons is
symmetric with respect to the transverse momentum. The polarization efficiency
is an oscillatory function of the barrier width. Spin filtering is most
effective, if the Fermi energy is close to the barrier height.Comment: 9 pages, 9 figures, more general boundary conditions are used, typos
correcte

### Efficient electron spin manipulation in a quantum well by an in-plane electric field

Electron spins in a semiconductor quantum well couple to an electric field
{\it via} spin-orbit interaction. We show that the standard spin-orbit coupling
mechanisms can provide extraordinary efficient electron spin manipulation by an
in-plane ac electric field

### Persistent spin current in spin-orbit coupling systems in the absence of an external magnetic field

The spin-orbit coupling systems with a zero magnetic field is studied under
the equilibrium situation, {\it i.e.}, without a voltage bias. A persistent
spin current is predicted to exist under most circumstances, although the
persistent charge current and the spin accumulation are identically zero. In
particular, a two-dimensional quantum wire is investigated in detail.
Surprisingly, a persistent spin current is found to flow along the confined
direction, due to the spin precession in accompany with the particle motion.
This provides an interesting example of constant spin flowing without inducing
a spin accumulation, contrary to common intuition.Comment: 4 pages, 5 figure

### Zero-conductance resonances and spin-filtering effects in ring conductors subject to Rashba coupling

We investigate the effect of Rashba spin-orbit coupling and of a tunnel
barrier on the zero conduc- tance resonances appearing in a one-dimensional
conducting Aharonov-Bohm (AB) ring symmet- rically coupled to two leads. The
transmission function of the corresponding one-electron problem is derived
within the scattering matrix approach and analyzed in the complex energy plane
with focus on the role of the tunnel barrier strength on the zero-pole
structure characteristic of trans- mission (anti)resonances. The lifting of the
real conductance zeros is related to the breaking of the spin-reversal symmetry
and time-reversal symmetry of Aharonov-Casher (AC)and AB rings, as well as to
rotational symmetry breaking in presence of a tunnel barrier. We show that the
polarization direction of transmitted electrons can be controlled via the
tunnel barrier strength and discuss a novel spin-filtering design in
one-dimensional rings with tunable spin-orbit interaction.Comment: 13 pages, 8 figure

### Intrinsic spin dynamics in semiconductor quantum dots

We investigate the characteristic spin dynamics corresponding to
semiconductor quantum dots within the multiband envelope function approximation
(EFA). By numerically solving an $8\times8$ $k\cdot p$ Hamiltonian we treat
systems based on different III-V semiconductor materials.It is shown that, even
in the absence of an applied magnetic field, these systems show intrinsic spin
dynamics governed by intraband and interband transitions leading to
characteristic spin frequencies ranging from the THz to optical frequencies.Comment: to be published in Nanotechnology. Separated figure file

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