1,241 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 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
Theory of spin injection
Diffusive theory of spin injection is reviewed and a number of new results is
presented for the dc and ac regimes. They were derived by means of the
"gamma-technique" allowing to simplify the calculations by choosing the spin
injection coefficients through different interfaces as the basic variables. The
prospects for increasing spin injection by using resistive spin-selective
contacts are emphasized and spin non-conserving contacts are introduced.
Finding the basic parameters of a junction from the ac data is discussed.Comment: 4 pages, 2 column REVTeX, to be published in Proceedings of Intern.
Symposium on Mesoscopic Superconductivity and Spintronics (Atsugi, March
2002
Diffusion theory of spin injection through resistive contacts
Insertion of a resistive contact between a ferromagnetic metal and a
semiconductor microstructure is of critical importance for achieving efficient
spin injection into a semiconductor. However, the equations of the diffusion
theory are rather cumbersome for the junctions including such contacts. A
technique based on deriving a system of self-consistent equations for the
coefficients of spin injection, "gamma", through different contacts are
developed. These equations are concise when written in the proper notations.
Moreover, the resistance of a two-contact junction can be expressed in terms of
"gamma"'s of both contacts. This equation makes calculating the spin valve
effect straightforward, allows to find an explicit expression for the junction
resistance and to prove that its nonequilibrium part is positive. Relation of
these parameters to different phenomena like spin-e.m.f. and the junction
transients is established. Comparative effect of the Coulomb screening on
different parameters is clarified. It is also shown that the spin
non-conservation in a contact can have a dramatic effect on the non-equilibrium
resistance of the junction.Comment: 16 pages, 2 column REVTeX format, minor editorial changes, references
to recent papers added, to appear in Euro. Phys. Journal
Complex impedance of a spin injecting junction
Theory of the ac spin injection from a ferromagnetic electrode into a normal
conductor through a tunnel or Schottky contact is developed. Diffusion and
relaxation of non-equilibrium spins results in a frequency dependent complex
impedance controlled by the spin relaxation rates and the resistances involved.
Explicit expression for the impedance is presented. Experimental investigation
of the frequency dependence of the impedance should allow measuring spin
relaxation times in both conductors, their effective resistances, and also the
parameters of the contact controlling the spin injection.Comment: 3 pages, 2 column REVTeX, to appear in Appl. Phys. Let
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
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