76 research outputs found
Pseudospin excitations in coaxial nanotubes
In a 2DEG confined to two coaxial tubes the `tube degree of freedom' can be
described in terms of pseudospin-1/2 dynamics. The presence of tunneling
between the two tubes leads to a collective oscillation known as pseudospin
resonance. We employ perturbation theory to examine the dependence of the
frequency of this mode with respect to a coaxial magnetic field for the case of
small intertube distances. Coulomb interaction leads to a shift of the
resonance frequency and to a finite lifetime of the pseudospin excitations. The
presence of the coaxial magnetic field gives rise to pronounced peaks in the
shift of the resonance frequency. For large magnetic fields this shift vanishes
due to the effects of Zeeman splitting. Finally, an expression for the
linewidth of the resonance is derived. Numerical analysis of this expression
suggests that the linewidth strongly depends on the coaxial magnetic field,
which leads to several peaks of the linewidth as well as regions where damping
is almost completely suppressed.Comment: 11 pages, 7 figure
Beating of Friedel oscillations induced by spin-orbit interaction
By exploiting our recently derived exact formula for the Lindhard
polarization function in the presence of Bychkov-Rashba (BR) and Dresselhaus
(D) spin-orbit interaction (SOI), we show that the interplay of different SOI
mechanisms induces highly anisotropic modifications of the static dielectric
function. We find that under certain circumstances the polarization function
exhibits doubly-singular behavior, which leads to an intriguing novel
phenomenon, beating of Friedel oscillations. This effect is a general feature
of systems with BR+D SOI and should be observed in structures with a
sufficiently strong SOI.Comment: 3 figure
Revivals, collapses and magnetic-pulse generation in quantum rings
Using a microscopic theory based on the density matrix formalism we
investigate quantum revivals and collapses of the charge polarization and
charge current dynamics in mesoscopic rings driven by short asymmetric
electromagnetic pulses. The collapsed state is utilized for sub-picosecond
switching of the current and associated magnetization, enabling thus the
generation of pulsed magnetic fields with a tunable time structure and shape
asymmetry which provides a new tool to study ultrafast spin-dynamics and
ratchet-based effects.Comment: 4 pages, 2 figure
Nonequilibrium charge dynamics of light-driven rings threaded by a magnetic flux
We study theoretically the charge polarization and the charge current
dynamics of a mesoscopic ring driven by short asymmetric electromagnetic pulses
and threaded by an external static magnetic flux. It is shown that the
pulse-induced charge polarization and the associated light-emission is
controllable by tuning the external magnetic flux. Applying two mutually
perpendicular pulses triggers a charge current in the ring. The interplay
between this nonequilibrium and the persistent currents is investigated and the
conditions under which the pulses stop the persistent current are identified.Comment: 6 pages, 2 figures; submitted to EP
Spin-orbit interaction induced singularity of the charge density relaxation propagator
The charge density relaxation propagator of a two dimensional electron
system, which is the slope of the imaginary part of the polarization function,
exhibits singularities for bosonic momenta having the order of the spin-orbit
momentum and depending on the momentum orientation. We have provided an
intuitive understanding for this non-analytic behavior in terms of the inter
chirality subband electronic transitions, induced by the combined action of
Bychkov-Rashba (BR) and Dresselhaus (D) spin-orbit coupling. It is shown that
the regular behavior of the relaxation propagator is recovered in the presence
of only one BR or D spin-orbit field or for spin-orbit interaction with equal
BR and D coupling strengths. This creates a new possibility to influence
carrier relaxation properties by means of an applied electric field.Comment: 4 figure
Spin-orbit coupling induced by a mass gradient
The existence of a spin-orbit coupling (SOC) induced by the gradient of the
effective mass in low-dimensional heterostructures is revealed. In structurally
asymmetric quasi-two-dimensional semiconductor heterostructures the presence of
a mass gradient across the interfaces results in a SOC which competes with the
SOC created by the electric field in the valence band. However, in graded
quantum wells subjected to an external electric field, the mass-gradient
induced SOC can be finite even when the electric field in the valence band
vanishes.Comment: 4 pages, 2 figures, 1 tabl
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