530 research outputs found
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
Spin selective transport through helical molecular systems
Highly spin selective transport of electrons through a helically shaped
electrostatic potential is demonstrated in the frame of a minimal model
approach. The effect is significant even in the case of weak spin-orbit
coupling. Two main factors determine the selectivity, an unconventional Rashba-
like spin-orbit interaction, reflecting the helical symmetry of the system, and
a weakly dispersive electronic band of the helical system. The weak electronic
coupling, associated with the small dispersion, leads to a low mobility of the
charges in the system and allows even weak spin-orbit interactions to be
effective. The results are expected to be generic for chiral molecular systems
displaying low spin-orbit coupling and low conductivity.Comment: 9 pages, 4 figures v2 (misprints corrected, new figures
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 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
Persistent spin and charge currents and magnification effects in open ring conductors subject to Rashba coupling
We analyze the effect of Rashba spin-orbit coupling and of a local tunnel
barrier on the persistent spin and charge currents in a one-dimensional
conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. First,
as an important consequence of the spin-splitting, it is found that a
persistent spin current can be induced which is not simply proportional to the
charge current. Second, a magnification effect of the persistent spin current
is shown when one tunes the Fermi energy near the Fano-type antiresonances of
the total transmission coefficient governed by the tunnel barrier strength. As
an unambiguous signature of spin-orbit coupling we also show the possibility to
produce a persistent pure spin current at the interference zeros of the
transmittance. This widens the possibilities of employing mesoscopic conducting
rings in phase-coherent spintronics applications.Comment: 6 pages, 5 figures, to appear in PR
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
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
Extra Current and Integer Quantum Hall Conductance in the Spin-Orbit Coupling System
We study the extra term of particle current in a 2D k-cubic Rashba spin-orbit
coupling system and the integer quantization of the Hall conductance in this
system. We provide a correct formula of charge current in this system and the
careful consideration of extra currents provides a stronger theoretical basis
for the theory of the quantum Hall effect which has not been considered before.
The non-trivial extra contribution to the particle current density and local
conductivity, which originates from the cubic dependence on the momentum
operator in the Hamiltonian, will have no effect on the integer quantization of
the Hall conductance. The extension of Noether's theorem for the 2D k-cubic
Rashba system is also addressed. The two methods reach to exactly the same
results.Comment: 6 page
Physical Limits of the ballistic and non-ballistic Spin-Field-Effect Transistor: Spin Dynamics in Remote Doped Structures
We investigate the spin dynamics and relaxation in remotely-doped two
dimensional electron systems where the dopants lead to random fluctuations of
the Rashba spin-orbit coupling. Due to the resulting random spin precession,
the spin relaxation time is limited by the strength and spatial scale of the
random contribution to the spin-orbit coupling. We concentrate on the role of
the randomness for two systems where the direction of the spin-orbit field does
not depend on the electron momentum: the spin field-effect transistor with
balanced Rashba and Dresselhaus couplings and the (011) quantum well. Both of
these systems are considered as promising for the spintronics applications
because of the suppression of the Dyakonov-Perel' mechanism there makes the
realization of a spin field effect transistor in the diffusive regime possible.
We demonstrate that the spin relaxation through the randomness of spin-orbit
coupling imposes important physical limitations on the operational properties
of these devices.Comment: 10 pages, 4 figure
Two Anderson impurities in a 2D host with Rashba spin-orbit interaction
We have studied the two-dimensional two-impurity Anderson model with
additional Rashba spin-orbit interaction by means of the modified perturbation
theory. The impurity Green's functions we have constructed exactly reproduce
the first four spectral moments. We discuss the height and the width of the
even/odd Kondo peaks as functions of the inter-impurity distance and the Rashba
energy (the strength of the Rashba spin-orbit interaction). For small
impurity separations the Kondo temperature shows a non-monotonic dependence on
being different in the even and the odd channel. We predict that the
Kondo temperature has only almost linear dependence on and not an
exponential increase with Comment: To be published in Phys. Rev.
Mesoscopic Spin Hall Effect in Multiprobe Ballistic Spin-Orbit Coupled Semiconductor Bridges
We predict that unpolarized charge current driven through the longitudinal
leads attached to ballistic quantum-coherent two-dimensional electron gas
(2DEG) in semiconductor heterostructure will induce a {\em pure} spin current,
which is not accompanied by any net charge flow, in the transverse voltage
probes. Its magnitude can be tuned by the Rashba spin-orbit (SO) interaction
and, moreover, it is resilient to weak spin-independent scattering off
impurities within the metallic diffusive regime. While the polarization vector
of the spin transported through the transverse leads is not orthogonal to the
plane of 2DEG, we demonstrate that only two components (out-of-plane and
longitudinal) of the transverse spin current are signatures of the spin Hall
effect in four-probe Rashba spin-split semiconductor nanostructures. The linear
response spin Hall current, obtained from the multiprobe Landauer-B\" uttiker
scattering formalism generalized for quantum transport of spin, is the
Fermi-surface determined nonequilibrium quantity whose scaling with the 2DEG
size reveals the importance of processes occurring on the spin precession
{\em mesoscale} (on which spin precesses by an angle )--the
out-of-plane component of the transverse spin current exhibits quasioscillatory
behavior for (attaining the maximum value in 2DEGs of
the size ), while it reaches the asymptotic value
in the macroscopic regime . Furthermore, these values of the
spin Hall current can be manipulated by the measuring geometry defined by the
attached leads.Comment: 12 pages, 6 color EPS figures; expanded discussion to emphasize
crucial role played by processes on the spin precession mesoscal
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