135 research outputs found
Rashba precession in quantum wires
The length over which electron spins reverse direction due to the Rashba
effect when injected with an initial polarization along the axes of a quantum
wire is investigated theoretically. A soft wall confinement of the wire
renormalizes the spin-orbit parameter (and the effective mass) stronger than
hard walls. Electron-electron interactions enhance the Rashba precession while
evidence is found that the coupling between transport channels may suppress it.Comment: 4 pages, 1 Postscript figur
Dephasing in Rashba spin precession along mutlichannel quantum wires and nanotubes
Coherent Rashba spin precession along interacting multi-mode quantum channels
is investigated, revisiting the theory of coupled Tomonaga-Luttinger liquids.
We identify susceptibilities as the key-parameters to govern exponents and
Rashba precession lengths. In semiconducting quantum wires spins of different
transport channels are found to {\em dephase} in their respective precession
angles with respect to one another, as a result of the interaction. This could
explain the experimental difficulty to realize the Datta Das transistor. In
single walled carbon nanotubes, on the other hand, interactions are predicted
to suppress dephasing between the two flavor modes at small doping.Comment: 6 pages, figures include
Wigner molecules in quantum dots
We perform unrestricted Hartree-Fock (HF) calculations for electrons in a
parabolic quantum dot at zero magnetic field. The crossover from Fermi liquid
to Wigner molecule behavior is studied for up to eight electrons and various
spin components . We compare the results with numerically exact
path-integral Monte Carlo simulations and earlier HF studies. Even in the
strongly correlated regime the symmetry breaking HF solutions provide accurate
estimates for the energies and describe the one-particle densities
qualitatively. However, the HF approximation favors the formation of a Wigner
molecule and produces azimuthal modulations of the density for even numbers of
electrons in one spatial shell.Comment: 5 pages, figures include
Interaction-induced conductance from zero modes in a clean magnetic graphene waveguide
We consider a waveguide formed in a clean graphene monolayer by a spatially
inhomogeneous magnetic field. The single-particle dispersion relation for this
waveguide exhibits a zero-energy Landau-like flat band, while finite-energy
bands have dispersion and correspond, in particular, to snake orbits. For
zero-mode states, all matrix elements of the current operator vanish, and a
finite conductance can only be caused by virtual transitions to finite-energy
bands. We show that Coulomb interactions generate such processes. In stark
contrast to finite-energy bands, the conductance is not quantized and shows a
characteristic dependence on the zero-mode filling. Transport experiments
thereby offer a novel and highly sensitive probe of electron-electron
interactions in clean graphene samples. We argue that this interaction-driven
zero-mode conductor may also appear in other physical settings and is not
captured by the conventional Tomonaga-Luttinger liquid description.Comment: 14 pages, 8 figures, published versio
Influence of spin on the persistent current of strongly interacting electrons
The lowest eigenenergies of few, strongly interacting electrons in a
one--dimensional ring are studied in the presence of an impurity barrier. The
persistent current , periodic in an Aharonov--Bohm flux penetrating the
ring, is strongly influenced by the electron spin. The impurity does not remove
discontinuities in at zero temperature. The total electron spin of the
ground state oscillates with the flux. Strong electron--electron interaction
enhances , albeit not up to the value of the clean ring which itself is
smaller than for free electrons. disappears on a temperature
scale that depends exponentially on the electron density. In the limit of very
strong interaction the response to small fluxes is diamagnetic.Comment: Latex file, 15 pages, 13 figures available in uuencoded PostScript
from the autho
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