2,232 research outputs found
Persistent charge and spin currents in the long wavelength regime for graphene rings
We address the problem of persistent charge and spin currents on a Corbino
disk built from a graphene sheet. We consistently derive the Hamiltonian
including kinetic, intrinsic (ISO) and Rashba spin-orbit interactions in
cylindrical coordinates. The Hamiltonian is carefully considered to reflect
hermiticity and covariance. We compute the energy spectrum and the
corresponding eigenfunctions separately for the intrinsic and Rashba spin-orbit
interactions. In order to determine the charge persistent currents we use the
spectrum equilibrium linear response definition. We also determine the spin and
pseudo spin polarizations associated with such equilibrium currents. For the
intrinsic case one can also compute the correct currents by applying the bare
velocity operator to the ISO wavefunctions or alternatively the ISO group
velocity operator to the free wavefunctions. Charge currents for both SO
couplings are maximal in the vicinity of half integer flux quanta. Such maximal
currents are protected from thermal effects because contributing levels plunge
(1K) into the Fermi sea at half integer flux values. Such a mechanism,
makes them observable at readily accessible temperatures. Spin currents only
arise for the Rashba coupling, due to the spin symmetry of the ISO spectrum.
For the Rashba coupling, spin currents are cancelled at half integer fluxes but
they remain finite in the vicinity, and the same scenario above protects spin
currents
Charge and spin polarized currents in mesoscopic rings with Rashba spin-orbit interactions coupled to an electron reservoir
The electronic states of a mesoscopic ring are assessed in the presence of
Rashba Spin Orbit coupling and a gauge field. Spin symmetric coupling to
an ideal lead is implemented following B\"uttiker's voltage probe. The exact
density of states is derived using the reservoir uncoupled eigenstates as basis
functions mixed by the reservoir coupling. The decay time of uncoupled electron
eigenstates is derived by fitting the broadening profiles. The spin and charge
persistent currents are computed in the presence of the SO interaction and the
reservoir coupling for two distinct scenarios of the electron filling fraction.
The degradation of the persistent currents depends uniformly on the reservoir
coupling but nonuniformly in temperature, the latter due to the fact that
currents emerge from different depths of the Fermi sea, and thus for some
regimes of flux, they are provided with a protective gap. Such flux regimes can
be tailored by the SO coupling for both charge and spin currents
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