6,356 research outputs found
The focusing of electron flow in a bipolar Graphene ribbon with different chiralities
The focusing of electron flow in a symmetric p-n junction (PNJ) of graphene
ribbon with different chiralities is studied. Considering the PNJ with the
sharp interface, in a armchair ribbon, the electron flow emitting from
in n-region can always be focused perfectly at in p-region in the whole
Dirac fermion regime, i.e. in whole regime where is the distance
between Dirac-point energy and Fermi energy and is the nearest hopping
energy. For the bipolar ribbon with zigzag edge, however, the incoming electron
flow in n-region is perfectly converged in p-region only in a very low energy
regime with . Moreover, for a smooth PNJ, electrons are
backscattered near PNJ, which weakens the focusing effect. But the focusing
pattern still remains the same as that of the sharp PNJ. In addition, quantum
oscillation in charge density occurs due to the interference between forward
and backward scattering. Finally, in the presence of weak perpendicular
magnetic field, charge carriers are deflected in opposite directions in the
p-region and n-region. As a result, the focusing effect is smeared. The lower
energy , the easier the focusing effect is destroyed. For the high energy
(e.g. ), however, the focusing effect can still survive in a
moderate magnetic field on order of one Tesla.Comment: 29 pages, 16 figure
Symmetry and transport property of spin current induced spin-Hall effect
We study the spin current induced spin-Hall effect that a longitudinal spin
dependent chemical potential induces a transverse spin
conductances . A four terminal system with Rashba and Dresselhaus
spin-orbit interaction (SOI) in the scattering region is considered. By using
Landauer-Bttiker formula with the aid of the Green function, various
spin current induced spin-Hall conductances are calculated. With the
charge chemical potential or spin chemical potential ,
there are 16 elements for the transverse conductances where . Due to the symmetry of our
system these elements are not independent. For the system with symmetry
half of elements are zero, when the center region only exists the Rashba SOI or
Dresselhaus SOI. The numerical results show that of all the conductance
elements, the spin current induced spin-Hall conductances are usually
much greater (about one or two orders of magnitude) than the spin Hall
conductances and the reciprocal spin Hall conductances . So
the spin current induced spin-Hall effect is dominating in the present device.Comment: 7 pages, 6 figure
Persistent spin current in a spin-orbit coupling/normal hybrid ring
We investigate the equilibrium property of a mesoscopic ring with spin orbit
(SO) interaction. It is well known that for a normal mesoscopic ring threaded
by a magnetic flux, the electron acquires a Berry phase that induces the
persistent (charge) current. Similarly, the spin of electron acquires a spin
Berry phase traversing the ring with SO interaction. It is this spin Berry
phase that induces a persistent spin current. To demonstrate its existence, we
calculate the persistent spin current without accompanying charge current in
the normal region in a hybrid mesoscopic ring. We point out that this
persistent spin current describes the real spin motion and can be observed
experimentally.Comment: 4 pages, 3 figure
The transport properties of Floquet topological superconductors at the transition from the topological phase to the Anderson localized phase
The Floquet topological superconducting state is a nonequilibrium
time-periodic state hosting Majorana fermions. We study its transport
properties by using the Kitaev model with time-periodic incommensurate
potentials, which experiences phase transition from the Floquet topological
superconducting phase to the Anderson localized phase with increasing driving
strength. We study both the real time dynamics of the current and the
non-analytic behavior of the tunneling conductance at the transition.
Especially, we find that the tunneling conductance changes continuously at the
transition, being a finite value in the presence of Floquet Majorana fermions,
but dropping to zero as the Majorana fermions vanish. For a special choice of
parameters, the Majorana fermions revive at larger driving strength,
accompanied by the revival of conductances.Comment: 8 pages, 5 figure
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