6,170 research outputs found
Spin-current diode with a ferromagnetic semiconductor
Diode is a key device in electronics: the charge current can flow through the
device under a forward bias, while almost no current flows under a reverse
bias. Here we propose a corresponding device in spintronics: the spin-current
diode, in which the forward spin current is large but the reversed one is
negligible. We show that the lead/ferromagnetic quantum dot/lead system and the
lead/ferromagnetic semiconductor/lead junction can work as spin-current diodes.
The spin-current diode, a low dissipation device, may have important
applications in spintronics, as the conventional charge-current diode does in
electronics.Comment: 5 pages, 3 figure
The spin-polarized state of graphene: a spin superconductor
We study the spin-polarized Landau-level state of graphene. Due to
the electron-hole attractive interaction, electrons and holes can bound into
pairs. These pairs can then condense into a spin-triplet superfluid ground
state: a spin superconductor state. In this state, a gap opens up in the edge
bands as well as in the bulk bands, thus it is a charge insulator, but it can
carry the spin current without dissipation. These results can well explain the
insulating behavior of the spin-polarized state in the recent
experiments.Comment: 6 pages, 4 figure
Theory for electric dipole superconductivity with an application for bilayer excitons
Exciton superfluid is a macroscopic quantum phenomenon in which large
quantities of excitons undergo the Bose-Einstein condensation. Recently,
exciton superfluid has been widely studied in various bilayer systems. However,
experimental measurements only provide indirect evidence for the existence of
exciton superfluid. In this article, by viewing the exciton in a bilayer system
as an electric dipole, we provide a general theory for the electric dipole
superconductivity, and derive the London-type and Ginzburg-Landau-type
equations for the electric dipole superconductors. By using these equations, we
discover the Meissner-type effect and the electric dipole current Josephson
effect. These effects can provide direct evidence for the formation of the
exciton superfluid state in bilayer systems and pave new ways to drive an
electric dipole current.Comment: 10 pages, 5 figures, 1 Supplementary Informatio
Topological Imbert-Fedorov shift in Weyl semimetals
The Goos-H\"anchen (GH) shift and the Imbert-Fedorov (IF) shift are optical
phenomena which describe the longitudinal and transverse lateral shifts at the
reflection interface, respectively. Here, we report the GH and IF shifts in
Weyl semimetals (WSMs) - a promising material harboring low energy Weyl
fermions, a massless fermionic cousin of photons. Our results show that GH
shift in WSMs is valley-independent which is analogous to that discovered in a
2D relativistic material - graphene. However, the IF shift has never been
explored in non-optical systems, and here we show that it is valley-dependent.
Furthermore, we find that the IF shift actually originates from the topological
effect of the system. Experimentally, the topological IF shift can be utilized
to characterize the Weyl semimetals, design valleytronic devices of high
efficiency, and measure the Berry curvature
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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