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 ν=0\nu=0 state of graphene: a spin superconductor

We study the spin-polarized $\nu=0$ 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 $\nu=0$ state in the recent experiments.Comment: 6 pages, 4 figure

Massive Overlap Fermions on Anisotropic Lattices

We formulate the massive overlap fermions on anisotropic lattices. We find that the dispersion relation for the overlap fermion resembles the continuum form in the low-momentum region once the bare parameters are properly tuned. The quark self-energy and the quark field renormalization constants are calculated to one-loop in bare lattice perturbation theory. We argue that massive domain wall quarks might be helpful in lattice QCD studies on heavy-light hadron spectroscopy.Comment: 21 pages, 5 figures, one reference added compared with v.

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

Experimentally realizable control fields in quantum Lyapunov control

As a hybrid of techniques from open-loop and feedback control, Lyapunov control has the advantage that it is free from the measurement-induced decoherence but it includes the system's instantaneous message in the control loop. Often, the Lyapunov control is confronted with time delay in the control fields and difficulty in practical implementations of the control. In this paper, we study the effect of time-delay on the Lyapunov control, and explore the possibility of replacing the control field with a pulse train or a bang-bang signal. The efficiency of the Lyapunov control is also presented through examining the convergence time of the controlled system. These results suggest that the Lyapunov control is robust gainst time delay, easy to realize and effective for high-dimensional quantum systems

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