Finger-gate array quantum pumps:pumping characteristics and mechanisms

We study the pumping effects, in both the adiabatic and nonadiabatic regimes, of a pair of \QTR{it}{finite} finger-gate array (FGA) on a narrow channel. Connection between the pumping characteristics and associated mechanisms is established. The pumping potential is generated by ac biasing the FGA pair. For a single pair (N=1) of finger gates (FG's), the pumping mechanism is due to the coherent inelastic scattering of the traversing electron to its subband threshold. For a pair of FGA with pair number $N>2$, the dominant pumping mechanism becomes that of the time-dependent Bragg reflection. The contribution of the time-dependent Bragg reflection to the pumping is enabled by breaking the symmetry in the electron transmission when the pumping potential is of a predominant propagating type. This propagating wave condition can be achieved both by an appropriate choice of the FGA pair configuration and by the monitoring of a phase difference $\phi$ between the ac biases in the FGA pair. The robustness of such a pumping mechanism is demonstrated by considering a FGA pair with only pair number N=4.Comment: 7 pages, 6 figure

A finite difference solution to a mixed boundary value problem for Laplace's equation

Finite difference solution to mixed boundary value problem for Laplace equatio

DC Spin Current Generation in a Rashba-type Quantum Channel

We propose and demonstrate theoretically that resonant inelastic scattering (RIS) can play an important role in dc spin current generation. The RIS makes it possible to generate dc spin current via a simple gate configuration: a single finger-gate that locates atop and orients transversely to a quantum channel in the presence of Rashba spin-orbit interaction. The ac biased finger-gate gives rise to a time-variation in the Rashba coupling parameter, which causes spin-resolved RIS, and subsequently contributes to the dc spin current. The spin current depends on both the static and the dynamic parts in the Rashba coupling parameter, $\alpha_0$ and $\alpha_1$, respectively, and is proportional to $\alpha_0 \alpha_1^2$. The proposed gate configuration has the added advantage that no dc charge current is generated. Our study also shows that the spin current generation can be enhanced significantly in a double finger-gate configuration.Comment: 4 pages,4 figure

M-Fivebrane from the Open Supermembrane

Covariant field equations of M-fivebrane in eleven dimensional curved superspace are obtained from the requirement of kappa-symmetry of an open supermembrane ending on a fivebrane. The worldvolume of the latter is a (6|16) dimensional supermanifold embedded in the (11|32) dimensional target superspace. The kappa-symmetry of the system imposes a constraint on this embedding, and a constraint on a modified super 3-form field strength on the fivebrane worldvolume. These constraints govern the dynamics of the M-fivebrane.Comment: 11 pages, Latex, references and appendix adde

Nonuniversality of the intrinsic inverse spin-Hall effect in diffusive systems

We studied the electric current induced in a two-dimensional electron gas by the spin current, in the presence of Rashba and cubic Dresselhaus spin-orbit interactions. We found out that the factor relating these currents is not universal, but rather depends on the origin of the spin current. Drastic distinction has been found between two cases: the spin current created by diffusion of an inhomogeneous spin density, and the pure homogeneous spin current. We found out that in the former case the ISHE electric current is finite, while it turns to zero in the latter case, if the spin-orbit coupling is represented by Rashba interaction.Comment: 1 figur