Adiabatic Quantum Pump of Spin-Polarized Current

We propose a mechanism by which an open quantum dot driven by two ac (radio frequency) gate voltages in the presence of a moderate in-plane magnetic field generates a spin-polarized, phase-coherent dc current. The idea combines adiabatic, nonquantized (but coherent) pumping through periodically modulated external parameters and the strong fluctuations of the electron wave function existent in chaotic cavities. We estimate that the spin polarization of the current can be observed for temperatures and Zeeman splitting energies of the order of the single-particle mean level spacing.

Figure 1

(a) Schematic view of the device. (b) The energy level diagram for the device in the presence of a parallel magnetic field.

Figure 2

Schematic plots of the pumped current dependence with an external parameter, such as dot deformation or perpendicular magnetic field. (a),(b) No in-plane magnetic field $B_{\parallel }$ is applied. The spin up $I_{\uparrow }$ and spin down $I_{\downarrow }$ components of the charge current are equal and no spin current $I_s$ is present. (c),(d) When a sufficiently strong in-plane field is applied, the spin component of the charge current responds in distinct ways to an external perturbation. As a result, total charge and total spin currents in the dot become uncorrelated. The vertical dashed line in (d) indicates a point where only spin is transferred across the dot with no net charge transport.

Figure 3

Relative spin polarization of the pumped current as a function of Zeeman energy for: (a) $N=4$ and different temperatures: $T/\Delta =0$ (upper curve), 0.1, 0.3, 0.5, 1.0, and 2.0s; (b) $T=\Delta$ and different numbers of channel.