Spin pump turnstile: Parametric pumping of a spin-polarized current through a nearly closed quantum dot

We investigate parametric pumping of a spin-polarized current through a nearly closed quantum dot in a perpendicular magnetic field. Pumping is achieved by tuning the tunnel couplings to the left and right lead—thereby operating the quantum dot as a turnstile—and changing either the magnetic field or a gate voltage. We analyze the quantum dynamics of a pumping cycle and the limiting time scales for operating the quantum dot turnstile as a pure spin pump. The proposed device can be used as a fully controllable double-sided and bipolar spin filter and to inject spins “on demand.”

Figure 1

Schematic picture of a spin-pumping cycle using an oscillating magnetic field. The levels represent the chemical potential of the dot when occupied by an electron with spin-↑ $\left({\mu }_{\uparrow }\right)$ and spin-↓ $\left({\mu }_{\downarrow }\right)$. $\mu$ denotes the chemical potential in the leads. See the explanation in the text.

Figure 2

Spin-pump turnstile with an oscillating gate voltage. The pump cycle is explained in the text.