Resonant Tunneling Spin Pump

NASA’s Jet Propulsion Laboratory, Pasadena, California

Monday, October 01 2007

Electrons in opposite spin states would flow in opposite directions across a spin filter.

The resonant tunneling spin pump is a proposed semiconductor device that would generate spin-polarized electron currents. The resonant tunneling spin pump would be a purely electrical device in the sense that it would not contain any magnetic material and would not rely on an applied magnetic field. Also, unlike prior sources of spin-polarized electron currents, the proposed device would not depend on a source of
circularly polarized light.

The resonant tunneling spin pump would have some features in common with other, similarly named devices, including resonant tunneling spin filters described in a previous NASA Tech Briefs article: “Electron-Spin Filters Based on the Rashba Effect” (NPO- 30635), Vol. 28, No. 10 (October 2004), page 58.

To recapitulate: Proposed semiconductor electron-spin filters would exploit the Rashba effect, which can induce energy splitting in what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural- inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. Theoretical studies have suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantummechanical tunneling.

The resonant tunneling spin pump (see figure) would include a spin filter between two reservoirs of initially unpolarized electrons. Like the devices of the cited prior article, the resonant tunneling spin pump would be designed and fabricated in the InAs/GaSb/ AlSb material system. One reservoir would be a highmobility InAs emitter channel and the other a high-mobility InAs collector channel. The spin filter would comprise an InAs/GaSb/ AlSb asymmetric resonant
tunneling structure.

The application of a lateral electric field in the emitter channel would a cause current of one spin state to flow from the emitter channel to the collector channel and a current of the opposite spin state to flow from the collector channel to the emitter channel, thereby inducing spin polarization in both reservoirs. This mode of operation would differ somewhat from that of a spin filter: In a spin filter, component currents containing spins of both states would flow from the emitter to the collector and spin polarization in the collector would be achieved by choosing the design and the operating conditions of the device to make one of the spin component currents larger than the other.

This work was done by David Z. Ting of Caltech for NASA’s Jet Propulsion Laboratory.