Spin Transport in Semiconductor and Metallic Nanowires

Abstract

Many spintronic devices require quantum wire channels with strong spin orbit interaction for electrical manipulation of spin precession while maintaining long spin coherence lengths and times. These two requirements are contradictory since strong spin-orbit interaction leads to rapid D'yakonov-Perel' (DP) spin relaxation. One possible remedy is to use semiconductor quantum wires where a single conduction subband is occupied at room temperature. Here, the DP relaxation is suppressed, leading to many fold increase in the spin relaxation time. We have self-assembled 50-nm diameter InSb nanowire spin-valves where a single subband is occupied by carriers at room temperature. Suppression of DP relaxation leads to a 10-fold increase in the spin relaxation time at room temperature over that reported in bulk or quantum well systems of the same material. We have observed clear spin-valve signals and Hanle oscillations in these systems at room temperature attesting to coherent spin injection, transport and detection. By using infrared light to change the subband occupation in the nanowires, we were able to modulate the DP rate and hence the spin relaxation length. This capability can be exploited to change the resistance of a spin valve device with light, thereby implementing a spintronic room temperature infrared photodetector that can ideally have zero dark current. We have observed infrared light modulation of the resistance in the same InSb system at room temperature [2] at low intensity levels where sample heating an photogeneration are insignificant. Finally, we have also studied the effect of mechanical strain on spin orbit interaction in a ferromagnetic metal and the resulting anisotropic magnetoresistance (AMR) in a metallic nanowire spin valve. AMR is found to be extremely sensitive to strain at room temperature and this offers a mechanism to implement a spintronic strain sensor. Acknowledgement: FUNDED BY NSF CMMI GRANT 1301013 Iftekhar's current affiliation Intel Corporation, Hillsboro, OR. Saumil's current affiliation MIT, Cambridge, MA. The AMR work was done in collaboration with Prof. A. Subramanian now at Univ. of Illinois at Chicago. THIS TALK IS ALSO AN IEEE DISTINGUISHED LECTURE SPONSORED BY IEEE