We have observed a super-giant (∼10,000,000%) negative magnetoresistance at 39 mT field in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over, these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This lowers the potential barrier at the accumulated edge and raises it at the depleted edge, causing a super-giant magnetoresistance at room temperature.
Abstract. Spintronic devices usually rely on long spin relaxation times and/or lengths for optimum performance. Therefore, the ability to modulate these quantities with an external agent offers unique possibilities. The dominant spin relaxation mechanism in most technologically important semiconductors is the D'yakonov-Perel' (DP) mechanism which vanishes if the spin carriers (electrons) are confined to a single conduction subband in a quantum wire grown in certain crystallographic directions, or polycrystalline quantum wires. Here, we report modulating the DP spin relaxation rate (and hence the spin relaxation length) in self assembled 50-nm diameter InSb nanowires with infrared light at room temperature. In the dark, almost all the electrons in the nanowires are in the lowest conduction subband at room temperature, resulting in nearcomplete absence of DP relaxation. This allows observation of spin-sensitive effects in the magnetoresistance. Under infrared illumination, electrons are photoexcited to higher subbands and the DP spin relaxation mechanism is revived, leading to a threefold decrease in the spin relaxation length. Consequently, the spin sensitive effects are no longer observable under illumination. This phenomenon may have applications in spintronic room-temperature infrared photodetection.
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