Mustafa Muhammad, University of Cincinnati
Abstract
I will talk about measurement of Coulomb drag (CD) between two spatially separated and electrically isolated short one-dimensional (1D) wires. The 500nm long dual-wire CD devices are fabricated with high mobility two-dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructure, using high resolution e-beam lithography, combined with metal deposition by e-beam evaporation to form surface Schottky gates.
Peak in the drag voltage occurs when the subband bottoms of the lowest energy subbands of the drive and drag wires line up with each other and the Fermi level. The drag signal is measured at different temperatures. We have observed both positive and negative drag in absence of any external magnetic field. The observed temperature dependence of drag resistance, of both positive and negative drag, suggests drag occurs due to small forward momentum transfer between the wires. We suggest positive drag happens when band curvature at Fermi point is positive and negative drag occurs when the curvature is negative and there exists particle-hole asymmetry in the wires. I will also talk about measurement of spin-polarized current in 1D quantum wire (quantum point contact – QPC) fabricated from semiconductor with high spinorbit coupling. The side-gated QPC devices are made from nominally symmetric InAs quantum well structures. The spin-polarized current is generated by purely electrical means when the lateral confinements that realize the QPC are made highly asymmetric. Such QPCs may contribute to developing semiconductor spintronic devices.