ELECTRON-TRANSPORT IN MULTIPROBE QUANTUM WIRES ANOMALOUS MAGNETORESISTANCE EFFECTS

The magnetoresistance anomalies that are observed in multiprobe quantum wires (such as quenching of the Hall effect and negative bend resistance) have been investigated using a semiclassical billiard-ball model that includes the effects of diffuse boundary scattering. This modeling predicts that two peaks are expected in the magnetoresistance of a quantum wire in which there is a significant amount of diffuse boundary scattering. One peak is due to diffuse boundary scattering in the wire and the other due to specular boundary scattering in the junctions at either end of the wire. The modeling also predicts that the well-known quenching of the Hall effect and negative bend resistance anomalies are both expected to be enhanced by diffuse boundary scattering. This is explained in terms of the way in which diffuse boundary scattering affects the angular distribution of the electrons entering the junctions in the multiprobe wires. "Diffuse collimation" of the electron distribution occurs, increasing the probability for direct transmission of the electrons across the junctions. Experiments performed on wires fabricated in GaAs/AlxGa1-xAs high-mobility heterostructure material, using implanted p-type gates to provide the lateral confinement, have confirmed the twin-peak structure in the magnetoresistance. Although the diffuse boundary scattering magnetoresistance peak has been observed often before, this is the first unambiguous observation of the junction scattering peak. Other device geometries are investigated using the semiclassical model, and a prediction is made for negative longitudinal resistance in a multiprobe wire in which the voltage probes are shadowed from either the current source or the drain. This phenomenon was experimentally verified with devices fabricated in GaAs/AlxGa1-xAs high-mobility heterostructure material using surface Schottky gates or wet etching to provide the lateral confinement. Thus, the trio of negative resistance effects in multiprobe quantum wires has been completed; in addition to the negative Hall resistance and the negative bend resistance a negative longitudinal resistance has now been measured. © 1995 American Institute of Physics.