Ballistic electron focusing by elliptic reflecting barriers

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Abstract
We investigate reflection of ballistic electrons off an elliptic barrier in a high quality AlGaAs/GaAs heterostructure. Electrons injected at one focal point of an ellipse are collected at the second focal point, or at the midpoint. Application of a magnetic field perpendicular to the plane of the ellipse modifies the focusing effects by distorting the electrons’ paths, resulting in a novel four-terminal negative magnetoresistance phenomenon. Several secondary features in the magnetoresistance are observed and are interpreted in the light of numerical path simulations.