MAGNETIC FOCUSING IN PARALLEL QUANTUM POINT CONTACTS

Using an air-bridged gate, we have fabricated two closely spaced paral lel quantum point contacts (QPC's) in a GaAs-AlxGa1-xAs heterostructur e. By biasing the gates appropriately, we have measured the magnetores istance (MR) at low fields for both single and parallel point contacts . Assuming a parabolic potential, the MR of a single QPC can be quanti tatively understood by a previous theory incorporating magnetic-field- suppressed backscattering. However, the MR of two QPC's in parallel di splays resistance peaks, implying a failure of Ohm's law due to coupli ng between the channels. These resistance peaks are shown to be due to magnetic focusing of electrons from one channel into the other.