Andreev reflection at high magnetic fields

Electron transport through a two-dimensional electron gas between superconducting contacts was studied in perpendicular magnetic fields of up to 6 T. Alloyed contacts with a high-critical field were used with a high-mobility GaAs:AlₓGa_1-xAs heterostructure, allowing the first observation of Andreev reflection at fields of up to 3 T and into the quantum Hall regime. An increase in the probability of Andreev reflection was seen with increasing field to 1.2 T, and excess conductance is seen in the range 60 mT--3 T. Above 0.85 T, spin splitting in the semiconductor channel inhibits Andreev reflection.