Observation of an energy gap in the condensed phase of a GaAs/Ga_0.77Al_0.23As heterojunction

A microwave photoconductivity technique has been used to observe directly an energy gap in the condensed phase of a GaAs/Ga0.77Al0.23As heterojunction. In this technique, microwaves are used to excite electrons across the gap, and the accompanying change in the DC conductivity is detected. In addition, the phase diagram in magnetic-field-temperature space has been determined experimentally, and the temperature dependence of the critical field is found to be the same as that predicted by the Gorter-Casimir two-fluid model of superconductivity. © 1987 IOP Publishing Ltd.