ABSTRACT
The development of InAs/AlSb quantum wells with high electron concentrations and high mobilities has recently made possible supercurrent flow in SNS structures with a quasi-2D electron gas (2DEG) as the N channel. Previous studies of such superconducting 2DEG structures have focused on dc transport. Here we use the far-infrared transmission through a 2DEG that periodically contacts a superconducting grating to probe how the vanishing d.c. resistance of the 2DEG affects its excitation spectrum at frequencies near the superconducting grating's gap. The striking features we observe in transmission spectra indicate a more complex spectrum of excitations out of the ground state than in a uniform BCS film, and seem inconsistent with a conventional proximity effect model.
