Far-infrared studies of induced superconductivity in quantum wells

Abstract Recent work on peridic SNS microstructures, in which a superconductor grating contacts an underlying InAs quantum well, has demonstrated that supercurrents can flow across the strips of quasi-two-dimensional electron gas between the superconductor grating lines. Here we show that the loss of DC resistance is accompanied by the emergence of striking features in the samples' excitation spectra, for energies below ∼ 2†. Although such series weak-link structures may display a Josephson plasmon resonance, the changes in the samples' far-infrared transmission in an applied H field appear to be inconsistent with the behavior expected for this mode. The transmission spectra also differ from the form expected for an energy gap in the quantum well strips between adjacent superconductor lines. We speculate that the observed absorption features instead arise from transitions between quasi-particle states produced by Andreev reflections at the superconductor/InAs interfaces.