Hybrid superinductance with Al/InAs

We report microwave spectroscopy of Josephson junction chains made from an epitaxial Al/InAs heterostructure. The chains exhibit superinductance, with characteristic wave impedance exceeding RQ=ℏ/(2e)2. The planar nature of the junctions results in a large plasma frequency, with no measurable dispersion attributable to the single-junction plasma frequency in the measurement range. Internal quality factors decrease sharply with frequency, which we describe with a simple loss model. The possibility of a loss mechanism intrinsic to the superconductor–semiconductor junction is considered.