Microwave Enhancement of Superconductivity in Aluminum Tunnel Junctions

Abstract

Microwave radiation (0.1 to 12 GHz) was propagated in a microstrip transmission line formed by a superconducting Al film on a Ba${\mathrm{F}}_{2}$ substrate. Cross strips formed Al-Al oxide-Al tunnel junctions that were used to study the effect of microwaves on the superconducting properties of the Al films. Large increases in the energy gap and transition temperature were observed for frequencies near 3.7 GHz. The enhancements were negligible below 1 GHz. Anomalous behavior of the features in the tunneling characteristics was observed above 5 GHz.