Subharmonic energy gap structure and gap-enhancement by the Josephson radiation in small dayem bridges

Abstract
We have observed subharmonic energy gap structure in the I-V characteristics of thin film indium and tin microbridges occurring at voltages of 2 Δ/ Ne. Under the influence of microwaves the subharmonics develop sidebands at (2 Δ ± Mħω)/Ne. We explain the observed behaviour in terms of pair-breaking in the region of the bridge by the Josephson radiation and have simulated the effect by analogue computation. Through the positions of the subharmonic peaks we deduce that the energy near the bridge is enhanced above the BCS bulk value, apparently by the Josephson radiation