Subharmonic Energy-Gap Structure and a Josephson-Radiation-Enhanced Gap in Dayem Bridges

Abstract

Superconducting thin-film microbridges are found to have subharmonic energy-gap structure in their $I-V$ characteristics at voltages of $\frac{2\Delta }{\mathrm{Ne}}$, which on the application of microwaves develop sidebands at $\frac{2\Delta }{\mathrm{Ne}}\pm \frac{M\hslash \omega }{\mathrm{Ne}}$. The structure is explained on the basis of pair breaking by the harmonics of the Josephson radiation, both directly and via the normal electrons. An enhancement of the energy gap apparently induced by the Josephson radiation is observed in the subharmonic structure.