Damping Rate of Josephson Plasmons by Photoexcited Quasiparticles in Small Tunnel Junctions
Takanobu Jujo · Journal of the Physical Society of Japan · 2014
We investigate the quasiparticle excitation by an electromagnetic field in a small tunnel junction and its effect on the damping rate of Josephson plasmons. By the time-dependent path integral method, we formulate the interaction between Josephson plasmons and external fields. Because both quantities are related to each other by the tunneling term, a microscopic derivation of the interaction is important in performing quantitative calculations consistently. We derive an analytical expression for the damping rate in the dispersive region where the oscillating electric field is detuned from Josephson plasmons, and then perform numerical calculations to obtain the relaxation time quantitatively. The result shows that by exciting quasiparticles, the electromagnetic field brings about the decay of Josephson plasmons even in the case that its frequency is lower than twice the superconducting gap. This indicates that there is another source of relaxation besides the spontaneous emission and Purcell effect.