Damping Rate of Josephson Plasmons by Quasiparticle Excitation in Small Tunnel Junctions
Takanobu Jujo · Journal of the Physical Society of Japan · 2013
We investigate the intrinsic damping rate of Josephson plasmons in small tunnel junctions. The effect of interactions between collective modes is calculated on the basis of the perturbative expansion. This expansion is valid for small values of EC/EJEC/EJ (ECEC and EJEJ are the charging and Josephson coupling energies, respectively). The rage of damping by quasiparticle excitation is dependent on this ratio and is qualitatively different from the lowest-order term studied in previous works. The relaxation time is roughly a quadratic function of frequency, which is peculiar to small tunnel junctions. A small value of EC/EJEC/EJ does not necessarily mean a long relaxation time owing to the nonmonotonic dependence of the damping rate on frequency. These nontrivial properties originate from the tunneling term, which depends on frequency and describes both the damping and interaction effects.