Nonequilibrium microwave emission due to tunnel injection of quasiparticles into a high-Tc Bi2Sr2CaCu2Oy superconductor

Nonequilibrium microwave emission due to tunnel injection of quasiparticles into a high-T-c Bi2Sr2CaCu2Oy (Bi2212) superconducting thin film using an Au/I/Bi2212 tunnel junction is reported. The microwaves were detected by a superheterodyne-mixer technique at a receiver frequency of 47 GHz. With increasing the injection current, the emitted microwave intensity increased almost linearly at relatively low temperatures, in qualitative agreement with the case of YBa2CU3O7-y films. Above 35 K, however, the intensity vs injection current curves exhibited nonlinear behavior. The results were consistently interpreted by the Josephson plasma excitation model due to quasiparticle injection recently proposed by Shafranjuk and Tachiki.