JOSEPHSON PLASMA IN THE MIXED-STATE OF HIGH T-C SUPERCONDUCTORS

Superconductivity along the c axis of cuprate superconductor is mainta ined by the Josephson coupling between the CuO2 layers. Combining the Josephson current with the electromagnetic field, we have the Josephso n plasma whose frequency appears in the range of 100 GHz and 1 Tera Hz in cuprate superconductors. In the presence of the vortices, the effe ctive Josephson coupling responsible for the plasma is weakened and th e plasma frequency is reduced. This effect may explain the temperature dependence of the plasma frequency observed in the mixed state of Bi2 Sr2CaCu2O8+delta. The interaction between the Josephson plasma and the vortices is strong enough to excite the plasma by the vortex flow. Th e excited plasma will decay by emitting the electromagnetic wave, sinc e the plasma frequency is much smaller than the superconducting energy gap and the plasma has no other decay process.