ELECTROMAGNETIC PHENOMENA RELATED TO A LOW-FREQUENCY PLASMA IN CUPRATE SUPERCONDUCTORS

The plasma with c-axis polarization in cuprate superconductors has a v ery low frequency. Experiments show that in some of the cuprate superc onductors the plasma frequency is lower than the superconducting energ y gap and the plasma damping is extremely weak in the superconducting state. Various electromagnetic phenomena caused by the excitation of t he low-frequency plasma are studied theoretically. The reflectivity an d transmissivity of the electromagnetic wave for a film of the cuprate superconductor depend strongly on the frequency and polarization of t he wave and the film thickness, since the wave strongly interacts with the transverse component of the plasma. When vortices are introduced by an external magnetic field, the vortex motion and the gapless excit ation in the vortex cores make the transmissivity and reflectivity str ongly field dependent. The effect of the low-frequency plasma is incor porated in the ac Josephson effect. When a voltage of (h/2e) X (plasma frequency) is applied to the Josephson junction of the cuprate superc onductor, the plasma is excited by the ac Josephson effect and then th e excited plasma will decay by emitting electromagnetic waves. The pla sma excitation also affects the current-voltage characteristics of the junction.