Electromagnetic phenomena related to a low-frequency plasma in cuprate superconductors

Abstract

The plasma with c-axis polarization in cuprate superconductors has a very low frequency. Experiments show that in some of the cuprate superconductors the plasma frequency is lower than the superconducting energy gap and the plasma damping is extremely weak in the superconducting state. Various electromagnetic phenomena caused by the excitation of the low-frequency plasma are studied theoretically. The reflectivity and transmissivity of the electromagnetic wave for a film of the cuprate superconductor depend strongly on the frequency and polarization of the 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 excitation in the vortex cores make the transmissivity and reflectivity strongly field dependent. The effect of the low-frequency plasma is incorporated in the ac Josephson effect. When a voltage of (h/2e)\ifmmode\times\else\texttimes\fi{}(plasma frequency) is applied to the Josephson junction of the cuprate superconductor, the plasma is excited by the ac Josephson effect and then the excited plasma will decay by emitting electromagnetic waves. The plasma excitation also affects the current-voltage characteristics of the junction.