Field dependence of c-axis plasma resonance in Josephson-coupled superconductors

The field and temperature dependence of the c-axis plasma frequency in Josephson-coupled layered superconductors is considered. In the zero-temperature limit the field dependence is expressed via the correlator of pancake density between adjacent layers. In the case of strong pinning, when ordering of pancakes along the c axis is destroyed, the predicted power-law field dependence is found to be in agreement with the experimental data for Bi2Sr2CaCU2O8+delta. For weaker pinning, the field dependence is different. Thus information on the pancake arrangement in the vortex glass phase can be obtained from plasma frequency measurements.