LONGITUDINAL JOSEPHSON PLASMA EXCITATION IN VORTEX STATE OF BI2SR2CACU2O8+DELTA

The Josephson plasma absorption at a microwave frequency of 45 GHz in a cavity (E(osc)-axis) has been studied in high quality single crystal line Bi2Sr2CaCu2O8+delta as functions of magnetic field, temperature, doping level, and angle between magnetic field and crystallographic ax es. The observed resonance line shape, which is rather symmetric, was analyzed in detail by solving the coupled equations of the Maxwell equ ation and the Josephson current as well as the charge equations. As a result the observed absorption is unambiguously assigned as the longit udinal plasma mode. The temperature dependence of the absorption agree s with the prediction based on the d-wave symmetry rather than the iso tropic s-wave one. The resonance line can be scaled by the perpendicul ar component of the field, indicating that the resonance position is d etermined by the number of vortices parallel to the c-axis.