EXCITATION OF THE JOSEPHSON PLASMA MODE IN BI2SR2CACU2O8+DELTA IN AN OBLIQUE FIELD

We present evidence identifying the resonance in microwave absorption observed in Bi2Sr2CaCu2O8+delta in a field H as the Josephson plasma m ode. The resonance field displays an unusual reentrant cusp when H is very close to alignment with the layers. By fitting to a model of Bula evskii et al., we obtain an anisotropy parameter gamma = 400-420 at 5 K, and a Josephson plasma frequency omega(j) equal to 5.3 cm(-1) (at H = 0). We also describe the dependence of omega(j) on H and T when the applied field H parallel to c.