Sample size dependence of the Josephson plasma resonance in Bi2Sr2CaCu2O8+delta

The Josephson plasma resonance in single crystalline Bi2Sr2CaCu2O8+delta has been investigated at a microwave frequency of 35 GHz in a TE102 cavity as functions of external magnetic field (H-ext//c-axis) and sample dimension L in the ab-plane. A sharp resonance is observed in Erf//c(1) whereas multi-peaks are found in H-rf//ab. The former is independent of the sample dimension, while the latter shifts to higher fields as the sample size L is reduced, and disappears when L less than or equal to L-c. The size dependence of the resonance field observed in H-rf//ab can be explained by the strong dispersion relation of the transverse Josephson plasma, and the size independent resonance can be described by the longitudinal Josephson plasma as predicted by the recent theory of Josephson plasma by Tachiki et al.