JOSEPHSON PLASMA RESONANCE IN A SINGLE-LAYERED CUPRATE BI-2(SR,LA)(2)CUOY

Microwave absorption was measured in the mixed state of (Bi or Tl)(2)( Sr or Ba)(2)Can-1CunOy. In a La-substituted Bi2Sr2CuOy (Bi-2201), a sh arp resonant structure was found in the absorption as a function of ma gnetic field only when the microwave current flowed across the CuO2 pl anes, as well as in Bi2Sr2CaCu2Oy (Bi-2212). Together with the frequen cy-dependence data, the resonant structure in the absorption in Bi-220 1 is considered to be the Josephson plasma resonance. The anisotropy r atio gamma drop(m(c)/m(ab))(1/2) was tentatively estimated to be simil ar to 750. A striking difference was found in the temperature dependen ce of the resonance field between Bi-2201 and Bi-2212. We argue that t his comes from. the difference in the dimensionality of the vortex sys tems. In Tl2Ba2CaCu2Oy, no such resonance was found in the microwave r egion, which is probably due to a smaller anisotropy in this material.