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 sharp resonant structure was found in the absorption as a function of magnetic field only when the microwave current flowed across the CuO2 planes, as well as in Bi2Sr2CaCu2Oy (Bi-2212). Together with the frequency-dependence data, the resonant structure in the absorption in Bi-2201 is considered to be the Josephson plasma resonance. The anisotropy ratio gamma drop(m(c)/m(ab))(1/2) was tentatively estimated to be similar to 750. A striking difference was found in the temperature dependence of the resonance field between Bi-2201 and Bi-2212. We argue that this comes from. the difference in the dimensionality of the vortex systems. In Tl2Ba2CaCu2Oy, no such resonance was found in the microwave region, which is probably due to a smaller anisotropy in this material.