MAGNETIC-FIELD DEPENDENCE OF THE C-AXIS PLASMA EDGE OF LA1.85SR0.15CUO4

We investigated the influence of a magnetic field on the c-axis reflectance edge of single-crystalline La1.85Sr0.15CuO4. We used fields up to 25 T oriented parallel to the superconducting layers. In contrast to theoretical predictions we find that the screened plasma frequency ωps itself is basically field independent. Also at ωps there is no change in the absorption. However, there is a small but significant field-dependent renormalization of the reflectance edge just below ωps, which indicates an enhanced dissipation in the vortex state. The data are discussed using several recent models for the interaction between electromagnetic radiation and vortices in a layered superconductor. © 1995 The American Physical Society.