Effects of gap anisotropy on the electromagnetic response of high- T sub c superconductors

We study the nature of the electromagnetic absorption in a superconductor with an anisotropic energy gap and a nonspherical Fermi surface that is either completely closed or open along the direction of the {ital c} axis of the crystal. The real part of the electromagnetic conductivity {sigma}{sub {mu}{nu}}({bold q},{omega}) has been calculated for a wide range of the normal-state collision frequency {omega}{sub {ital c}} and the parameter {ital Q}=max{l brace}{vert bar}{bold q}{center dot}{bold V}{sub {ital F}}{vert bar}{r brace}, where {bold q} is the incident wave vector of the electromagnetic wave and {bold V}{sub {ital F}} is quasiparticle velocity at the Fermi surface. For simplicity, the model gap parameter {Delta}({bold k}) is assumed to vary only with the angle {theta} between the direction {bold {cflx k}} of the quasiparticle wave vector and the {ital c} axis of the crystal (chosen to be the {ital z} direction). We employ a formulation for calculating the linear conductivity in which the collision frequency is directly related to the imaginary part of the single-particle self-energy resulting from various elastic and inelastic collisions.