Microwave resistivity at 48 GHz in high-T-c superconductor films in magnetic fields

We consider the field dependence of the microwave resistivity in high-T-c s uperconductors. We present field-dr-pendent microwave resistivity measureme nts at 48 GHz on thin YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta films. The fi eld dependence of the microwave resistivity cannot be satisfactorily descri bed in terms of a single model for the flux motion when both materials are considered. We introduce and discuss a simple model that incorporates the e ffect of the enhanced field-induced quasiparticle increase in a superconduc tor with Lines of nodes in the gap, together with viscous flux motion. A go od description of the data is obtained, for YBa2Cu3O7-delta as well as for Bi2Sr2CaCu2O8+x.