Interprentation of microwave magnetoresistance above and below T_c in a single crystal YBa_2Cu_3O_7-delta superconductor

Field dependence of the microwave surface resistance in YBa_2Cu_3O_7-delta single crystal is analysed in terms of the mixed state and superconducting fluctuations. Careful fitting of the appropriate parts of the magnetoresistance curves yields the upper critical field, and mean field T_c. The microwave fluctuations conductivity is found to scale as predicted for a three dimensional (3D) superconductor