Measurements of the flux flow resistivity in YBa2Cu3O6.95 by microwave techniques

Measurements of the microwave surface resistance have been made at 5.4, 27 and 35 GHz on a high quality single crystal of YBa2Cu3O6.95 in magnetic fields up to 8T (applied parallel to the c-axis) and at temperatures from 20K to 100K. The Coffey-Clem[1] expression for the surface impedance of a superconductor in the mixed state is used to extract the free flux flow resistivity, ϱff. Using the Bardeen-Stephen[2] expression for the flux flow resistivity and a reasonable estimate of Hc2(T), our result is seen to be consistent with a scattering rate inside the vortex cores that decreases approximately linearly below Tc and does not reflect the rapid decrease in the quasiparticle scattering rate observed in zero field microwave measurements[3].