Effects of superconducting gap anisotropy on the flux flow resistivity in (formula presented)

The microwave complex surface impedance (formula presented) of (formula presented) was measured at 0.5 K under magnetic fields H up to 7 T. In nominally pure (formula presented) which is a strongly anisotropic s-wave superconductor, the flux flow resistivity (formula presented) calculated from (formula presented) was twice as large as that expected from the conventional normal-state vortex core model. In Pt-doped samples where the gap anisotropy is smeared out, the enhancement of (formula presented) is reduced and (formula presented) approaches the conventional behavior. These results indicate that the energy dissipation in the vortex core is strongly affected by the anisotropy of the superconducting gap.