Anomalous flux flow resistivity in the two-gap superconductor MgB2 -: art. no. 060501

The flux flow resistivity rho(f) associated with purely viscous motion of vortices in high-quality MgB2 was measured by microwave surface impedance. Flux flow resistivity exhibits unusual field dependence with strong enhancement at low field, which is markedly different to conventional s-wave superconductors. A crossover field which separates two distinct flux flow regimes having different rho(f) slopes was clearly observed in Hparallel toab plane. The unusual H dependence indicates that two very differently sized superconducting gaps in MgB2 manifest in the vortex dynamics and almost equally contribute to energy dissipation. The carrier scattering rate in two different bands is also discussed with the present results, compared to heat-capacity and thermal-conductivity results.