Temperature Dependence of the Flux-Flow Resistance nearHc2in Type-II Superconductors

We have found that at nonzero temperatures the flux-flow resistivity in type-II superconducting foils is exponential in field near $H_{c2\mathrm{}}$. The fraction of the normalized resistivity which can be represented by the exponential field dependence increases as the temperature approaches $T_c$. The quantity $\alpha ={\left[\right(\frac{H}{{\rho }_N})\times (\frac{d{\rho }_F}{\mathrm{dH}}\left)\right]}_{H=H_{c2\mathrm{}}}$ increases monotonically with temperature, in qualitative agreement with the recent theory of Caroli and Maki, but quantitative comparison of the temperature dependence indicates substantial disagreement. The exponential dependence of the flux-flow resistivity on field suggests that overlap of fluxoids may be important in determining the resistivity at high fields. Alternatively, a recent theory of Clem's describes a thermal dissipation mechanism in addition to the electrical dissipation (Joule heat). Inclusion of this thermal dissipation yields results which are qualitatively suggestive of those which we present here.