Free flux flow in two single crystals of V$_{3}$Si with differing pinning strengths

Results of measurements on two very clean, single-crystal samples of the A15 superconductor V$_{3}$Si are presented. Magnetization and transport data have confirmed the ``clean'' quality of both samples, as manifested by: (i) high residual electrical resistivity ratio, (ii) very low critical current densities Jc, and (iii) a ``peak'' effect in the field dependence of critical current. The (H,T) phase line for this peak effect is shifted down for the slightly ``dirtier'' sample, which consequently also has higher critical current density J$_{c}$(H). Large Lorentz forces are applied on mixed-state vortices via large currents, in order to induce the highly ordered free flux flow (FFF) phase, using experimental methods developed previously. The traditional model by Bardeen and Stephen (BS) predicts a simple field dependence of flux flow resistivity \textit{$\rho $}$_{f}$\textit{(H) $\sim $ H/H}$_{c2}$, presuming a field-independent flux core size. A model by Kogan and Zelezhina (KZ) takes into account the effects of magnetic field on core size, and predict a clear deviation from the linear BS dependence. In this study, $\rho _{f}$(H) is confirmed to be consistent with predictions of KZ.