Effects of charge density wave phase on free flux flow in weak-pinning single crystals of NbSe$_{2}$

The co-existence of two different ordering schemes in the conduction electrons of superconductors -- charge density waves (CDWs) and superconductivity, particularly in the motion of quanta of magnetic flux -- is studied in high-quality samples of the compound, NbSe$_{2}$. Of specific interest is the magnetic-field dependence of transport critical current density $J_{c}$ and that of the Lorentz-driven free flux flow (FFF) resistivity associated with the ordered motion of vortices when the CDWs are switched on and off -- as effected by doping with Ta. The CDW phase is manifested as a broadening of NMR peaks and as a ``knee'' in the temperature dependence of normal-state resistivity. While both doped and non-doped samples show similar field dependence in FFF resistivity, $J_{c}(H)$ reveals a surprising double peak, probably due to sample inhomogeneity combined with the effects of crystal anisotropy.