Upper Critical Field in C-Doped MgB2 Thin Films and Coated Fibers

We have studied H$_{c2}$ and its anisotropy $\gamma $ of C-doped MgB$_{2}$ thin films grown on (0001) SiC single crystal substrates and SiC/W fibers by hybrid physical-chemical vapor deposition (HPCVD). Residual resistivity increases systematically with doping, but Tc is not affected seriously. The H$_{c2}$ in both direction was found to increase with increasing residual resistivity. In the field range between 1 - 9 T, the slope of Hc$_{2}^{\bot ab}$ (T) increases from about 0.1Tesla/K to1.1Tesla/K and the slope of Hc$_{2}^{//ab}$ (T) increases from about 0.6 T/K to 2.2 T/K. The temperature dependence of the anisotropy changes dramatically with the doping level. In the fiber samples, large upper critical field similar to Hc$_{2}^{//ab}$ (T) in thin films was obtained. The results measured in pulsed higher magnetic fields (60T) will also be presented. The effects will be compared with the recent theoretical predictions on two band superconductors.