Properties of $MgB2$ thin films with carbon doping

We have studied structural and superconducting properties of $MgB2$ thin films doped with carbon during the hybrid physical-chemical vapor deposition process. A carbon-containing precursor metalorganic bis(methylcyclopentadienyl)magnesium was added to the carrier gas to achieve carbon doping. As the amount of carbon in the film increases, the resistivity increases, $Tc$ decreases, and the upper critical field increases dramatically as compared to clean films. The self-field $Jc$ in the carbon doped film is lower than that in the clean film, but $Jc$ remains relatively high to much higher magnetic fields, indicating stronger pinning. Structurally, the doped films are textured with columnar nano-grains and highly resistive amorphous areas at the grain boundaries. The carbon doping approach can be used to produce $MgB2$ materials for high magnetic-field applications.