Anisotropic superconductivity in epitaxial MgB2 films

We measure the in-plane electrical resistivity of epitaxial MgB2 thin films in magnetic fields to 60 T and estimate the superconducting upper critical field Hpc(0)≈24±3 T for field oriented along the c-axis, and Hρab(0)≈30±2 T in the plane of the film. We find the zero-temperature coherence lengths ξc(0)≈30 Å and ξab(0)≈37 Å to be shorter than the calculated electronic mean free path l≈100±50 Å, which places our films in the clean limit. These large upper critical fields make MgB2 a strong candidate for technological applications.