Upper critical fields in as-grown MgB2 films prepared by ultra-high-vacuum MBE

Abstract We report on the upper critical fields ( H c2 ’s) of as-grown MgB 2 thin films deposited on the epitaxial Ti buffer layer on c -plane ZnO substrates by using a molecular beam epitaxy (MBE) apparatus. The H c2 was estimated from the magnetoresistance measurements under the pulsed magnetic field up to 37 T. H c2 ( T ) for both H  ∥  ab -plane and H  ∥  c -axis were measured to obtain the anisotropic superconducting properties. The results are successfully analyzed with the Gurevich theory of dirty two-gap superconductivity with a cleaner π band case.