Two-band nature of upper critical fields in MgB2 thin films investigated by 37 T pulsed magnet

Abstract We present experimental and calculated phase diagrams of the upper critical field H c2 and the anisotropy parameter γ of various MgB 2 thin films prepared by the molecular beam epitaxy (MBE) and the multiple-targets sputtering system. Experimental data of the H c2 ( T ) and γ are analyzed by fitting the Gurevich theory. We obtained the result that for these MgB 2 films the H c2 ( T ) is explained as the case of D π / D σ >1, which means the films are classified to the cleaner π band than the σ band. We discuss temperature dependence of the transition width obtained from the magnetoresistance measurements.