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

We present experimental and calculated phase diagrams of the upper critical field Hc2 and the anisotropy parameter γ of various MgB2 thin films prepared by the molecular beam epitaxy (MBE) and the multiple-targets sputtering system. Experimental data of the Hc2(T) and γ are analyzed by fitting the Gurevich theory. We obtained the result that for these MgB2 films the Hc2(T) is explained as the case of Dπ/Dσ>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.