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

摘要

We present experimental and calculated phase diagrams of the upper critical field H-c2 and the anisotropy parameter gamma of various MgB2 thin films prepared by the molecular beam epitaxy (MBE) and the multipletargets Sputtering system. Experimental data of the H-c2(T) and gamma are analyzed by fitting the Gurevich theory. We obtained the result that for these MgB2 films the H-c2(T) is explained as the case of D-pi/D-sigma > 1, which means the films are classified to the cleaner pi band than the sigma band. We discuss temperature dependence of the transition width obtained from the magnetoresistance measurements. (C) 2008 Elsevier Ltd. All rights reserved.