Upper critical field and the effect of Li doping on the activation energy in MgB 2

Abstract

MgB 2 and Mg 0.93Li 0.07B 2 superconductors have been prepared by solid-state reaction. The temperature dependence of electrical resistivity in MgB 2 and Mg 0.93Li 0.07B 2 have been measured in magnetic field up to 14 T. They have almost the same superconducting transition temperature T c. The upper critical fields H c2(0) were determined. The activation energy of MgB 2 and Mg 0.93Li 0.07B 2 bulk sample have been calculated from the Arrhenius activation law ρ= ρ 0exp(− U/ k B T). Compared to MgB 2, the activation energy of Mg 0.93Li 0.07B 2 rises by 25.0%, 20.4% and 16.5% at the magnetic field 14, 10 and 7 T, respectively. A small amount of Li doping in MgB 2 that almost not changes the T c of MgB 2 has raised the activation energy U, especially at high magnetic field.