The temperature dependence of the lower critical field HC1(T) for the superconducting diboride was studied in the vicinity of TC using a 2-band Ginzburg–Landau theory. The theoretically calculated HC1(T) near TC exhibited a negative curvature. The results were shown to be in good agreement with the experimental data. In addition, two-band Ginzburg–Landau theory calculations gave a temperature dependence of the Ginzburg–Landau parameter κ(T) = λ(T)/ξ(T), which varies little with the temperature in a manner similar to the microscopic single-band BSC theory.

Two-Band Ginzburg–Landau Theory for the Lower Critical Field HC1 in MgB2. I.N.Askerzade, A.Gencer, N.Güçlü, A.Kiliç: Superconductor Science and Technology, 2002, 15, L17-20