Ginzburg–Landau theory for two-band s-wave superconductors: application to non-magnetic borocarbides LuNi2B2C, YNi2B2C and magnesium diboride MgB2

Abstract

Abstract Temperature dependence of the upper critical field H c2 ( T ), lower critical field H c1 ( T ) and thermodynamic magnetic field H cm ( T ) are studied in the vicinity of T c by using a two-band Ginzburg–Landau (G–L) theory. The results are shown to be in a good agreement with experimental data for the superconducting magnesium diboride, MgB 2 , and non-magnetic borocarbides LuNi 2 B 2 C, YNi 2 B 2 C. In addition, two-band G–L theory was applied for the calculation of specific heat jump, which is smaller than in single-band G–L theory. Peculiarities of Little–Parks effect in two-band G–L theory are studied also. It is shown that quantization of the magnetic flux and relation between surface magnetic field H c3 ( T ) and upper critical field H c2 ( T ) are the same as in single-band G–L theory.