Interface energy of two-band superconductors

Using the Ginzburg-Landau theory for two-band superconductors, we determine the surface energy σₛ between coexisting normal and superconducting states at the thermodynamic critical magnetic field. Close to the transition temperature, where the Ginzburg-Landau theory is applicable, we demonstrate that the two-band problem maps onto an effective single band problem. While the order parameters of the two bands may have different amplitudes in the homogeneous bulk, near Tc the Josephson-type coupling between the bands leads to the same spatial dependence of both order parameters near the interface. This finding puts into question the possibility of intermediate, so-called type-1.5 superconductivity, in the regime where the Ginzburg-Landau theory applies.