Shrinking of the fluctuation region in a two-band superconductor

Abstract

In a two-band superconductor, two qualitatively different fluctuation modes related to the gap modules contribute to the free energy and heat capacity, together with the phase fluctuations. The first mode has divergent temperature behaviour since it accounts for critical fluctuations around the phase transition point, , along with pseudo-critical ones associated with the former instability of the weaker superconductivity component. The involvement of these two factors, competing under interband interaction, results in a Ginzburg number that varies with non-monotonically, allowing a reduction of up to 75%. This makes the fluctuations effective in revealing additional superconducting components in the system. The second mode does not diverge, but has a jump at , defined uniquely by the strength of the interband interaction. This mode contributes fundamentally beyond the critical domain.