Simultaneous Action of Intra- and Interband Pair Channels in Multiband Superconductivity

Abstract

Interband superconductivity channels with pairs formed from the same (a) and different bands (b) are compared in common action. A simple mean-field multiband model is inspected. There are three order parameters Δ _a , Δ _{a d} and ${\Delta }_{b} \left ({\Delta }_{b1}^{2}={\Delta }_{b2}^{2} \right )$. Complicated quasiparticle energies induced by interactions of strengths W _a and W _b follow. The calculated operator averages lead to a coupled nonlinear system for the gap-type parameters. Illustrative calculations of them vs temperature have been made. Overlapping dispersive bands intersected by the chemical potential have been used. A novel result is that at a fixed parameter set the system of basic equations has two independent solutions. The free energy is of a complicated structure under the action of both channels. There are stable and metastable states. The W _a and W _b channels compete in simultaneous functioning. The phenomenon of the effective logout of one of the channels can be traced. Starting by the temperature where Δ _i reached zero, the solutions induced by W _j behaving as W _i were zero and define T _{c i} . The pairs Δ _a and Δ _{a d} have the same vanishing temperature. The general results are very sensible to |W _b | inclusive to critial behaviour. Reduced |W _b | stimulates the formation of closed “bubbles” built up by Δ _a , Δ _b and Δ _{a d} belonging to parallel solutions. The corresponding metastable state vanishes when the bubble closes.