Extended Uniform Ginzburg-Landau Theory for Novel Multiband Superconductors

TL;DR

This paper extends the Ginzburg-Landau theory to multiband superconductors, revealing new collective modes and limitations of the theory at lower temperatures due to interband couplings.

Contribution

It introduces a generalized expansion for the GL theory in multiband superconductors, highlighting unexpected behaviors and the concept of hidden criticality.

Findings

Generalized $ au^{(2n+1)/2}$ expansion for multiband superconductors

Uncovering weaker validity of GL theory at lower temperatures

Evidence for hidden criticality near the critical temperature

Abstract

The recently discovered multiband superconductors have created a new class of novel superconductors. In these materials multiple superconducting gaps arise due to the formation of Cooper pairs on different sheets of the Fermi surfaces. An important feature of these superconductors is the interband couplings, which not only change the individual gap properties, but also create new collective modes. Here we investigate the effect of the interband couplings in the Ginzburg-Landau theory. We produce a general $\tau^{(2n+1)/2}$ expansion ($\tau = 1-T/T_c$) and show that this expansion has unexpected behaviour for $n\geq 2$. This point emphasises the weaker validity of the GL theory for lower temperatures and gives credence to the existence of hidden criticality near the critical temperature of the uncoupled subdominant band.