Stable Sarma State in Two-band Fermi Systems

TL;DR

This paper explores how two-band Fermi systems can stabilize the Sarma state, which is usually unstable in single-band systems, by analyzing the effects of inter-band interactions and asymmetry.

Contribution

It demonstrates that the Sarma state can be stable in two-band systems under specific conditions involving inter-band exchange and band asymmetry.

Findings

Stable Sarma state possible with inter-band exchange

Large asymmetry enhances Sarma state stability

Conditions for visible mismatch window identified

Abstract

We investigate fermionic superconductivity with mismatched Fermi surfaces in a general two-band system. The exchange interaction between the two bands changes significantly the stability structure of the pairing states. The Sarma state with two gapless Fermi surfaces which is always unstable in single-band systems, can be the stable ground state in two-band systems. To realize a visible mismatch window for the stable Sarma state, two conditions should be satisfied: a nonzero inter-band exchange interaction and a large asymmetry between the two bands.