Interband electron pairing for superconductivity from the breakdown of the Born-Oppenheimer approximation

TL;DR

This paper explains how the breakdown of the Born-Oppenheimer approximation during electron-phonon interactions naturally leads to interband electron pairing, which enhances superconductivity, with the pairing strength depending on Fermi surface properties.

Contribution

It demonstrates that interband electron pairing arises from the Born-Oppenheimer approximation breakdown and identifies factors influencing its strength in superconductors.

Findings

Interband pairing results from Born-Oppenheimer breakdown.

Favorable Fermi surfaces for pairing were identified.

Implications for superconductivity enhancement were discussed.

Abstract

The origin of interband electron pairing responsible for enhancing superconductivity and the factors controlling its strength were examined. We show that the interband electron pairing is a natural consequence of breaking down the Born-Oppenheimer approximation during the electron-phonon interactions. Its strength is determined by the pair-state excitations around the Fermi surfaces that take place to form a superconducting state. Fermi surfaces favorable for the pairing were found and its implications were discussed.