Anomalous isotope effect in phonon-dressed iron-based superconductor

TL;DR

This paper investigates the complex isotope effect in iron-based superconductors, revealing that phonon dressing influences whether the isotope effect appears normal or reversed, linked to unconventional pairing mechanisms.

Contribution

It employs renormalization-group analysis to show that electron-phonon interactions are subdominant but significantly affect isotope effects in iron-based superconductors.

Findings

Phonon dressing can cause normal or reversed isotope effects.

Unconventional pairing symmetry is connected to isotope effect anomalies.

Electron-electron interactions primarily drive superconductivity.

Abstract

The role of electron-phonon interactions in iron-based superconductor is currently under debate with conflicting experimental reports on the isotope effect. To address this important issue, we employ the renormalization-group method to investigate the competition between electron-electron and electron-phonon interactions in these materials. The renormalization-group analysis shows that the ground state is a phonon-dressed unconventional superconductor: the dominant electronic interactions account for pairing mechanism while electron-phonon interactions are subdominant. Because of the phonon dressing, the isotope effect of the critical temperature can be normal or reversed, depending on whether the retarded intra- or inter-band interactions are altered upon isotope substitutions. The connection between the anomalous isotope effect and the unconventional pairing symmetry is discussed at the end.