Electronic correlations in the iron pnictides

TL;DR

This paper investigates electronic correlations in the iron pnictide superconductor LaFePO, revealing significant correlation effects that reduce electron kinetic energy, highlighting a new pathway to correlated electron states beyond Mott insulators.

Contribution

The study provides experimental evidence of strong electronic correlations in LaFePO using optical spectroscopy, emphasizing correlation effects without involving a Mott transition.

Findings

Electron kinetic energy is halved compared to band theory predictions.

Clear evidence of electronic correlations in LaFePO.

Highlights a new pathway to correlated electron states.

Abstract

In correlated metals derived from Mott insulators, the motion of an electron is impeded by Coulomb repulsion due to other electrons. This phenomenon causes a substantial reduction in the electron's kinetic energy leading to remarkable experimental manifestations in optical spectroscopy. The high-Tc superconducting cuprates are perhaps the most studied examples of such correlated metals. The occurrence of high-Tc superconductivity in the iron pnictides puts a spotlight on the relevance of correlation effects in these materials. Here we present an infrared and optical study on single crystals of the iron pnictide superconductor LaFePO. We find clear evidence of electronic correlations in metallic LaFePO with the kinetic energy of the electrons reduced to half of that predicted by band theory of nearly free electrons. Hallmarks of strong electronic many-body effects reported here are important because the iron pnictides expose a new pathway towards a correlated electron state that does not explicitly involve the Mott transition.