Gutzwiller density functional calculations of the electronic structure of FeAs-based superconductors: Evidence for a three-dimensional Fermi surface

TL;DR

This study uses Gutzwiller density functional calculations to accurately model FeAs-based superconductors, revealing a three-dimensional Fermi surface and weaker Fe-As bonding, which explains experimental observations like soft phonons.

Contribution

It introduces a Gutzwiller density functional approach to better predict electronic structures of FeAs superconductors, highlighting the importance of Hund's coupling in these materials.

Findings

Fe-As bonding is 30% weaker, explaining soft phonons.

Bands are narrowed by a factor of 2, with the $d_{3z^2-r^2}$ orbital crossing the Fermi level.

Formation of a three-dimensional Fermi surface reduces anisotropy and nesting.

Abstract

The electronic structures of FeAs-compounds strongly depend on the Fe-As bonding, which can not be described successfully by the local density approximation (LDA). Treating the multi-orbital fluctuations from $ab$-$initio$ by LDA+Gutzwiller method, we are now able to predict the correct Fe-As bond-length, and find that Fe-As bonding-strength is 30% weaker, which will explain the observed "soft phonon". The bands are narrowed by a factor of 2, and the $d_{3z^2-r^2}$ orbital is pushed up to cross the Fermi level, forming 3-dimensional Fermi surfaces, which suppress the anisotropy and the ($\pi,\pi$) nesting. The inter-orbital Hund's coupling $J$ rather than $U$ plays crucial roles to obtain these results.