Electronic Structure and Doping in BaFe$_2$As$_2$ and LiFeAs: Density Functional Calculations

TL;DR

This study uses density functional calculations to analyze how doping affects the electronic structure and Fermi surface in BaFe$_2$As$_2$ and LiFeAs, revealing that doping mainly alters Fermi surface sizes rather than the density of states at the Fermi level.

Contribution

It demonstrates that doping changes the Fermi surface topology and As position rather than the density of states, challenging the rigid band approximation in these materials.

Findings

Doping causes a change in the relative sizes of electron and hole Fermi surfaces.

The density of states at the Fermi energy is weakly dependent on doping.

Doping reduces Fermi surface nesting, influencing superconductivity.

Abstract

We report density functional calculations of the electronic structure and Fermi surface of the BaFe$_2$As$_2$ and LiFeAs phases including doping via the virtual crystal approximation. The results show that contrary to a rigid band picture, the density of states at the Fermi energy is only weakly doping dependent and that the main effect of doping is a change in the relative sizes of the electron and hole Fermi surfaces as required by Luttinger's theory. This is a consequence of a change in As height with doping, in particular a shift of As towards Fe as holes are introduced in the Fe plane, as might be expected from simple ionic considerations. The main effect of doping is therefore a reduction in the degree of nesting of the Fermi surface. This provides a framework for understanding the approximate electron-hole symmetry in the phase diagrams of the Fe-As based superconductors.