Mott State and Quantum Critical Points in Rare-Earth Oxypnictides $RO_{1-x}F_xFeAs$ ($R=La, Sm, Nd, Pr, Ce$)

TL;DR

This study explores the magnetic phase diagram of rare-earth oxypnictide superconductors, revealing a Mott insulating state in undoped LaOFeAs and identifying quantum critical points near superconducting phases influenced by electronic correlations.

Contribution

It provides the first ab initio computational analysis of magnetic phases and quantum critical points in rare-earth oxypnictide superconductors, highlighting the role of electronic correlations.

Findings

LaOFeAs is a Mott insulator with electronic correlations.

Doped compounds transition from antiferromagnetic to non-magnetic states at specific doping levels.

Superconductivity occurs near magnetic quantum critical points influenced by Mott insulating behavior.

Abstract

We investigate the magnetic phase diagram of the newly discovered iron-based high temperature oxypnictide superconductors of the type RO$_{1-x}$F$_x $FeAs, with rare earths R=La, Sm, Nd, Pr and Ce by means of {\it ab initio} SGGA and SGGA+U density functional computations. We find undoped LaOFeAs to be a Mott insulator when incorporating electronic correlations via SGGA+U for any physically relevant value of $U$. The doped compounds are according to SGGA conductors with a transition from an antiferromagnetic to a non-magnetic state at a hole doping of concentration $x_c$=0.075 for R=Nd, Pr and at electron doping $x_c$=0.25 for Ce and 0.6 for Sm. Superconductivity in these rare-earth oxypnictides thus appears in the vicinity of a magnetic quantum critical point where electronic correlations are expected to play an important role because of the vicinity of a Mott insulating state at zero doping.