Fermi-liquid, non-Fermi-liquid, and Mott phases in iron pnictides and cuprates

TL;DR

This paper investigates the effects of Coulomb correlations in iron pnictides using advanced dynamical mean field theory, revealing phase transitions between Fermi-liquid and non-Fermi-liquid states, with implications for understanding high-temperature superconductors.

Contribution

It extends dynamical mean field theory to five orbitals in iron pnictides, identifying continuous and first-order transitions influenced by Hund's coupling and comparing these to cuprate phase diagrams.

Findings

Continuous transition from Fermi-liquid to non-Fermi-liquid phase at moderate Coulomb energies.

First-order transition under Ising-like exchange occurs at lower Coulomb energy.

Correlation effects in LaFeAsO are qualitatively similar to the Hubbard model in cuprates.

Abstract

The role of Coulomb correlations in the iron pnictide LaFeAsO is studied by generalizing exact diagonalization dynamical mean field theory to five orbitals. For rotationally invariant Hund's rule coupling a continuous transition from a paramagnetic Fermi-liquid phase to a non-Fermi-liquid metallic phase exhibiting frozen moments is found at moderate Coulomb energies. For Ising-like exchange, this transition is first order and occurs at a lower critical Coulomb energy. The correlation-induced scattering rate as a function of doping relative to half-filling, i.e., delta = n/5-1, where n=6 for the undoped material, is shown to be qualitatively similar to the one in the two-dimensional single-band Hubbard model. In this scenario, the parent Mott insulator of LaFeAsO is the half-filled n=5 limit, while the undoped n=6 material corresponds to the critical doping region delta_c ~ 0.2 in the cuprates, on the verge between the Fermi-liquid phase of the overdoped region and the non-Fermi-liquid pseudogap phase in the underdoped region.