Fermi surfaces of iron-pnictide high-Tc superconductors from the limit of local magnetic moments

TL;DR

This paper models the electronic structure of iron-pnictide high-Tc superconductors using a 2-orbital t-J model, identifying a quantum critical point that separates different magnetic states and predicting Fermi surfaces consistent with experiments.

Contribution

It introduces a 2-orbital t-J model analyzed via meanfield theory and exact diagonalization, revealing a quantum critical point and associated Fermi surface features in iron-pnictides.

Findings

Identification of a quantum critical point separating magnetic states

Prediction of anisotropic spinwave dispersion at the QCP

Nested Fermi surfaces matching experimental observations

Abstract

A 2-orbital t-J model over the square lattice that describes low-energy electronic excitations in iron-pnictide high-Tc superconductors is analyzed with Schwinger-boson-slave-fermion meanfield theory and by exact numerical diagonalization on a finite system. A quantum critical point (QCP) is identified that separates a commensurate spin-density wave (cSDW) state at strong Hund's rule coupling from a hidden half-metal state at weak Hund's rule coupling when inter-orbital hole hopping is suppressed. Low-energy spinwaves that disperse anisotropically from cSDW momenta are predicted at the QCP. Nested Fermi surfaces similar to those observed experimentally in iron-pnictide materials are also predicted in such case.