A Three-Dimensional Tight-Binding Model and Magnetic Instability of KFe2e2

TL;DR

This paper develops a three-dimensional tight-binding model for KFe2Se2, revealing magnetic instability towards Néel-type antiferromagnetism and ferromagnetic interlayer coupling, with implications for understanding its superconducting properties.

Contribution

It introduces a novel 3D five-orbital tight-binding model fitted to experimental data and analyzes magnetic susceptibilities to predict magnetic ordering in KFe2Se2.

Findings

Fermi surface mainly from t2g orbitals, consistent with ARPES data.

Magnetic susceptibility peaks at ($\pi$, $\pi$), indicating Néel-type antiferromagnetic instability.

Ferromagnetic coupling along the c-axis between FeSe layers.

Abstract

For a newly discovered iron-based high T_c superconducting parent material KFe2Se2, we present an effective three-dimensional five-orbital tight-binding model by fitting the band structures. The three t2g-symmetry orbitals of the five Fe 3d orbitals mainly contribute to the electron-like Fermi surface, in agreement with recent angle-resolved photoemission spectroscopy experiments. To understand the groundstate magnetic structure, the two- and three-dimensional dynamical spin susceptibilities within the random phase approximation are investigated. It obviously shows a sharp peak at wave vector $\mathbf{Q}$ $\thicksim$ ($\pi$, $\pi$), indicating the magnetic instability of {\it N$\acute{e}$el}-type antiferromagnetic rather than ($\pi$/2, $\pi$/2)-type antiferromagnetic ordering. While along $\emph{c}$ axis, it exhibits a ferromagnetic coupling between the nearest neighboring FeSe layers. The difference between the present results and the experimental observation in KxFe2-ySe2 is attributed to the presence of Fe vacancy in the latter.