Ternary iron selenide K$_{0.8}$Fe$_{1.6}$Se$_2$ is an antiferromagnetic semiconductor

TL;DR

This study uses first-principles calculations to reveal that K$_{0.8}$Fe$_{1.6}$Se$_2$ is an antiferromagnetic semiconductor with a significant energy gap and magnetic moment, highlighting its potential as a parent compound for superconductivity.

Contribution

It provides the first detailed electronic and magnetic structure analysis of K$_{0.8}$Fe$_{1.6}$Se$_2$, identifying it as a semiconductor with antiferromagnetic order driven by chemical-bonding-induced lattice distortion.

Findings

K$_{0.8}$Fe$_{1.6}$Se$_2$ is a quasi-2D AFM semiconductor with a 594 meV gap.

The magnetic moment per Fe atom is 3.37 μ_B.

Doping with excess potassium turns it into a doped AFM semiconductor.

Abstract

We have studied electronic and magnetic structures of K$_{0.8+x}$Fe$_{1.6}$Se$_2$ by performing the first-principles electronic structure calculations. The ground state of the Fe-vacancies ordered K$_{0.8}$Fe$_{1.6}$Se$_2$ is found to be a quasi-two-dimensional blocked checkerboard antiferromagnetic (AFM) semiconductor with an energy gap of 594 meV and a large ordering magnetic moment of 3.37 $\mu_B$ for each Fe atom, in excellent agreement with the neutron scattering measurement. The underlying mechanism is the chemical-bonding-driven tetramer lattice distortion. K$_{0.8+x}$Fe$_{1.6}$Se$_2$ with finite $x$ is a doped AFM semiconductor with low conducting carrier concentration which is approximately proportional to the excess potassium content, consistent qualitatively with the infrared observation. Our study reveals the importance of the interplay between antiferromagnetism and superconductivity in these materials. This suggests that K$_{0.8}$Fe$_{1.6}$Se$_2$, instead of KFe$_2$Se$_2$, should be regarded as a parent compound from which the superconductivity emerges upon electron or hole doping.