Electronic structure of vacancy-ordered iron-selenide K$_{0.5}$Fe$_{1.75}$Se$_2$

TL;DR

This study investigates the electronic structure of vacancy-ordered K0.5Fe1.75Se2 using first-principles calculations, revealing magnetic, electronic, and Fermi surface properties relevant to its superconducting behavior.

Contribution

It provides detailed insights into the electronic and magnetic properties of K0.5Fe1.75Se2, including effects of electron doping on susceptibility and Fermi surface topology.

Findings

Ground state is stripe-like antiferromagnetic.

Electron doping suppresses susceptibility peaks and enhances Fermi surface nesting.

Fermi surfaces near the Fermi level are dominated by Fe-3d orbitals.

Abstract

The electronic structure of the vacancy-ordered K$_{0.5}$Fe$_{1.75}$Se$_2$ iron-selenide compound (278 phase) is studied using the first-principles density functional method. The ground state of the 278 phase is stripe-like antiferromagnetic, and its bare electron susceptibility shows a large peak around $(\pi, \pi)$ in the folded Brillouin zone. Near Fermi level, the density of states are dominated by the Fe-3d orbitals, and both electron-like and hole-like Fermi surfaces appear in the Brillouin zone. Unfolded band structure shows limited similarities to a hole doped 122 phase. With 0.1e electron doping, the susceptibility peak is quickly suppressed and broadened; while the two-dimensionality of the electron-like Fermi surfaces are greatly enhanced, resulting in a better nesting behavior. Our study should be relevant to the recently reported superconducting phase K$_{0.5+x}$Fe$_{1.75+y}$Se$_2$ with both $x$ and $y$ very tiny.