K$_2$Cr$_8$O$_{16}$ predicted as a half-metallic ferromagnet: Scenario for a metal-insulator transition

TL;DR

This paper predicts that K$_2$Cr$_8$O$_{16}$ is a half-metallic ferromagnet with potential for a metal-insulator transition driven by Fermi-surface nesting and density wave formation.

Contribution

First-principles calculations reveal K$_2$Cr$_8$O$_{16}$ as a half-metallic ferromagnet with a proposed mechanism for its metal-insulator transition.

Findings

K$_2$Cr$_8$O$_{16}$ is a half-metallic ferromagnet.

Double-exchange mechanism explains ferromagnetism.

Fermi-surface nesting may cause the metal-insulator transition.

Abstract

Based on the first-principles electronic structure calculations, we predict that a chromium oxide K$_2$Cr$_8$O$_{16}$ of hollandite type should be a half-metallic ferromagnet where the Fermi level crosses only the majority-spin band, whereas the minority-spin band has a semiconducting gap. We show that the double-exchange mechanism is responsible for the observed saturated ferromagnetism. We discuss possible scenarios of the metal-insulator transition observed at low temperature and we argue that the formation of the incommensurate, long-wavelength density wave of spinless fermions caused by the Fermi-surface nesting may be the origin of the opening of the charge gap.