Electronic structure and magnetism of the Hund insulator CrI3

TL;DR

This study investigates the electronic structure and magnetism of CrI3, revealing it as a Mott-Hund insulator with a charge gap of 1.1 eV, and explores how structural phase transitions relate to magnetic fluctuations.

Contribution

The paper combines density functional theory and dynamical mean-field theory to identify CrI3 as a Mott-Hund insulator and links magnetic fluctuations to structural phase transitions.

Findings

CrI3 has a charge gap of 1.1 eV in the paramagnetic state.

CrI3 is characterized as a Mott-Hund insulator due to half-filled Cr 3d t2g orbitals.

Structural phase transition is driven by ferromagnetic spin fluctuations.

Abstract

CrI3 is a two-dimensional ferromagnetic van der Waals material with a charge gap of 1.1-1.2 eV. In this study, the electronic structure and magnetism of CrI3 are investigated by using density functional theory and dynamical mean-field theory. Our calculations successfully reproduce a charge gap of 1.1 eV in the paramagnetic state when a Hund coupling JH = 0.7 eV is included with an on-site Hubbard U = 5 eV. In contrast, with a large U value of 8 eV and negligible Hund coupling JH, CrI3 is predicted to be a moderately correlated metal in the paramagnetic state. We conclude that CrI3 is a Mott-Hund insulator due to the half-filled configuration of the Cr 3d t2g orbitals. The Cr 3d eg orbitals are occupied by approximately one electron, which leads to strong valence fluctuations so that the Cr 3d orbitals cannot be described by a single state. Moreover, at finite temperature, the calculated ordered static magnetic moment in the ferromagnetic state is significantly larger in the R3 phase than in the C2/m phase. This observation indicates that the structural phase transition from the C2/m phase to the R3 phase with decreasing temperature is driven by ferromagnetic spin fluctuations.