Half-metallicity and two-dimensional hole gas at the $\text{BiFeO}_\text{3}$(001) surface

TL;DR

This study uses density functional theory to explore the electronic properties and stability of tetragonal BiFeO3(001) surfaces, revealing half-metallicity and a spin-polarized two-dimensional hole gas at the surface, with stability depending on surface termination.

Contribution

It demonstrates the presence of half-metallicity and 2D hole gas at the BiFeO3 surface, highlighting the importance of surface termination and stability in these phenomena.

Findings

FeO2 termination is more stable than BiO termination.

Half-metallicity and spin-polarized 2DHG are present at the surface.

Half-metallic 2DHG persists only in the most stable structure across thicknesses.

Abstract

The electronic structure and thermodynamic stability of tetragonal $\rm{BiFeO_3}$(001) surfaces have been investigated using density functional theory. In this work, four different structures having different lattice constants with two possible surface terminations have been studied. We have found that the surface electronic structure and the thermodynamic stability is quite sensitive with respect to the nature of the surface termination. The $\rm{FeO_2}$ terminated surface is found to be energetically more stable compared to $\rm{BiO}$ terminated surface in all the cases. Interestingly, we have found evidences of half-metallicity and spin-polarized two-dimensional hole gas (2DHG) at the one mono-layer thick surface in all the structures. The effect of the surface thickness have been systematically studied. It has been demonstrated that the half-metallic 2DHG survives only in one of the structures for all the thicknesses, incidentally, which is the most thermodynamically stable structure.