# Magnetic properties of 2D topological insulators

## TL;DR

This paper investigates how Hubbard-type interactions influence magnetic properties in 2D topological insulators, specifically within the BHZ model for HgTe/CdTe quantum wells, revealing conditions for ferromagnetic ground states.

## Contribution

It introduces a mean field approach to identify magnetic instabilities in the Hubbard-BHZ model and maps it to the one band Hubbard model to explain ferromagnetism emergence.

## Key findings

- Ferromagnetic ground state occurs at strong hole orbital interactions.
- Magnetic phases are more likely in large gap topological insulators.
- Mapping to the Hubbard model explains magnetic instability conditions.

## Abstract

The effects of Hubbard-type on-site interactions on the BHZ model is studied in this paper for model parameters appropriate for the HgTe/CdTe quantum well. Within a simple mean field theory we search for plausible magnetic instabilities in the model and find that the ground state becomes {\em ferromagnetic} when the interaction strength between electrons in hole orbital is strong enough. The result can be understood by an approximate mapping of the Hubbard-BHZ model to the one band Hubbard model. The same mapping suggests that the magnetic and/or other ordered phases are more likely to occur in large gap topological insulators whose occupations are close to 1/2 for both electron and hole orbital.