# Influence of interactions on the anomalous quantum Hall effect

## TL;DR

This paper proves that in certain 2+1D topological insulators and 3+1D Weyl semimetals, the anomalous quantum Hall conductivity in the presence of interactions can be expressed using the full two-point Green function, extending previous noninteracting formulas.

## Contribution

The paper provides a rigorous proof that the Hall conductivity with interactions can be represented by the same Green function-based expression as in noninteracting systems, within specific models.

## Key findings

- Hall conductivity expressed via Green functions remains valid with interactions.
- Interactions do not alter the topological invariant expression for Hall conductivity at one-loop level.
- Topological phase transitions involve changes in Hall conductivity linked to Green function properties.

## Abstract

The anomalous quantum Hall conductivity in the 2+1D topological insulators in the absence of interactions may be expressed as the topological invariant composed of the two - point Green function. For the noninteracting system this expression is the alternative way to represent the TKNN invariant. It is widely believed that in the presence of interactions the Hall conductivity is given by the same expression, in which the noninteracting two - point Green function is substituted by the complete two - point Green function with the interactions taken into account. However, the proof of this statement has not been given so far. In the present paper we give such a proof in the framework of the particular tight - binding models of the $2+1$ D topological insulator. Besides, we extend our consideration to the $3+1$ D Weyl semimetals. It was known previously that with the interactions neglected the Hall conductivity in those systems is expressed through the two - point Green function in the way similar to that of the $2+1$ D topological insulators. Again, the influence of interactions on this expression has not been investigated previously. We consider this problem within the framework of the particular $3+1$D model of Weyl semimetal in the presence of the contact four - fermion interactions and Coulomb interactions. We prove (up to the one - loop approximation), that the Hall conductivity is given by the same expression as in the noninteracting case, in which the noninteracting Green function is substituted by the complete two - point Green function with the interactions included. Basing on the obtained expressions we discuss the topological phase transitions accompanied by the change of Hall conductivity.