Emergent dome of nematic order around a quantum anomalous Hall critical point

TL;DR

This paper investigates a model of spinful fermions on a triangular lattice, revealing an emergent nematic phase around a topological quantum phase transition between Chern insulator and normal insulator phases, with implications for materials like ferromagnetic double perovskites.

Contribution

It introduces a detailed analysis of the nematic dome emergence near a topological transition, combining renormalization group and mean field methods, highlighting novel phases in quantum anomalous Hall systems.

Findings

Emergent nematic phase forms around the CI-NI transition.

Short-range interactions are marginally relevant at the transition.

The phase diagram includes a nematic dome influenced by weak repulsive interactions.

Abstract

We consider a model of spinful fermions on the triangular lattice which exhibits a C=2 Chern insulator (CI) phase with a quantized anomalous Hall effect, sandwiched between two normal insulator (NI) phases. The first NI-CI quantum phase transition is driven by simultaneous mass inversion of a pair of Dirac fermions, with short range interactions being perturbatively irrelevant. The second CI-NI transition is driven by a single quadratic band touching point protected by momentum space topology and C_6 lattice symmetry. A one-loop renormalization group analysis shows that short range interactions lead to a single marginally relevant perturbation at this transition. We obtain the mean field phase diagram of this model incorporating weak repulsive Hubbard interactions, finding an emergent nematic dome around this CI-NI topological phase transition. We discuss the crossovers in the anomalous Hall conductivity at nonzero temperature, and the Landau theory of the quantum and thermal transitions out of the nematic phase. Our results may be relevant to ferromagnetic double perovskite films with spin-orbit coupling which have been proposed to host such a NI-CI transition. Our work provides perhaps the simplest example of an emergent phase near a quantum phase transition.