Correlated interaction effects in an anisotropic flat band fermion system

Abstract

An anisotropic flat band fermion system with a novel dispersion that is linear along one direction and cubic along another is proposed in Phys. Rev. X. 13, 021012 (2023). We study the effects of Coulomb interaction in this fermion system by renormalization group theory and Dyson-Schwinger gap equation. We perform renormalizaton group analysis and find that fermion velocity is always restored along the direction that the fermions take cubic dispersion originally. Accordingly, the system takes the similar behaviors to the two-dimensional Dirac fermion system with Coulomb interaction in the low energy regime. Based on Dyson-Schwinger gap equation method, we find that an excitonic gap is generated if the Coulomb strength is large enough, and the system becomes a novel excitonic Chern insulator with quantized anomalous Hall conductivity. Observable quantities of this system in free case, under weak and strong enough Coulomb interaction are all analyzed.