Topological features of Haldane model on a dice lattice: role of flat band on transport properties

TL;DR

This paper investigates how topological properties and transport behaviors of a Haldane model on a dice lattice evolve under different hopping anisotropies, highlighting the role of flat bands and phase transitions in topological insulators.

Contribution

It introduces a systematic study of topological phase transitions in a deformed dice lattice Haldane model with flat bands, revealing the effects of anisotropic hopping on topological invariants and edge states.

Findings

Presence of Chern insulating lobes with C=±2 under certain deformations.

Distortion of flat bands affects topological properties and Hall conductivity.

Phase transition from topological to trivial insulator with changing hopping anisotropy.

Abstract

We study the topological properties of a Haldane model on a band deformed dice lattice, which has three atoms per unit cell (call them as A, B and C) and the spectrum comprises of three bands, including a flat band. The bands are systematically deformed with an aim to study the evolution of topology and the transport properties. The deformations are induced through hopping anisotropies and are achieved in two distinct ways. In one of them, the hopping amplitudes between the sites of B and C sublattices and those between A and B sublattices are varied along a particular direction, and in the other, the hopping between the sites of A and B sublattices are varied (keeping B-C hopping unaltered) along the same direction. The first case retains some of the spectral features of the familiar dice lattice and yields Chern insulating lobes in the phase diagram with $C=\pm2$ till a certain critical deformation. The topological features are supported by the presence of a pair of chiral edge modes at each edge of a ribbon and the plateaus observed in the anomalous Hall conductivity support the above scenario. Whereas, a selective tuning of only the A-B hopping amplitudes distorts the flat band and has important ramifications on the topological properties of the system. The insulating lobes in the phase diagram have distinct features compared to the case above, and there are dips observed in the Hall conductivity near the zero bias. The dip widens as the hopping anisotropy is made larger, and thus the scenario registers significant deviation from the familiar plateau structure observed in the anomalous Hall conductivity. However, a phase transition from a topological to a trivial insulating region demonstrated by the Chern number changing discontinuously from $\pm2$ to zero beyond a certain critical hopping anisotropy remains a common feature in the two cases.