Giant Anomalous Hall Effect due to Double-Degenerate Quasi Flat Bands

TL;DR

This paper introduces a method to achieve giant anomalous Hall effects in materials with flat bands by leveraging small bandwidths to increase Berry curvature, validated through theoretical models and first-principles calculations.

Contribution

It presents a novel approach linking flat bands with giant AHE, supported by a simple model and realistic pyrochlore lattice calculations, suggesting experimental realizations.

Findings

Giant AHE is achieved by decreasing bandwidth in flat band systems.

Double-degenerate flat bands maximize momentum separation and Berry curvature.

First-principles calculations identify candidate pyrochlore and spinel compounds.

Abstract

We propose a novel approach to achieve giant AHE in materials with flat bands (FBs). FBs are accompanied by small electronic bandwidths, which consequently increases the momentum separation ($K$) within pair of Weyl points and thus the integrated Berry curvature. Starting from a simple model with a single pair of Weyl nodes, we demonstrated the increase of $K$ and AHE by decreasing bandwidth. It is further expanded to a realistic pyrochlore lattice model with characteristic double degenerated FBs, where we discovered a giant AHE while maximizing the $K$ with nearly vanishing band dispersion of FBs. We identify that such model system can be realized in both pyrochlore and spinel compounds based on first-principles calculations, validating our theoretical model and providing a feasible platform for experimental exploration.