Higher-Order Van Hove Singularities in Kagome Topological Bands

TL;DR

This paper explores higher-order Van Hove singularities in kagome lattice systems with complex topological bands, revealing diverse singularities, their effects on density of states, and implications for electronic orders.

Contribution

It provides a detailed analytical and numerical study of HOVHS in kagome topological bands with NNN hopping, uncovering new singularities and topological features.

Findings

Power-law divergences in DOS with exponents 1/2, 1/3, 1/4.

Formation of higher Chern number bands C=±2, ±4.

Localization of electronic states near high-symmetry points.

Abstract

Motivated by the growing interest in band structures featuring higher-order Van Hove singularities (HOVHS), we investigate a spinless fermion kagome system characterized by nearest-neighbor (NN) and next-nearest-neighbor (NNN) hopping amplitudes. While NN hopping preserves time-reversal symmetry, NNN hopping, akin to chiral hopping on the Haldane lattice, breaks time-reversal symmetry and leads to the formation of topological bands with Chern numbers ranging from $C = \pm 1$ to $ \pm 4$. We perform analytical and numerical analysis of the energy bands near the high-symmetry points $\boldsymbol{\Gamma}$, $\pm \boldsymbol{K}$, and $\boldsymbol{M_i}$ ($i=1,2,$ and $3$), which uncover a rich and complex landscape of HOVHS, controlled by the magnitude and phase of the NNN hopping. We observe power-law divergences in the density of states (DOS), $\rho(\epsilon) \sim |\epsilon|^{-\nu}$, with exponents $\nu = 1/2, 1/3, 1/4$, which can significantly affect the anomalous Hall response at low temperatures when the Fermi level crosses the HOVHS. Additionally, the NNN hopping induces the formation of higher Chern number bands $C = \pm 2, \pm 4$ in the middle of the spectrum obeying a sublattice interference whereupon electronic states are maximally localized in each of the sublattices when the momentum approaches the three high-symmetry points $\boldsymbol{M_i}$ ($i=1,2,$ and $3$) on the Brillouin zone boundary. This classification of HOVHS in kagome systems provides a platform to explore unconventional electronic orders induced by electronic correlations.