Correlated topological flat bands in rhombohedral graphite

TL;DR

This paper provides experimental evidence of topological flat bands on the surface of rhombohedral graphite, revealing their protection by bulk topology and their evolution under electron doping, highlighting the interplay of topology and correlations.

Contribution

It reports the first experimental observation of topological flat bands in rhombohedral graphite and explores their doping-dependent behavior and correlation effects.

Findings

Topological flat bands are observed on the surface of bulk rhombohedral graphite.

Doping causes splitting and bandwidth increase of the surface flat bands.

Correlation effects are suggested to play a significant role in the system.

Abstract

Flat bands and nontrivial topological physics are two important topics of condensed matter physics. With a unique stacking configuration analogous to the Su-Schrieffer-Heeger (SSH) model, rhombohedral graphite (RG) is a potential candidate for realizing both flat bands and nontrivial topological physics. Here we report experimental evidence of topological flat bands (TFBs) on the surface of bulk RG, which are topologically protected by bulk helical Dirac nodal lines via the bulk-boundary correspondence. Moreover, upon {\it in situ} electron doping, the surface TFBs show a splitting with exotic doping evolution, with an order-of-magnitude increase in the bandwidth of the lower split band, and pinning of the upper band near the Fermi level. These experimental observations together with Hartree-Fock calculations suggest that correlation effects are important in this system. Our results demonstrate RG as a new platform for investigating the rich interplay between nontrivial band topology, correlation effects, and interaction-driven symmetry-broken states.