Thickness-dependent Topological Phases and Flat Bands in Rhombohedral Multilayer Graphene

TL;DR

This study uses advanced spectroscopy to reveal how the topological electronic structures of rhombohedral multilayer graphene evolve with layer thickness, uncovering a transition from flatbands to Dirac nodes and topological surface states.

Contribution

It provides the first systematic spectroscopic analysis of thickness-dependent topological phase transitions in rhombohedral multilayer graphene.

Findings

Flatbands persist around the Fermi level across thicknesses.

Transformation of gapped subbands into 3D Dirac nodes with increasing layers.

Observation of topological drumhead surface states in bulk limit.

Abstract

Rhombohedral multilayer graphene has emerged as an extraordinary platform for investigating exotic quantum states, such as superconductivity and fractional quantum anomalous Hall effects, mainly due to the existence of topological surface flatbands. Despite extensive research efforts, a systematic spectroscopic investigation on the evolution of its electronic structure from thin layers to bulk remains elusive. Using state-of-the-art angle-resolved photoemission spectroscopy with submicron spatial resolution, we directly probe and trace the thickness evolution of the topological electronic structures of rhombohedral multilayer graphene. As the layer number increases, the gapped subbands transform into the 3D Dirac nodes that spirals in the momentum space; while the flatbands are constantly observed around Fermi level, and eventually evolve into the topological drumhead surface states. This unique thickness-dependent topological phase transition can be well captured by the 3D generalization of 1D Su-Schrieffer-Heeger chain in thin layers, to the topological Dirac nodal spiral semimetal in the bulk limit. Our findings establish a solid foundation for exploring the exotic quantum phases with nontrivial topology and correlation effects in rhombohedral multilayer graphene.