High-order minibands and interband Landau level reconstruction in graphene moire superlattice

TL;DR

This study explores the complex band structure of graphene on hBN, revealing higher-order minibands and Landau level interactions through transport spectroscopy, advancing understanding of moiré superlattice phenomena.

Contribution

It provides the first detailed experimental investigation of higher-order minibands and their Landau level reconstructions in aligned graphene/hBN heterostructures.

Findings

Observation of 3rd and 4th minibands via transport spectroscopy.

Detection of interband Landau level crossings causing gap closures.

Qualitative agreement between experimental results and simulations.

Abstract

The propagation of Dirac fermions in graphene through a long-period periodic potential would result in a band folding together with the emergence of a series of cloned Dirac points (DPs). In highly aligned graphene/hexagonal boron nitride (G/hBN) heterostructures, the lattice mismatch between the two atomic crystals generates a unique kind of periodic structure known as a moir\'e superlattice. Of particular interests is the emergent phenomena related to the reconstructed band-structure of graphene, such as the Hofstadter butterfly, topological currents, gate dependent pseudospin mixing, and ballistic miniband conduction. However, most studies so far have been limited to the lower-order minibands, e.g. the 1st and 2nd minibands counted from charge neutrality, and consequently the fundamental nature of the reconstructed higher-order miniband spectra still remains largely unknown. Here we report on probing the higher-order minibands of precisely aligned graphene moir\'e superlattices by transport spectroscopy. Using dual electrostatic gating, the edges of these high-order minibands, i.e. the 3rd and 4th minibands, can be reached. Interestingly, we have observed interband Landau level (LL) crossinginducing gap closures in a multiband magneto-transport regime, which originates from band overlap between the 2nd and 3rd minibands. As observed high-order minibands and LL reconstruction qualitatively match our simulated results. Our findings highlight the synergistic effect of minibands in transport, thus presenting a new opportunity for graphene electronic devices.