Tailoring Dirac fermions by in-situ tunable high-order moire pattern in graphene-monolayer xenon heterostructure

TL;DR

This study demonstrates in-situ tuning of high-order moire patterns in graphene-monolayer xenon heterostructures, revealing how Dirac fermions can be manipulated via intervalley coupling and providing insights into moire-induced quantum phenomena.

Contribution

It introduces a method to continuously tune moire patterns in G/mXe heterostructures and models the resulting electronic structure with a continuum Hamiltonian, highlighting differences from twisted bilayer graphene.

Findings

Moire period tuned from nanometers to infinity.

Energy gap at Dirac point due to Kekule distortion.

Predicted narrow moire bands with tunable intervalley coupling.

Abstract

A variety of novel quantum phases have been achieved in twist bilayer graphene (tBLG) and other moire superlattices recently, including correlated insulators, superconductivity, magnetism, and topological states. These phenomena are very sensitive to the moire superlattices, which can hardly be changed rapidly or intensely. Here, we report the experimental realization of a high-order moire pattern (a high-order interference pattern) in graphene-monolayer xenon heterostructure (G/mXe), with moire period in-situ tuned from few nanometers to infinity by changing the lattice constant of Xe through different annealing temperatures and pressures. We use angle-resolved photoemission spectroscopy to directly observe that replicas of graphene Dirac cone emerge and move close to each other in momentum-space as moire pattern continuously expands in real-space. When the moire period approaches infinity, the replicas finally overlap with each other and an energy gap is observed at the Dirac point induced by intervalley coupling, which is a manifestation of Kekule distortion. We construct a continuum moire Hamiltonian, which can explain the experimental results well. The form of moire Hamiltonian in G/mXe is similar to that in tBLG, and moire band with narrow bandwidth is predicted in G/mXe. However, the moire Hamiltonian couples Dirac fermions from different valleys in G/mXe, instead of ones from different layers in tBLG. Our work demonstrates a novel platform to study the continuous evolution of moire pattern and its modulation effect on electronic structure, and provides an unprecedented approach for tailoring Dirac fermions with tunable intervalley coupling.