Photocurrent Spectroscopy Study of Graphene / Hexagonal Boron Nitride Moiré Superlattice In the Far-Infrared Regime

Abstract

Two-dimensional (2D) materials and their heterostructures, especially those with moiré superlattices, have been one of the most fascinating topics in physics in recent years. Many interesting physics, for example the correlated insulating state at half- or quarter- fillings of the moiré band, happened in the far-infrared energy range. However, there are very few optical spectroscopic studies of these 2D materials due to many intrinsic limitations. In this thesis, I will introduce a method named Fourier-transform infrared (FTIR) photocurrent spectroscopy. I will discuss the advantage of this method, and why it is suitable for far-infrared studies of 2D materials. Then I will apply it to the monolayer graphene / hexagonal boron nitride (hBN) moiré superlattices, where I accurately measure the gap ∆ opened at charge-neutral point (CNP) by the moiré superlattice. The relationship between the gap size and the moiré wavelength will also be discussed. Finally, I will discuss the possibility of applying this technique to other novel physics phenomena and other 2D systems.