Spectroscopy Signatures of Electron Correlations in a Trilayer Graphene/hBN Moir\'e Superlattice

TL;DR

This study uses infrared spectroscopy to explore electron correlations in a trilayer graphene/hBN moiré superlattice, revealing optical signatures of bandgap opening and Mott insulating states, advancing understanding of correlated electron physics.

Contribution

It provides the first spectroscopic evidence of Mott gaps and correlated insulating states in TLG/hBN, offering key parameters for Hubbard model descriptions.

Findings

Observation of a narrowing optical transition with gating.

Emergence of an ~18 meV Mott gap at half-filling.

Detection of similar insulating states at quarter- and half-filling.

Abstract

ABC-stacked trilayer graphene/hBN moir\'e superlattice (TLG/hBN) has emerged as a playground for correlated electron physics. We report spectroscopy measurements of dual-gated TLG/hBN using Fourier transformed infrared photocurrent spectroscopy. We observed a strong optical transition between moir\'e mini-bands that narrows continuously as a bandgap is opened by gating, indicating a reduction of the single particle bandwidth. At half-filling of the valence flat band, a broad absorption peak emerges at ~18 meV, indicating direct optical excitation across an emerging Mott gap. Similar photocurrent spectra are observed in two other correlated insulating states at quarter- and half-filling of the first conduction band. Our findings provide key parameters of the Hubbard model for the understanding of electron correlation in TLG/hBN.