Abstract

ABC -stacked trilayer graphene/hexagonal boron nitride moiré superlattice (TLG/hBN) has emerged as a playground for correlated electron physics. A spectroscopy study of this system is, however, challenging due to the device configuration. In this talk, I will introduce our recent efforts on FTIR photocurrent spectroscopy measurements of dual-gated TLG /hBN. We observed strong gate-tunable optical transitions that originated from the moiré flat band. 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. Furthermore, I will talk about a unique moiré-enabled interlayer electron-phonon coupling phenomenon in this system. The ZO phonon in hBN hybridizes with electron-hole excitations in trilayer graphene and appear as an asymmetric peak in the photocurrent spectrum. This Fano line-shaped peak evolves continuously as we tune the displacement field. If time permits, I will also talk about our recent work on probing the electron correlation and topology in rhombohedral stacked graphene in the absence of moiré.

References: 1. Ju, L. et al., “Tunable excitons in bilayer graphene.” Science 358.6365 (2017): 907-910.

2. Han, T. et al., “Accurate Measurement of the Gap of Graphene/h−BN Moiré Superlattice through Photocurrent Spectroscopy.” Physical Review Letters 126.14 (2021): 146402.

3. Yang, J. et al., “Spectroscopy signatures of electron correlations in a trilayer graphene/hBN moiré superlattice.” Science 375.6586 (2022): 1295-1299.