Long Ju – MIT Physics Department 

Title: Electron Correlation and Coupling with Phonon in the Trilayer Graphene/hBN Moire Superlattice

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 moire 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 moire-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. I’ll talk about the implications of this phenomenon to engineering the physics of moire quantum matters.

Bio: Long Ju joined the MIT Physics Department as an assistant professor in January 2019. He received his B.S. in Physics in 2009 from Tsinghua University, China, and his Ph.D. in Physics in 2015 from the University of California, Berkeley. He then moved to Cornell University, where he was a Kavli postdoctoral fellow until December 2018.

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