Stacking angle-tunable photoluminescence from interlayer exciton states in twisted bilayer graphene

Hiral Patel, Lujie Huang, Cheol-Joo Kim, Jiwoong Park and Matt W. Graham ()
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Hiral Patel: Oregon State University
Lujie Huang: University of Chicago
Cheol-Joo Kim: Pohang University of Science and Technology
Jiwoong Park: University of Chicago
Matt W. Graham: Oregon State University

Nature Communications, 2019, vol. 10, issue 1, 1-7

Abstract: Abstract Twisted bilayer graphene (tBLG) is a metallic material with two degenerate van Hove singularity transitions that can rehybridize to form interlayer exciton states. Here we report photoluminescence (PL) emission from tBLG after resonant 2-photon excitation, which tunes with the interlayer stacking angle, θ. We spatially image individual tBLG domains at room-temperature and show a five-fold resonant PL-enhancement over the background hot-electron emission. Prior theory predicts that interlayer orbitals mix to create 2-photon-accessible strongly-bound (~0.7 eV) exciton and continuum-edge states, which we observe as two spectral peaks in both PL excitation and excited-state absorption spectra. This peak splitting provides independent estimates of the exciton binding energy which scales from 0.5–0.7 eV with θ = 7.5° to 16.5°. A predicted vanishing exciton-continuum coupling strength helps explain both the weak resonant PL and the slower 1 ps−1 exciton relaxation rate observed. This hybrid metal-exciton behavior electron thermalization and PL emission are tunable with stacking angle for potential enhancements in optoelectronic and fast-photosensing graphene-based applications.

Date: 2019
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DOI: 10.1038/s41467-019-09097-x

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