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Stacking angle-tunable Photoluminescence from Interlayer Excitons in Twisted Bilayer Graphene

Title
Stacking angle-tunable Photoluminescence from Interlayer Excitons in Twisted Bilayer Graphene
Authors
Hiral PatelLujie HuangCheol-Joo KimJiwoong ParkMatt W. Graham
Date Issued
Mar-2019
Publisher
Nature Publishing Group
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.
URI
http://oasis.postech.ac.kr/handle/2014.oak/99055
ISSN
2041-1723
Article Type
Article
Citation
Nature Communications, vol. 10, page. 1445, 2019-03
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 KIM, CHEOL JOO
Dept. of Chemical Enginrg
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