TY - JOUR
T1 - Origin of van Hove singularities in twisted bilayer graphene
AU - Ribeiro, H. B.
AU - Sato, K.
AU - Eliel, G. S.N.
AU - De Souza, E. A.T.
AU - Lu, Chun Chieh
AU - Chiu, Po Wen
AU - Saito, R.
AU - Pimenta, M. A.
N1 - Funding Information:
This work was partially supported by Fapesp (SPEC project 2012/50259-8), the Brazilian Nanocarbon Institute of Science and Technology (INCT/Nanocarbono), and the Brazilian agencies CNPq and FAPEMIG. K.S. acknowledges support from MEXT Grant (No. 23710118 ). R.S. acknowledges support from MEXT Grants (No. 25017005 ). H.B.R. acknowledges support from CNPq. All author acknowledges Pilkyung Moon for good discussions.
Publisher Copyright:
© 2015 Elsevier Ltd. All rights reserved.
PY - 2015/5/16
Y1 - 2015/5/16
N2 - In this work, we present a resonance Raman spectroscopy study of more than 100 samples of twisted bilayer graphene (TBG) with a continuous distribution of twisting angles from 0° to 30°, using three different laser excitation energies (1.96, 2.33 and 2.54 eV). From the Raman images of all investigated samples we could observe giant enhancements of the G band for samples with twisting angles between 9°and 17°, in agreement with previous Raman studies of TBGs. However, although we investigated a large number of samples with low (<9°) or high (>17°) twisting angles, we could not observe the G-band enhancement that was predicted for these samples from the zone-folding of the single layer graphene electronic structure. Our results allow us to conclude that the van Hove singularities in the density of states are associated with the Moiré pattern, which does not necessarily exhibit a translational symmetry. Moreover, we could observe that the Raman intensity ratio ITBG/ISLG in non-resonance cases is always smaller than two, and this value depends on the laser energy. This result is discussed in terms of the relaxation of photo-excited carriers in TBG, which is expected to increase with increasing laser excitation energy.
AB - In this work, we present a resonance Raman spectroscopy study of more than 100 samples of twisted bilayer graphene (TBG) with a continuous distribution of twisting angles from 0° to 30°, using three different laser excitation energies (1.96, 2.33 and 2.54 eV). From the Raman images of all investigated samples we could observe giant enhancements of the G band for samples with twisting angles between 9°and 17°, in agreement with previous Raman studies of TBGs. However, although we investigated a large number of samples with low (<9°) or high (>17°) twisting angles, we could not observe the G-band enhancement that was predicted for these samples from the zone-folding of the single layer graphene electronic structure. Our results allow us to conclude that the van Hove singularities in the density of states are associated with the Moiré pattern, which does not necessarily exhibit a translational symmetry. Moreover, we could observe that the Raman intensity ratio ITBG/ISLG in non-resonance cases is always smaller than two, and this value depends on the laser energy. This result is discussed in terms of the relaxation of photo-excited carriers in TBG, which is expected to increase with increasing laser excitation energy.
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U2 - 10.1016/j.carbon.2015.04.005
DO - 10.1016/j.carbon.2015.04.005
M3 - Article
AN - SCOPUS:84929306346
VL - 90
SP - 138
EP - 145
JO - Carbon
JF - Carbon
SN - 0008-6223
ER -