TY - JOUR
T1 - Observation of room-temperature high-energy resonant excitonic effects in graphene
AU - Santoso, I.
AU - Gogoi, P. K.
AU - Su, H. B.
AU - Huang, H.
AU - Lu, Y.
AU - Qi, D.
AU - Chen, W.
AU - Majidi, Muhammad Aziz
AU - Feng, Y. P.
AU - Wee, A. T.S.
AU - Loh, K. P.
AU - Venkatesan, T.
AU - Saichu, R. P.
AU - Goos, A.
AU - Kotlov, A.
AU - Rübhausen, M.
AU - Rusydi, A.
PY - 2011/8/10
Y1 - 2011/8/10
N2 - Using a combination of ultraviolet-vacuum ultraviolet reflectivity and spectroscopic ellipsometry, we observe a resonant exciton at an unusually high energy of 6.3 eV in epitaxial graphene. Surprisingly, the resonant exciton occurs at room temperature and for a very large number of graphene layers N≈75, thus suggesting a poor screening in graphene. The optical conductivity (σ1) of a resonant exciton scales linearly with the number of graphene layers (up to at least 8 layers), implying the quantum character of electrons in graphene. Furthermore, a prominent excitation at 5.4 eV, which is a mixture of interband transitions from π to π* at the M point and a π plasmonic excitation, is observed. In contrast, for graphite the resonant exciton is not observable but strong interband transitions are seen instead. Supported by theoretical calculations, for N≤ 28 the σ1 is dominated by the resonant exciton, while for N> 28 it is a mixture between exitonic and interband transitions. The latter is characteristic for graphite, indicating a crossover in the electronic structure. Our study shows that important elementary excitations in graphene occur at high binding energies and elucidate the differences in the way electrons interact in graphene and graphite.
AB - Using a combination of ultraviolet-vacuum ultraviolet reflectivity and spectroscopic ellipsometry, we observe a resonant exciton at an unusually high energy of 6.3 eV in epitaxial graphene. Surprisingly, the resonant exciton occurs at room temperature and for a very large number of graphene layers N≈75, thus suggesting a poor screening in graphene. The optical conductivity (σ1) of a resonant exciton scales linearly with the number of graphene layers (up to at least 8 layers), implying the quantum character of electrons in graphene. Furthermore, a prominent excitation at 5.4 eV, which is a mixture of interband transitions from π to π* at the M point and a π plasmonic excitation, is observed. In contrast, for graphite the resonant exciton is not observable but strong interband transitions are seen instead. Supported by theoretical calculations, for N≤ 28 the σ1 is dominated by the resonant exciton, while for N> 28 it is a mixture between exitonic and interband transitions. The latter is characteristic for graphite, indicating a crossover in the electronic structure. Our study shows that important elementary excitations in graphene occur at high binding energies and elucidate the differences in the way electrons interact in graphene and graphite.
UR - http://www.scopus.com/inward/record.url?scp=80052505381&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.84.081403
DO - 10.1103/PhysRevB.84.081403
M3 - Article
AN - SCOPUS:80052505381
SN - 1098-0121
VL - 84
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 8
M1 - 081403
ER -