Observation of room-temperature high-energy resonant excitonic effects in graphene

I. Santoso, P. K. Gogoi, H. B. Su, H. Huang, Y. Lu, D. Qi, W. Chen, Muhammad Aziz Majidi, Y. P. Feng, A. T.S. Wee, K. P. Loh, T. Venkatesan, R. P. Saichu, A. Goos, A. Kotlov, M. Rübhausen, A. Rusydi

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)

Abstract

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.

Original languageEnglish
Article number081403
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume84
Issue number8
DOIs
Publication statusPublished - 10 Aug 2011

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