Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 107, Issue 34, Pages 14999-15004Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1004595107
Keywords
electronic structures; infrared spectroscopy; zone-folding method
Categories
Funding
- Nanoscale Science and Engineering Initiative of the National Science Foundation [CHE-06-41523]
- New York State Office of Science, Technology, and Academic Research (NYSTAR)
- Office of Naval Research under the Multidisciplinary University Research Initiative (MURI)
- US Department of Energy, Brookhaven [DE-AC02-98CH10886]
- NSLS at Brookhaven
- Center for Synchrotron Biosciences, Case Western Reserve University [P41-EB-01979]
- National Institute for Biomedical Imaging and Bioengineering
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The massless Dirac spectrum of electrons in single-layer graphene has been thoroughly studied both theoretically and experimentally. Although a subject of considerable theoretical interest, experimental investigations of the richer electronic structure of few-layer graphene (FLG) have been limited. Here we examine FLG graphene crystals with Bernal stacking of layer thicknesses N 1,2,3,...8 prepared using the mechanical exfoliation technique. For each layer thickness N, infrared conductivity measurements over the spectral range of 0.2-1.0 eV have been performed and reveal a distinctive band structure, with different conductivity peaks present below 0.5 eV and a relatively flat spectrum at higher photon energies. The principal transitions exhibit a systematic energy-scaling behavior with N. These observations are explained within a unified zone-folding scheme that generates the electronic states for all FLG materials from that of the bulk 3D graphite crystal through imposition of appropriate boundary conditions. Using the Kubo formula, we find that the complete infrared conductivity spectra for the different FLG crystals can be reproduced reasonably well within the framework a tight-binding model.
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