Submitted on November 8, 2007
Accepted on March 3, 2008
Gate-Variable Optical Transitions in Graphene
Feng Wang 1*, Yuanbo Zhang 1, Chuanshan Tian 1, Caglar Girit 2, Alex Zettl 2, Michael Crommie 2, Y. Ron Shen 2
1 Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA.
2 Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA.; Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
* To whom correspondence should be addressed.
Feng Wang , E-mail: fengwang76{at}berkeley.edu
Two-dimensional graphene monolayers and bilayers exhibit fascinating electrical transport behaviors. Using infrared spectroscopy, we find that they also have strong interband transitions and that their optical transitions can be significantly modified through electrical gating, much like electrical transport in field effect transistors. This gate dependence of interband transitions adds a valuable dimension for optically probing graphene band structure. For a graphene monolayer, it yields directly the linear band dispersion of Dirac fermions, while in a bilayer, it reveals a dominating van Hove singularity arising from interlayer coupling. The strong and layer-dependent optical transitions of graphene and the tunability via simple electrical gating hold promise for new applications in infrared optics and optoelectronics.
