Gate-Variable Optical Transitions in Graphene
Feng Wang,1*
Yuanbo Zhang,1
Chuanshan Tian,1
Caglar Girit,1,2
Alex Zettl,1,2
Michael Crommie,1,2
Y. Ron Shen1,2
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 substantially 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, whereas
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 by simple electrical
gating hold promise for new applications in infrared optics
and optoelectronics.
2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
* To whom correspondence should be addressed. E-mail: fengwang76{at}berkeley.edu
