Infrared spectroscopy of electronic bands in bilayer graphene*

We present infrared spectra (0.1-1 eV) of electrostatically gated bilayer graphene as a function of doping and compare them with tight binding calculations. All major spectral features corresponding to the expected interband transitions are identified in the spectra: a strong peak due to transitions between parallel split-off bands and two onset-like features due to transitions between valence and conduction bands. A significant electron-hole asymmetry is observed.