Infrared observation of gate-tunable bandgap and a giant Fano electron-phonon resonance in bilayer graphene

We studied infrared spectra of bottom gated bilayer graphene on SiO$_{2}$/Si substrate. The two major results of our study are: (i) a determination of the gate-voltage dependent bandgap, and (ii) an observation of a new giant phonon resonance at 0.2 eV. In addition, the Slonczewski-Weiss-McClure tight binding model parameters were extracted by a simultaneous fitting of infrared data at all gate voltages. The gate-voltage dependence of the bandgap supports the calculations, which take electrostatic self-screening effects into account. The phonon peak shows several remarkable anomalies: (i) a giant enhancement with the applied gate voltage, which we ascribe to the so-called ``charged-phonon'' effect and (ii) a pronounced Fano lineshape, which is a manifestation of a coupling of this phonon to a continuum of electron-hole excitations. The obtained results show an outstanding potential of bilayer graphene for applications in electronics and opto-electronics.