Phonon renormalisation in doped bilayer graphene
  We report phonon renormalisation in bilayer graphene as a function of doping. The Raman G peak stiffens and sharpens for both electron and hole doping, as a result of the non-adiabatic Kohn anomaly at the $\Gamma$ point. The bilayer has two conduction and valence subbands, with splitting dependent on the interlayer coupling. This results in a change of slope in the variation of G peak position with doping, which allows a direct measurement of the interlayer coupling strength. 
A. Das, B. Chakraborty, S. Piscanec, S. Pisana, A. K. Sood and A. C.   Ferrari