Phonon anomaly by massive Dirac fermions of graphene

Massless Dirac fermions in graphene can acquire a mass through different kinds of sublattice-symmetry-breaking perturbations, and there is a growing need to determine this mass using a conventional method. We describe how the mass caused by a staggered sublattice potential changes the phonon self-energy and explain the mechanism in terms of the pseudospin polarization of massive Dirac fermions. We argue that the mass is detectable using Raman spectroscopy.