Comment on 'Gapless Spin-1 Neutral Collective Mode Branch for Graphite

Abstract

The interest in strongly correlated systems in frustrated lattices has been increased recently due to the possible realization of exotic magnetic states, spin, and charge separation in two dimensions, and the discovery of superconductivity in NaxCoO2 yH2O. In a recent Letter, Baskaran and Jafari have proposed the existence of a neutral spin collective mode for a graphene sheet that is modeled as a half-filled Hubbard model in the honeycomb lattice. These calculations were based on the random phase approximation (RPA), but the tensor character of the susceptibility for the honeycomb lattice was not considered in the calculations. Since inelastic neutron scattering can be used to study this spin collective mode in graphite, we decided to revisit the problem, taking into account the entire band structure and the sublattice structure of the honeycomb lattice.We found that such a spin collective mode does not exist within the RPA when the full tensorial character of the spin susceptibility is taken into account.