Violation of the Wiedemann-Franz law in graphene: plasmon contribution to the heat conductivity

It is well established that close to the Dirac point in graphene the Wiedemann-Franz law is violated. Using a microscopic Boltzmann approach we first show that a theory of electrons and holes cannot quantitatively account for the heat conductivity observed in experiment. We argue that the missing heat conductivity is due to plasmons which make a sizeable contribution in the vicinity of the Dirac point.