Thermo-electric response close to the Dirac point: The role of particle-hole pairs*

Clean Dirac liquids are expected to show hydrodynamic transport properties dominated by inelastic scattering. Nowadays, this hydrodynamic limit can be accessed in high quality graphene samples. We investigate whether the customary two fluid Boltzmann treatment of electrons and holes and their inelastic scattering correctly captures the heat conductivity. We include a third dynamical degree of freedom, particle-hole pairs, and find that is modifies the heat transport characteristics under realistic conditions. We conclude that a quantitative modelling of thermo-electric transport properties in clean graphene should include collective excitations.