  Clean two-dimensional Dirac systems have received a lot of attention for
being a prime candidate to observe hydrodynamical transport behavior in
interacting electronic systems. This is mostly due to recent advances in the
preparation of ultrapure samples with sufficiently strong interactions. In this
paper, we investigate the role of collective modes in the thermo-electric
transport properties of those systems. We find that dynamical particle-hole
pairs, plasmons, make a sizeable contribution to the thermal conductivity.
While the increase at the Dirac point is moderate, it becomes large towards
larger doping. We suspect, that this is a generic feature of ultraclean
two-dimensional electronic systems, also applicable to degenerate systems.
