Bulk Hydrodynamic Transport in Weyl Semimetals

The role of collective longitudinal modes, plasmons, in bulk hydrodynamic transport in Weyl semimetals is explored. In contrast to graphene, where these modes are gapless, plasmons in Weyl semimetals are gapped. This gap, however, can be made arbitrarily small by decreasing the temperature or the chemical potential, making plasmon modes thermally accessible, both in thermodynamics and transport. In very clean Weyl semimetals near charge-neutrality where the plasmon gap is minimal, we find that they leave an imprint in the thermal conductivity and the viscosity.