  We have measured the differential resistance in a two-dimensional topological
insulator (2DTI) in a HgTe quantum well, as a function of the applied dc
current. The transport near the charge neutrality point is characterized by a
pair of counter propagating gapless edge modes. In the presence of an electric
field, the energy is transported by counter propagating channels in the
opposite direction. We test a hot carrier effect model and demonstrate that the
energy transfer complies with the Wiedemann Franz law near the charge
neutrality point in the edge transport regime.
