  A system of electrons in two dimensions and strong magnetic fields can be
tuned to create a gapped 2D system with one dimensional channels along the
edge. Interactions among these edge modes can lead to independent transport of
charge and heat, even in opposite directions. Measuring the chirality and
transport properties of these charge and heat modes can reveal otherwise hidden
structure in the edge. Here, we heat the outer edge of such a quantum Hall
system using a quantum point contact. By placing quantum dots upstream and
downstream along the edge of the heater, we can measure both the chemical
potential and temperature of that edge to study charge and heat transport,
respectively. We find that charge is transported exclusively downstream, but
heat can be transported upstream when the edge has additional structure related
to fractional quantum Hall physics.
