Thermal transport driven by charge imbalance in graphene in a magnetic field close to the charge neutrality point at low temperature: Nonlocal resistance.
Tagliacozzo A., Giuliano D., Jouault B.
II - Fisica della materia
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Graphene grown epitaxially on SiC, close to the charge neutrality point, in an orthogonal magnetic field, shows an ambipolar behavior of the transverse resistance accompanied by a puzzling nonlocal magnetoresistance. We derive a hydrodynamic approach to transport in this system, which involves particle and hole Dirac carriers, in the form of charge and energy currents. We find that thermal diffusion can take place on a large distance scale, thanks to long recombination times, provided a non-insulating bulk of the Hall bar is assumed, as recent models seem to suggest. We argue that leakage of carriers from the edges generates an imbalance of carriers of opposite sign, which are separated in space by the magnetic field and diffuse along the Hall bar generating a nonlocal transverse voltage. The question arises as to the whether thermal Hall conductivity of edge states is quantized in this system.