Spectroscopy of heat transport and violation of the Wiedemann-Franz law in GaAs hydrodynamic mesoscopic channel

The Wiedemann-Franz law, which determines the universality of the ratio of thermal conductivity to electrical conductivity, is studied in the hydrodynamic electron transport regime, where scattering between electrons predominates over their scattering by disorder. In this case the different relaxation of electric and thermal currents can lead to a violation of the Wiedemann-Franz law, which is expected to be even more pronounced in mesoscopic electron systems. This paper reports the propagation of hot electrons in a GaAs hydrodynamic narrow channel, studied using micrometer-resolution photoluminescence thermometry. As a result, a temperature dependence of the Lorentz number was obtained, indicating a violation of the WF law. The important role of narrow constrictions in the violation of the WF law was also shown and theoretical arguments are presented.