The magnetotransport properties of a two-dimensional electron liquid in graphene are analyzed in the hydrodynamic limit under isothermal conditions. It is shown that the Wiedemann-Franz law does not hold in this regime and that the Lorenz ratios constructed from the diagonal and Hall conductivities generally differ from each other. The breakdown of the Wiedemann-Franz law is most pronounced near charge neutrality, where the Lorenz ratio can exceed its nominal universal Sommerfeld value by an order of magnitude. The corresponding Lorenz ratios exhibit a nonmonotonic dependence on the magnetic field, which is caused by emergent magnetic friction arising in liquids lacking Galilean invariance and possessing finite intrinsic conductivity.
@article{arxiv.2503.19194,
title = {Lorenz ratios of diagonal and Hall conductivities in a Dirac electron liquid},
author = {Alex Levchenko},
journal= {arXiv preprint arXiv:2503.19194},
year = {2025}
}