Violation of the Wiedemann-Franz law in a large-Nsolution of thet−Jmodel

We show that the Wiedemann-Franz law, which holds for Landau Fermi liquids, breaks down in a large-$n$ treatment of the $t-J$ model. The calculated ratio of the in-plane thermal and electrical conductivities agrees quantitatively with experiments on the normal state of the electron-doped ${\mathrm{Pr}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ $\mathrm{}(x=0.15\mathrm{})\mathrm{}$ cuprate superconductor. The violation of the Wiedemann-Franz law in the uniform phase contrasts with other properties of the phase that are Fermi liquid like.