Determining the Wiedemann-Franz ratio from the thermal Hall   conductivity: Application to Cu and YBa_2Cu_3O_6.95
  The Wiedemann-Franz (WF) ratio compares the thermal and electrical conductivities in a metal. We describe a new way to determine its value, based on the thermal Hall conductivity. The technique is applied to copper and to untwinned YBaCuO. In the latter, we uncover a T-linear dependence and suppression of the Hall-channel WF ratio. We discuss the implications of this suppressions. The general suppression of the WF ratio in systems with predominant electron-electron scattering is discussed. 
Y. Zhang, N. P. Ong, Z. A. Xu (Princeton University), R. Gagnon   (McGill University) and L. Taillefer (University of Toronto)