The in-plane and out-of-plane thermal conductivity, ${\kappa }_{\mathrm{ab}}$ and ${\kappa }_c$, of a large single crystal of twinned $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ has been studied as a function of temperature for several annealing conditions. The present result strongly supports ascribing an observed peak in ${\kappa }_{\mathrm{ab}}$ below $T_c$ to an electron contribution. The super-conducting enhancement of ${\kappa }_{\mathrm{ab}}$ becomes rather small and the position of the peak value gradually shifts to higher temperatures with an increase of annealing time. This behavior is not well explained by the Kadanoff-Martin expression on the assumption of Matthiessen's rule but probably implies that the screening effect due to charge carrier doping yields a suppression of strong electron-electron interaction in the normal state.

• Received 11 December 1995

DOI:https://doi.org/10.1103/PhysRevB.53.R6034