We report systematic, high-precision measurements of the low-T (down to 70 mK) thermal conductivity \kappa of YBa_{ 2}Cu_{ 3}O_{ y}, La_{ 2-x}Sr_{ x}CuO_{ 4} and Bi_{ 2}Sr_{ 2}CaCu_{ 2}O_{ 8+\delta}. Careful examinations of the Zn- and hole-doping dependences of the residual thermal conductivity \kappa_{ 0}/T, as well as the in-plane anisotropy of \kappa_{ 0}/T in Bi_{ 2}Sr_{ 2}CaCu_{ 2}O_{ 8+\delta}, indicate a breakdown of the universal thermal conductivity, a notable theoretical prediction for d-wave superconductors. Our results point to an important role of electronic inhomogeneities, that are not considered in the standard perturbation theory for thermal conductivity, in the under- to optimally-doped regime.
Categories: cond-mat.supr-con cond-mat.str-el