Thermal conductivity of Bi-Sr-Ca-Cu-O superconductors: Correlation with the low-temperature specific-heat behavior

Thermal conductivity has been measured on Bi-Sr-Ca-Cu-O high-$T_c$ superconductors down to 70 mK. Samples included a sintered specimen as well as two hot-pressed samples cut from the same ingot parallel and perpendicular, respectively, to the pressing direction. Below 3 K the thermal conductivities of all samples follow an approximately quadratic temperature variation with no indication of the limiting $T$-linear dependence typically observed for the superconducting state of Y-Ba-Cu-O and La-Sr-Cu-O ceramics. We discuss the apparent correlation between the occurrence or absence at low temperatures of a $T$-linear thermal conductivity and a $T$-linear ($\gamma$) term in the specific heat in all high-$T_c$ superconducting ceramics.