Superconducting-state enhancement of thermal conductivity in the cuprates: Correlation with the pair density

The systematics of the superconducting-state enhancements of in-plane thermal conductivity for YBa2Cu3O6+x (Y-123), Bi2Sr2CaCu2O8, Tl2Ba2CuO6, and La2-xSrxCuO4 single crystals are examined. For Y-123 the enhancements are shown to correlate with specific-heat jumps, a measure of the superconducting pair density. The substantially larger enhancements observed for Y-123 are attributed to the condensate arising from oxygen-filled CuO chains. We discuss the constraints imposed by measurements of microwave conductivity on the electronic contribution to this phenomenon