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 (Formula presented) (Y-123), (Formula presented)(Formula presented)Ca(Formula presented)(Formula presented), (Formula presented)(Formula presented)Cu(Formula presented), and (Formula presented) 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.