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), Bi₂{Sr}₂$Ca${Cu}₂O₈, Tl₂{Ba}₂$Cu${O}₆$, and ${La}_{2{-}x}{Sr}ₓCu{O}₄$ 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.