THERMAL-CONDUCTIVITY OF OXYGEN-DEFICIENT YBCO - EVIDENCE FOR THE SPIN-PHONON COUPLING

We have studied the in-plane thermal conductivity in oxygen-deficient single crystals of YBa2Cu3O6+x (0 < x < 1). Strong temperature depende nce of K(T) observed in antiferromagnetic YBa2Cu3O6 near the Neel temp erature indicates the strong coupling of the acoustic phonons with loc alized Cu spins. In the underdoped superconducting crystals the system atic evolution of the metallic normal state K(T) correlates with pseud o-gap behavior of the spin excitation spectrum. This suggests that the upturn in K(T) below T-c may arise from the spin-gap opening.