SUPERCONDUCTIVE PHONON ANOMALIES IN HIGH-TC CUPRATES

We consider the effects on phonon dynamics of spin-lattice coupling wi thin the slave-boson mean-field treatment of the extended t-J model. W ith no additional assumptions the theory is found to give a semi-quant itative account of the frequency and linewidth anomalies observed by R aman and neutron scattering for the 340cm(-1) B-1g phonon mode in YBa2 Cu3O7 at the superconducting transition. We discuss the applicability of the model to phonon modes of different symmetries, and report a con nection to spin-gap features observed in underdoped YBCO. The results suggest the possibility of a unified understanding of the anomalies in transport, magnetic and lattice properties.