Towards a macroscopic coherent phonon state in strongly coupled superconductors

In superconductors where the electrons are tightly coupled to local molecul ar deformations a macroscopic coherent phonon state can be envisaged. Signa tures for that are a rigidification of the lattice upon entering the superc onducting state at T-c. Experimental verifications for that can be sought i n a temperature dependence of the polaron induced local lattice deformation s and the corresponding Debye-Waller factors showing kinks at T-c and a pai r distribution function evolving from a typical two-peak structure above T- c into a single peak structure below T-c. Such features could possibly occu r in High-T-c materials. (C) 1999 Elsevier Science Ltd. All rights reserved .