Evidence for critical lattice fluctuations in the high T-c cuprates

Here we provide a direct experimental evidence for critical local lattice f luctuations in the high T-c superconductors. Cu K-edge extended X-ray absor ption fine structure (EXAFS) has been used to measure the distribution of C u-O bond lengths and the amplitude of local lattice distortions in differen t materials with increasing chemical pressure on the CuO2 layers. The strip e formation temperature T-infinity. is determined by the upturn of the Deby e Waller factor due to the onset of local lattice distortions. A decrease o f the amplitude of lattice fluctuations at the superconducting transition r eveals their role in the pairing mechanism. The dynamical lattice fluctuati ons in the normal phase for T > T-infinity. show diverging lattice fluctuat ions at the critical chen-deal pressure epsilon (c).