Relevance of electron-lattice coupling in cuprate superconductors

We study the oxygen isotope (O-16, O-18) and finite size effects in Y1-xPrxBa2Cu3O7-delta by in-plane penetration depth (lambda(ab)) measurements. A significant change of the length L-c of the superconducting domains along the c-axis and lambda(ab)(2) is deduced, yielding the relative isotope shift DeltaL(c)/L-c approximate to Deltalambda(ab)(2/)lambda(ab)(2) approximate to 0.14 for x = 0. 0.2 and 0.3. This uncovers the existence and relevance of the coupling between the superfluid, lattice distortions and anharmonic phonons which involve the oxygen lattice degrees of freedom.