Isotope effects and possible pairing mechanism in optimally doped cuprate superconductors - art. no. 220506

We have studied the oxygen-isotope effects on T-c and in-plane penetration depth lambda (ab)(0) in an optimally doped three-layer cuprate Bi1.6Pb0.4Sr 2Ca2Cu3O10+y (T-c similar to 107 K). We find a small oxygen-isotope effect on T-c (alpha (0) = 0.019), and a substantial effect on lambda (ab)(0) [Del ta lambda (ab)(0)/lambda (ab)(0)= 2.5 +/-0.5%]. The present results along w ith the previously observed isotope effects in single-layer and double-laye r cuprates indicate that the isotope exponent alpha (O) in optimally doped cuprates is small while the isotope effect on the in-plane effective superc arrier mass is substantial and nearly independent of the number of the CuO2 layers. A plausible pairing mechanism is proposed to explain the isotope e ffects, high-T-c superconductivity, and tunneling spectra in a consistent w ay.