OXYGEN-ISOTOPE EFFECT ON THE EFFECTIVE-MASS OF CARRIERS FROM MAGNETICMEASUREMENTS ON LA2-XSRXCUO4

Oxygen isotope effects on T-c and the Meissner fraction f have been in vestigated in fine-grained, decoupled La2-xSrxCuO4 with x=0.105, 0.110 , and 0.115. We find that these oxygen isotope effects are related to each other: dInT(c)/dInM approximate to dInf/dInM (where M is the mass of oxygen). We also show that the trapped flux due to intergrain weak -link and intragrain flux pinning is negligible in our samples, and th at the Meissner fractions for the samples with the same O-16 isotope a re nearly equal The observed large oxygen isotope effects on T-c and t he Meissner fraction can be explained as due to the oxygen-mass depend ence of m (effective mass of carriers). The results may suggest that the conducting carriers in the cuprate superconductors are of polaroni c type.