Oxygen isotope effect on the effective mass of carriers from magnetic measurements on La2-xSrxCuO4.

Oxygen isotope effects on {ital T}{sub {ital c}} and the Meissner fraction {ital f} have been investigated in fine-grained, decoupled La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4} with {ital x}=0.105, 0.110, and 0.115. We find that these oxygen isotope effects are related to each other: {ital d} ln{ital T}{sub {ital c}}/{ital d} ln{ital M}{approx}{ital d} ln{ital f}/{ital d} ln{ital M} (where {ital 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 that the Meissner fractions for the samples with the same {sup 16}O isotope are nearly equal The observed large oxygen isotope effects on {ital T}{sub {ital c}} and the Meissner fraction can be explained as due to the oxygen-mass dependence of {ital m}{sup *} (effective mass of carriers). The results may suggest that the conducting carriers in the cuprate superconductors are of polaronic type.