Abstract
Magnetization measurements have been performed on the oxygen-isotopeexchanged samples (16O and 18O) of the one-layer cuprate superconductorsLa2−xSrxCuO4 (0.06≤x≤0.20). We find that there is an oxygen-isotopeeffect on the effective supercarrier mass m**, which is huge for x=0.06,and reduced to a smaller value for x=0.15. We also find that there coexistsmall (bi)polarons and free carriers for x≥0.09, but only small (bi)polaronsare present for x≤0.09. The normal-state gap is related to the bipolaronbinding energy which is inversely proportional to x for 0.05≤x≤0.15. Theobserved isotope effects, supercarrier mass anisotropy, normal-state gap,and mid-infrared spectra for x≤0.09 can be quantitatively explained by the small(bi)polaron theory of superconductivity proposed by Alexandrov, Kabanov, andMott (AKM).
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