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Anomalous oxygen isotope effect on the in-plane FIR conductivity of detwinned YBa2Cu316,18O6.9

C. Bernhard, T. Holden, A. V. Boris, N. N. Kovaleva, A. V. Pimenov, J. Humlicek, C. Ulrich, C. T. Lin, J. L. Tallon

cond-mat.supr-conarXiv:cond-mat/0306097

Abstract

We observe an anomalous oxygen isotope effect on the a-axis component of the far-infrared electronic response of detwinned YBa2Cu316,18O6.9. For 18O a pronounced low-energy electronic mode (LEM) appears around 240 cm-1. This a-axis LEM exhibits a clear aging effect, after one year it is shifted to 190 cm-1. For 16O we cannot resolve a corresponding a-axis LEM above 120 cm-1. We interpret the LEM in terms of a collective electronic mode that is pinned by `isotopic defects', i.e. by the residual 16O in the matrix of 18O.

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