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Anomalous oxygen isotope effect on the in-plane FIR conductivity of detwinned YBa2Cu3$^{16,18}$O$_{6.9}$

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

We observe an anomalous oxygen isotope effect on the a-axis component of the far-infrared electronic response of detwinned YBa2Cu3$^{16,18}$O$_{6.9}$. For $^{18}$O 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 $^{16}$O 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 $^{16}$O in the matrix of $^{18}$O.

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C. Bernhard, T. Holden, A. V. Boris, N. N. Kovaleva, A. V. Pimenov, J. Humlicek, C. Ulrich, C. T. Lin, J. L. Tallon. 2003-06-04. Anomalous oxygen isotope effect on the in-plane FIR conductivity of detwinned YBa2Cu3$^{16,18}$O$_{6.9}$. https://doi.org/10.1103/physrevb.69.052502

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