Isotope Effect on the Superconducting Transition Temperature of NaxCoO2.yH2O

TL;DR

This study investigates the oxygen isotope effect on the superconducting transition temperature of NaxCoO2.yH2O and finds no significant change, suggesting a limited role of phonons in its superconductivity.

Contribution

It provides experimental evidence that oxygen isotope substitution does not significantly affect Tc in NaxCoO2.yH2O, challenging phonon-mediated superconductivity assumptions.

Findings

No significant Tc difference with isotope substitution

Suggests limited phonon involvement in superconductivity

Supports strong correlation effects suppress isotope effect

Abstract

The effect of the 16O-->18O substitution on the superconducting transition temperatures Tc of NaxCoO2.yH2O has been studied for several sets of samples. Each set has two kinds of samples, one with the oxygen sites in the CoO2 layers filled with 16O atoms and another with these sites partially substituted with 18O isotope. These two kinds of samples were prepared in parallel in whole preparation processes. For all the sample sets, we have not found any significant difference of the Tc values between the non-substituted and substituted samples, which indicates that the oxygen isotope effect is not appreciable in NaxCoO2.yH2O. The result, however, does not necessarily exclude the possibility of the phonon mechanism of the superconductivity, because the strong correlation effect suppresses the isotope effect as pointed out previously.