Isotope coefficient of optimally doped high-Tc cuprates

TL;DR

This paper demonstrates that in pure BCS theory, the isotope coefficient is always below 0.5 and can be very small in polyatomic superconductors, explaining experimental observations in various high-Tc materials.

Contribution

It provides a quantitative explanation for the small isotope coefficients in optimally doped cuprates and other polyatomic superconductors within the pure BCS framework.

Findings

Isotope coefficient always less than 0.5 in pure BCS.

Small isotope coefficients observed in experiments are consistent with pure electron-phonon interaction.

Explains magnitude of isotope coefficients in cuprates, magnesium diboride, and fullerenes.

Abstract

Within the framework of pure BCS(i.e. when the critical temperature is proportional to the Debye temperature), we show that the isotope coefficient is always less than 1/2 and could be extremely small in polyatomic superconductors depending on the chemical formula unit. This finding leads to quantitative explanation of observed values(correct orders of magnitude and sometimes exact numerical values) in optimally doped cuprates, magnesium diboride and alkali-doped fullerenes. Consequently, the smallness of the isotope coefficient is not only compatible with pure electron-phonon interaction, but this is perhaps the rule in polyatomic systems.