Isotope effects in multiband superconductors

TL;DR

This paper investigates isotope effects in multiband superconductors, showing that small electron-phonon interactions can produce observable isotope effects on various superconducting properties, with trends consistent with experimental observations.

Contribution

It introduces a multiband model for cuprates that explains isotope effects on multiple superconducting parameters, highlighting the role of interband pairing and small electron-phonon contributions.

Findings

Isotope exponents of $T_c$, supercarrier density, effective mass, and penetration depth are calculated.

Opposite trends of $eta$ and $T_c$ are confirmed.

$eta_ ext{penetration depth}$ is mainly driven by $eta_ ext{carrier density}$.

Abstract

Isotope effects in a multiband superconductor with a leading interband pairing channel are investigated. A relatively small electron-phonon contribution into the pair-transfer interaction can cause effects of observed magnitude. A multiband model which interpolates the cuprate properties is used for illustrative calculations. Isotope exponents of the transition temperature ($\alpha$), supercarrier density ($\alpha_n$), paired carrier effective mass ($\alpha_m$) and of the penetration depth ($\alpha_{\lambda}$) on the doping scale have been obtained. The known opposite trend of $\alpha$ and $T_c$ is reflected. The trends of $\alpha$ and $\alpha_n$ are similar. In contrast with the usual assumption in the interband case $\alpha_{\lambda}$ is driven by $\alpha_n$, which overwhelmes $\alpha_m$.