Isotope effects and possible pairing mechanism in optimally doped cuprate superconductors

TL;DR

This study investigates isotope effects on critical temperature and penetration depth in optimally doped cuprates, revealing small T_c isotope effects but significant changes in supercarrier mass, suggesting a complex pairing mechanism.

Contribution

It provides new insights into isotope effects in multi-layer cuprates, proposing a plausible pairing mechanism consistent with observed isotope effects and superconducting properties.

Findings

Small isotope effect on T_c (0.019)

Significant isotope effect on penetration depth (0.025)

Isotope effect on supercarrier mass nearly independent of layer number

Abstract

We have studied the oxygen-isotope effects on T_{c} and in-plane penetration depth \lambda_{ab}(0) in an optimally doped 3-layer cuprate Bi_{1.6}Pb_{0.4}Sr_{2}Ca_{2}Cu_{3}O_{10+y} (T_{c} \sim 107 K). We find a small oxygen-isotope effect on T_{c} (\alpha_{O} = 0.019), and a substantial effect on \lambda_{ab} (0) (\Delta \lambda_{ab} (0)/\lambda_{ab} (0) = 2.5\pm0.5%). The present results along with the previously observed isotope effects in single-layer and double-layer cuprates indicate that the isotope exponent \alpha_{O} in optimally doped cuprates is small while the isotope effect on the in-plane effective supercarrier mass is substantial and nearly independent of the number of the CuO_{2} layers. A plausible pairing mechanism is proposed to explain the isotope effects, high-T_{c} superconductivity and tunneling spectra in a consistent way.