Comment on: Role of inelastic tunneling through the insulating barrier in scanning-tunneling-microscope experiments on cuprate superconductors

TL;DR

The paper critiques a proposed experiment on isotope effects in cuprate superconductors, arguing that previous data shows no isotope effect in the insulating layer and that the experiment is unlikely to yield new insights.

Contribution

It provides a critical analysis of a proposed isotope effect experiment, emphasizing existing data and questioning the experiment's potential outcomes.

Findings

Previous data shows no isotope effect in the insulating layer.

Oxygen isotope effects are primarily from CuO2-planes.

Polaronic behavior is evidenced in the CuO2-planes.

Abstract

In a recent letter [1] Pilgram, Rice and Sigrist (PRS) propose to perform oxygen isotope dependent conductivity measurements along the c-axis of the cuprate superconductor BSSCO. In Raman isotope data for vibrations along the c-axis from 1988 [2], and in site selective susceptibility experiments determining Tc, no isotope effects were observed for oxygen ions in the insulating layer [3]. Based on these earlier not by PRS quoted experiments, we argue that the suggestion made in Ref. 1 is not worth to be undertaken, and if it is carried through, no effect will be seen. From the meanwhile 12 years old site selective data [3] the observed isotope effects stem to nearly 100% from oxygen ions in the CuO2-planes. These results evidence polaronic behavior in these planes [4].