Oxygen Isotope Effect Resulting from Polaron-induced Superconductivity in Cuprates

TL;DR

This paper investigates the oxygen isotope effect in cuprate superconductors, showing it supports the polaron-based mechanism of superconductivity in the CuO2 planes, consistent with a theoretical model by Kresin and Wolf.

Contribution

It provides experimental evidence that the oxygen isotope effect aligns with polaron-induced superconductivity models, extending the validity of the Kresin-Wolf formula to in-plane polarons in cuprates.

Findings

Oxygen isotope effect coefficient follows the Kresin-Wolf formula in YBCO and LSCO.

Inverse isotope effect at pseudogap temperature also follows the same formula.

Results support polarons or bipolarons as the mechanism for superconductivity in cuprates.

Abstract

The planar oxygen isotope effect coefficient measured as a function of hole doping in the Pr- and La-doped YBa2Cu3O7 (YBCO) and the Ni-doped La1.85Sr0.15CuO4 (LSCO) superconductors quantitatively and qualitatively follows the form originally proposed by Kresin and Wolf, which was derived for polarons perpendicular to the superconducting planes. Interestingly, the inverse oxygen isotope effect coefficient at the pseudogap temperature also follows the same formula. These findings allow the conclusion that the superconductivity in YBCO and LSCO results from polarons or rather bipolarons in the CuO2 plane. The original formula, proposed for the perpendicular direction only, is obviously more generally valid and accounts for the superconductivity in the CuO2 planes.