Isotope exponent in disordered underdoped and overdoped La214

TL;DR

This study investigates how oxygen isotope substitution affects the superconducting transition temperature in La214 compounds with varying doping levels and Zn content, revealing different behaviors in underdoped and overdoped regimes.

Contribution

It provides a comparative analysis of isotope effects in underdoped and overdoped La214, highlighting the limitations of impurity-induced pair-breaking models in overdoped samples.

Findings

Isotope exponent more affected by Zn in underdoped samples.

Impurity model explains underdoped behavior well.

Model fails to describe overdoped isotope effects.

Abstract

The effect of oxygen isotope substitution on Tc has been analyzed for heavily underdoped and overdoped La2-xSrxCu1-yZnyO4 compounds with different Zn contents in the CuO2 plane. The effect of Zn on the isotope exponent, {\alpha}, was more pronounced in the case of the underdoped (x = 0.09) compounds compared to the overdoped (x = 0.22) ones. The variation of {\alpha} with in-plane disorder can be described quite well within a model based solely on impurity induced Cooper pair-breaking in the case of the underdoped compounds. This model, on the other hand, fails to describe the behavior of {\alpha}(y) for the overdoped samples, even though Zn still breaks pairs very effectively at this hole (Sr) content. We discuss the implications of these finding in details by considering the Zn induced magnetism, stripe correlations, and possible changes in the superconducting order parameter as number of charge carriers in the CuO2 plane, p (\equiv x), is varied.