Role of impurity oxygen in superconductivity of "non-doped" T'-(La,RE)2CuO4

TL;DR

This study investigates how oxygen nonstoichiometry affects superconductivity in nominally undoped T'-(La,Y)2CuO4+y, revealing that residual oxygen plays a crucial role in enabling superconductivity.

Contribution

It demonstrates the sensitivity of superconductivity to reduction conditions and highlights the influence of residual apical oxygen in non-doped T'-cuprates.

Findings

Superconductivity increases with reduction, showing continuous resistivity decrease.

Absence of insulating state suggests intrinsic carriers in the material.

Residual apical oxygen negatively impacts superconductivity.

Abstract

We have systematically investigated the effect of oxygen nonstoichiometry in a nominally undoped superconductor T'-(La,Y)2CuO4+y. In the experiments, the reduction condition was changed after the sample growth by MBE. The superconductivity is very sensitive to the reduction condition. With systematically increasingly reduced atmospheres, resistivity shows a continuous drop and no discontinuity is observed even until the appearance of superconductivity. The absence of the highly insulating state expected for Mott insulators around y ~ 0 suggests that T'-(La,Y)2CuO4 has intrinsic carriers. The role of residual apical oxygen, which is detrimental to superconductivity, is also discussed based on the resistivity-temperature characteristics in insufficiently reduced samples.