Origin of superconductivity in nominally "undoped" T'-La$_{2-x}$Y$_{x}$CuO$_{4}$ films

TL;DR

This study investigates the origin of superconductivity in nominally undoped T'-phase La$_{2-x}$Y$_{x}$CuO$_{4}$ films, revealing that oxygen deficiency induces electron doping and that cation size influences superconductivity.

Contribution

It provides evidence that oxygen deficiency causes electron doping in undoped T'-cuprates and highlights the importance of A-site cation radii for superconductivity.

Findings

Superconductivity appears in specific Y doping range (0.10 to 0.20).

Transport measurements indicate intrinsic electron doping due to oxygen deficiency.

Cation size plays a crucial role in the emergence of superconductivity.

Abstract

We have systematically studied the transport properties of the La$_{2-x}$Y$_{x}$CuO$_{4}$(LYCO) films of T'-phase ($0.05\leq x \leq 0.30$). In this nominally "undoped" system, superconductivity was acquired in certain Y doping range ($0.10\leq x \leq 0.20$). Measurements of resistivity, Hall coefficients in normal states and resistive critical field ($H^\rho_{c2}$)in superconducting states of the T'-LYCO films show the similar behavior as the known Ce-doped n-type cuprate superconductors, indicating the intrinsic electron-doping nature. The charge carriers are induced by oxygen deficiency. Non-superconducting Y-doped Pr- or Nd-based T'-phase cuprate films were also investigated for comparison, suggesting the crucial role of the radii of A-site cations in the origin of superconductivity in the nominally "undoped" cuptates. Based on a reasonable scenario in the microscopic reduction process, we put forward a self-consistent interpretation of these experimental observations.