Origin of superconductivity in nominally "undoped" T'-La 2−x Y x CuO 4 films
L. Zhao, R. H. Liu, G. Wu, G. Y. Wang, T. Wu, X. G. Luo, X. H. Chen
Abstract
We have systematically studied the transport properties of the La
2−x
Y
x
CuO
4
(LYCO) films of T'-phase (
0.05≤x≤0.30
). In this nominally "undoped" system, superconductivity was acquired in certain Y doping range (
0.10≤x≤0.20
). Measurements of resistivity, Hall coefficients in normal states and resistive critical field (
H
ρ
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.