Origin of superconductivity in nominally "undoped" T'-La${}_{2-x}$Y${}_x$CuO${}_4$ films

Abstract

We have systematically studied the transport properties of the La${}_{2-x}$Y${}_x$CuO${}_4$(LYCO) films of T'-phase ($0.05\le x\le 0.30$). In this nominally "undoped" system, superconductivity was acquired in certain Y doping range ($0.10\le x\le 0.20$). Measurements of resistivity, Hall coefficients in normal states and resistive critical field ($H_{c2}^{\rho }$)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.

8 pages, 9 figures

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