Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T'-Superconductors

Abstract

In this review article, we show our recent results relating to the undoped (Ce-free) superconductivity in the electron-doped high-Tc cuprates with the so-called T' structure. For an introduction, we briefly mention the characteristics of the electron-doped T'-cuprates, including the reduction annealing, conventional phase diagram and undoped superconductivity. Then, our transport and magnetic results and results relating to the superconducting pairing symmetry of the undoped and underdoped T'-cuprates are shown. Collaborating spectroscopic and nuclear magnetic resonance results are also shown briefly. It has been found that, through the reduction annealing, a strongly localized state of carriers accompanied by an antiferromagnetic pseudogap in the as-grown samples changes to a metallic and superconducting state with a short-range magnetic order in the reduced superconducting samples. The formation of the short-range magnetic order due to a very small amount of excess oxygen in the reduced superconducting samples suggests that the T'-cuprates exhibiting the undoped superconductivity in the parent compounds are regarded as strongly correlated electron systems, as well as the hole-doped high-Tc cuprates. We show our proposed electronic structure model to understand the undoped superconductivity. Finally, unsolved future issues of the T'-cuprates are discussed.

13 pages, 8 figures

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• Vortex Dynamics and Phase Diagram in the Electron Doped Cuprate Superconductor Pr${}_{0.87}$LaCe${}_{0.13}$CuO${}_4$
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• Continuously Doping Bi 2 Sr 2 CaCu 2 O 8+δ into Electron-Doped Superconductor by CaH 2 Annealing Method
• Correlation between the strength of low-temperature T-linear normal-state resistivity and $T_{\mathrm{c}}$ in overdoped electron-doped cuprate superconductors
• Introduction to High-Temperature Superconductivity for Solid State Chemists
• Renormalization of dispersion in electron-doped bilayer cuprate superconductors
• Electronic State of T'-Pr${}_{1.3-x}$La${}_{0.7}$Ce${}_x$CuO${}_4$ ($x=0.10$) Studied by Compton Scattering
• Cu-spin Correlation in the Electron-overdoped High-Tc Cuprate Thin Films of La_2-x_Ce_x_CuO_4_ Probed by Low-energy Muons