The Renaissance of High-<i>T</i><sub>c</sub> Superconductivity―Discovery of Undoped Cuprate Superconductors and Revise of the Electronic Phase Diagram

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  • 高温超伝導ルネサンス―ノンドープ超伝導体の発見と新しい電子相図
  • コウオン チョウデンドウ ルネサンス : ノンドープ チョウデンドウタイ ノ ハッケン ト アタラシイ デンシソウズ

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Abstract

<p>More than 30 years have passed since the discovery of high-Tc superconducting copper oxides. While the mechanism of the high-Tc superconductivity still remains elusive, the electronic phase diagram is a key ingredient to understand it. It has been believed that parent compounds of cuprates were universally antiferromagnetic Mott insulators and that superconductivity would develop upon doping either holes or electrons in the insulators (“doped Mott-insulator scenario”). However, our recent discovery of superconductivity in the parent and heavily-underdoped compounds with the Nd2CuO4(T′) structure urged a serious reassessment to the above scenario. We start this review with our experimental results for the T′ cuprates and their implications. The key material issue is to remove excess oxygen ions residing in the interstitial sites without introducing oxygen vacancies in the CuO2 planes, the playground of high-Tc superconductivity, by elaborate synthesis procedures. There has been significant progress also in the electronic-structure calculation techniques. Unlike 30 years ago, it is now possible to predict the coordination-dependent different ground states between T- and T′-La2CuO4: Cu is octahedral and square-planar coordinated in the T and T′ structures, respectively. High-Tc superconductivity remains confined, at least at present, only to copper oxides. Reassessment of the electronic state by the state-of-the-art calculation methods may unveil unique features of copper oxides not shared by other transition-metal oxides.</p>

Journal

  • Butsuri

    Butsuri 73 (4), 204-213, 2018-04-05

    The Physical Society of Japan

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