Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10653236 | Solid State Communications | 2005 | 5 Pages |
Abstract
High-temperature superconductivity has been discovered in La2âxBaxCuO4 [J.G. Bednorz, K.A. Müller, Z. Phys. B 64 (1986) 189. [1]], a compound that derives from the undoped La2CuO4 crystallizing in the perovskite T-structure. In this structure oxygen octahedra surround the copper ions. It is common knowledge that charge carriers induced by doping in such an undoped antiferromagnetic Mott-insulator lead to high-temperature superconductivity [V.J. Emery, Phys. Rev. Lett. 58 (1987) 2794; C.M. Varma, S. Schmitt-Rink, E. Abrahams, Solid State Commun. 62 (1987) 681; E. Dagotto, Rev. Mod. Phys. 66 (1994) 763. [2], [3], [4]]. The undoped material La2CuO4 is also the basis of the electron-doped cuprate superconductors [Y. Tokura, H. Takagi, S. Uchida, Nature (London) 337 (1989) 345. [5]] of the form La2âxCexCuO4+y [M. Naito, M. Hepp, Jpn. J. Appl. Phys. 39 (2000) L485; A. Sawa, M. Kawasaki, H. Takagi, Y. Tokura, Phys. Rev. B 66 (2002) 014531. [6], [7]] which, however, crystallize in the so-called Tâ²-structure, i.e. without apical oxygen above or below the copper ions of the CuO2-plane. It is well known that for La2âxCexCuO4+y the undoped Tâ²-structure parent compound cannot be prepared due to the structural phase transition back into the T-structure occurring around xâ¼0.05. Here, we report that if La is substituted by RE=Y, Lu, Sm, Eu, Gd, or Tb, which have smaller ionic radii but have the same valence as La, nominally undoped La2âxRExCuO4 can be synthesized by molecular beam epitaxy in the Tâ²-structure. The second important result is that all these new Tâ²-compounds are superconductors with fairly high critical temperatures up to 21Â K. For this new class of cuprates La2âxRExCuO4, which forms the Tâ²-parent compounds of the La-based electron doped cuprates, we have not been able to obtain the Mott-insulating ground state for small x before the structural phase transition into the T-structure takes place.
Related Topics
Physical Sciences and Engineering
Materials Science
Materials Science (General)
Authors
A. Tsukada, Y. Krockenberger, M. Noda, H. Yamamoto, D. Manske, L. Alff, M. Naito,