Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 1: Superconductivity - Fabrication, Technical Optimization and Characterization

TT 1.3: Vortrag

Freitag, 4. März 2005, 10:45–11:00, TU H104

Superconductivity in nominally undoped La based T^′-structure cuprates — •Yoshiharu Krockenberger^1,2, Akio Tsukada¹, Hideki Yamamoto¹, Dirk Manske², Michio Naito³, and Lambert Alff⁴ — ¹NTT Basic Research Laboratories, 3-1 Morinosato-Wakamiya,Atsugi, Kanagawa 243-0198, Japan — ²Max-Planck-Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany — ³Department of Applied Physics, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan — ⁴Vienna University of Technology, ISAS, Applied Electronic Materials, Gusshausstr. 27-29/366,A-1040 Vienna, Austria

La₂CuO₄ in the T-structure is classified as the Mott-insulating No-dqparent compoundNo-dqof the high-temperature supeconductors. However, La₂CuO₄ with Nd₂CuO₄ (T^′) structure has not yet been synthesized and investigated due to the ionic size driven structural instability to the T-phase. We report the synthesis of La_2−xRE_xCuO₄ with the T^′ structure by molecular beam epitaxy, using isovalent substituents RE = Sm, Eu, Gd, Tb, Lu, and Y for La stabilizing the T^′ phase. Surprisingly, all these nominally undoped T^′-compounds show metallic behavior and even become superconducting at critical temperatures up to 25 K. The observed smooth decrease of the resistivity of samples grown in increasingly reducing atmosphere suggests that for these materials the expected Mott-insulating state is not obtained even close to the undoped compound. The phase diagram of the electron-doped T^′-compounds therefore seems to depend strongly on details of the crystal structure.