Searching for superconductivity in epitaxial films of copper-free layered oxides with the K2NiF4 structure

Darrell G. Schlom; Yunfa Jia; L. N. Zou; J. H. Hanei; S. Briczinski; M. A. Zurbuchen; Christopher W. Leitz; Sethu Madhavan; S. Wozniak; Yanning Liu; Marilyn E. Hawley; Geoffrey W. Brown; A. Dabkowski; H. A. Dabkowska; R. Uecker; Peter Reiche

doi:10.1117/12.335882

22 December 1998 Searching for superconductivity in epitaxial films of copper-free layered oxides with the K2NiF4 structure

Darrell G. Schlom, Yunfa Jia, L. N. Zou, J. H. Hanei, S. Briczinski, M. A. Zurbuchen, Christopher W. Leitz, Sethu Madhavan, S. Wozniak, Yanning Liu, Marilyn E. Hawley, Geoffrey W. Brown, A. Dabkowski, H. A. Dabkowska, R. Uecker, Peter Reiche

Author Affiliations +

Proceedings Volume 3481, Superconducting and Related Oxides: Physics and Nanoengineering III; (1998) https://doi.org/10.1117/12.335882
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1998, San Diego, CA, United States

Abstract

We have grown epitaxial films of Sr₂RuO₄, Ba₂RuO₄, and Sr₂TiO₄ and studied their structural and transport properties. These phases are all layered perovskites with the K₂NiF₄ structure. Sr₂RuO₄ is the only known superconducting layered perovskite that is free of copper (T_c equals 1.35 K in bulk single crystals). In light of the observation that hydrostatic pressure reduces the T_c of Sr₂RuO₄, we have investigated the effect of replacing Sr²⁺ with the larger Ba²⁺ ion. In bulk samples, Ba₂RuO₄ is not isostructural with Sr₂RuO₄ when synthesized at atmospheric pressure. However, using pressures of 65,000 atm., the synthesis of a tetragonal form of Ba₂RuO₄ (with the K₂NiF₄ structure) has been reported. We have grown epitaxial films of the tetragonal form of Ba₂RuO₄ through the use of epitaxial stabilization. In addition to studying these ruthenates that are isostructural to the high-T_c superconductor (La,Sr)₂CuO₄, we have also investigated La-doped Sr₂TiO₄. Doped SrTiO₃ is a well-known superconductor, but the effect of reducing the dimensionality of SrTiO₃ from 3-D to 2-D (i.e., Sr₂TiO₄) has never been reported. The Sr₂RuO₄ and Ba₂RuO₄ films have been grown by pulsed laser deposition (PLD); Sr₂TiO₄ films have been grown by reactive molecular beam epitaxy (MBE). The growth conditions yielding phase-pure films have been mapped out. The orientation of the epitaxial films has been controlled by choosing appropriate substrates. Resistivity versus temperature measurements show that all three materials exhibit metallic conductivity. A resistivity, (rho) varies direct as T² has been observed in many samples at low temperatures, T. However, superconductivity has not been observed in any samples. In addition to growing Sr₂TiO₄, the n equals 1 member of the Sr_n+1Ti_nO_3n+1 Ruddlesden-Popper homologous series, we also used the atomic layering capability of MBE to grow phase-pure, epitaxial, thin films of the n equals 2 - 5 members of this homologous series (i.e., Sr₃Ti₂O₇, Sr₄Ti₃O₁₀, Sr₅Ti₄O₁₃, and Sr₆Ti₅O₁₆).

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Darrell G. Schlom, Yunfa Jia, L. N. Zou, J. H. Hanei, S. Briczinski, M. A. Zurbuchen, Christopher W. Leitz, Sethu Madhavan, S. Wozniak, Yanning Liu, Marilyn E. Hawley, Geoffrey W. Brown, A. Dabkowski, H. A. Dabkowska, R. Uecker, and Peter Reiche "Searching for superconductivity in epitaxial films of copper-free layered oxides with the K2NiF4 structure", Proc. SPIE 3481, Superconducting and Related Oxides: Physics and Nanoengineering III, (22 December 1998); https://doi.org/10.1117/12.335882

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