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(left) Superconducting transition shifts to higher temperature under hydrostatic pressure.

How to Raise T c Further in High-T c Superconductors James S. Schilling, Washington University, DMR 0703896.

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(left) Superconducting transition shifts to higher temperature under hydrostatic pressure.

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  1. How to Raise Tc Further in High-Tc SuperconductorsJames S. Schilling, Washington University, DMR 0703896 Even though it is still an open question why the cuprate oxides superconduct at temperatures as high as 134 K, the ob-servation of systematics in experiment may give hints on how to further enhance Tc. For example, Tc normally increases if a cuprate is subjected to high pressure, as seen the data in the figure for a HgBa2CuO4+ (Hg-1201) single crystal. The question is why! Hydrostatic pressure both reduces the area of the CuO2 planes and pushes them closer together. To clarify this, one needs to apply pressure to the crystal along specific directions. c a (left) Superconducting transition shifts to higher temperature under hydrostatic pressure. (right) Tetragonal structure of Hg-1201 consists of CuO2 planes (octahedra) with dimensions a-by-a and separation c. Recent ultrahigh resolution thermal expansion studies on Hg-1201 reveal that Tc increases if: (1) the CuO2 planes are compressed (their area reduced), or (2) the separation of the CuO2 planes is increased. Searching for perovskite structures which realize these conditions has the potential to lead to the discovery of materials with even higher values of Tc.

  2. How to Raise Tc Further in High-Tc SuperconductorsJames S. Schilling, Washington University, DMR 0703896 As seen in the figure, the results found for Hg-1201 also appear to hold for other cuprate superconductors: compressing the CuO2 planes along the a or b directions drives Tc up whereas reducing the separa-tion between planes by applying pressure along the c direction drives Tc down. These results may aid in the synthesis of materials with even higher values of Tc with potential applications of benefit to society. This work was an international collabor-ative effort with F. Hardy and C. Meingast (Karlsruhe, Germany), D. Colson (Saclay, France), Y. Li, N. Barisic and X. Zhao (Stanford U.), G. Yu and M. Greven (U. Minnesota). The PI is co-organizer of an International Conference on “Pressure Effects on Materials”, August 22-27, 2010 at the University of California, Santa Barbara. (above) Rate of change of the superconducting transition temperature Tc for pressure applied along specific directions to crystals of several cuprate superconductors.

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