On Monday, November 11, 2013, Shin-ichi Uchida of Tokyo University will give his talk:
To uncover the mechanism of high-Tc superconductivity is one of the most challenging problems in physics. Equally challenging is to enhance the superconducting transition temperature Tc. However, Tc of copper oxide superconductors has stopped rising for almost 20 years. A new route toward higher Tc has been found in 2008 thanks to the discovery of a family of the iron-based high-Tc superconductors (pnictides). The pnictides belong to a completely different class of materials from the cuprates. This encourages effort to search for new high-Tc superconductors in classes of materials for which superconductivity is unexpected to occur from conventional view. To our regret, Tc of pnictides has also stopped rising soon after the discovery. At the moment, most realistic route to higher Tc is to enhance Tc of the cuprates.
The cuprates continue to be an only material class with Tc exceeding the liquid N2 temperature, and it is widely anticipated that there is a room for enhancing Tc. In this talk, I will show our efforts of enhancing Tc of the known cuprate materials by reducing disorder outside the CuO planes or ordering dopant atoms, and by pursuing the mechanism of Tc enhancement in multilayered cuprates. The first way has led to an appreciable Tc enhancement in two classes of cuprates, the Bi-based bilayer cuprate (Bi2212) and the oxygen-deficient Sr2CuO4. Tc’s of both compounds were enhanced to 98 K. For the second, we found that the interplane coupling strength within a multilayer is a key ingredient for the Tc enhancement, and predict that Tc would go up to 180 K or higher if the intra-multilayer coupling strength could be optimized.