High-Tc superconductivity in ruthenates
Asst. Prof. Dr. Hiroyoshi Nobukane, Department of Physics, Hokkaido University, Sapporo, Japan
Layered perovskite materials can control quantum states from superconductivity to a Mott insulator by tuning physical and chemical pressure. By reducing the thickness of a layered crystal to nanometer range, a nanofilm due to a negative pressure effect leads to novel quantum states that have not been found yet in bulk crystals. We will discuss the emergence of high-Tc superconductivity near 100 K in Ca2RuO4 nanofilms. A thin film of Ca2RuO4 exhibits supercurrent and typical Berezinskii-Kosterlitz-Thouless transition behavior. We also found that the tuned film thickness and the induced bias current cause a superconductor-insulator transition. Our results demonstrate the presence of two-dimensional superconductivity from a high temperature. The fabrication of nanofilms made of layered material enables us to discuss rich superconducting phenomena in ruthenates.