Observation of two-dimensional high-T_c superconductivity in a Ca₂RuO₄ nanofilm single crystal

We report two-dimensional superconductivity from high-temperature in a Ca₂RuO₄ nano film single crystal. A thin film of Ca₂RuO₄ exhibits typical BKT transition behaviour around T_BKT = 30 K. We also found that the bias current applied to the thin film causes a SI transition at low temperatures. The film is superconductive for small bias currents and insulating for large bias currents. The two phases are well separated by the critical sheet resistance of the thin film 16.5 kΩ ≈ (8/π) h/4e². In addition to these findings, our results suggest the presence of superconducting fluctuations at a high temperature. The fabrication of nanofilms made of layered material enables us to discuss rich superconducting phenomena in ruthenates.