Pressure effects on the superconducting thin film Ba1−xKxFe2As2

We report electrical resistivity measurements on a high-quality Ba1−xKxFe2As2 thin film (x = 0.4) under pressure. The superconducting transition temperature (=39.95 K) of the optimally doped thin film shows a dome shape with pressure, reaching a maximal value 40.8 K at 11.8 kbar. The unusually high superconducting transition temperature and its anomalous pressure dependence are ascribed to a lattice mismatch between the LaAlO3 substrate and the thin film. The local temperature exponent of the resistivity (n=dlnΔρ/dlnT) shows a funnel shape around the optimal pressure, suggesting that fluctuations associated with the anomalous normal state are responsible for high-temperature superconductivity.