Direct Observation of High-Temperature Superconductivity in One-Unit-Cell FeSe Films

We prepared one-unit-cell (1-UC) thick FeSe films on insulating SrTiO3 substrates with non-superconducting FeTe protection layers by molecular beam epitaxy for ex situ studies. By direct transport and magnetic measurements, we provide definitive evidence for high temperature superconductivity in the 1-UC FeSe films with an onset T-C above 40K and an extremely large critical current density J(C) similar to 1.7x10(6) A/cm(2) at 2 K, which are much higher than T-C similar to 8K and J(C)similar to 10(4) A/cm(2) for bulk FeSe, respectively. Our work may pave the way to enhancing and tailoring superconductivity by interface engineering.