Superconductivity in diamond thin films well above liquid helium temperature

We report unambiguous evidence for superconductivity in a heavily boron-doped diamond thin film grown by microwave plasma-assisted chemical vapor deposition (MPCVD). An advantage of the MPCVD-deposited diamond is that it can contain boron at high concentration, especially in (111)-oriented films. Superconducting transition temperatures are determined by transport measurements to be 7.4 K for TC onset and 4.2 K for zero resistance. The upper critical field is estimated to be 7 T. Magnetization as a function of magnetic fields shows typical type-II superconducting properties.