Ultrathin epitaxial MgB₂superconducting films with high critical current density andTcabove 33 K

High quality ultrathin MgB 2 superconducting films with thickness down to 7.5 nm have been synthesized via hybrid physical–chemical vapor deposition. The films are phase-pure and oxygen-free. The 7.5 nm thin film shows a T c (0) of 32.8 K and residual resistivity of 120 µΩ cm, and the 10 nm thin film shows a T c (0) of 35.5 K and high critical current density J c ∼10 6 A cm −2 at 20 K.