Ultrathin MgB2 filmsfabricated on Al2O3 substrate by hybrid physical–chemical vapor deposition with highTc andJc

Abstract

Ultrathin MgB2 superconducting films with a thickness down to 7.5 nm are epitaxially grown on (0001)Al2O3 substrate by a hybrid physical–chemical vapor deposition method. The filmsare phase-pure, oxidation-free and continuous. The 7.5 nm thin film shows aTc(0) of 34 K, which isso far the highest Tc(0) reported in MgB2 with the same thickness. The critical current density of ultrathinMgB2 films below 10 nm is demonstrated for the first time asJc ∼ 106 A cm − 2 for theabove 7.5 nm sample at 16 K. Our results reveal the excellent superconducting properties of ultrathinMgB2 films with thicknesses between 7.5 and 40 nm onAl2O3 substrate.