Ultrathin MgB₂films fabricated on Al₂O₃substrate by hybrid physical–chemical vapor deposition with high<i>T</i>_cand<i>J</i>_c

Abstract

Ultrathin MgB2 superconducting films with a thickness down to 7.5 nm are\nepitaxially grown on (0001) Al2O3 substrate by hybrid physical-chemical vapor\ndeposition method. The films are phase-pure, oxidation-free and continuous. The\n7.5 nm thin film shows a Tc(0) of 34 K, which is so far the highest Tc(0)\nreported in MgB2 with the same thickness. The critical current density of\nultrathin MgB2 films below 10 nm is demonstrated for the first time as Jc ~\n10^6 A cm^{-2} for the above 7.5 nm sample at 16 K. Our results reveal the\nexcellent superconducting properties of ultrathin MgB2 films with thicknesses\nbetween 7.5 and 40 nm on Al2O3 substrate.\n