Superconducting phase of TixOy thin films grown by molecular beam epitaxy

Here we investigate the complex relationship between the growth conditions and the structural and transport properties of Ti_xO_y thin films grown by molecular beam epitaxy. Transport properties ranging from metallicity to superconductivity and insulating states are stabilized by effectively tuning the O/Ti ratio via the Ti flux rate and the O partial pressure P_Ox for films grown on (0001)-Al₂O₃ substrates at 850° C. A cubic c-TiO_1±δ buffer layer is formed for low O/Ti ratios, while a corundum cr-Ti₂O₃ layer is formed under higher-oxidizing conditions. Metallicity is observed for c-TiO_1-δ buffer layers. The superconducting γ -Ti₃O₅ Magnéli phase is found to nucleate on a c-TiO_1-δ buffer for intermediate POx conditions, and an insulator-superconducting transition is observed at 4.5 K (T$^{onset}_{C}$ = 6K) for 85 nm thick films. Strain relaxation of γ -Ti₃O₅ occurs with increasing film thickness and correlates with a thickness-dependent increase in T_C observed for Ti_xO_y thin films.