Superconducting Phase of TixOy Thin Films Grown by Molecular Beam Epitaxy
Abstract
We investigate the complex relationship between the growth conditions and the structural and transport properties of TixOy 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, POx, for films grown on (0001)-Al2 O3 substrates at 850 C. A cubic c-TiO1δ buffer layer is formed for low O/Ti ratios while a corundum cr-Ti2 O3 layer is formed under higher oxidizing conditions. Metallicity is observed for c-TiO1-δ buffer layers. The superconducting γ-Ti3 O5 Magn\'eli phase is found to nucleate on a c-TiO1-δ buffer for intermediate POx conditions and an insulator-superconducting transition is observed at 4.5 K (TConset=6 K) for 85 nm thick films. Strain relaxation of the γ-Ti3 O5 occurs with increasing film thickness and correlates with a thickness-dependent increase in TC observed for TixOy thin films.
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