Effects of phase fraction on superconductivity of low-valence eutectic titanate films

Abstract

Creation and characterization of mixed valence states in transition-metal oxides are a fundamental approach to search for the unprecedented electronic and magnetic properties. In contrast to complex oxides, mixed-valence simple oxides tend to form binary or ternary phases, and turning a valence from one to next must be accompanied by structural transformations owing to a lower tolerance for oxygen non-stoichiometry. In this paper, epitaxial growth and transport properties of low-valence titanate thin films are reported to shed light on recently discovered superconducting γ-phase Ti3O5 (γ-Ti3O5). Single-phase TiO and Ti2O3 films and eutectic films including TiO, Ti2O3, and γ-Ti3O5 phases were independently grown on α-Al2O3 (0001) substrates by using pulsed-laser deposition. The X-ray diffraction measurements revealed clear epitaxial relationships with substrates and among three eutectic phases. Temperature dependence of the resistivity revealed that the γ-Ti3O5-rich films exhibited superconductivity with a maximum of transition temperature (TC) of 6.3 K. Distinct effects of the phase fraction on TC are found between TiO- and Ti2O3-enriched samples, suggesting the complex mechanisms of the superconducting proximity effect.