Observation of superconductivity in structure-selected Ti2O3 thin films

The search for new superconductors capable of carrying loss-free current has been a research theme in condensed matter physics for the past decade. Among superconducting compounds, titanates have not been pursued as much as Cu (3d) (cuprate) and Fe (3d) (pnictide) compounds. Particularly, Ti-based compounds or electron systems with a special 3d filling are thought to be promising candidates as high-T superconductors, but there has been no report on such pure Ti-based superconducting titanates. With the advent of thin-film growth technology, stabilizing new structural phases in single-crystalline thin films is a promising strategy to realize physical properties that are absent in the bulk counterparts. Herein, we report the discovery of unexpected superconductivity in orthorhombic-structured thin films of TiO, a 3d electron system, which is in strong contrast to the conventional semiconducting corundum-structured TiO. This is the first report of superconductivity in a titanate with a pure 3d electron configuration. Superconductivity at 8 K was observed in the orthorhombic TiO films. Leveraging the strong structure-property correlation in transition-metal oxides, our discovery introduces a previously unrecognized route for inducing emergent superconductivity in a newly stabilized polymorph phase in epitaxial thin films.