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 Cu2+ (3d(9)) (cuprate) and Fe2+ (3d(6)) (pnictide) compounds. Particularly, Ti3+-based compounds or electron systems with a special 3d(1) filling are thought to be promising candidates as high-TC superconductors, but there has been no report on such pure Ti3+-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 Ti2O3, a 3d(1) electron system, which is in strong contrast to the conventional semiconducting corundum-structured Ti2O3. This is the first report of superconductivity in a titanate with a pure 3d(1) electron configuration. Superconductivity at 8 K was observed in the orthorhombic Ti2O3 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.