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⁺ (3d⁹) (cuprate) and Fe²⁺ (3d⁶) (pnictide) compounds. Particularly, Ti³⁺-based compounds or electron systems with a special 3d¹ filling are thought to be promising candidates as high-T_C 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 3d¹ 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 3d¹ 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.