Titanium monoxide (TiO), an important member of the rock salt 3d transition-metal monoxides, has not been studied in the stoichiometric single-crystal form. It has been challenging to prepare stoichiometric TiO due to the highly reactive Ti²⁺. We adapt a closely lattice-matched MgO(001) substrate and report the successful growth of single-crystalline TiO(001) film using molecular beam epitaxy. This enables a first-time study of stoichiometric TiO thin films, showing that TiO is metal but in proximity to Mott insulating state. We observe a transition to the superconducting phase below 0.5 K close to that of Ti metal. Density functional theory (DFT) and a DFT-based tight-binding model demonstrate the extreme importance of direct Ti–Ti bonding in TiO, suggesting that similar superconductivity exists in TiO and Ti metal. Our work introduces the new concept that TiO behaves more similar to its metal counterpart, distinguishing it from other 3d transition-metal monoxides.

一氧化钛（TiO）是岩盐3d过渡金属一氧化碳的重要组成部分，尚未以化学计量单晶形式进行研究。由于高反应性Ti ²⁺，制备化学计量的TiO一直是一项挑战。。我们适应紧密晶格匹配的MgO（001）衬底，并报告使用分子束外延成功生长单晶TiO（001）薄膜。这使得首次对化学计量的TiO薄膜进行研究成为可能，表明TiO是金属，但接近Mott绝缘态。我们观察到，在接近钛金属的0.5 K以下，过渡到超导相。密度泛函理论（DFT）和基于DFT的紧密结合模型证明了TiO中Ti-Ti直接键合的极端重要性，这表明TiO和Ti金属中存在相似的超导性。我们的工作引入了新的概念，即TiO的行为与其金属同类物更为相似，从而将其与其他3d过渡金属一氧化碳区分开来。