Li Fengmiao, Zou Yuting, Han Myung-Geun, Foyevtsova Kateryna, Shin Hyungki, Lee Sangjae, Liu Chong, Shin Kidae, Albright Stephen D, Sutarto Ronny, He Feizhou, Davidson Bruce A, Walker Frederick J, Ahn Charles H, Zhu Yimei, Cheng Zhi Gang, Elfimov Ilya, Sawatzky George A, Zou Ke
Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Sci Adv. 2021 Jan 8;7(2). doi: 10.1126/sciadv.abd4248. Print 2021 Jan.
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 Ti 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）是岩盐结构的3d过渡金属单氧化物中的重要一员，但尚未对其化学计量比的单晶形式进行研究。由于钛具有高反应活性，制备化学计量比的TiO一直具有挑战性。我们采用晶格匹配度高的MgO(001)衬底，并报道了利用分子束外延法成功生长出单晶TiO(001)薄膜。这使得首次对化学计量比的TiO薄膜进行研究成为可能，结果表明TiO是金属，但接近莫特绝缘态。我们观察到在低于0.5 K时向超导相的转变，这与钛金属的转变温度相近。密度泛函理论（DFT）和基于DFT的紧束缚模型表明，TiO中直接的Ti-Ti键极为重要，这表明TiO和钛金属中存在类似的超导性。我们的工作引入了一个新概念，即TiO的行为与其金属对应物更为相似，这使其有别于其他3d过渡金属单氧化物。
