Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal
Fengmiao Li, Yuting Zou, Myung‐Geun Han, Kateryna Foyevtsova, Hyungki Shin, Sangjae Lee, Chong Liu, Kidae Shin, Stephen D. Albright, Ronny Sutarto, Feizhou He, B. A. Davidson, F. J. Walker, Charles Ahn, Yimei Zhu, Zhi Gang Cheng, Ilya Elfimov, G. A. Sawatzky, Ke Zou
Abstract
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.