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; Bruce A Davidson; Frederick J Walker; Charles H Ahn; Yimei Zhu; Zhi Gang Cheng; Ilya Elfimov; George A Sawatzky; Ke Zou

doi:10.1126/sciadv.abd4248

Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal

Sci Adv. 2021 Jan 8;7(2):eabd4248. doi: 10.1126/sciadv.abd4248. Print 2021 Jan.

Authors

Fengmiao Li^{1

2}, Yuting Zou^{3

4}, Myung-Geun Han⁵, Kateryna Foyevtsova^{6

2}, Hyungki Shin^{6

2}, Sangjae Lee⁷, Chong Liu^{6

2}, Kidae Shin⁸, Stephen D Albright⁷, Ronny Sutarto⁹, Feizhou He⁹, Bruce A Davidson^{6

2}, Frederick J Walker⁸, Charles H Ahn^{7

8}, Yimei Zhu⁵, Zhi Gang Cheng^{3

4

10}, Ilya Elfimov^{6

2}, George A Sawatzky^{1

2}, Ke Zou^{1

2}

Affiliations

¹ Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada. fengmiao.li@qmi.ubc.ca sawatzky@physics.ubc.ca kzou@phas.ubc.ca.
² Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
³ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
⁴ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
⁵ Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
⁶ Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
⁷ Department of Physics, Yale University, New Haven, CT 06520, USA.
⁸ Department of Applied Physics, Yale University, New Haven, CT 06520, USA.
⁹ Canadian Light Source, Saskatoon, Saskatchewan S7N 2V3, Canada.
¹⁰ Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China.

Abstract

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.

Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).