Quantum materials are the basis for many emerging quantum technologies, but the extent to which individual elements are understood depends on scientists’ ability to produce these materials in the laboratory and study them. 3D transition metal monoxides, a class of compounds, represent a well-studied family of quantum materials, and most are insulators; one exception is titanium monoxide (TiO) that had not been examined in its single-crystal state.
A collaboration between George Sawatzky’s and Ke Zou’s teams at the Stewart Blusson Quantum Matter Institute at UBC and teams at the Canadian Light Source (CLS) in Saskatchewan, with support from partners at Yale University, Brookhaven National Lab, and Chinese Academy of Science, has resulted in new clarity around the intrinsic properties of TiO. Published January 8 in Science Advances, these results resolve a lingering uncertainty around the behaviour of TiO, revealing that it behaves similarly to its metal counterpart, distinguishing it from other transition-metal monoxides.
“Prior to our work, it was not clear whether TiO is a metal or an insulator,” explained Fengmiao Li, a Research Associate who works closely with Sawatzky and Zou and first author on the paper. “We demonstrate with this new publication that TiO is both a metal and, below 0.5 degrees Kelvin, transitions to a superconducting state, similar to Ti in its metal state; it is the only superconductor in a family of compounds that are otherwise insulators at low temperatures.”
It has been difficult to develop a pure TiO crystalline sample for study; atomic titanium favors a bond with two oxygen atoms forming titanium dioxide (TiO2). Using a technique called molecular beam epitaxy, Li and colleagues were able to stabilize the compound and generate the cleanest TiO thin film to date.
“This recipe for growth was established at CLS, where they have the capacity to do the kind of in situ spectroscopy necessary to examine the cultivated films, guiding crystal growth in order to produce clean samples for research,” said Li.
Now that the team has a recipe for the thin film, they can grow pure crystals in the lab at the University of British Columbia, and work to further understand the material and its potential applications. It is important to note, however, that the formula could not have been developed without collaboration and support from the Resonant Elastic and Inelastic X-ray Scattering (REIXS) staff at the CLS, the beamline of which is also driven by Sawatzky as one of the beam team leaders.
The REIXS beamline at CLS was funded by the Canada Foundation for Innovation and commissioned in 2010. It opened for general users in July 2011, and since then has been important asset for SBQMI researchers, and the collaborative connections SBQMI researchers have at CLS are essential for this study.
Li, Fengmiao, Yuting Zou, Myung-Geun Han, Kateryna Foyevtsova, Hyungki Shin, Sangjae Lee, Chong Liu et al. "Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal." Science Advances 7, no. 2 (2021): eabd4248. DOI: 10.1126/sciadv.abd4248.
Story originally shared by the Stewart Blusson Quantum Matter Institute.