A group of researchers at Stewart Blusson QMI at the University of British Columbia have successfully grown the parent compound of a high superconducting transition temperature material (perovskite bismuthate). Strontium bismuth oxide (SrBiO3) was grown in a thin film form on a strontium titanate substrate using molecular beam epitaxy (MBE). Experimental results were recently reported in Physical Review Materials.
The article provides general guidance on the MBE synthesis process, which involved two different growth methods: high-temperature co-depositon and a new "recrystallization” growth method. The “recrystallization” method is a recent development for synthesizing bismuth oxide that can produce thin films of a high quality. By improving the process for making high-quality thin films, researchers have opened the door to further experimentation using the material as an “ingredient” in quantum heterostructures – a “sandwich” of atomically-thin layers of substances exhibiting quantum effects. (The superconductivity observed in cuprates and nickel oxides is an example of a quantum effect seen at the macro scale.)
Above: A modelling of interfaces between the lanthanum lutetium oxide compound and the perovskite bismuthate thin film layers (in purple). The BiO6 octahedra highlighted in blue and red indicate regions in the "sandwich" where the electrons are expected to move to and fro respectively.
Previously published in Physical Review Materials from the article, "Epitaxial growth of perovskite SrBiO3 film on SrTiO3 by oxide molecular beam epitaxy". Graphic: K. Foyevtsova.
Theorists in George Sawatzky’s research group have predicted that strontium bismuth oxide can be stacked on a compound made from lanthanum lutetium oxides (LaLuO3). Such a heterostructure might result in interesting phenomena occurring at the interfaces between the sandwiched layers of compounds. For example, it is believed that on one side of the strontium bismuth oxide layer, a region with an enhanced concentration of free electrons would emerge while on the other side, a region with a depleted concentration of free electrons would appear. Researchers theorize that the polar nature of LaLuO3 will cause a movement of electrons from one region to the other in a process described as "electron hole doping."
While the heterostructure is a “sandwich” at the quantum scale, the research has implications for the study of superconductivity at the macro scale.
The complexity of the project involves a close collaboration between Kateryna Foyevtsova, a theorist from the George Sawatzky group who modelled the heterostructure, and Fengmiao Li, Bruce Davidson, Hyungki Shin, and Chong Liu, experimentalists working with the Ke Zou research group who specialize in crystal growth using MBE, along with additional support from Ilya Elfimov, DFTU manager at QMI. Experimentalists are now working on fabricating the heterostructure using MBE with the “recrystallization” method mentioned above.
F. Li, B.A. Davidson, R. Sutarto, H. Shin, C. Liu, I. Elfimov, K. Foyevtsova, F. He, G.A. Sawatzky, and K. Zou. Epitaxial growth of perovskite SrBiO3 film on SrTiO3 by oxide molecular beam epitaxy. Phys. Rev. Mat. 3, 100802(R) – Published 14 October 2019.