Crystal phase control in an YBiO3 thin film by using a BaBiO3 buffer layer

Topological insulators have a non-trivial band structure, forming gapless surface states when coupled to a normal insulator [1]. Until now, applications are hindered by the competition between the insulating bulk and conducting surface states. Perovskite oxides offer a good alternative, since topological insulating phases are theoretically predicted with band gaps larger than the thermal excitation energy at room temperature [2]. Therefore, promising applications for these materials lie in the elds of quantum computing and spintronics.

In YBiO3, a topological insulating phase is predicted for the perovskite crystal structure with yttrium and bismuth located at the A-site and B-site, respectively [3]. However, the fluorite phase is thermodynamically more stable than the perovskite phase as proven when an YBiO3 lm is grown directly on a SrTiO3 substrate. By using a buffer layer, a possibility is given to stabilise the perovskite phase in the YBiO3 film.

As buffer layer material BaBiO3 is chosen, since it grows in the perovskite phase and has a comparable lattice constant as predicted for the perovskite YBiO3 structure. By various characterisation techniques, it is shown that BaBiO3 grows as a single oriented perovskite lm in a relaxed state despite the large lattice mismatch with the underlying SrTiO3 substrate.

When the YBiO3 is deposited on top of the buer layer, a single oriented perovskite phase is also observed in this lm with the expected lattice constants. These ndings pave a way towards the fabrication of quantum devices for testing the hypothesised topological insulating phase in YBiO3.

[1] Y. Ando et al., Journal of the Physical Society Japan 82(10), 102001 (2013).
[2] Y. Zhang et al., Phys. Chem. Chem. Phys. 18(11), 8205-8211 (2016).
[3] H. Jin et al., Scientic Reports 3, 1651 (2013).