Understanding the electronic behavior of iridium-based perovskites

When cubic strontium iridium oxide is deposited onto a surface as a monolayer, it acts like layered strontium iridate, a bulk material that could allow researchers to probe new types of quantum behavior such as unconventional superconductivity. Researchers, however, have not yet understood why the iridium oxide demonstrates such interesting electronic properties.

In a recent paper, Schütz et al. found that the electronic properties of ultrathin, cubic strontium iridium oxide films are highly influenced by their surface termination – the chemical composition and structure of the films at the surface.

Normally, films with perovskite crystal structures – like the strontium iridium oxide in the study – are composed of two alternating layers with same structure and composition. The authors found that strontium iridium oxide exhibits an unexpected, specific termination at the topmost, surface level.

The main evidence for these findings comes from two techniques: reflection high-energy electron diffraction, which can indirectly show if there are structural differences between layers that make up a nanomaterial, and scanning transmission electron microscopy, which can directly image single atoms and thus the structure of a surface layer.

Using these methods, the authors showed that their thin film was terminated by a strontium oxide – not an iridium oxide atomic layer as might be expected from the material’s perovskite structure – which in turn enabled the material’s interesting properties. The authors partially attributed this conversion to their deposition method, pulsed laser deposition, which may have caused the thin film to absorb excess oxygen and expel iridium in the form of gaseous iridium oxides.

The authors plan to continue probing strontium iridium oxide thin films to further understand their electronic properties and potentially induce unconventional superconductivity.

Source: “Electronic structure of epitaxial perovskite films in the two-dimensional limit : Role of the surface termination,” by P. Schütz, M. Kamp, D. Di Sante, A. Lubk, B. Büchner, G. Sangiovanni, M. Sing, and R. Claessen, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0002985 .