The electronic structure of epitaxially stabilized 5d perovskite Ca_{1 − x}Sr_xIrO₃ (x = 0, 0.5, and 1) thin films: the role of strong spin–orbit coupling

We have investigated the electronic structure of meta-stable perovskite Ca_{1 − x}Sr_xIrO₃(x = 0, 0.5, and 1) thin films using transport measurements, optical spectroscopy, and first-principles calculations. We artificially fabricated the perovskite phase of Ca_{1 − x}Sr_xIrO₃, which has a hexagonal or post-perovskite crystal structure in bulk form, by growing epitaxial thin films on perovskite GdScO₃ substrates using an epi-stabilization technique. The transport properties of the perovskite Ca_{1 − x}Sr_xIrO₃ films systematically change from nearly insulating (or semi-metallic) for x = 0 to weakly metallic for x = 1. Due to the extended wavefunctions, 5d electrons are usually delocalized. However, the strong spin–orbit coupling in Ca_{1 − x}Sr_xIrO₃ results in the formation of effective total angular momentum J_eff = 1/2 and 3/2 states, which puts Ca_{1 − x}Sr_xIrO₃ in the vicinity of a metal–insulator phase boundary. As a result, the electrical properties of the Ca_{1 − x}Sr_xIrO₃ films are found to be sensitive to x and strain.