  We have investigated the electronic structure of meta-stable perovskite
Ca1-xSrxIrO3 (x = 0, 0.5, and 1) thin films using transport measurements,
optical spectroscopy, and first-principles calculations. We artificially
fabricated the perovskite phase of Ca1-xSrxIrO3, which has a hexagonal or post
perovskite crystal structure in bulk form, by growing epitaxial thin films on
perovskite GdScO3 substrates using epi-stabilization technique. The transport
properties of the perovskite Ca1-xSrxIrO3 films systematically changed from
nearly insulating (or semi-metallic) for x = 0 to bad metallic for x = 1. Due
to the extended wavefunctions, 5d electrons are usually delocalized. However,
the strong spin-orbit coupling in Ca1-xSrxIrO3 results in the formation of
effective total angular momentum Jeff = 1/2 and 3/2 states, which puts
Ca1-xSrxIrO3 in the vicinity of a metal-insulator phase boundary. As a result,
the electrical properties of the Ca1-xSrxIrO3 films are found to be sensitive
to x and strain.
