Thickness-dependent transport in epitaxial CaIrO₃ perovskite thin films

The coexistence of strong electron–electron correlation and strong spin–orbit coupling makes CaIrO₃ a promising candidate for the exploration of emergent phenomena in thin film form. We have realized epitaxial CaIrO₃ films on (La_0.18Sr_0.82)(Al_0.59Ta_0.41)O₃ single crystal substrates with excellent crystallinity and thicknesses ranging from 3 to 32 nm. Electronic properties range from semiconducting to insulating behavior as a function of decreasing thickness and correlate with increased tetragonal distortion due to substrate-imposed strain. Hall effect measurements indicate that conduction is dominated by electron-type carriers at room temperature but crosses over to transport dominated by hole-like carriers at lower temperatures. Longitudinal magnetoresistance measurements reveal both a quadratic Lorentz dependence and an additional positive component in the field dependence that cannot be explained purely by semi-classical orbital magnetoresistance effects.