Effects of dimensionality on the electronic structure of Ruddlesden-Popper chromates Srn+1Crn O3n+1

Transition-metal oxides host a wide variety of electronic phenomena that can be significantly influenced by the effective dimensionality of the system under consideration. These include charge, spin, and orbital orderings, as well as unconventional superconductivity. In this context, the Ruddlesden-Popper chromates Srn+1CrnO3n+1 emerge as a particularly intriguing series of materials. Formally, the chromium atom displays a rather special 4+ oxidation state throughout the entire series. However, the effective dimensionality changes from quasi-2D to 3D as n increases from 1 to ∞. As a result, the insulating antiferromagnetic behavior observed for n=1,2,3 transforms into itinerant antiferromagnetism with reduced transition temperature for the n=∞ end member of the series, i.e., the perovskite SrCrO3. Further, distinct orbital orderings with exotic singlet states have been predicted for these systems. However, the lack of single-crystal bulk or thin-film samples has made experimental progress difficult. Here we demonstrate the synthesis of thin films of the perovskite SrCrO3 and the associated layered chromates via oxide molecular beam epitaxy for n=1 to n=5. Our electrical transport measurements reveal a gradual evolution from a strongly insulating state in Sr2CrO4 to a metallic state in the end member SrCrO3. X-ray absorption spectroscopy measurements demonstrate a varying hybridization strength of the Cr4+ valence electrons across the series, helping to explain the trend in conduction. Density functional theory calculations further confirm the observed transport trend and identify additional distortions present in the system.