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 ${\mathrm{Sr}}_{n+1}{\mathrm{Cr}}_n{\mathrm{O}}_{3n+1}$ 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 $\infty$. As a result, the insulating antiferromagnetic behavior observed for $n=1,2,3$ transforms into itinerant antiferromagnetism with reduced transition temperature for the $n=\infty$ end member of the series, i.e., the perovskite ${\mathrm{SrCrO}}_3$. 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 ${\mathrm{SrCrO}}_3$ 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 ${\mathrm{Sr}}_2{\mathrm{CrO}}_4$ to a metallic state in the end member ${\mathrm{SrCrO}}_3$. X-ray absorption spectroscopy measurements demonstrate a varying hybridization strength of the ${\mathrm{Cr}}^{4+}$ 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.

Close

PrevNext

View figure in article

• Electronic structure
• Perovskites
• Ruddlesden-Popper compounds
• Thin films
• Electron microscopy
• Molecular beam epitaxy
• X-ray absorption spectroscopy
• X-ray diffraction