Effects of dimensionality on the electronic structure of Ruddlesden-Popper chromates Srn+1CrnO3n+1

Oxide molecular beam epitaxy is a powerful synthesis technique capable of creating complex layered structures with elements in high oxidation states. The authros start with the Sr${}_{n+1}$Cr${}_{n}$O${}_{3n+1}$ Ruddlesden-Popper series. This system contains the magnetic Cr${}^{4+}$ cation which gives rise to electronic correlations that vary as a function of structural dimensionality: Sr${}_{2}$CrO${}_{4}$ and Sr${}_{3}$Cr${}_{2}$O${}_{7}$ possess enhanced spin and orbital ordering temperatures compared to the SrCrO${}_{3}$ end member. In this work, they synthesize films for $n=1$ to $n=5$, uncovering a metal to insulator transition. They seek the physical origins of the concomitant spin and orbital orderings -- both experimentally with x-ray absorption spectroscopy measurements, and theoretically with density functional theory calculations. Their results unveil the basis of these exotic ground states, including additional structural distortions that play a key role in the system and enable the metal-insulator transitions.