Orbital correlations and dimensional crossover in epitaxial Pr0.5Ca0.5MnO3/La0.5Sr0.5MnO3 superlattices.

We studied the charge-orbital ordering in the superlattice of charge-ordered insulating Pr_0.5Ca_0.5MnO₃ and ferromagnetic metallic La_0.5Sr_0.5MnO₃ by resonant soft x-ray diffraction (RSXD) and hard x-ray photoemission spectroscopy (HXPES). A temperature-dependent incommensurability is found in the orbital ordering by RSXD. In addition, a large hysteresis is observed that is caused by phase competition between the insulating charge ordered and metallic ferromagnetic states. No magnetic phase transitions are observed in contrast to pure Pr_0.5Ca_0.5MnO₃ thin films, confirming the unique character of the superlattice. Mn HXPES spectra revealed a hysteresis in the metalicity, supporting the picture of phase competition. The deviation from the commensurate orbital order can be directly related to the decrease of ordered-layer thickness that leads to dimensional crossover from three-dimensional to two-dimensional orbital ordering. [ABSTRACT FROM AUTHOR]