  We studied the charge-orbital ordering in the superlattice of charge-ordered
insulating Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ and ferromagnetic metallic
La$_{0.5}$Sr$_{0.5}$MnO$_3$ by resonant soft x-ray diffraction. A
temperature-dependent incommensurability is found in the orbital order. In
addition, a large hysteresis is observed that is caused by phase competition
between insulating charge ordered and metallic ferromagnetic states. No
magnetic phase transitions are observed in contrast to bulk, confirming the
unique character of the superlattice. The deviation from the commensurate
orbital order can be directly related to the decrease of ordered-layer
thickness that leads to a decoupling of the orbital-ordered planes along the c
axis.
