Interplay between electronic and lattice superstructures in La_(2-x)Ca_(x)CuO₄

Complex oxides are well known to develop oxygen ordering patterns with well defined periodicities, but their interplay with electronic correlations remains largely unexplored. Here, we report resonant and non-resonant x-ray diffraction data indicating a four-unit-cell periodic superstructure related to oxygen vacancy ordering in La$_{2-x}$Ca$_{x}$CuO$_{4}$ films with doping levels from the underdoped ($x = 0.15$) to the extremely overdoped ($x = 0.50$) regime. Whereas the lattice superstructure is temperature independent up to 300 K, a strongly temperature dependent electronic charge density wave (CDW) is observed in the underdoped and slightly overdoped regimes ($x\leq0.20$). The periodicity, in-plane and out-of-plane correlation lengths of the CDW are locked in by the lattice superstructure. Our results highlight the necessity to consider lattice and electronic energetics on equal footing in the high-temperature oxygen-disordered phase to explain oxygen ordering phenomena in complex oxides.