Orientation-controlled epitaxy of A₂CuO₃ (A: Sr, Ca) films with large optical nonlinearity

The one-dimensional Cu-O chains responsible for the large optical nonlinearity in Sr₂CuO₃ (SCO) and Ca₂CuO₃ (CCO) are aligned in one direction in films grown on LaSrAlO₄ (LSAO) (1 0 0) substrates by using pulsed laser deposition. The CCO films deposited directly on lattice matched LSAO substrates have a single orientation with high crystallinity, while the SCO films include small portions of misoriented domains. Using a simple model of lattice mismatch, we developed a Sr₂TiO₄ buffer layer in order to grow orientation-controlled SCO films with both high crystallinity and a sharp optical absorption edge. This technique will be a key to fabricating ultrafast all-optical switches with a waveguide structure.