Temperature dependent optical properties of LaCoO3/SrTiO3 thin film studied by spectroscopic ellipsometry

We report the spectroscopy ellipsometry study for LaCoO3 epitaxy thin films grown on different SrTiO3 substrates [LCO/STO(001) and LCO/STO(111)]. Reciprocal space mapping measurements show that the as-prepared LCO/STO films are fully strained at the interface. The optical constants (the refractive index and the extinction coefficient) of LCO films from 300 K to 800 K are obtained based on the ellipsometry measurements. The optical absorption at the near-infrared region increases with heating and sharply enhances around 500 K due to the occurrence of insulator–metal transition. The observed isosbestic point reveals the evolution of the band structure along with the insulator–metal transition. The red shift of the isosbestic point from the (001) sample to the (111) sample indicates the important role interfacial strain plays in affecting the spin states. We also provide the optical conductivity and the relative effective number of interband transition electrons for different energy regions.