IR absorption of trapped and free Jahn-Teller polarons in 3D-crystals and films of LaMnO3 and La2/3Sr1/3MnO3

Abstract

The experimental and theoretical study of IR-absorption in LaMnO3 (LMO) single crystals has led to the observation of new five well-defined peaks. Their positions at RT are the following: 0.161 eV, 0.147 eV, 0.130 eV, 0.117 eV, and a much more broadened peak at similar to0.24 eV. The IR-absorption and its temperature and heat treatment dependence was studied with the help of a Fourier IR spectrometer Bruker IFS 120 HR. Analogous peaks of IR-absorption in LMO films are shifted to the lower energy side. The La-2/3 Sr-1/3 MnO3 film IR-absorption is characterized by additional broadening. The results were interpreted as direct detection of Jahn-Teller hole free polarons, as well as trapped hole and electronic polarons in LMO and related systems. Two type of Jahn-Teller hole states were used in this model. There were free Jahn-Teller hole polarons, and Jahn-Teller hole polarons within localized charge transfer vibronic excitons (Mn4+-Mn2+ pairs). IR-absorption peak induced by electronic polaron within such type exciton mentioned above was also interpreted.