Strong influence of polaron-polaron interaction on the magnetoresistance effect in La_0.7A_0.3MnO₃ thin films

The colossal magnetoresistance effect endows La_0.7A_0.3MnO₃ manganites distinctive fascination. Both theoretical and experimental studies demonstrated that the interplay among polarons could significantly influence magnetoresistance. However, the underlying microscopic mechanism of the influence remains elusive due to the lack of experimental evidences. Utilizing ultrafast optical spectroscopy to track the polaron dynamics around Curie temperatures, we observed a diverse two-step recovery process in three sibling manganite thin films with various magnetoresistance effects and Curie temperatures, while the slow step was proposed to be the formation evolution of correlated polarons through the polaron-polaron interaction. Polarons in La_0.7Ca_0.3MnO₃ equilibrate much faster than those in La_0.7(Ca_0.58Sr_0.42)_0.3MnO₃ and La_0.7Sr_0.3MnO₃, indicating a comparatively tighter interaction between polarons and subsequently a stronger magnetoresistance effect.