Crossover from Large to Small Polarons across the Metal-Insulator Transition in Manganites

This is the authors' abstract. We don't add key points for this paper.

We report Mn K-edge extended x-ray absorption fine structure spectra on La0.75Ca0.25MnO₃ up to high momentum transfer across the metal-insulator (M-I) transition. The data show compelling evidence for (i) large or intermediate Jahn-Teller polarons (IJTP), characterized by an anomalous longer Mn-O bond (ΔR0ex0ex=0ex0ex0.09) in the metallic phase (T<170K), and (ii) appearance of small JT polarons (SJTP) at T>170K, characterized by a longer Mn-O bond (ΔR0ex0ex=0ex0ex0.21), which coexist with the IJTP above the M-I transition and has equal probability in the temperature range of colossal magnetoresistance.