Colossal magnetoresistancemanganites: A new approach

摘要

Manganites of the LA_(1-x)Ca_xMnO_3 family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degenerate e_g states at the Mn sites dynamically reorganize themselves into localised, JT polarons I with exponentially small inter-site hopping, and band-like, nonpolaronic states b, leading to a new 2-band model for manganites which includes strong Coulomb and Hund's couplings. We also discuss some results from a dynamical mean-field theory treatment of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and CMR,in terms of the influence of physical conditions on the relative energies and occupation of the I and b states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and spatial correlation is thekey to mangam'te physics.