A new theory of doped manganites exhibiting colossal magnetoresistance

Abstract

Rare earth manganites doped with alkaline earths, namely $Re_1_-_xAxMnO_3$, exhibit colossal magnetoresistance, metal insulator transitions, competing magnetic, orbital and charge ordering, and many other interesting but poorly understood phenomena. In this article I outline our recent theory based on the idea that in the presence of strong Jahn-Teller, Coulomb and Hund's couplings present in these materials, the low-energy electronic states dynamically reorganize themselves into two sets: one set (l) which are polaronic, i.e., localized and accompanied by large local lattice distortion, and another (b) which are non-polaronic and band-like. The coexistence of the radically different l and b states, and the sensitive dependence of their relative energies and occupation upon doping x, temperature T, magnetic field H, etc., underlies the unique effects seen in manganites. I present results from strong correlation calculations using dynamical mean-field theory and simulations on a new 2-fluid model which accord with a variety of observations.