Double degeneracy and Jahn-Teller effects in colossal-magnetoresistance perovskites

Jahn-Teller (JT) electron-phonon-coupling effects in the colossal-magnetoresistance perovskite compounds ${\mathrm{La}}_{1-x}{A}_x\mathrm{Mn}{\mathrm{O}}_3$ are investigated. Electron-electron correlations between two degenerate Mn $e_g$ orbitals are studied in the Gutzwiller approximation. The static JT distortion and nonadiabatic polaron effects are studied in a modified Lang-Firsov approximation. We find that (i) the electron or hole character of the charge carrier depends on the static JT distortion and (ii) due to the two-component nature of the JT coupling, fluctuations in the JT distortion direction contribute to the charge transport in similar fashion as the local spins.