DOUBLE DEGENERACY AND JAHN-TELLER EFFECTS IN COLOSSAL-MAGNETORESISTANCE PEROVSKITES

Jahn-Teller (JT) electron-phonon-coupling effects in the colossal-magn etoresistance perovskite compounds La(1-x)A(x)MnO(3) are investigated. Electron-electron correlations between two degenerate Mn e(g) orbital s are studied in the Gutzwiller approximation. The static JT distortio n and nonadiabatic polaron effects are studied in a modified Lang-Firs ov approximation. We find that (i) the electron or hole character of t he charge carrier depends on the static JT distortion and (ii) due to the two-component nature of the JT coupling, fluctuations in the JT di stortion direction contribute to the charge transport in similar fashi on as the local spins.