Orbital Correlations in Monolayer Manganites | From Spin t¡J Model to Orbital t¡J Model

On the example of monolayer manganites we show that the theoretical ideas developed long ago along the derivation of the spin tiJ model from the Hubbard model are nowadays very helpful in strongly correlated oxides with partly fllled degenerate orbitals. We analyze a realistic orbital tiJ model for eg electrons in La1ixSr1+xMnO4 monolayer manganites, and discuss the evolution of spin and orbital correlations under increasing doping by performing exact diagonalization of flnite clusters, with electronic kinetic energy determined self-consistently at a flnite temperature by classical Monte Carlo for t2g spins. Several experimental results are reproduced.