Dilution effects on orbital order in strongly correlated electron systems

Dilution effects in orbital ordered systems with strong electron correlation are studied theoretically. Vacancy-concentration x dependence of the orbital-ordering temperature TOO calculated in the two-representative orbital models, i.e. the eg-orbital model in a three dimensional square lattice and the two-dimensional orbital compass model. Reduction of TOO as a function of x is stronger than that in dilute magnets and is not explained by the simple percolation theory. This phenomenon is attributed to the directional interaction between orbitals. It is shown that due to the quantum effects, the effective dimensionality in the system is increased and the orbital order becomes robust against dilution. The present calculation provides a new aspect of the dilute ordered state in strongly correlated electron systems.