Ordering Phenomena in Transition Metal Oxides

Frustration of orbital ordering   

The relative importance of electron-lattice and exchange interactions for orbital ordering is for many Jahn-Teller materials a controversial issue. The interplay between these interactions is further complicated by frustration of the orbital exchange. This generic frustration results from the strong anisotropy of orbital interactions and occurs for many types of crystal lattice and orbital degeneracy. At low temperatures it gives rise to the Peierls-like instability towards lattice distortions that stabilize an orbitally ordered state. I will discuss orbital ordering in cubic perovskites, spinels, and layered materials resulting from the frustration-induced lattice instability.