Ordering Phenomena in Transition Metal Oxides

Charge Ordering as Alternative to Jahn-Teller Distortion   

Is the physics of the Mott-Hubbard transition in orbitally degenerate systems qualitatively different from the one-orbital case? We argue that for some realistic parameters the answer is affirmative: a new phenomenon emerges when U is smaller than t but not much smaller, namely spontaneous charge disproportionation. I will give two examples (experiment and first principles calculations) of how this scenario is realized in perovskites (YbNiO₃, LuNiO₃) and in triangular layered oxides (AgNiO₂).

References:

I. I. Mazin et al, Phys. Rev. Lett. 98, 176406 (2007);

E. Wawrzynska et al., Phys. Rev. Lett. 99, 157204 (2007).