Electronic Structure, Charge and Orbital order and Metal-insulator Transition in Nickelates

In the series RNiO3, all the members except LaNiO3 are insulators at T=0K while LaNiO3 is a strongly correlated metal. Rare earth Nickelates have a sharp transition from a high temperature paramagnetic metallic state to a low temperature antiferromagnetic insulator at finite temperature TMI, which increases systematically as the atomic number of the rare-earth ions increases. It can be tuned by external parameters like strain, hydrostatic pressure and electric field. The magnetic and resistive transitions are coupled for NdNiO3 and PrNiO3, but independent for the other members of the series. In the present paper we explain the difference in the observed ground states of RNiO3 (R=La, Nd, Pr) by calculating their band structure and possible orbital and charge order. We also discuss the effects of disorder thereof.