Electronic structure modification of rare-earth nickelates by hole doping

RENiO3 is a negative charge transfer energy system which exhibits a temperature-driven metal-insulator transition (MIT), which is also accompanied by a bond disproportionation (BD) transition. The insulating phase is gradually suppressed with hole doping. We have investigated the underlying microscopic changes of the electronic structure parameters by employing several techniques on epitaxial thin films. We have found that the doped holes are localized on Ni around the dopant in the doping range where it is insulating. While, as expected the effective charge transfer energy increases with hole doping, our analysis suggests that it still remains negative and hence a BD is expected [1]. Above a critical concentration, the BD phase cannot be sustained and the sample becomes metallic. This study firmly demonstrates that the insulating state that emerges upon hole doping has polaronic distortions that localize the doped hole, while the BD state still exists.

 

[1]. B. Mandal et al., arXiv 1701.06819.