Hole doping in a negative charge transfer insulator

RENiO3 is a negative charge transfer energy system and exhibits a temperature-driven metal-insulator transition (MIT), which is also accompanied by a bond disproportionation (BD) transition. In order to explore how hole doping affects the BD transition, we have investigated the electronic structure of single-crystalline thin films of Nd1-xCaxNiO3 by synchrotron based experiments and ab-initio calculations. Here we show that for a small value of x, the doped holes are localized on one or more Ni sites around the dopant Ca2+ ions, while the BD state for the rest of the lattice remains intact. The effective charge transfer energy (Delta) increases with Ca concentration and the formation of BD phase is not favored above a critical x, suppressing the insulating phase. Our present study firmly demonstrates that the appearance of BD mode is essential for the MIT of the RENiO3 series. The metal-insulator transition is well-known phenomenon in condensed-matter physics but the mechanisms driving the insulating state can vary from system to system and so understanding the underlying physics is complex. Here, the authors investigate electronic structure of single crystalline, Ca-doped NdNiO3 using synchrotron measurements and DFT calculations, illuminating the importance of bond disproportionation in the observed properties.

Automated summary

This study investigates the effect of Ca doping on the electronic structure of NdNiO3 thin films, highlighting the importance of bond disproportionation in the observed properties.