Controlling dual Mott states by hydrogen doping to perovskite rare-earth nickelates

Doping hydrogen in correlated oxides is a promising way to control the materials functionalities. With in situ measurements of the resistance and hydrogen concentration by a nuclear reaction analysis, we have derived the detailed relation between the resistance and hydrogen concentration (x) for RNiO3Hx (R = Sm, Nd, and La), which reveal a clear resistance jump at a certain concentration. Taking account of the spatial distribution of hydrogen in both in-plane and depth directions, we have clarified that an insulating state is realized at x = 0.5 and another insulating state is formed at x = 1. The electronic mechanisms for the two states are proposed in terms of Mott phases.