Revealing the role of lattice distortions in the hydrogen-induced metal-insulator transition of SmNiO3

The discovery of hydrogen-induced electronic phase transitions in strongly correlated materials such as rare-earth nickelates has opened up a new paradigm in regulating materials’ properties for both fundamental study and technological applications. However, the microscopic understanding of how protons and electrons behave in the phase transition is lacking, mainly due to the difficulty in the characterization of the hydrogen doping level. Here, we demonstrate the quantification and trajectory of hydrogen in strain-regulated SmNiO 3 by using nuclear reaction analysis. Introducing 2.4% of elastic strain in SmNiO 3 reduces the incorporated hydrogen concentration from ~10 21 cm −3 to ~10 20 cm −3 . Unexpectedly, despite a lower hydrogen concentration, a more significant modification in resistivity is observed for tensile-strained SmNiO 3 , substantially different from the previous understanding. We argue that this transition is explained by an intermediate metastable state occurring in the transient diffusion process of hydrogen, despite the absence of hydrogen at the post-transition stage. Proton doping can induce metal-insulator transitions in rare-earth nickelates, demonstrating the complex interplay between dopants and electronic degrees of freedom. Chen et al. use results on strained films to argue that local proton-induced lattice distortions strongly influence the transition.