Disentangled transitions in artificial rare-earth nickelates

The observation of simultaneous metal-insulator transition, charge ordering transition, and structural transition in rare-earth nickelates hinders our understanding of the underlying mechanism. We have devised a series of new superlattices by combining EuNiO₃ and LaNiO₃ to form ultrashort period superlattices, which allow one to disentangle the simultaneous orderings. Tailoring an incommensurate heterostructure period relative to the bulk charge ordering pattern suppresses the charge order transition while preserving metal-insulator and antiferromagnetic transitions. Such selective decoupling of the entangled phases resolves the long-standing puzzle about the driving force behind the metal-insulator transition and points to the site-selective Mott transition as the operative mechanism.