Nickelate superconductors—a renaissance of the one-band Hubbard model

The recently discovered nickelate superconductors appear, at first glance, to be even more complicated multi-orbital systems than cuprates. To identify the simplest model describing the nickelates, we analyse the multi-orbital system and find that it is instead the nickelates which can be described by a one-band Hubbard model, albeit with an additional electron reservoir and only around the superconducting regime. Our calculations of the critical temperature T C are in good agreement with experiment, and show that optimal doping is slightly below 20% Sr-doping. Even more promising than 3 d nickelates are 4 d palladates.