Many-Body Electronic Structure of NdNiO2 and CaCuO2

The demonstration of superconductivity in nickelate analogs of high T-c cuprates provides new perspectives on the physics of correlated electron materials. The degree to which the nickelate electronic structure is similar to that of cuprates is an important open question. This paper presents results of a comparative study of the many-body electronic structure and theoretical phase diagram of the isostructural materials CaCuO2 and NdNiO2. Both NdNiO2 and CaCuO2 are found to be charge transfer materials. Important differences include the proximity of the oxygen 2p bands to the Fermi level, the bandwidth of the transition metal-derived 3d bands, and the presence, in NdNiO2, of both Nd-derived 5d states crossing the Fermi level and a van Hove singularity that crosses the Fermi level as the out-of-plane momentum is varied. The low-energy physics of NdNiO2 is found to be that of a single Ni-derived correlated band, with additional accompanying weakly correlated bands of Nd-derived states that dope the Ni-derived band. The effective correlation strength of the Ni-derived d band crossing the Fermi level in NdNiO2 is found to be greater than that of the Cu-derived d band in CaCuO2, but the predicted magnetic transition temperature of NdNiO2 is substantially lower than that of CaCuO2 because of the smaller bandwidth.