Conductivity of Infinite-Layer Nickelate as a Probe of Spectator Bands

Throughout this thesis, we have systematically investigated the similarities and differences of the layered nickelates with each other, as well as the cuprates. While there are many similarities between the nickelates and the cuprates, a notable difference is the presence of rare-earth state near the Fermi level. As we have shown in Chaps. 3 – 5 , these \(R(5d)\) states are a tunable feature of the electronic structure with either the number of NiO \({ }_{2}\) layers (n) or the average d filling of the Ni sites. As the presence of the rare-earth states is strongest in the infinite-layer RNiO \({ }_2\) nickelates (see Fig. 5.2 ), understanding the role they play in the normal-state, undoped electronic structure of RNiO \({ }_2\) is an important question to be tackled. In this chapter, we use DFT+DMFT to compute the many-body electronic structure and optical conductivity of NdNiO \({ }_{2}\) under the influence of large scattering rates on the Nd(5d) bands and including dynamical interactions on the Nd(5d) orbitals with shifts of the Nd-Ni d-level energy difference. We find a robust conducting pathway in the out-of-plane direction arising from strong hybridization between the Ni- \(d_{z^2}\) and Nd(5d) orbitals. This pathway can be “short-circuited” if this hybridization is suppressed through large electronic scattering rates but is not reduced to zero even by very large beyond-DFT shifts of the Nd-Ni d-level energy splitting. The computed in-plane conductivity for NdNiO \({ }_{2}\) predicts the material to be a “good metal” in contrast to experiments indicating the material is a “bad metal” or “weak insulator”. Our results motivate future experiments measuring the c-axis resistivity as a proxy for the spectator bands and suggest the essential difference between the infinite-layer nickelates and the cuprates is the dimensionality of their electronic structures. This chapter is based on results published in Phys. Rev. B 107, 205155 (2023) .