Orbital-selective mixed-valent Mott/metal phase coexistence in NdNiO2 films

Abstract

A plethora of fundamentally different electronic states can coexist in orbital-selective systems, including Mott-localized, pseudogapped, Fermi, and non-Fermi-liquid phases. Understanding their emergence as a result of electronic correlations remains a fundamental challenge in condensed matter theory. Superconductivity in infinite-layer nickelates is driven by a subtle balance between valence charge and crystal structures, two aspects that are strongly affected by synthetic protocols. Here, using density functional plus dynamical mean-field theory, we explore correlation and hole-doping-induced electronic reconstruction in the ${\mathrm{NdNiO}}_{2}$ superconductor. Based on a direct comparison with extant RIXS data, we show that the electronic spectra of ${\mathrm{NdNiO}}_{2}$ films can be understood as mixed valence due to static modulation of $3{d}^{9}/3{d}^{8}$ Mott/metal states. The coexistence of Mott-localized $3{d}^{9}$ and partially restored Fermi-liquid $3{d}^{8}$ low-energy excitations results in a two-fluid system exhibiting different coupling parameters, a novel scenario in infinite-layer nickelate superconductors. We expect that our present results are also applicable to access novel phases of matter in other quantum systems, in which structural domains can host different doping levels.