A d8 anti-Hund's singlet insulator in an infinite-layer nickelate

The status of nickelate superconductors in relation to cuprate high temperature superconductors is one of the concepts being discussed in high temperature superconductivity in correlated transition metal oxides. New additions to the class of infinite layer nickelates can provide essential input relating to connections or distinctions. A recently synthesized compound Ba2NiO2(AgSe)(2), which contains isolated 'infinite layer' NiO2 planes, may lead to new insights. Our investigations have discovered that, at density functional theory mean field level, the ground state consists of an unusual e(g) singlet on the Ni2+ ion arising from large but separate Mott insulating gaps in both e(g) orbitals, but with different, anti-Hund's, spin directions of their moments. This textured singlet incorporates at the least new physics, and potentially a new platform for nickelate superconductivity, which might be of an unconventional form for transition metal oxides due to the unconventional undoped state. We include in this paper a comparison of electronic structure parameters of Ba2NiO(2)(AgSe)(2) with a better characterized infinite layer nickelate LaNiO2. We provide more analysis of the d(8) anti-Hund's singlet that emerges in this compound, and consider a minimally correlated wavefunction for this singlet in an itinerant background, and begin discussion of excitations-real or virtual-that may figure into new electronic phases.