Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni$^{2+}$ ions

Jiří Chaloupka; Giniyat Khaliullin

doi:10.1103/s5b6-crzc

paper

Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni $^{2 +}$ ions

arXiv:2506.16362 · doi:10.1103/s5b6-crzc

Abstract

We theoretically study quasi-two-dimensional nickel compounds, where the nickel ions assume Ni $^{2 +}$ $d^{8}$ valence state and feature a low-spin $S = 0$ ground state quasidegenerate with $S = 1$ ionic excitations. Such a level structure is supported by square-planar coordination of nickel ions or a suitable substitution of apical oxygens. We construct the corresponding singlet-triplet exchange model and explore its phase diagram and excitation spectrum. By hole doping, we further introduce mobile Ni $^{3 +}$ $d^{7}$ ionic configurations with effective spins $S = 1/2$ , and analyze their interactions with the $d^{8}$ singlet-triplet background. The interplay with the triplet excitations in the $d^{8}$ sector is found to have a deep impact on the propagation of the doped hole-like charge carriers and is identified as a powerful source of Cooper pairing among them.

13 pages, 6 figures, extended Conclusions section

Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni2+ ions

Abstract

References in corpus (19)

Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni $^{2 +}$ ions