Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni$^{2+}$ ions
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arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866914034980225024 |
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| author | Chaloupka, Jiří Khaliullin, Giniyat |
| author_facet | Chaloupka, Jiří Khaliullin, Giniyat |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_16362 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni$^{2+}$ ions Chaloupka, Jiří Khaliullin, Giniyat Strongly Correlated Electrons 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. |
| title | Superconductivity in the spin-state crossover materials: Nickelates with planar-coordinated low-spin Ni$^{2+}$ ions |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2506.16362 |