Orbital Order and Superconductivity in Bilayer Nickelate Compounds
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| Format: | Preprint |
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2025
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| author | Khaliullin, Giniyat Chaloupka, Jiří |
| author_facet | Khaliullin, Giniyat Chaloupka, Jiří |
| contents | We propose a theory for bilayer nickelate materials, where a large tetragonal field - intrinsic or induced by epitaxial strain - lifts the orbital degeneracy and localizes the $3z^2-r^2$ orbital states. These states host local spins $S=1/2$ bound into singlets by strong interlayer coupling, and their dynamics is described by weakly dispersive singlet-triplet excitations ("triplons"). The charge carriers occupy the wide bands of $x^2-y^2$ symmetry, and their Cooper pairing is mediated by the high-energy triplon excitations. As the $x^2-y^2$ band filling increases, i.e., moving further away from the Ni$^{3+}$ valence state, the indirect Ruderman-Kittel-Kasuya-Yosida interactions between local spins induce spin-density-wave order via triplon condensation. Implications of the model for compressively strained La$_3$Ni$_2$O$_7$ films and electron doped oxychloride Sr$_3$Ni$_2$O$_5$Cl$_2$ are discussed. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_16360 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Orbital Order and Superconductivity in Bilayer Nickelate Compounds Khaliullin, Giniyat Chaloupka, Jiří Strongly Correlated Electrons We propose a theory for bilayer nickelate materials, where a large tetragonal field - intrinsic or induced by epitaxial strain - lifts the orbital degeneracy and localizes the $3z^2-r^2$ orbital states. These states host local spins $S=1/2$ bound into singlets by strong interlayer coupling, and their dynamics is described by weakly dispersive singlet-triplet excitations ("triplons"). The charge carriers occupy the wide bands of $x^2-y^2$ symmetry, and their Cooper pairing is mediated by the high-energy triplon excitations. As the $x^2-y^2$ band filling increases, i.e., moving further away from the Ni$^{3+}$ valence state, the indirect Ruderman-Kittel-Kasuya-Yosida interactions between local spins induce spin-density-wave order via triplon condensation. Implications of the model for compressively strained La$_3$Ni$_2$O$_7$ films and electron doped oxychloride Sr$_3$Ni$_2$O$_5$Cl$_2$ are discussed. |
| title | Orbital Order and Superconductivity in Bilayer Nickelate Compounds |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2506.16360 |