High spin, low spin or gapped spins: magnetism in the bilayer nickelates
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| Main Authors: | , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866908810629611520 |
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| author | Oh, Hanbit Wu, Yi-Ming May-Mann, Julian Yu, Yijun Hwang, Harold Y. Zhang, Ya-Hui Raghu, S. |
| author_facet | Oh, Hanbit Wu, Yi-Ming May-Mann, Julian Yu, Yijun Hwang, Harold Y. Zhang, Ya-Hui Raghu, S. |
| contents | Inspired by the recent discovery of high-temperature superconductivity in bilayer nickelates, we investigate the role of magnetism emerging from a hypothetical insulating $d^8$ parent state. We demonstrate that due to the interplay of superexchange and Hund's coupling, the system can be in a high-spin, low-spin or spin-gapped state. The low-spin state has singlets across the bilayer in the $d_{z^2}$ orbital, with charge carriers in the $d_{x^2-y^2}$ orbital. Thus, at low energy scales, it behaves as an effective one band system when hole doped. By contrast, the high-spin state is a more robust, spin-1 antiferromagnet. Using Hartree-Fock methods, we find that for fixed interaction strength and doping, high-spin magnetism remains more robust than the low-spin counterpart. Whether this implies that the high spin state provides a stronger pairing glue, or more strongly competes with superconductivity remains an open question. Our analysis therefore underscores the importance of identifying the spin state for understanding superconductivity in nickelates. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_18973 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | High spin, low spin or gapped spins: magnetism in the bilayer nickelates Oh, Hanbit Wu, Yi-Ming May-Mann, Julian Yu, Yijun Hwang, Harold Y. Zhang, Ya-Hui Raghu, S. Strongly Correlated Electrons Superconductivity Inspired by the recent discovery of high-temperature superconductivity in bilayer nickelates, we investigate the role of magnetism emerging from a hypothetical insulating $d^8$ parent state. We demonstrate that due to the interplay of superexchange and Hund's coupling, the system can be in a high-spin, low-spin or spin-gapped state. The low-spin state has singlets across the bilayer in the $d_{z^2}$ orbital, with charge carriers in the $d_{x^2-y^2}$ orbital. Thus, at low energy scales, it behaves as an effective one band system when hole doped. By contrast, the high-spin state is a more robust, spin-1 antiferromagnet. Using Hartree-Fock methods, we find that for fixed interaction strength and doping, high-spin magnetism remains more robust than the low-spin counterpart. Whether this implies that the high spin state provides a stronger pairing glue, or more strongly competes with superconductivity remains an open question. Our analysis therefore underscores the importance of identifying the spin state for understanding superconductivity in nickelates. |
| title | High spin, low spin or gapped spins: magnetism in the bilayer nickelates |
| topic | Strongly Correlated Electrons Superconductivity |
| url | https://arxiv.org/abs/2506.18973 |