Abstract
The recent discovery of superconductivity in bilayer (327-LNO) under pressure stimulated much interest in layered nickelates. However, superconductivity was not found in another bilayer nickelate system, (326-LNO), even under pressure. To understand the similarities and differences between 326-LNO and 327-LNO, using density functional theory and the random phase approximation (RPA), we systematically investigate 326-LNO under pressure. The large crystal-field splitting between the orbitals caused by the missing apical oxygen moves the orbital farther away from the Fermi level, implying that the orbital plays a less important role in 326-LNO than in 327-LNO. This also results in a smaller bandwidth for the orbital and a reduced energy gap for the bonding-antibonding splitting of the orbital in 326-LNO, as compared to 327-LNO. Moreover, the in-plane hybridization between the and orbitals is found to be small in 326-LNO, while it is much stronger in 327-LNO. Furthermore, the low-spin ferromagnetic state is found to be the likely ground state in 326-LNO under high pressure. The weak interlayer coupling suggests that -wave pairing is unlikely in 326-LNO. The robust in-plane ferromagnetic coupling also suggests that -wave superconductivity, which is usually caused by antiferromagnetic fluctuations of the orbital, is also unlikely in 326-LNO. These conclusions are supported by our many-body RPA calculations of the pairing behavior. In addition, for the bilayer cuprate , we find a strong self-doping effect of the orbital under pressure, with the charge of Cu being reduced by approximately 0.13 electrons from 0 GPa to 25 GPa. In contrast, we do not observe such a change in the electronic density in 326-LNO under pressure, establishing another important difference between the nickelates and the cuprates.
1 More- Received 26 October 2023
- Revised 9 January 2024
- Accepted 11 January 2024
DOI:https://doi.org/10.1103/PhysRevB.109.045151
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