Theoretical perspective on superconductivity in the Ruddlesden-Popper bilayer nickelates
ORAL · Invited
Abstract
The recent discovery of superconductivity in the Ruddlesden-Popper bilayer nickelate La3Ni2O7 (Tc ~80 K) and the trilayer La4Ni3O10 (Tc ~20-30 K) under pressure opened the newest branch of high-Tc superconductivity. This presentation will focus on the theoretical study of the bilayer nickelates. Via Density Functional Theory (DFT) we found that the Fermi surface of La3Ni2O7 consists of two-electron sheets with mixed eg orbitals, and a hole pocket defined by the 3z2−r2 orbital, suggesting a Ni two-orbital minimum model [1], as opposed to the single active x2−y2 orbital in the cuprates. The role of the 3z2−r2 orbital in the bilayer is different than in the infinite layer nickelates [2], playing a crucial role due to its large interlayer electronic hopping [1, 3]. A first-order structural phase transition in La3Ni2O7 under pressure induces hole pockets around (π, π) at the Fermi surface [4]. A strong antiferromagnetic coupling along the z-axis and a strong competition between antiferromagnetic and ferromagnetic tendencies in the plane were observed using DFT as well as the random phase approximation (RPA) and Lanczos approaches [1, 4, 5]. Pairing is induced in the s±-wave channel due to nesting between the M= (π, π) centered pockets and portions of the Fermi surface centered at X= (π, 0) and Y= (0, π) points [4]. To explore whether the critical pressure to stabilize superconductivity in bilayer nickelates could be reduced, we replaced La with other rare-earth (RE) elements. Six candidates were found to become stable in the high-symmetry phase in the pressure range studied [5]. As in La3Ni2O7, the s±-wave pairing tendency dominates in all cases. Our results suggest that LNO is already the “optimal" candidate, with Ce a close competitor, among the whole RE bilayer nickelates [6]. The properties of the bilayer La3Ni2O7 will be here contrasted with the trilayer La4Ni3O10 [3]. Our studies also indicate that the absence of superconductivity in La3Ni2O6 is due to the lack of nesting and pockets around M = (π, π) [7].
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Publication: [1] Y. Zhang, L. F. Lin, A. Moreo, and E. Dagotto, PRB 108, L180510 (2023).<br>[2] Y. Zhang, L. F. Lin, A. Moreo, and E. Dagotto, PRB 102, 195117 (2020).<br>[3] Y. Zhang, L. F. Lin, A. Moreo, T. A. Maier, and E. Dagotto, PRL 133,136001 (2024).<br>[4] Y. Zhang, L. F. Lin, A. Moreo, T. A. Maier, and E. Dagotto, Nat. Comm. 15, 2470 (2024). <br>[5] L. F. Lin, Y. Zhang, N. Kaushal, G. Alvarez, T. A. Maier, A. Moreo, and E. Dagotto, arXiv: 2408.05689 (2024).<br>[6] Y. Zhang, L. F. Lin, A. Moreo, T. A. Maier, and E. Dagotto, PRB 108, 165141 (2023).<br>[7] Y. Zhang, L. F. Lin, A. Moreo, T. A. Maier, and E. Dagotto, PRB 109, 045151 (2024).
