Superconducting pairing symmetry in bilayer La₃Ni₂O₇ under pressure: the role of interlayer interactions.

The recent discovery [1,2] of high-temperature superconductivity in the nickelate compound La₃Ni₂O₇ at high pressure has spurred considerable research on this class of materials [3]. Despite a significant body of theoretical work on the subject, some questions remain regarding the pairing symmetry, with both s^± and d_xy pairing symmetries being proposed. In this work, we explore the role of interlayer interactions, which have been largely neglected in theoretical studies to date. Starting from a minimal bilayer two-orbital tight-binding model [4] that captures the main features of the band structure, including the α , β, and γ pockets in the Fermi surface, we calculate the pairing vertex using the matrix random-phase approximation (mRPA) [5], considering both intralayer [6] and interlayer Coulomb interactions. Our mRPA results show that interlayer interactions enhance the interorbital contribution to the pairing vertex. More importantly, for a given value of the onsite interaction, increasing the interlayer interaction strength tends to favor d_xy -wave pairing over s^± -wave pairing. Additionally, our findings indicate that contributions from all three Fermi surface pockets play a role in stabilizing the d_xy -wave pairing, highlighting the importance of both d_x²-y² and d_3z²-r² orbitals for the superconducting pairing in this system.

[1] H. Sun et al., Nature 621, 493 (2023).

[2] G. Wang et al. Phys. Rev. X 14, 011040 (2024).

[3] See also the review by Meng Wang et al. arXiv:2406.04837 (2024).

[4] Y.-B. Liu, et al. , Phys. Rev. Lett. 131, 236002 (2023).

[5] S. Graser, T. A. Maier, P. J. Hirschfeld, and D. J. Scalapino, New J. Phys. 11, 025016 (2009).

[6]Y. Zhang, L.-F. Lin, A. Moreo, T. A. Maier, and E. Dagotto, Nat. Comm. 15, 2470 (2024).