Superconductivity and magnetism in bilayer nickelates: itinerant perspective

TL;DR

This paper investigates superconductivity and magnetism in bilayer nickelates using an itinerant electron model, highlighting the influence of Hund's coupling on the emergence of different pairing symmetries and magnetic orders.

Contribution

It introduces a comprehensive itinerant model incorporating ARPES data and onsite interactions, revealing Hund's coupling as a key factor in the system's ground states.

Findings

Strong Hund's coupling favors s-wave superconductivity and SDW at (,)

Weaker Hund's coupling leads to d-wave pairing and SDW at (,)

Results align with previous DMRG studies, emphasizing Hund's role

Abstract

We study superconductivity and magnetism in bilayer nickelates from an itinerant perspective. Starting from a tight binding fit to recent ARPES measurements on compressively strained thin films, we incorporate the standard set of onsite repulsive interactions among partially filled $e_g$ orbitals: intra-orbital $U$, inter-orbital $U'$, Hund's coupling $J_H$ and a pair hopping $J_P$. We obtain the effective pairing interaction by dressing these bare interactions with particle-hole fluctuations via the RPA. In the strong Hund's coupling regime, we find that $s$-wave superconductivity and $(\pi/2, \pi/2)$ SDW order are the favored ground states. With weaker Hund's coupling, we find that $d$-wave pairing and $(\pi, \pi)$ SDW are the leading ground states. Our results are qualitatively consistent with earlier DMRG studies, and point to the key role played by Hund's coupling in determining the nature of superconductivity and magnetism in this system.