Fermi liquid and isotropic superconductivity of Hund scenario for bilayer nickelates

TL;DR

This paper investigates whether Hund's coupling or hybridization primarily drives superconductivity in bilayer nickelates, finding that Hund's scenario alone cannot fully explain experimental observations.

Contribution

The study compares Hund's coupling and hybridization mechanisms using a dynamic Schwinger boson approach, highlighting key differences in their superconducting properties.

Findings

Hund-driven superconductivity exhibits isotropic s-wave gap

Hund scenario results in lower maximum T_c

Normal state remains Fermi liquid in Hund scenario

Abstract

Recent experiments on bulk and thin film bilayer nickelate high-$T_c$ superconductors urge for clarification of their pairing mechanism. Debates exist on whether the hybridization or the Hund's coupling between the nickel $d_{x^2-y^2}$ and $d_{z^2}$ orbitals plays a primary role in driving the superconductivity. Here, we study the Hund scenario and make comparisons with the hybridization scenario using the same dynamic Schwinger boson approach. Our calculations reveal several key features of the Hund-driven superconductivity, including an isotropic $s$-wave gap, a lower maximum $T_c$, and Fermi liquid normal states, that differ from the hybridization-driven mechanism. We attribute these differences to their distinct low-energy dynamics. Comparison with recent experiments suggests that the Hund scenario alone is not enough to explain the bilayer nickelate superconductivity in both bulk and thin films.