Inter-layer valence bonds and two-component theory for high-$T_c$ superconductivity of La${}_3$Ni${}_2$O${}_7$ under pressure

Abstract

The recent discovery of high-$T_c$ superconductivity in bilayer nickelate La${}_3$Ni${}_2$O${}_7$ under high pressure has stimulated great interest concerning its pairing mechanism. We argue that the weak coupling model from the almost fully-filled $d_{z^2}$ bonding band cannot give rise to its high $T_c$, and thus propose a strong coupling model based on local inter-layer spin singlets of Ni-$d_{z^2}$ electrons due to their strong on-site Coulomb repulsion. This leads to a minimal effective model that contains local pairing of $d_{z^2}$ electrons and a considerable hybridization with near quarter-filled itinerant $d_{x^2-y^2}$ electrons on nearest-neighbor sites. Their strong coupling provides a unique two-component scenario to achieve high-$T_c$ superconductivity. Our theory highlights the importance of the bilayer structure of superconducting La${}_3$Ni${}_2$O${}_7$ and points out a potential route for the exploration of more high-$T_c$ superconductors.

6 pages, 3 figures