Correlation-Driven Orbital-Selective Fermiology and Superconductivity in the Bilayer Nickelate La$_3$Ni$_2$O$_7$

TL;DR

This study uses advanced computational methods to show how electronic correlations reshape the Fermi surface and influence superconductivity in La$_3$Ni$_2$O$_7$, highlighting a shift in pairing mechanisms.

Contribution

It reveals a correlation-driven orbital reconstruction and a transition in pairing symmetry, challenging previous theoretical models and explaining experimental observations.

Findings

The $d_{z^2}$ spectral weight diminishes and sinks below the Fermi level.

Fermi arcs become dominated by the $d_{x^2-y^2}$ orbital at strong coupling.

Superconducting correlations shift from $d_{z^2}$- to $d_{x^2-y^2}$-dominated pairing.

Abstract

Recent angle-resolved photoemission measurements on La$_3$Ni$_2$O$_7$ have challenged the density-functional-theory-based picture of three Fermi surfaces by revealing that the $d_{z^2}$-derived $\gamma$ band can reside below the Fermi level. Motivated by this discrepancy, we investigate a realistic bilayer two-orbital Hubbard model using time-dependent variational principle (TDVP)-based cluster perturbation theory (CPT), alongside large-scale density matrix renormalization group (DMRG) calculations. Our TDVP-CPT calculations, performed on clusters of up to 16 physical sites, reveal that electronic correlations drive a pronounced orbital-selective reconstruction of the low-energy spectrum: the $d_{z^2}$ spectral weight is progressively depleted, the $\gamma$ band sinks below the Fermi level, and pseudogaps open on the remaining $\alpha$ and $\beta$ bands, leaving Fermi arcs dominated by the $d_{x^2-y^2}$ orbital at strong coupling. Furthermore, large-scale DMRG calculations demonstrate that the leading superconducting correlations evolve consistently with this Fermi surface reconstruction, transitioning from $d_{z^2}$-dominated to $d_{x^2-y^2}$-dominated interlayer spin-singlet pairing while retaining an $s_{\pm}$ structure. Consequently, our results indicate that the disappearance of the $\gamma$ pocket is not detrimental to superconductivity; rather, it signals a correlation-driven shift of the pairing channel mediated by interlayer antiferromagnetism, Hund's coupling, and inter-orbital hybridization.