Orbital-selective Superconductivity in the Pressurized Bilayer Nickelate La$_3$Ni$_2$O$_7$: An Infinite Projected Entangled-Pair State Study

TL;DR

This study uses infinite projected entangled-pair states to investigate orbital-selective superconductivity in pressurized La$_3$Ni$_2$O$_7$, revealing distinct behaviors of $d_{x^2-y^2}$ and $d_{z^2}$ orbitals and suggesting pathways to higher $T_c$ superconductors.

Contribution

It introduces an orbitally selective iPEPS approach to analyze the bilayer $t$-$J$ model in La$_3$Ni$_2$O$_7$, uncovering the different roles of $e_g$ orbitals in superconductivity.

Findings

$d_{x^2-y^2}$ orbitals exhibit strong superconducting order driven by interlayer coupling.

$d_{z^2}$ orbitals show weaker superconductivity due to limited coherence and strong Pauli blocking.

Substituting rare-earth elements enhances superconducting order, indicating potential for higher $T_c$.

Abstract

The newly discovered high-$T_c$ nickelate superconductor La$_3$Ni$_2$O$_7$ has generated significant research interest. To uncover the pairing mechanism, it is essential to investigate the intriguing interplay between the two $e_g$, i.e., $d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Here we perform an infinite projected entangled-pair state (iPEPS) study of the bilayer $t$-$J$ model, directly in the thermodynamic limit and with orbitally selective parameters for $d_{x^2-y^2}$ and $d_{z^2}$ orbitals, respectively. The $d_{x^2-y^2}$ electrons exhibit significant intralayer hopping $t_\parallel$ and spin couplings $J_\parallel$, with interlayer $J_\perp$ passed from the $d_{z^2}$ electrons. However, the interlayer $t_\perp$ is negligible in this case. In contrast, the $d_{z^2}$ orbital demonstrates strong interlayer $t_\perp$ and $J_\perp$, while the inherent intralayer $t_\parallel$ and $J_\parallel$ are small. Based on the iPEPS results, we find clear orbital-selective behaviors in La$_3$Ni$_2$O$_7$. The $d_{x^2-y^2}$ orbitals exhibit robust superconductive (SC) order driven by the interlayer coupling $J_\perp$; while the $d_{z^2}$ band shows relatively weak SC order as a result of small $t_\parallel$ (lack of coherence) but large $t_\perp$ (strong Pauli blocking). Furthermore, by substituting rare-earth element Pm or Sm with La, we find an enhanced SC order, which opens up a promising avenue for discovering nickelate superconductors with even higher $T_c$.