Pairing symmetry and superconductivity in La$_3$Ni$_2$O$_7$ thin films

TL;DR

This study uses a renormalized mean-field theory to analyze superconductivity in La$_3$Ni$_2$O$_7$ thin films, revealing an $s_$-wave pairing symmetry driven by interlayer superexchange, consistent with experimental observations.

Contribution

It introduces a bilayer two-orbital $t-J$ model to explain the pairing symmetry and gap structure in La$_3$Ni$_2$O$_7$ thin films, providing theoretical insight into their superconductivity.

Findings

Reveals $s_$-wave pairing symmetry driven by interlayer superexchange.

Reproduces the nodeless superconducting gap observed experimentally.

Identifies inter-orbital $d$-wave pairing that enhances the dominant $s_$-wave pairing.

Abstract

The recent discovery of superconductivity with a transition temperature $T_c$ over 40 K in La$_3$Ni$_2$O$_7$ and (La,Pr)$_{3}$Ni$_2$O$_7$ thin films at ambient pressure marks an important step in the field of nickelate superconductors. Here, we perform a renormalized mean-field theory study of the superconductivity in $\mathrm{La_3Ni_2O_7}$ thin films, using a bilayer two-orbital $t-J$ model. Our result reveals an $s_\pm$-wave pairing symmetry driven by the strong interlayer superexchange coupling of $d_{z^2}$ orbital, resembling the pressurized bulk case. Also, we roughly reproduce the experimentally observed nodeless shape of the superconducting gap at the $\beta$ pocket and the superconducting $T_c$. In addition, by analysing the orbital-resolved pairing configurations and their projections onto Fermi surface, we find that the nodeless feature of $\beta$ pocket is related to the interlayer pairing within both $d_{z^2}$ and $d_{x^2-y^2}$ orbitals. Moreover, we identify a formation of the inplane inter-orbital $d$-wave pairing between $d_{z^2}$ and $d_{x^2-y^2}$ orbitals, which can even enhance the dominated interlayer $s_\pm$-wave.