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

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 $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ 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. Our study particularly highlights the diverse relations of different pairing channels in $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ that holds a complex Fermi surface.

9 pages, 6 figures