Discriminating Gap Symmetries of Superconducting La${}_3$Ni${}_2$O${}_7$

Abstract

The discovery of high-T${}_c$ superconductor in Ruddlesden-Popper nickelate materials represented by La${}_3$Ni${}_2$O${}_7$ has opened new directions in the quest for unconventional superconductivity. A central unresolved issue concerns the pairing symmetry of the superconducting order. In this paper, we model the superconducting order of La${}_3$Ni${}_2$O${}_7$ using the established Fermi surface structure together with phenomenological pairing functions belonging to $s_{\pm }$ and $d$-wave symmetry classes, which are the leading possibilities in the current debate. We compute several experimentally accessible observables-including tunneling density of states, point contact spectroscopy, superfluid density, and Raman spectroscopy-each of which exhibits distinct characteristics for different gap symmetries. These quantities provide a concrete and experimentally testable route for identifying the pairing symmetry of La${}_3$Ni${}_2$O${}_7$ and for clarifying the microscopic nature of nickelate superconductivity.

10+3 pages, 4 figures