Spin resonance peak in Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O superconductors: A probe of the pairing symmetry

TL;DR

This paper theoretically studies spin resonance peaks in Na$_{x}$CoO$_{2}\\cdot y$H$_{2}$O superconductors to identify pairing symmetry via neutron scattering, analyzing different possible gap symmetries and their spin susceptibility signatures.

Contribution

It predicts distinct spin resonance signatures for different pairing symmetries, providing a method to determine the pairing symmetry experimentally.

Findings

Resonance peak appears in both in-plane and out-of-plane spin susceptibility for d+id'-wave.

Resonance peak appears only in out-of-plane component for p_x+ip_y-wave.

Resonance peak appears only in in-plane component for f-wave.

Abstract

Motivated by the recent discovery of superconductivity in layered Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O compound, we investigate theoretically the spin dynamics in the superconducting state with three possible $p_{x}+ip_{y}$-, $d+id'$-, and $f$-wave pairing symmetries in two-dimensional triangular lattices. We find that a spin resonance peak, which is elaborated to have a close relevance to the relative phase of the gap function and the geometry of the Fermi surface, appears in both in-plane and out-of-plane components of the spin susceptibility $\chi$ for the spin-singlet $d+id'$-wave pairing, while only in the out-of-plane(in-plane) component of $\chi$ for the spin-triplet $p_{x}+ip_{y}$-wave ($f$-wave) pairing. Because the pairing symmetry in this compound is still hotly debated at present, this distinct feature may be used to probe or determine it unambiguously with future neutron scattering experiments.