Spin resonance peak in Na x CoO 2 ⋅y H 2 O superconductors: A probe of the pairing symmetry
Abstract
Motivated by the recent discovery of superconductivity in layered Na
x
CoO
2
⋅y
H
2
O compound, we investigate theoretically the spin dynamics in the superconducting state with three possible
p
x
+i
p
y
-,
d+i
d
′
-, 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
χ
for the spin-singlet
d+i
d
′
-wave pairing, while only in the out-of-plane(in-plane) component of
χ
for the spin-triplet
p
x
+i
p
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.