Abstract
Superconductivity in Na$_x$CoO$_2$$\cdot$yH$_2$O is likely to be a p or
d-wave; however, experiments are unable to pinpoint the symmetry. A simple
estimate of pair breaking effects from an unavoidable `Na$^+$ vacancy disorder'
in an ordered Na$^+$ lattice, at an optimal $x_{\rm opt} \approx 0.30$ is shown
to destroy a Fermi liquid based p or d-wave superconductivity. However, a
robustness of superconducting and normal states, seen in experiments is pointed
out and argued to imply presence of a `quantum protectorate', possibly a
`spin-charge decoupling' that protects a d$_1$+id$_2$ and not a p-state. A
calculation of Knight shift and ${1\over T_1}$ in the framework of RVB mean
field theory and a fit to the data of Kobayashi ${\it et al.}$ [9] is made.
Citation
ID:
282318
Ref Key:
baskaran2003superconductivity