Analysis of NMR data in the superconducting state of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

We have extended a weak-coupling theory of antiferromagnetic fluctuations to the superconducting state and analyzed NMR data for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. Within this framework we find that while an s-wave gap structure with 2Δ(0)/${\mathit{kT}}_{\mathit{c}}$=4 can fit the Knight-shift data for Cu(2) and O(2,3), it does not provide a satisfactory fit to the ${\mathit{T}}_1^{\mathrm{-}1}$ data. Using a ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$-wave gap with 2Δ(0)/${\mathit{kT}}_{\mathit{c}}$ of order 6 to 8 provides a reasonable fit to both the Knight-shift and ${\mathit{T}}_1^{\mathrm{-}1}$ data.