Superconducting energy gap and antiferromagnetic spin fluctuations in the superconductor YNi 2 B 2 C: an NMR study

摘要: Pulsed NMR studies of $^{11}\mathrm{B}$ and $^{89}\mathrm{Y}$ have been carried out in the recently discovered quaternary borocarbide superconductor ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C (${\mathit{T}}_{\mathit{c}}$=15.5 K). These results are as follows: (a) Superconducting state: Though there is only one crystallographic B site this structure, we observed two resonances superconducting state. One signal comes from a region, other normal-metal region. As for former signal, nuclear relaxation rate, ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$ decreases drastically with further decrease temperature no appreciable enhancement just below ${\mathit{T}}_{\mathit{c}}$, it starts to saturate 6 K. (b) Normal (${\mathit{T}}_{1}$T${)}^{\mathrm{\ensuremath{-}}1}$ increases decreases. We interpret dependence arising due two-dimensional or three-dimensional antiferromagnetic spin fluctuations (structure tetragonal highly anisotropic).