SUPERCONDUCTING ENERGY-GAP AND ANTIFERROMAGNETIC SPIN FLUCTUATIONS IN THE SUPERCONDUCTOR YNI2B2C - AN NMR-STUDY

Pulsed NMR studies of B11 and Y89 have been carried out in the recently discovered quaternary borocarbide superconductor YNi2B2C (Tc=15.5 K). These results are as follows: (a) Superconducting state: Though there is only one crystallographic B site in this structure, we have observed two B11 resonances in the superconducting state. One signal comes from a superconducting region, and the other from a normal-metal region. As for the former signal, the nuclear relaxation rate, T1-1 decreases drastically with further decrease of temperature with no appreciable enhancement just below Tc, and it starts to saturate below 6 K. (b) Normal state: (T1T)-1 increases as temperature decreases. We interpret this temperature dependence as arising due to two-dimensional or three-dimensional antiferromagnetic spin fluctuations (structure of YNi2B2C is tetragonal and highly anisotropic). © 1995 The American Physical Society.