11B and 13C NMR studies of borocarbide superconductor YNi2B2C

We have carried out the measurements of the nuclear spin-lattice relaxation rate, (T1)−1, of 11B in YNi2B2C, Y(Ni0.8Co0.2)2B2C and Y(Ni0.7Co0.3)2B2C and of 13C in YNi2B2C in a wide temperature range. In the normal state, (T1T)−1 increases with decreasing temperature presumably due to the antiferromagnetic spin fluctuations. (T1)−1 in the superconducting state decreases rapidly with decreasing temperature with no Hebel–Slichter peak just below Tc. On further decreasing the temperature, (T1)−1 decreases linearly with temperature. Such behavior of (T1)−1 shows the possibility of unconventional superconductivity, such as d-wave superconductivity in high-Tc cuprates.