PT-195 AND B-11 NMR-STUDIES OF LAPT2B2C AND YNI2B2C

Pt-195 and B-11 have been investigated by NMR in the normal state of t he quaternary superconductors, LaPt2B2C (T-c = 12 K) and YNi2B2C (T-c = 16 K) between 4 and 400 K. The B-11 Knight shift and 1/T1T increase with decreasing temperature in YNi2B2C. In contrast, T1T and the Knigh t shift of Pt-195 in LaPt2B2C are almost temperature independent. The value of 1/T1T of Pt-195 in LaPt2B2C is 6 times smaller than that of m etal Pt, indicating that the density of states of 5d conduction electr ons at the Pt site is small and that there is no evidence of dominant antiferromagnetic correlations. The NMR results are considered to be c onsistent with band structure calculations, and suggest a conventional superconductivity mediated by electron-phonon interactions in the qua ternary borocarbides.