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The mixed state of the weakly disordered superconductor YNi 2 B 2 C is found to be similar to that of high-T c materials due to its large fluctuations. The very sharp resistive transition with a kink and the S-shaped I-V curve appear below H 1 T indicating a lattice melting transition. The scaling behavior of the vortex glass transition in R-T and I-V curves for H $ 2 T is observed with critical exponents n 1.23 6 0.02 and z 5.46 6 0.32, which are field independent. The vortex solid state changes from the vortex lattice at low fields to the vortex glass at high fields due to a field-enhanced pinning effect. The type of multicriticality is not yet conclusive.

Results of Raman measurements on RNi 2 B 2 C ͑RϭLu, Ho, Y͒ single crystals are reported. Raman peaks are observed at 190 cm Ϫ1 and near 830 cm Ϫ1 . From the polarization-dependence measurements, these peaks are assigned to be the Ni-B 1g and the B-A 1g modes, respectively. Raman study on the effects of boron isotope 10 B substitution for 11 B in the LuNi 2 B 2 C crystals confirms that the mode near 830 cm Ϫ1 is due to the vibration of B atoms. However, from these single crystals, the expected Ni-E g and B-E g modes are not observed.