K.H. Kang

11B NMR measurements of vortex dynamics for YNi2B2C superconductor

Abstract 11 B Pulsed nuclear magnetic resonance (NMR) measurements have been performed on a single crystal of YNi 2 B 2 C superconductor to investigate the vortex structure and dynamical behavior. Spectrum, line width and transverse relaxation rate of 11 B NMR are measured at 1.8 and 3.0 T. The spectrum below 4 K exhibits a typical local field distribution for a square lattice at 3.0 T parallel to the c -axis. However, the shape of the spectrum at higher temperature changes to a symmetric narrow line, which indicates significant motion of vortices. Furthermore, thermal hysteresis of the saddle-point field, motional narrowing of line width, and enhancement of transverse relaxation rate also confirm substantial distortion and fluctuation of vortices in this low T c and nearly isotropic 3D superconductor.

11B NMR study of vortex dynamics in LuNi2B2C

Abstract 11 B NMR measurements have been performed on single crystals of LuNi2B2C superconductor to investigate vortex lattice structure and dynamical behavior. The spectrum in the superconducting state is significantly broadened by local field inhomogeneity due to the vortex lattice and the peak point of the spectrum shifts toward low magnetic field due to the imperfect field penetration. The linewidth of the spectrum reflecting local field variation is much smaller than expected for conventional vortex lattices and shows a peculiar increase at low temperature. Furthermore, the transverse relaxation rate, 1/T2, probing slow motion of vortices, exhibits a peak as temperature decreases. These results highlight significant fluctuation of vortices even for this low Tc and nearly isotropic 3D superconductor.