11B NMR measurements of vortex dynamics for YNi2B2C superconductor

B-11 Pulsed nuclear magnetic resonance (NMR) measurements have been performed on a single crystal of YNi2B2C superconductor to investigate the vortex structure and dynamical behavior. Spectrum, line width and transverse relaxation rate of B-11 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. (C) 2001 Elsevier Science B.V. All rights reserved.