Local field distribution and NMR line shape in YNi2B2C

Local field distribution in the mixed state of type II superconductors is numerically calculated and compared with 11B NMR spectrum of YNi2B2C single crystal. We find that just small distortion of vortex positions severely distorts and broadens the line shape. Thus the NMR linewidth is susceptible to a small degree of vortex distortion. Also, since NMR signals are usually very weak due to significant line broadening in the vortex state, only a limited range of the full distribution around the saddle-point tends to be observed. Therefore, unless the characteristic edges of field distribution at the minimum field and the maximum field values are observed confirming that the full NMR line in the vortex state is securely measured, then analysis based only on the limited part of the full spectrum may lead to erroneous conclusions regarding vortex structure and dynamics