Four-fold anisotropy of the basal plane magnetization of YNi2B2C: nonlocal effects

We present studies of the vortex state magnetization M of a single crystal of the nonmagnetic borocarbide superconductor YNi2B2C. With magnetic field H applied in the square basal plane of the tetragonal unit cell, M has a four-fold anisotropy. This pi /2 periodicity occurs deep in the superconductive mixed state, with an unusual field dependence, for a range of temperatures T < T-c. The observations are well explained by a generalized London model incorporating non-local electrodynamics, using parameters from complementary experiments.