Four-fold anisotropy of the basal plane magnetization of YNi 2B 2C: nonlocal effects

Abstract

We present studies of the vortex state magnetization M of a single crystal of the nonmagnetic borocarbide superconductor YNi 2B 2C. With magnetic field H applied in the square basal plane of the tetragonal unit cell, M has a four-fold anisotropy. This π/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.