Fourfold Basal Plane Anisotropy of the Nonlocal Magnetization ofYNi2B2C

Studies of single crystal YNi{sub 2}B {sub 2}C have revealed a fourfold anisotropy of the equilibrium magnetization in the square crystallographic basal plane. This {pi}/2 periodicity occurs deep in the superconductive mixed state. In this crystal symmetry, an ordinary superconductive mass anisotropy (as in usual London theory) allows only a constant, isotropic response. In contrast, the experimental results are well described by generalized London theory incorporating nonlocal electrodynamics, as needed for this clean, intermediate-{kappa} superconductor. {copyright} {ital 1999} {ital The American Physical Society }