Fourfold basal plane anisotropy of the nonlocal magnetization of YNi₂B₂C

Studies of single crystal YNi₂B₂C have revealed a fourfold anisotropy of the equilibrium magnetization in the square crystallographic basal plane. This π/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-κ superconductor.