Small angle neutron scattering study of the magnetic flux-line lattice in single crystal 2H-NbSe2

We report on a small angle neutron scattering study of the flux-line lattice in single crystal 2H-NbSe2. As the magnetic field is tilted away from the crystalline c axis, we find distortions in the flux lattice as would be expected for a mass anisotropy Γ=10.1±0.9. However, we find that the lattice orientation is in disagreement with the predictions of both anisotropic London and Ginzburg-Landau theories. The observed flux lattice orientation remains pinned to that of the crystal lattice for the field orientations studied. The form factors can be quantitatively understood within the framework of Ginzburg-Landau corrections to the London equations.