The phenomenon of magnetic quantum oscillations in the superconducting state poses several questions that still defy satisfactory answers. A key controversial issue concerns the additional damping observed in the vortex state. Here, we show results of mu SR, dHvA, and SQUID magnetization measurements on borocarbide superconductors, indicating that a sharp drop observed in the dHvA amplitude just below H_{c2} is correlated with enhanced disorder of the vortex lattice in the peak-effect region, which significantly enhances quasiparticle scattering by the pair potential.
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