de Haas-van Alphen effect in the mixed state of LuNi2B2C: Anisotropy and field dependence of the damping due to superconductivity

We report observation of the de Haas-van Alphen oscillations in the mixed state as well as in the normal state of LuNi2B2C. Two oscillations alpha and eta are observed in the mixed state. In particular, the alpha oscillation can be studied not only deep in the mixed state as a function of magnetic field but also as a function of field direction. The damping rate of the oscillations due to superconductivity is found to be very anisotropic. For fields far below H-c2, the damping behavior is anomalous and cannot be explained only in terms of the superconducting gap. We argue that both the anisotropy of the gap and a disorder of the flux line lattice are responsible for the anisotropic and anomalous behavior of the damping in the mixed state.