Quantum oscillations in the normal and superconducting state of LuNi₂B₂C

We present de Haas-van Alphen (dHvA) investigations in the nonmagnetic borocarbide superconductor LuNi₂B₂C both in the normal and in the superconducting state. The measurements have been carried out by use of the torque method as well as by the field-modulation method. The quantum oscillations in the normal state give information on the elaborated Fermi surfaces which consists of several open and closed parts [1]. In the superconducting state we observe dHvA oscillations that belong to a spheroidal Fermi surface deep into the superconducting state down to B = 2.5 T far below the upper critical field, B_c2. We find only a minor additional damping of the dHvA oscillation amplitude in the superconducting state compared to the normal state. Only close to B_c2 the oscillations appear to be more strongly damped. There, the background signal shows a strong peak effect which complicates the analysis of the dHvA signal in this region. However, the apparent increase of the additional damping in the peak-effect range hints at the influence of increased flux-line pinning in this region