Quantum oscillations in the superconducting state of LuNi₂B₂C

We have studied the de Haas-van Alphen (dHvA) effect of the borocarbide superconductor LuNi₂B₂C both in the normal and in the superconducting state by use of the field-modulation method in high magnetic fields up to 15 T and at low temperatures down to 0.5 K. In the superconducting state we observed an additional damping of the dHvA oscillation amplitudes compared to the normal state for different dHvA frequencies. This is due to the opening of the superconducting gap and, therefore, enables us to determine the magnetic-field-dependent gap for different bands from this experiment. The possibility to perform the measurements at various crystal orientations in the magnetic field allows to examine the angular dependence of the superconducting gap parameter.