deHaas-vanAlphen study in the superconducting state of YNi2B2C

In the borocarbide superconductor YNi2B2C the de Haas-van Alphen (dHvA) oscillations have been observed continuously at the upper critical field B-c2 for the transition from the normal into the superconducting state. In the normal state above B-c2 = 10.5 T six different frequencies were found in magnetic fields up to 23 T and for Theta = 14.4 degrees. The smallest orbit with F-alpha = 511 T is present down to about 4 T, but with an additional attenuation of the dHvA signal in the superconducting state relative to an extrapolation of the standard Lifshitz-Kosevich formula. The observation of magnetoquantum oscillations over such a wide field range and very close to B-c2 enables a detailed discussion of the damping in the context of recent theories of these oscillations in the superconducting state.