MAGNETOQUANTUM OSCILLATIONS IN THE NORMAL AND SUPERCONDUCTING STATE OF YNI2B2C

In the nonmagnetic borocarbide superconductor YNi2B2C the de Haas-van Alphen (dHvA) oscillations persist continuously at the upper critical field B-c2 = 10.5 T for the transition from the normal into the superc onducting state down to about 4 T. The measurements were carried out o n a single crystal with T-c = 15.7 K by the torque method in high magn etic fields up to 23 T and at low temperatures down to T = 0.4 K. Belo w B-c2 an additional damping of the dHvA amplitude occurs which is dis cussed in the context of recent theories of these oscillations in the mixed state.