Abstract: | We present de Haas-van Alphen (dHvA) measurements in the normal and in the
superconducting state of LuNi2B2C. Inside the superconducting state,
we observe quantum oscillations of a spherical Fermi-surface sheet in all crystallographic
directions. Apart from the field region close to the phase transition where a strong peak
effect hampers the analysis of the dHvA signal, the additional damping of the quantum
oscillations inside the superconducting state is much smaller than expected from theory.
For the magnetic field aligned along the 100] direction, three different dHvA frequencies
are visible in the superconducting state. In particular, the orbit related to a
cushion-like Fermi surface does not show any additional damping at and below the upper
critical field contrary to theoretical expectations of simple effective one-band theories.
Consequently, the superconducting gap on this Fermi-surface sheet can only evolve at lower
fields than the observed bulk critical field,
B
c2 ≈ 8 T, which clearly points to a
Fermi-surface-sheet-dependent gap opening in LuNi2B2C. |