QUANTUM OSCILLATIONS IN THE MIXED-STATE OF THE TYPE-II SUPERCONDUCTOR2H-NBSE2

Quantum oscillations have been investigated far into the mixed state o f the type II superconductor 2H-NbSe2. The de Haas-van Alphen effect i s found to persist to fields as low as approximately 0.3B(C2) and to t emperatures of approximately 0.003T(C). A self-consistent band structu re calculation, performed for 2H-NbSe2 in the normal non-charge-densit y-wave state using a full potential linearized augmented plane wave (F LAPW) method, accounts well for the experimental angular dependence of the quantum oscillations in terms of a small flat hole Fermi surface around the GAMMA point. This feature derives mainly from chalcogen p b ands and has a mass-enhancement factor much smaller than expected from the specific heat. Quantum oscillations in the presence of the vortex lattice are observed to experience an additional damping, from which the order parameter is estimated to be DELTA(0) = 0.6 +/- 0.1 meV.