GINZBURG-LANDAU-GORKOV THEORY OF MAGNETIC OSCILLATIONS IN A TYPE-II 2-DIMENSIONAL SUPERCONDUCTOR

We investigate de Haas-van Alphen (dHvA) oscillations in the mixed sta te of a type-II two-dimensional superconductor within a self-consisten t Gor'kov perturbation scheme. Assuming that the order parameter forms a vortex lattice we can calculate the expansion coefficients exactly to any order. We have tested the results of the perturbation theory to fourth and eighth order against an exact numerical solution of the co rresponding Bogoliubov-de Gennes equations. The perturbation theory is found to describe well the onset of superconductivity close to the tr ansition point H-c2. Contrary to earlier calculations by other authors we do not find that the perturbative scheme predicts any maximum of t he dHvA oscillations below H-c2. Instead we obtain a substantial dampi ng of the magnetic oscillations in the mixed state as compared to the normal state. We have examined the effect of an oscillatory chemical p otential due to particle conservation and the effect of a finite Zeema n splitting. Furthermore; we have investigated the recently debated is sue of the possibility of a sign change of the fundamental harmonic of the magnetic oscillations. Our theory is compared with experiment and we have found good agreement.