ANOMALOUS BEHAVIOR OF MAGNETO-QUANTUM OSCILLATIONS IN THE ORGANIC SUPERCONDUCTOR KAPPA-(BEDT-TTF)(2)I-3

kappa-(BEDT-TTF)(2)I-3 is an extreme case of an electronically two-dim ensional (2D) organic metal with a superconducting transition at aroun d 4 K. In magnetic fields up to 27 T the field, angular and the temper ature dependence of de Haas-van Alphen (dHvA) and Shubnikov-de Haas (S dH) oscillation amplitudes were investigated. From the temperature dep endence of the oscillation amplitudes the cyclotron effective mass m was investigated using Lifshitz-Kosevich formula (LK) and the surprisi ng result is, that m appears to be magnetic field dependent as soon a s the magnetic field is applied exactly perpendicular to the conductin g planes so that the cyclotron orbit lies within those planes (i.e. Th eta = 0 degrees), but field independent at Theta not equal 0 degrees. It is shown that the LK formula can satisfactorily be used for the int erpretation of all data obtained at Theta not equal 0 degrees but not in the case where Theta = 0 degrees. An explanation of the anomalous d ata at Theta = 0 degrees can furthermore neither be given satisfactori ly by the descriptions of magneto-quantum oscillations in 2D electroni c systems nor by the occurrence of magnetic interaction effects (MI). Tentatively, the observed smaller oscillation amplitudes in kappa-(BED T-TTF)(2)I-3 at Theta = 0 degrees above 12 T and below 1 K compared to the standard LK theory will be discussed in terms of a loss in the nu mber of fermions by the occurrence of quasiparticles with fractional s tatistics.