Magnetic field dependence of the cyclotron effective mass in the organic Superconductor κ-(BEDT-TTF)2I3

κ-(BEDT-TTF)2I3 is an electronically extreme two-dimensional (2d) organic metal with a superconducting transition at around 4K. In magnetic fields above 12T the effective mass, as obtained from the temperature dependence of the amplitudes of Shubnikov-de Haas (SdH) oscillations, is magnetic field dependent mass, as long as the magnetic field is arranged perpendicular to the conducting planes. In contrast to this by turning the magnetic field 27° or even only by 9° the observed effective mass (as obtained from SdH- and de Haas-van Alphen (dHvA)-measurements) is field independent. We suppose that the occurrence of anyons at temperatures below 1K and in fields above 12T is the reason for the observed field dependence of the effective mass.