MAGNETIC-FIELD DEPENDENT EFFECTIVE-MASS IN THE ORGANIC SUPERCONDUCTORKAPPA-(BEDT-TTF)(2)I-3

kappa-(BEDT-TTF)(2)I-3 is an electronically extreme two-dimensional or ganic metal with a superconducting transition at around 4 K. In magnet ic fields above 12 T the effective mass, as obtained from the temperat ure dependence of the amplitudes of Shubnikov-de Haas oscillations, is magnetic field dependent as long as the magnetic field is arranged pe rpendicular to the conducting planes. In contrast to this, by turning the magnetic field by 27 degrees or even only 9 degrees the observed e ffective mass (as obtained from Shubnikov-de Haas and de Haas-van Alph en measurements) is field independent. We suppose that the occurrence of anyons at temperatures below 1 K in fields above 12 T is the reason for the observed field dependence of the effective mass.