Magnetic field dependence of the cyclotron effective mass in the organic superconductor k-(BEDT-TTF)/sub 2/I/sub 3/

Summary form only given. k-(BEDT-TTF)/sub 2/I/sub 3/ is an organic superconductor [1] with a T/sub c/ = 4 K. High quality single crystals of x-(BEDT-TTF)/sub 2/I/sub 3/ can be grown by electrochemical methods [2] and show already in magnetic fields from 5 to 12 Tesla giant quantum oscillations in Shubnikov de Haas (SdH)- and de Haas van Alphen (dHvA)- experiments. Therefore the cyclotron effective mass m* and the Fermi-surface can be determined in such fields with high accuracy [3]. In order to investigate whether m* is enhanced due to many body correlations such as electron-phonon or electron-electron interactions SdH- and dHvA- oscillations have been measured in fields up to 23.5 Tesla. Using the Lifshitz - Kosevich (LK) formula, from the temperature dependence of the SdH - amplitudes a relative strong magnetic field dependence of in* (m*=3.8m/sub 0/ at 10 Tesla, in*= 2.9m/sub 0/ at 23 Tesla) is obtained. In order to discriminate whether many body interactions are important or not, corrections on the LK-formula have to be discussed taking into account the quasi-two dimensional electronic properties of the material