Quasi-two-dimensional spin-split Fermi-liquid behavior of κ-(BEDT-TTF)2I3 in strong magnetic fields

Measurements of both the magnetization and magnetotransport of kappa-(BEDT-TTF)(2)I-3 (BEDT-TTF is bisethylenedithio-tetrathiafulvalene) in magnetic fields extending to 60 T at 0.4 K and 20 T at 35 mK are reported. Strong eddy currents observed in the magnetization are found to exhibit critical currentlike behavior. This might be connected with the breakdown of the quantum Hall effect, as proposed previously for alpha-phase salts. The strong two dimensionality leads to an apparent fall of the effective mass together with an overall suppression of the amplitude of the magnetic quantum oscillations at high magnetic fields or very low temperatures. These effects are more pronounced for the Shubnikov-de Haas (SdH) effect but clearly visible also for the de Haas-van Alphen (dHvA) oscillations. The apparent fall of the effective mass and the deviations of the dHvA signal from the behavior predicted by the standard Lifshitz-Kosevich theory can quantitatively be explained by the influence of chemical-potential oscillations on the wave form in a two-dimensional, spin-split Fermi liquid. The much stronger deviations from the conventional behavior in the transport data hint to an additional mechanism unique to the SdH effect. [S0163-1829(98)01940-7].