Anomalous behavior of magneto-quantum oscillations in the organic superconductor κ-(BEDT-TTF)2I3

Abstract

κ-(BEDT-TTF)2I3 is an extreme case of an electronically two-dimensional (2D) organic metal with a superconducting transition at around 4 K. In magnetic fields up to 27 T the field, angular and the temperature dependence of de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillation amplitudes were investigated. From the temperature dependence of the oscillation amplitudes the cyclotron effective massm* was investigated using Lifshitz-Kosevich formula (LK) and the surprising result is, thatm* appears to be magnetic field dependent as soon as the magnetic field is applied exactly perpendicular to the conducting planes so that the cyclotron orbit lies within those planes (i.e. Θ=0o) but field independent at Θ≠0o. It is shown that the LK formula can satisfactorily be used for the interpretation of all data obtained at Θ≠0o but not in the case where Θ=0o. An explanation of the anomalous data at Θ=0o can furthermore neither be given satisfactorily by the descriptions of magneto-quantum oscillations in 2D electronic systems nor by the occurrence of magnetic interaction effects (MI). Tentatively, the observed smaller oscillation amplitudes in κ-(BEDT-TTF)2I3 at Θ=0o above 12 T and below 1 K compared to the standard LK theory will be discussed in terms of a loss in the number of fermions by the occurrence of quasiparticles with fractional statistics.