Magnetotransport studies of the Fermi surface in the organic superconductor: κ-(BEDT-TTF)2Cu[N(CN)2]Br

The interlayer magnetoresistance of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br has been measured at ambient pressure and under pressure up to 12 kbar. Shubnikov-de Haas oscillations of two main frequencies, F − 3900 T and F − 150 T, corresponding to 100% and 3.5–4% of the Brillouin zone cross-section area, are observed in the pressure ranges p = 0 − 9.4 kbar and p > 5 kbar respectively. The parameters of the slow oscillations indicate a considerable deviation of the Fermi surface from the theoretically predicted one. We propose to explain the experimental data by taking into account a low-temperature superstructure which doubles the lattice period in the c-direction.