Shubnikov-de Haas effect and Yamaji oscillations in the antiferromagnetically ordered organic superconductor kappa-(BETS)(2)FeBr4: a fermiology study

Shubnikov-de Haas (SdH) effect and angular dependent magnetoresistance osci llations (AMRO) were observed in the organic superconductor: kappa-(BETS)(2 )FeBr4. In contrast to its isostructural compound kappa-(BETS)(2)FeCl4, SdH oscillations, for fields perpendicular to the conducting planes, reveal th ree Fermi Surface (FS) closed orbits alpha, beta, and gamma whose cross-sec tional areas are 19.8, 99.9, and 2.4% of the first Brillouin zone, respecti vely. The conduction electron effective masses were found to be: mu (alpha) = (4.7 +/- 0.2)m(e), mu (beta) = (8.0 +/- 1.0)m(e), and mu (gamma) = (2.0 +/- 0.2)m(e). The observation of a gamma orbit is not expected from band st ructure calculations, mu (beta) is among the heaviest masses ever reported for an organic conductor. The observed Yamaji-like AMRO indicates a 2D clos ed FS, warped along the k(z) direction. (C) 2000 Elsevier Science Ltd. All rights reserved.