DOI: 10.1051/jp1:1996177
J. Phys. I France 6 (1996) 1597-1608

The Fermi Surfaces of -(BEDT-TTF) X

J. Wosnitza¹, G. Goll^{1, 2}, D. Beckmann¹, S. Wanka¹, D. Schweitzer³ and W. Strunz<sup>4

1</sup>  Physikalisches Institut, Universität Karlsruhe, 76128 Karlsruhe, Germany
²  Grenoble High Magnetic Field Laboratory, Max-Planck-Institut für Festkörperforschung and Centre National de la Recherche Scientifique, BP 166, 38042 Grenoble, France
³  Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart, Germany
⁴  Anorganisch-chemisches Institut, Universität Heidelberg, 69120 Heidelberg, Germany

(Received 24 april 1996, received in final form 27 June 1996, accepted 1 July 1996)

Abstract
We present de Haas-van Alphen (dHvA) measurements of the isostructural quasi two-dimensional (quasi-2D) organic superconductors -(BEDT-TTF) ₂IBr ₂ and -(BEDT-TTF) ₂I ₃ with superconducting transition temperatures of  K and 7 K, respectively. For both salts almost the same dHvA frequency and a beating behavior of the dHvA signal are found which reflect the similarity of the Fermi surface (FS) topology in both materials. The FS can be well described by a slightly corrugated quasi-2D cylinder. the corresponding overlap integral between the highly conducting organic layers could be determined with high precision is larger for -(BEDT-TTF) ₂I ₃ although this salt has the larger interlayer distance. The effective cyclotron masses are very similar in both materials . On the other hand the observed spin-splitting zeros suggest a rather large difference and large absolute values of the conduction electron g-factor which seems to reflect the importance of electron-electron interactions in the -phase salts.

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