J. Phys. I France
Volume 6, Numéro 12, December 1996
Page(s) 1597 - 1608
DOI: 10.1051/jp1:1996177
J. Phys. I France 6 (1996) 1597-1608

The Fermi Surfaces of $\mathsf{\beta}$-(BEDT-TTF) $\mathsf{_2}$X

J. Wosnitza1, G. Goll1, 2, D. Beckmann1, S. Wanka1, D. Schweitzer3 and W. Strunz4

1  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)

We present de Haas-van Alphen (dHvA) measurements of the isostructural quasi two-dimensional (quasi-2D) organic superconductors $\beta$-(BEDT-TTF) 2IBr 2 and $\beta_{\rm H}$-(BEDT-TTF) 2I 3 with superconducting transition temperatures of $T_c \approx 2.5$ K and $T_c \approx$ 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 $t_\tau$ between the highly conducting organic layers could be determined with high precision $t_\tau$ is larger for $\beta$-(BEDT-TTF) 2I 3 although this salt has the larger interlayer distance. The effective cyclotron masses are very similar in both materials $(m_{\rm c} \approx 4 m_{\rm e})$. 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 $\beta$-phase salts.

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