J. Phys. IV France
Volume 114, April 2004
Page(s) 205 - 209

J. Phys. IV France
114 (2004) 205
DOI: 10.1051/jp4:2004114045

Fermiology of new charge-transfer salts, ${\beta''}$-(BEDT-TTF) 4[ (H 3O)M(C 2O 4) 3] $\cdot $solvent where M = Ga, Cr and Fe

A.I. Coldea1, A.F. Bangura1, A. Ardavan1, J. Singleton2, A. Akutsu-Sato3, 1, H. Akutsu3, S.S. Turner3 and P. Day3

1  Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
2  National High Magnetic Field Laboratory, Los Alamos National Laboratory, TA-35, MS-E536, Los Alamos, NM 87545, USA
3  Davy-Faraday Research Laboratory, The Royal Institution, 21 Albemarle Street, London, W1S 4BS, UK

We report high-field magnetotransport measurements on ${\beta''}$-(BEDT-TTF) 4[ (H 3O)M(C 2O 4) 3] $\cdot $ solvent, where M=Ga 3+, Cr 3+ and Fe 3+ and solvent=C 5H 5N. In spite of their differing transition metal-ions, M, the three compounds exhibit similar magnetic quantum oscillation spectra superimposed on a positive magnetoresistance. At least four independent quantum oscillation frequencies have been identified, corresponding to two different hole and electron pockets of the Fermi surface which follow the rules of a compensated metal. Observation of the small pockets could be the result of the Fermi surface reconstruction induced by a possible density wave. The effective masses are very similar for different samples and for different pockets range between $m_{\rm eff} \approx
0.5-1.1~m_e$ whereas the Dingle temperatures varies between $T_{\rm D} \approx
1.4-4$  K. At low temperature, the longitudinal magnetoresistance violates Kohler's rule, suggesting that the interlayer transport in these quasi-2D systems cannot be related to a single scattering time and that the disorder plays an important role. Key words. Magnetoresistance-quantum oscillations.

© EDP Sciences 2004