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

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

A.I. Coldea¹, A.F. Bangura¹, A. Ardavan¹, J. Singleton², A. Akutsu-Sato^{3, 1}, H. Akutsu³, S.S. Turner³ and P. Day<sup>3

1</sup>  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

Abstract
We report high-field magnetotransport measurements on -(BEDT-TTF) ₄[ (H ₃O)M(C ₂O ₄) ₃] 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 whereas the Dingle temperatures varies between  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