DOI: 10.1051/jp1:1997178
J. Phys. I France 7 (1997) 599-610

Magnetic Field-Induced Phase Transition in the Quasi Two-Dimensional Organic Superconductor (BEDO-TTF) ReO H O

A. Audouard¹, V.N. Laukhin², C. Proust¹, L. Brossard¹ and N.D. Kushch<sup>1

1</sup>  Laboratoire de Physique de la Matière Condensée, UMR CNRS 5646, Service National des Champs Magnétiques Pulsés, UMS CNRS 5642, INSA, Complexe Scientifique de Rangeuil, 31077 Toulouse, France
²  Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, Chernogolovka, MD 142432, Russia

(Received 3 October 1996, accepted 19 December 1996)

Abstract
Transverse magnetoresistance of the two-dimensional (2D) organic superconductor (BEDO-TTF) ₂ReO ₄ H ₂O has been measured in pulsed magnetic fields up to 52 T and in the temperature range from 1.7 K to 4.2 K. For magnetic field lower than ~15 T, applied perpendicularly to the conducting planes, the data are in good agreement with previous studies, namely, the two Shubnikov-de Haas oscillation series with frequency  T and  T attributed to electron and hole orbits, respectively, are observed. However, as the magnetic field is rotated in the plane perpendicular to the best conductivity direction, the behaviour of the oscillations is not consistent with a perfect 2D picture. In addition, a new oscillation series with frequency about twice  T) rises up at high magnetic field while the amplitude of the oscillations with the F₂ frequency decreases. Furthermore, magnetic fields higher than 10 T, applied parallel to the conducting planes, yield negative magnetoresistance. These features are discussed on the basis of the available Fermi surface calculations.

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