MAGNETIC-FIELD-INDUCED PHASE-TRANSITION IN THE QUASI-2-DIMENSIONAL ORGANIC SUPERCONDUCTOR (BEDO-TTF)(2)REO4-CENTER-DOT-H2O

Transverse magnetoresistance of the two-dimensional (2D) organic super conductor (BEDO-TTF)(2)ReO4 . H2O has been measured in pulsed magnetic fields up to 52 T and in the temperature range from 1.7 K to 4.2 K. F or magnetic field lower than similar to 15 T, applied perpendic ularly to the conducting planes, the data are in good agreement with previou s studies, namely, the two Shubnikov-de Haas oscillation series with f requency F-1 = (38+/-2) T and F-2 = (74+/-2) 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 d irection, the behaviour of the oscillations is not consistent with a p erfect 2D picture. In addition, a new oscillation series with frequenc y about twice F-2 (F-4 = (150+/-10) T) rises up at high magnetic field while the amplitude of the oscillations with the F-2 frequency decrea ses. Furthermore, magnetic fields higher than 10 T, applied parallel t o the conducting planes, yield negative magnetoresistance. These featu res are discussed on the basis of the available Fermi surface calculat ions.