Two-dimensional Fermi surface for the organic conductor κ-(BETS)2FeBr4

Magnetoresistance measurements have been performed for the organic conductor -(BETS) FeBr to investigate the Fermi surface. Three fundamental Shubnikov-de Haas oscillations (, and ) were observed. The cross-sectional areas corresponding to the and oscillations are about 20% and 100% in the "rst Brillouin zone, respectively. The oscillations can be assigned to the closed orbit and the magnetic breakdown orbit. The e!ective masses of the conduction electrons are determined to be 5.2m for and 7.9m for . The heavy masses are probably due to the antiferromagnetic #uctuation e!ect of the Fe spins. The origin of the oscillation with very low frequency is not explained by the band calculation. 2001 Elsevier Science B.V. All rights reserved.