NEW CLUES IN THE MYSTERY OF THE GROUND-STATE OF THE (BEDT-TTF)2MHG(SCN)4 FAMILY OF ORGANIC CONDUCTORS

Since the discovery of a kink in the magnetoresistance of (BEDT-TTF)2K Hg(SCN)4 by the Tokyo group [Osada et al., Phys. Rev. B 41 (1990) 5428 ] several years ago, this family (where K may be replaced by NH4, Tl, or Rb) has become one of the most exciting areas of organic conductor research. At the heart of the matter is the interplay of the open and closed orbit sections of the Fermi surface, in which subtle details of topology apparently play major roles in the low temperature state (LT S). Recent experiments involving angular dependent magnetoresistance, and determinations of magnetic breakdown orbits provide clues to the m echanisms which act in the LTS. We present a model which addresses the anomalous magnetoresistance phenomena in the LTS. The model involves the connection via magnetic breakdown of otherwise disconnected closed hole and open electron bands.