OPEN AND CLOSED FERMI-SURFACE CONTRIBUTIONS TO THE ANOMALOUS ANGULAR MAGNETORESISTANCE OF ALPHA-(BEDT-TTF)2RBHG(SCN)4

Anomalous angular magnetoresistance (AMR) in the quasi-two dimensional organic conductor alpha-(BEDT-TTF)2RbHg(SCN)4 is reported. The AMR ap pears as oscillations with sharp minima below the anitiferromagnetic o rdering temperature. The period of these oscillations is anisotropic w ith respect to the plane of rotation cutting through the conducting la yers. Above the ordering temperature, the nature of the AMR changes fu ndamentally. We propose a model for the AMR that incorporates both ope n and closed Fermi surfaces, and discuss how temperature and field dep endent behaviors of the individual FS contribute to the conductivity.