New High Field Angular Dependent Aspects of Quasi-2 Dimensional Organic Conductors α- (BEDT-TTF)2MHg(SCN)4(M=K or NH4)

Angular dependent transport measurements on α-(BEDT-TTF)2MHg(SCN)4 (M=K or NH4) have been performed in magnetic fields up to 33 Tesla. In this high field regime, well defined Shubnikov de Haas (SdH) oscillations arise. When a field is rotated perpendicular to the conductive planes, symmetric SdH oscillations appear and show pronounced spin splitting effects. The magnetorestistance oscillations arising from geometrical warping on the Fermi surface cylinder shows an asymmetric behavior about theta. To explain the transport behavior in the M= NH4 salt, a Fermi surface with a 12.8 ° tilting of the warping axis is proposed.