THE EFFECTS OF OPEN SECTIONS OF THE FERMI-SURFACE ON THE PHYSICAL-PROPERTIES OF 2D ORGANIC MOLECULAR-METALS

We report two cases in which the quasi-one-dimensional (Q1D) sections of Fermi surface (FS) in contribute to the low temperature behaviour o f the magnetoresistance (MR). In kappa-(ET)2Cu(NCS)2, breakdown orbits are observed between the Q2D and Q1D sections of FS; the MR oscillati ons contain a probable contribution from the Stark quantum interferenc e effect. The results for the FS parameters are compared with theoreti cal calculations and the effects of many-body interactions are deduced . In alpha-(ET)2KHg(NCS)4, nesting of the Q1D open orbits gives a SDW ground state which considerably modifies the FS and leads to a field-i nduced transition known as the 'kink' between 22 and 23 T. Measurement s of MR as a function of orientation of the crystal in the magnetic fi eld reveal that the changes in FS at the 'kink' are rather subtle.