Magic angles (lebedʹs and others), and the phase diagram of the bechgaard Salts

We present transport data on the metallic and Field Induced Spin Density Wave phases of the Bechgaard Salts (TMTSF)2PF6 and (TMTSF)2ClO4. The a and c axis resistivities (ρxxand ρzz) of these compounds have been measured for magnetic field rotations in the b-c planes (Lebed geometry) and striking resistance dips are observed at magic angles. We examine the differences between the two materials and the status of our understanding of the Lebed resonances. We then investigate the resistivities for magnetic fields rotated in the a-c plane. In this case we find a new set of resonances which for the first time allow direct measurements of the Fermi surface parameters of quasi-one-dimensional metals. Extending ρxxand ρzz measurements to 30 Tesla we have found that the phase boundary for the FISDW in (TMTSF)2ClO4 is most easily investigated by temperature dependent studies of ρzz at high field. We find a new phase below a nearly temperature independent and we discuss some of the properties of this phase.