Giant lebed magic angle effects and more — Bechgaard salts with pressure and magnetic field

Abstract

When (TMTSF)2 PF6 at 10kbar pressure and low temperature is rotated in a moderate magnetic field it exhibits a striking set of phenomena at “Magic Angles”. As in the predictions of Lebed, these are manifest in both the normal metallic state magnetoresistance and in the field induced spin density wave (FISDW) states as changes in the critical fields. However, the magic angle dependences are significantly different from all previous models and we present a simple new model which accounts for the magnetoresistance, its overall angular dependence and the magic angles. The new model suggests the presence of regions of high scattering “hot spots” on the Fermi surface into which the carriers are swept by the magnetic field. The hot spots suggest an important role for electron-electron interactions. We also present the pressure, P, temperature, T, magnetic field, H, phase diagram for (TMTSF)2 ClO4. Above 5kbar the anion ordering vanishes in (TMTSF)2 ClO4, and the N=0 transition appears in it's “proper” position.