Effective electrons and angular oscillations in quasi-one-dimensional conductors

We show via calculation and experiment that a recently observed angular magnetoresistance effect in low-dimensional conductors can be explained by ``effective electrons,'' which dominate the conductivity for magnetic-field orientations near inflection points on a warped Fermi surface. Closed orbits, which form in certain field orientations, play an insignificant role. In studies of the quasi-one-dimensional molecular metal (TMTSF)₂PF₆, we observe, in addition to sharp kink structure of the effect, a series of strong angular oscillations that we ascribe to the Lebed' commensurability resonance (magic angle) effect.