Slow oscillations of magnetoresistance in layered organic metals

We show that the slow oscillations observed, in addition to the fundamental Shubnikov-de Haas oscillations, in the interlayer magnetoresistance of β-(BEDT-TTF) 2 IBr 2 do not reveal a separate small group of carriers but are ultimately determined by the weak warping of the cylindrical Fermi surface. We propose a simple explanation of the phenomenon based on interfering contributions from oscillating relaxation time and Fermi velocity to the Shubnikov-de Haas effect.