Unconventional cyclotron resonance in the organic superconductor β″-(ET)2SF5CH2CF2SO3

We have measured angle-dependent magnetoresistance oscillations and the interplane millimetre-wave conductivity of the organic superconductor β-(ET) 2 SF 5 CH 2 CF 2 SO 3 as a function of the orientation of the applied magnetic field. We observe harmonics of the cyclotron frequency in the real-space velocity of quasiparticles orbiting the Fermi surface (FS). The harmonic amplitudes depend on the field orientation, providing a new way to measure the quasi-two-dimensional FS topology.