Observation of High-Order Harmonic Resonances in Magnetooptical Measurements of (BEDT-TTF)2Br(DIA)

Magnetooptical measurements of a quasi-two-dimensional (q2D) organic conductor (BEDT-TTF)2Br(DIA) (DIA=diiodoacetylene) were performed using a cavity perturbation technique with a millimeter vector network analyzer (MVNA). Harmonic resonances were observed periodically as a function of the inverse field up to the 7th order. This is the first observation of higher-order harmonics up to the 7th order in an organic conductor. The observed resonance is assigned as a periodic orbit resonance (POR) which arises from a q2D elliptic Fermi surface (FS). The obtained effective mass (4.7me) is consistent with Shubnikov-de Haas measurements. Temperature dependence of the spectra observed in two different sample configurations will be presented.