Quantum oscillations of a linear chain of coupled orbits with small effective masses: the organic metal θ-(BETS) 4 CoBr 4 (C 6 H 4 Cl 2 )

accepted for publication in Synthetic MetalsDe Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillations of the organic metal θ-(BETS) 4 CoBr 4 (C 6 H 4 Cl 2) are studied in magnetic fields of up to 55 T at liquid helium temperatures. In line with Fermi surfaces (FS) illustrating the linear chain of coupled orbits, the observed Fourier components are linear combinations of the frequencies linked to the two basic orbits α and β, which have small effective masses compared to other organic metals with the same FS topology. Analytical formulas based on a second order development of the free energy within the canonical ensemble, not only account for the field and temperature dependence of the dHvA amplitudes but also for their relative values. In addition, strongly non-Lifshitz-Kosevich behaviours are quantitatively interpreted. In contrast, Shubnikov-de Haas oscillations are not accounted for by this model. short title: Quantum oscillations of θ-(BETS) 4 CoBr 4 (C 6 H 4 Cl 2