Shubnikov-de Haas effect and Yamaji oscillations in the antiferromagnetically ordered organic superconductor k-(BETS)2FeBr4: A Fermiology study

Shubnikov-De Haas effect (SdH) effect and angular dependent magnetoresistance oscillations (AMRO) were observed in the organic superconductor: $\kappa$-(BETS)$_2$FeBr$_4$. In contrast to its isostructural compound $\kappa-(BETS)$_2$FeCl$_4$, SdH oscillations, for fields perpendicular to the conducting planes, reveal three Fermi Surface (FS) closed orbits $\alpha$, $\beta$, and $\gamma$ whose cross sectional areas are 19.8 %, 99.9 %, and 2.4 % of the first Brillouin zone, respectively. The conduction electron effective masses were found to be: $\mu_{\alpha} = (4.7 \pm 0.2)$ m$_e$, $\mu_{\beta} = (8.0 \pm 1.0)$ m$_e$, and $\mu_{\gamma} = (2.0 \pm 0.2)$ m$_e$. The observation of a $\gamma$ orbit is not expected from band structure calculations, $\mu_{\beta}$ is among the heaviest masses ever reported for an organic conductor. The observed Yamaji-like AMRO indicates a 2-D closed FS, warped along the $k_z$ direction.