Fermi surface in new layered organic conductors (BEDT-TTF)3Br(pBIB) and (BEDT-TTF)3Cl(DFBIB)

We report the measurements of Shubnikov–de Haas (SdH) oscillation and angular dependent magnetoresistance oscillation (ADMRO) in a new layered organic conductor (BEDT-TTF)3Br(pBIB), where pBIB stands for p-bis(iodoethynyl)benzene. When magnetic fields are applied perpendicular to the layers, two distinct SdH oscillations are clearly observed, which arise from the two extremal cross-sectional areas of the slightly warped cylindrical Fermi surface (FS). The cross-sectional areas correspond to 50.9 and 51.6% of the first Brillouin zone. From the analysis of the ADMRO, the area of FS is estimated to be 52.5% of the first Brillouin zone. The ADMRO data also shows that the anisotropy of the FS is enhanced by change of Br(pBIB) for Cl(DFBIB), where DFBIB stands for 1,4-difluoro-2,5-bis(iodoethynyl)benzene. These results are consistent with the band calculation.