Quantum oscillations and negative magnetoresistance in the organic metal β’’(BEDT-TTF)2AuBr2

Shubnikov–de Haas oscillations are observed in the low-temperature magnetoresistance of the organic metal β’ ’(BEDT-TTF${)}_2$ ${\mathrm{AuBr}}_2$, which indicate the presence of small carrier pockets in the Fermi surface. The nonoscillatory part of the magnetoresistance is highly anisotropic, and in one current direction an anomalously large negative magnetoresistance is observed. Some possible explanations for the negative magnetoresistance are considered, including an explanation based on magnetic-field–induced alignment of the carrier motion in the presence of scattering from internal boundaries.