Anomalous influence of a small amount of neutral impurity on the longitudinal Shubnikov-de Haas oscillation

Longitudinal magnetoresistance of pure and neutral impurity (0.03, 0.1, 0.3, 0.6, 1.0, 1.5, 2.3 and 3.0 at% antimony)-doped bismuth single crystals was measured up to 5 T at 4.2 K. The longitudinal Shubnikov-de Haas (SdH) oscillation became larger in magnitude with increasing concentration of antimony, and became largest at 1.5 at% of antimony. A simple numerical simulation was carried out to understand this anomalous behavior. The simulation positively demonstrates that the anomalous behavior of the amplitude in the longitudinal SdH oscillations is due to competition between the effects of the impurity concentration and collision broadening of Landau levels.