Anomalous magneto-transport properties in nearly gapless materials

We have measured magnetoresistance (MR) for semimetals Bi and graphite, nearly gapless materials Bi-Sb and Bi-Te alloys, and narrow gap semiconductor Ag2Se single crystals at 4.2 K and up to 4 T. We have observed a giant MR for Bi, a giant linear MR (LMR) for Bi-Sb alloy and Ag2Se single crystals. Anomalous completely linear weak-field LMR has been found for nearly gapless materials: this is transferred into the ordinal MR or other LMR in relatively strong field range. It suggests the linear band dispersion in nearly gapless materials as proposed by Abrikosov.