Negative transverse magnetoresistance due to the negative off-diagonal mass in linear dispersion materials.

We calculate the magnetoresistance (MR) in Dirac electron system, the Dresselhaus-Kip-Kittel (DKK) model, and nodal-line semimetals based on the semiclassical Boltzmann theory focusing on the detailed energy dispersion structure. We found that the negative off-diagonal effective-mass induces negative transverse MR simply due to the energy dispersion effect. The impact of the off-diagonal mass becomes more prominent when the energy dispersion is linear. In Dirac electron systems, the negative MR is realized even if the Fermi surface is perfectly spherical. The obtained negative MR in the DKK model can provide a reasonable explanation for the long-standing mystery in p-type Si.