  Recently discovered Dirac and Weyl semimetals display unusual
magnetoresistance phenomena, including a large, non-saturating, linear
transverse magnetoresistance and a negative longitudinal magnetoresistance. The
latter is often considered as evidence of fermions having a defined chirality.
Classical mechanisms, due to disorder or non-uniform current injection, can
however, also produce negative longitudinal magnetoresistance. Here, we report
on magnetotransport measurements performed on epitaxial thin films of Cd3As2, a
three-dimensional Dirac semimetal. Quasi-linear positive transverse
magnetoresistance and negative longitudinal magnetoresistance are observed. By
evaluating films of different thickness and by correlating the temperature
dependence of the carrier density and mobility with the magnetoresistance
characteristics, we demonstrate that both the quasi-linear positive and the
negative magnetoresistance are caused by conductivity fluctuations. Chiral
anomaly is not needed to explain the observed features.
