  We have investigated the magnetoresistive behavior of Dirac semi-metal Cd3As2
down to low temperatures and in high magnetic fields. A positive and linear
magnetoresistance (LMR) as large as 3100% is observed in a magnetic field of 14
T, on high-quality single crystals of Cd3As2 with ultra-low electron density
and large Lande g factor. Such a large LMR occurs when the magnetic field is
applied perpendicular to both the current and the (100) surface, and when the
temperature is low such that the thermal energy is smaller than the Zeeman
splitting energy. Tilting the magnetic field or raising the temperature all
degrade the LMR, leading to a less pronounced quadratic behavior. We propose
that the phenomenon of LMR is related to the peculiar field-induced
shifting/distortion of the helical electrons' Fermi surfaces in momentum space.
