  Anisotropic magnetoresistance is the change tendency of resistance of a
material on the mutual orientation of the electric current and the external
magnetic field. Here, we report experimental observations in the Dirac
semimetal Cd3As2 of giant anisotropic magnetoresistance and its transverse
version, called the planar Hall effect. The relative anisotropic
magnetoresistance is negative and up to -68% at 2 K and 10 T. The high
anisotropy and the minus sign in this isotropic and nonmagnetic material are
attributed to a field-dependent current along the magnetic field, which may be
induced by the Berry curvature of the band structure. This observation not only
reveals unusual physical phenomena in Weyl and Dirac semimetals, but also finds
additional transport signatures of Weyl and Dirac fermions other than negative
magnetoresistance.
