  The material termed three-dimensional (3D) Dirac semimetal has attracted
great interests recently, since it is an electronic analogue to two-dimensional
graphene. Starting from this novel phase, various topologically distinct phases
may be obtained, such as topological insulator, Weyl semimetal, quantum spin
Hall insulator, and topological superconductor. Soon after the theoretical
predictions, the angle-resolve photoemission spectroscopy and scanning
tunnelling microscopy experiments gave evidences for 3D Dirac points in Na3Bi
and Cd3As2. Here we report quantum transport properties of Cd3As2 single
crystal in magnetic field. A sizable linear quantum magnetoresistance is
observed at high temperature. With decreasing temperature, the Shubnikov-de
Haas oscillations appear in both longitudinal resistance Rxx and transverse
Hall resistance Rxy. From the strong oscillatory component \Delta Rxx, the
linear dependence of Landau index n on 1/B gives an n-axis intercept 0.58. Our
quantum transport result clearly reveals a nontrivial \pi\ Berry's phase, thus
provides strong bulk evidence for a 3D Dirac semimetal phase in Cd3As2. This
may open new perspectives for its use in electronic devices.
