  The extremely stringent requirement on material quality has hindered the
investigation and potential applications of exotic chiral magnetic effect in
Dirac semimetals. Here, we propose that gray tin is a perfect candidate for
observing the chiral anomaly effect and Shubnikov-de-Haas (SdH) oscillation at
relatively low magnetic field. Based on effective $k.p$ analysis and
first-principles calculations, we discover that gray tin becomes a Dirac
semimetal under tensile uniaxial strain, in contrast to a topological insulator
under compressive uniaxial strain as known before. In this newly found Dirac
semimetal state, two Dirac points which are tunable by tensile [001] strains,
lie in the $k_z$ axis and Fermi arcs appear in the (100) surface. Duo the low
carrier concentration and high mobility of gray tin, a large chiral anomaly
induced negative magnetoresistance and a strong SdH oscillation are anticipated
in this half of strain spectrum. Comparing to other Dirac semimetals, the
proposed Dirac semimetal state in the nontoxic elemental gray tin can be more
easily manipulated and accurately controlled. We envision that gray tin
provides a perfect platform for strain engineering of chiral magnetic effects
by sweeping through the strain spectrum from positive to negative and vice
versa.
