  Chiral magnetic effect is a quantum phenomenon that is breaking of chiral
symmetry of relativistic Weyl fermions by quantum fluctuation under paralleled
electric field E and magnetic field B. Intuitively, Weyl fermions with
different chirality, under stimulus of paralleled E and B, will have different
chemical potential that gives rise to an extra current, whose role likes a
chiral battery in solids. However, up to now, the experimental evidence for
chiral magnetic effect is the negative longitudinal magnetoresistance rather
than a chiral electric source. Here, totally different from previous reports,
we observed the giant chiral magnetic effect evidenced by: 'negative'
resistivity and corresponding voltage-current curves lying the second-fourth
quadrant in type-II Weyl semimetal WP$_{2+\delta}$ under following conditions:
the misaligned angle between E and B is smaller than 20$^\circ$, temperature
<30 K and externally applied E<50 mA. Phenomenologically, based on macroscopic
Chern-Simon-Maxwell equation, the giant chiral magnetic effect observed in
WP$_{2+\delta}$ is attributed to two-order higher coherent time of chiral
Weyl-fermion quantum state over Drude transport relaxation-time. This work
demonstrates the giant chiral-magnetic/chiral-battery effect in Weyl
semimetals.
