Experimental evidence of giant chiral magnetic effect in type-II Weyl semimetal WP2+δ crystals

Abstract

The chiral magnetic effect (CME) is a quantum phenomenon arising from the breaking of chiral symmetry in relativistic Weyl fermions due to quantum fluctuations under parallel electric (E) and magnetic fields (B). Intuitively, Weyl fermions with opposite chirality, under the stimulus of parallel E and B, will have different chemical potentials that give rise to an extra current, whose role is like a chiral battery in solids. However, up until now, the experimental evidence for the chiral magnetic effect is the negative longitudinal magnetoresistance, rather than a chiral electric source. Here, different from previous reports, we observed a giant chiral magnetic effect evidenced by “negative” resistance and corresponding voltage–current curves located in the second-fourth quadrant in the type-II Weyl semimetal WP2+δ. These phenomena occur under the following conditions: the misalignment angle between B and E is smaller than 20°, the temperature is below 40 K, the externally applied electrical current is less than 50 mA, and the magnetic field is larger than 3 T. Phenomenologically, based on the macroscopic Chern–Simons–Maxwell equation, this giant chiral magnetic effect observed in WP2+δ is attributed to the chirality of Weyl fermions possessing a two-order longer coherent time than the Drude transport relaxation time. Our findings provide evidence of the giant chiral-magnetic/chiral-battery effect in Weyl semimetals.