A comparison of magnetoconductivities between type-I and type-II Weyl semimetals

Abstract

It is well known that Weyl semimetals (WSMs) are classified into two types of type-I and type-II depending on whether or not they have electron and hole pockets. Also, these WSMs have peculiar transport properties such as negative longitudinal magnetoresistance and planar Hall effect because of a chiral anomaly. In this paper, however, we show that the chiral anomaly can cause positive longitudinal magnetoresistance in type-II WSMs. Here, we investigate longitudinal and transverse magnetoconductivities of time reversal symmetry broken type-I and type-II WSMs using a tight-binding model. The model allows us to describe both types of type-I and type-II WSMs by tuning parameters, and it has two Weyl points that are separated along the kx-direction. The numerical calculations of these conductivities are performed using the Boltzmann equation including the Berry curvature. It is found that longitudinal magnetoconductivities in the x-direction can have both positive and negative values depending on the magnitude of the inclination of a Weyl cone. This is because the zeroth Landau energy-level becomes either a hole-like one or an electron-like one depending on the magnitude of the inclination of the Weyl cone in type-II WSMs. These results imply that we can make a high MR-ratio device using type-II WSMs by tuning the inclination of their cones if it is possible to change their energy bands by the application of electric field and so on.

General formula of chiral anomaly for type-I and type-II Weyl semimetals

“…25,29,30 In addition, recently we have revealed that type-II WSMs show not only the negative but also the positive longitudinal magnetoresistance originating from the chiral anomaly in our paper of Journal of Applied Physics. 31 The negative longitudinal magnetoresistance in type-I WSMs can be explained by the conventional formula of the chiral anomaly developed by Nielsen and Ninomiya, 32 which does not include the term related to the inclination of the Weyl cones. However, the positive and the negative longitudinal magnetoresistance in type-II WSMs cannot be explained by it.…”