Transitions of the anomalous positive longitudinal magnetoconductivity of a Weyl semimetal in an ac electric field

Abstract

Considering the Landau quantization and chiral anomaly, we develop a semiclassical theory of the positive longitudinal magnetoconductivity (LMC) of a Weyl semimetal induced by the chiral anomaly in an ac driving electric field. We find that for low angular frequencies, the anomalous LMC behaves in the same manner as in the dc case. However, the LMC decreases rapidly to zero with increasing the angular frequency of the electric field to be above a critical frequency, which is equal to the inverse of the intervalley relaxation time. With further increasing the frequency, the zero-magnetic-field conductivity diminishes above a critical frequency, which is equal to the inverse of the intravalley relaxation time. The two distinct transitions might be observed experimentally, so that the intervalley and intravalley relaxation times can be determined directly, which are considered to be two key parameters controlling the anomalous positive LMC effect in existing theories.