Optical and transport properties in three-dimensional Dirac and Weyl semimetals

Abstract

Within a Kubo formalism, we study dc transport and ac optical properties of 3D Dirac and Weyl semimetals. Emphasis is placed on the approach to charge neutrality and on the differences between Dirac and Weyl materials. At charge neutrality, the zero-temperature limit of the dc conductivity is not universal and also depends on the residual scattering model employed. However, the Lorenz number L retains its usual value L0. With increasing temperature, the Wiedemann-Franz law is violated. At high temperatures, L exhibits a new plateau at a value dependent on the details of the scattering rate. Such details can also appear in the optical conductivity, both in the Drude response and interband background. In the clean limit, the interband background is linear in photon energy and always extrapolates to the origin. This background can be shifted to the right through the introduction of a massless gap. In this case, the extrapolation can cut the axis at a finite photon energy as is observed in some experiments. It is also of interest to differentiate between the two types of Weyl semimetals: those with broken time-reversal symmetry and those with broken spatialinversion symmetry. We show that, while the former will follow the same behaviour as the 3D Dirac semimetals, for the zero magnetic field properties discussed here, the latter type will show a double step in the optical conductivity at finite doping and a single absorption edge at charge neutrality. The Drude conductivity is always finite in this case, even at charge neutrality.

Optical Response of MoTe2 and WTe2 Weyl Semimetals: Distinguishing between Bulk and Surface Contributions

“…Thus the characteristics of the monolayers come into play at frequencies larger than 100 meV. Although the appearance of peaks in the optical spectra is due to interband transitions, the observed linear increase with frequency may be attributed to the Dirac‐like energy spectra of these 3D materials, as shown by effective models calculations within the linear response Kubo approach . Our calculated results agree reasonably well with the previously reported experimental measurements for bulk .…”

Light-Driven Raman Coherence as a Nonthermal Route to Ultrafast Topology Switching in a Dirac Semimetal

“…The system is still a gapped massless (Dirac) state [26]. Most interestingly, in contrast to the above, by moving in the other direction with more positive λ, the band gap decreases.…”

Dynamical density and spin response of Fermi arcs and their consequences for Weyl semimetals

“…The electromagnetic and transport properties exhibited by WSMs has been studied theoretically using semi- * carsten.timm@tu-dresden.de classical transport theory [22,[36][37][38], field-theoretic approaches [21,39], and the Kubo formalism [40][41][42]. The dynamical density, spin, and current responses to inhomogenous and time-dependent external fields have been investigated for Weyl fermions in the bulk, using Kohn-Luttinger-type (k · p) models [43][44][45].…”