Optical evidence of the type-II Weyl semimetals MoTe2 and WTe2

Abstract

The carrier dynamics and electronic structures of type-II Weyl semimetal candidates ${\mathrm{MoTe}}_{2}$ and ${\mathrm{WTe}}_{2}$ have been investigated by using temperature-dependent optical conductivity $[\ensuremath{\sigma}(\ensuremath{\omega})]$ spectra. Two kinds of Drude peaks (narrow and broad) have been separately observed. The width of the broad Drude peak increases with elevating temperature above the Debye temperature of about 130 K in the same way as those of normal metals, on the other hand, the narrow Drude peak becomes visible below 80 K and the width is rapidly suppressed with decreasing temperature. Because the temperature dependence of the narrow Drude peak is similar to that of a type-I Weyl semimetal TaAs, it was concluded to originate from Dirac carriers of Weyl bands. The result suggests that the conductance has the contribution of two kinds of carriers, normal semimetallic and Dirac carriers, and this observation is evidence of the type-II Weyl semimetals ${\mathrm{MoTe}}_{2}$ and ${\mathrm{WTe}}_{2}$. The obtained carrier mass of the semimetallic bands and the interband transition spectra suggest the weak electron correlation effect in both materials.