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

Abstract

The carrier dynamics and electronic structures of type-II Weyl semimetal candidates MoTe2 and WTe2 have been investigated by using temperature-dependent optical conductivity [σ(ω)] 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 an evidence of type-II Weyl semimetals of MoTe2 and WTe2. The obtained carrier mass of the semimetallic bands and the interband transition spectra suggest the weak electron correlation effect in both materials.

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

“…[]. Similarly, our obtained peaks at 100 meV of and at 750 meV of agree with those from the recent report on bulk .…”

“…However, probing the Weyl physics of this material in its optical response has proven difficult due to limitations of the measurement techniques or difficulties in relating energy band transitions involving Weyl points to signatures in the optical spectra . For the case of , to our knowledge there is only one very recent report on its optical spectrum . The results show a similar to linear in ω behavior, just with slightly larger overall values, which has been attributed to the increased density of states of near the Fermi level.…”

“…There are a limited number of experimental studies reporting measurements for the optical properties of . These results show an overall approximately linear increase in the optical conductivity with frequency and they are analyzed in terms of a Drude model with two types of carriers.…”

“…These results show an overall approximately linear increase in the optical conductivity with frequency and they are analyzed in terms of a Drude model with two types of carriers. However, probing the Weyl physics of this material in its optical response has proven difficult due to limitations of the measurement techniques or difficulties in relating energy band transitions involving Weyl points to signatures in the optical spectra . For the case of , to our knowledge there is only one very recent report on its optical spectrum .…”

“…In addition to the electronic structure of the materials, the relaxation time also affects the optical response (Equations (–)). Experimental measurements of the optical conductivities performed at different temperatures reveal a quite large range of values for the relaxation time parameter τ. For example, for measurements at temperatures between 10K and room temperature, the obtained for ranges in about 4–640 cm −1 (0.5 to 80 meV), while for in between 1.6–320 cm −1 (0.2–40 meV) respectively.…”