ESPCI web site
Jeudi 31 Mars 2016 14h
Amphi Holweck, Esc C
1ème etage
Optical spectroscopy study of the Weyl semimetal TaAs
Yaomin Dai
Weyl semimetals (WSMs) are materials with two non-degenerate bands linearly crossing at
the Fermi level in three-dimensional (3D) momentum space. The band crossing points are called Weyl points. This class of materials, a 3D analogue of graphene, provide a platform for a condensed-matter realization of the fascinating Weyl fermions, fundamental particles that were theoretically predicted more than 80 years ago, yet have not been experimentally found in high-energy physics. Recently, transition-metal monoarsenides and monophosphides (TaAs, TaP, NbAs, and NbP) have been theoretically predicted and experimentally confirmed to be natural WSMs with 12 pairs of Weyl points, paving the way for further investigations into the WSM state.
In this seminar, I’ll present our recent optical studies on the WSM TaAs. The optical conductivity of TaAs is characterized by a narrow Drude response alongside a pronounced linear dependence on the photon energy. The spectral weight of the Drude response vanishes as T2, in good agreement with theoretical predictions for a WSM. The low-temperature optical conductivity features two linear components with distinct slopes. By comparing the experimental results with first-principles calculations, we found that the linear conductivity below 230 cm-1 arises purely from the interband transitions in proximity to 4 pairs of Weyl points lying very close to the Fermi energy. These interband transitions contain rich information about the the WSM state in TaAs. In addition, an infrared-active lattice vibration mode was observed at about 250 cm-1 in the optical conductivity spectra. This mode exhibits a Fano-like lineshape, indicating strong coupling with the continuum of transitions near the Weyl points.