Ultrafast dynamics of photoexcited carriers in tellurium in the vicinity of Weyl nodes

Tellurium (Te) has recently attracted research interest for its outstanding electronic and optoelectronic properties and interesting topological physical related to topological Weyl cones in its band structure. To explore its high field transport and optoelectronic properties, the study of the ultrafast dynamics of photoexcited carriers plays a pivotal role. In this work, we study the ultrafast dynamics of photoexcited carriers in Te at the vicinity of Weyl nodes using transient reflection spectroscopy with 2-mu m pump and 4-mu m probe. We find that the relaxation process in a 100-nm Te flake is dominated by a 30-ps Auger recombination at high carrier density and a 200-ps multiphonon emission process at low carrier density. In contrast, the relaxation process in a 20-nm flake is ten times faster than the 100-nm flake due to the assistance of surface defects. The reflection modulation depth of the 20-nm sample is up to 60%, promising great potential for fast optical switch and optical modulator applications in the midinfrared region.