Unusual ultrafast photocarrier dynamics in type II Dirac semimetal PtTe2 thin film in terahertz band

A type II Dirac semimetal PtTe 2 thin film on YAG substrate was studied at room temperature by optial pump THz probe spectroscopy. After photoexcitation, an abrupt photoinduced positive THz photoconductivity (Δσ) occurs, which was developed into negative one within time scale of a few ps, and the negative Δσ reaches the maximum at delay time of 10 ps. The subsequent relaxation of the negative Δσ takes place within time scale of ~700 ps. The unusual photoexcitated relaxation reflects the dynamics of holes in Dirac cone and electrons beyond the linear cone in PtTe 2 thin film after photoexcitation.