Light wave induced nanosecond-long persistent state in the Dirac semimetal Cd3⁢As2

Abstract

Unraveling light induced ultrafast dynamics in three-dimensional Dirac materials is crucial for deepening our fundamental understanding and for advancing potential optoelectronic applications. While time-resolved pump-probe spectroscopy has predominantly revealed carrier dynamics governed by Dirac fermion cooling and population inversion, the full picture of relaxation pathways remains incomplete. In this Letter, we identify a relaxation channel in these materials. Using strong terahertz (THz) field excitation combined with a near-infrared (NIR) probe, we detect a long-lived carrier population persisting on the nanosecond timescale. This extended lifetime suggests that carriers become trapped in defect states, leading to sub-band-gap absorption in the NIR and pointing to the significant role of defect-assisted relaxation in the carrier dynamics of Dirac semimetals.