Slowing down photocarrier relaxation in Dirac semimetal CdAs via Mn doping.

In this Letter, we successfully introduce a long-lived non-radiative photocarrier decay component in a Dirac semimetal CdAs thin film via Mn doping. The long-lived decay component is found to vary between 200 ps and 2.8 ns with different Mn concentrations and probing wavelengths. Most remarkably, the elongated transients persist over the important mid-infrared wavelengths (observed up to 4 μm). Saturable absorption measurement reveals stronger modulation effects for long-width pulses (∼80  ps) from the Mn-doped samples. Our results provide new insights into the effect of transition-metal doping on the ultrafast optical properties of Dirac semimetal CdAs and establish CdAs as a highly amendable material for mid-infrared photonic applications.