Scattering Rate Collapse Driven By A Van Hove Singularity In The Dirac Semimetal Pdte2

We present optical measurements of the transition metal dichalcogenide PdTe2. The reflectivity displays an unusual temperature and energy dependence in the far infrared, which we show can only be explained by a collapse of the scattering rate at low temperature, resulting from the vicinity of a van Hove singularity near the Fermi energy. An analysis of the optical conductivity suggests that below 150 K a reduction in the available phase space for scattering takes place, resulting in long-lived quasiparticle excitations. We suggest that this reduction in phase space provides experimental evidence for a van Hove singularity close to the Fermi level. Our data furthermore indicates a very weak electron-phonon coupling. Combined this suggests that the superconducting transition temperature is set by the density of states associated with the van Hove singularity.