Scattering rate collapse driven by a van Hove singularity in the Dirac semimetal ${\mathrm{PdTe}}_2$

We present optical measurements of the transition metal dichalcogenide ${\mathrm{PdTe}}_2$. 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.

Figure 1

Reflectivity for selected temperatures. A steplike feature that develops at approximately 37 meV is indicated by S1, while a second feature 17 meV is indicated by S2. Both features become more prominent with decreasing temperature. The inset shows the reflectivity over the full range.

Figure 2

Optical conductivity at selected temperatures. We observe a midinfrared band centered around 0.5 eV. A second interband transition features prominently in the visible range (1.5 eV). The inset shows the low energy, optical response. Dashed lines are extrapolations based on the Drude-Lorentz model, while full lines are Kramers-Kronig transformed data. Note the formation of an optical gap around 0.03 eV at low temperature.

Figure 3

(a) Frequency and temperature dependent optical scattering rate for selected temperatures. The scattering rate displays a linear frequency dependence at high temperature, whereas it becomes frequency independent at low temperature and energy. (b) The mass enhancement factor shows a strong decrease of the mass renormalization with decreasing temperature. The inset displays the temperature dependent scattering rate at 0.025 eV.