Observation of a van Hove singularity of a surface Fermi arc with prominent coupling to phonons in a Weyl semimetal

A van der Waals coupled Weyl semimetal ${\mathrm{NbIrTe}}_{4}$ is investigated by combining scanning tunneling microscopy/spectroscopy and first-principles calculations. We observe a sharp peak in the tunneling conductance near the Fermi energy (${E}_{F}$). Comparison with calculations indicates that the peak originates from a van Hove singularity (vHs) associated with a Lifshitz transition of the surface Fermi-arc state. Interestingly, our tunneling spectroscopy also shows signatures of strong electron-boson coupling. This is potentially due to an anomalously enhanced charge susceptibility coming from the near-${E}_{F}$ vHs formation.