A minimal ``hydrogen atom" version of a time reversal invariant Weyl semimetal*

Typical Weyl semimetals host many Weyl points; for instance, TaAs has 24 Weyl points. However, the minimal nonzero number of Weyl points for a time reversal invariant crystal is four. Finding such a material would provide the simplest ``hydrogen atom" example of a Weyl semimetal. Applications may also be simpler in a system with as few Weyl points as possible. TaIrTe$_4$ is predicted to be a minimal Weyl semimetal. However, the Weyl points are well above the Fermi level, making them inaccessible to conventional ARPES. Here, we use pump-probe ARPES to directly observe Weyl points and topological Fermi arcs in TaIrTe$_4$ above the Fermi level. We find a total of four Weyl points, demonstrating the first minimal Weyl semimetal.