Direct observation of handedness-dependent quasiparticle interference in the two enantiomers of topological chiral semimetal PdGa.

It has recently been proposed that combining chirality with topological band theory may result in a totally new class of fermions. These particles have distinct properties: they appear at high symmetry points of the reciprocal lattice, they are connected by helicoidal surface Fermi arcs spanning the entire Brillouin zone, and they are expected to exist over a large energy range. Additionally, they are expected to give rise to totally new effects forbidden in other topological classes. Understanding how these unconventional quasiparticles propagate and interact is crucial for exploiting their potential in innovative chirality-driven device architectures. These aspects necessarily rely on the detection of handedness-dependent effects in the two enantiomers and remain largely unexplored so far. Here, we use scanning tunnelling microscopy to visualize the electronic properties of both enantiomers of the prototypical chiral topological semimetal PdGa at the atomic scale. We reveal that the surface-bulk connectivity goes beyond ensuring the existence of topological Fermi arcs, but also determines how quasiparticles propagate and scatter at impurities, giving rise to chiral quantum interference patterns of opposite handedness and opposite spiralling direction for the two different enantiomers, a direct manifestation of the change of sign of their Chern number. Additionally, we demonstrate that PdGa remains topologically non-trivial over a large energy range, experimentally detecting Fermi arcs in an energy window of more than 1.6 eV symmetrically centerd around the Fermi level. These results are rationalized in terms of the deep connection between chirality in real and reciprocal space in this class of materials, and they allow to identify PdGa as an ideal topological chiral semimetal.