Coalescence of Andreev Bound States on the Surface of a Chiral Topological Semimetal

We experimentally investigate the magnetic field dependence of Andreev transport through a region of proximity-induced superconductivity in the CoSi topological chiral semimetal. With increasing magnetic field parallel to the CoSi surface, the sharp subgap peaks, associated with Andreev bound states, move together to nearly-zero bias position, while there is only monotonic peaks suppression for normal to the surface fields. The zero-bias resistance value is perfectly stable with changing the in-plane magnetic field. As the effects are qualitatively similar for In and Nb superconducting leads, they reflect the properties of a proximized CoSi surface. The Andreev states coalescence and stability of the zero-bias value with increasing in-plane magnetic field are interpreted as the joined effect of the strong spin–orbit coupling and the Zeeman interaction, known for proximized semiconductor nanowires. We associate the observed magnetic field anisotropy with the recently predicted in-plane polarized spin texture of the Fermi arcs surface states.