Coalescence of Andreev bound states on the surface of a chiral topological semimetal

TL;DR

This study explores how magnetic fields influence Andreev bound states on the surface of a CoSi topological semimetal, revealing state coalescence and stability linked to spin texture and spin-orbit coupling effects.

Contribution

It provides experimental evidence of magnetic field effects on Andreev states in CoSi, highlighting anisotropic behavior and the role of spin texture in topological surface states.

Findings

Andreev bound states move to zero bias with in-plane magnetic field

Zero-bias resistance remains stable under in-plane magnetic field

Magnetic field effects are consistent across different superconducting leads

Abstract

We experimentally investigate the magnetic field dependence of Andreev transport through a region of proximity-induced superconductivity in CoSi topological chiral semimetal. With increasing parallel to the CoSi surface magnetic field, the sharp subgap peaks, associated with Andreev bound states, move together to nearly-zero bias position, while there is only monotonous peaks suppression for normal to the surface fields. The zero-bias $dV/dI$ 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 proximized CoSi surface. The Andreev states coalescence and stability of the zero-bias $dV/dI$ value with increasing in-plane magnetic field are interpreted as the joined effect of the strong SOC 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.