On Co ₃ Sn ₂ S ₂ surfaces: crystal growth, surface recognition, atomic engineering and novel quantum structures

Kagome-lattice magnetic Weyl semimetal Co₃Sn₂S₂has emerged as a versatile platform for exploring interplays among band topology, magnetism, and electron correlations, exhibiting potentials for next-generation electronic and spintronic applications. This review provides an overview of recent advances in understanding the surface atomic and electronic structures and discovering novel physical properties of this material. We first present the synthesis of ultra-high quality Co₃Sn₂S₂single crystals by iterative chemical vapor transport growth methodology, which enables the growth of large, stoichiometric crystals with significantly enhanced physical properties. Next, we elucidate atomic scale identification of cleaved surfaces using joint work function measurements, bond-resolved non-contact atomic force microscopy, short-range force spectroscopy, and density functional theory calculations. Based on the explicitly identified surface, we next highlight the discovery and manipulation of localized spin-orbit polarons (SOPs) at S vacancies on the S surface, emphasizing their electronic and magnetic properties and the ability of manipulating specific SOP configurations at the atomic scale. We further show oxygen-induced quantum clusters, where O dopants modify the electronic states of surrounding atoms, providing building blocks for scalable functional quantum structures. Finally, we present the discovery of kagome electronic states on the Sn-terminated triangular-lattice surface and outline a proposed strategy for constructing such states with tunable properties. Collectively, these developments illustrate how high-quality crystal growth, atomic-scale imaging and manipulation, and defect/dopant engineering can be effectively integrated to discover and manipulate emergent novel physical properties of a kagome Weyl semimetal, opening new avenues for atomically precise design and surface state engineering in quantum materials.