Survey of Sn and S Surface Terminations and Sulfur Migration on Co₃Sn₂S₂ With Experimental STM Measurements

Co₃Sn₂S₂ is a kagome magnet Weyl semimetal with Fermi arc contours and Weyl node connectivity that is directly influenced by its three surface terminations. Using scanning tunneling microscopy (STM), we investigate the two most common surface terminations, the Sn and S surfaces, to determine the boundaries between different atomic regions and categorize defect sites. As a result of the Sn-Sn bonding and distance between the Sn and the S layers, partial cleaving terminations can occur with variable coverage of Sn vacancies on the Sn surface and Sn adatoms on the S surface. Along with vacancies and adatoms, the boundary between Sn and S surfaces has intermediate zones that have changing S and Sn coverage.[1] For the Sn termination face, we have observed a high density of Sn vacancies near step edges, revealing sulfur sites below and increasing Sn coverage away from the step edge. We are continuing to study the density of vacancies and their configurations around defect sites. The length scale and varying density of boundary transitions will also be observed. For the S sites, we are also investigating the possible migration behavior as a function of time and temperature.

[1] Yin et al, Nature Physics 15, 444 (2019).