Surface Preparation of Weyl Semimetal Mn₃Sn

Weyl semimetals are a class of topological materials whose low-energy quasiparticle excitations behave like Weyl fermions, particles long predicted in high-energy physics. These unique excitations are related to several phenomena of interest including topologically-protected surface states called Fermi arcs. Recent ARPES and first-principle studies have suggested that Mn₃Sn is a magnetic Weyl semimetal. However, experimental observation of the Weyl nodes and the Fermi arcs remain elusive. One major difficulty is that the naturally cleaved surface of Mn₃Sn is not atomically flat, making it difficult to use surface-based techniques such as scanning tunneling microscopy and spectroscopy (STM/STS). To address this issue, we treated the surface with in-situ sputtering and annealing and found that the annealing temperature and duration were most important to cleaning the surface. The quality of the surface was assessed by STM and low-energy electron diffraction. We used our findings to begin to develop a reasonably reproducible recipe for improving the quality of the Mn₃Sn surface, taking a step towards exploring the Weyl physics of this material with STM/STS.