TOP. This is a typical image of the surface of the CrBiSbTe sample and the location of each Cr magnetic dopant atom is known because each produces a dark triangular 'depression' in the surface.
BOTTOM. This is a typical image of the Dirac mass of topological surface electrons in CrBiSbTe. The location of each Cr magnetic dopant atom is marked as a red dot. The Dirac mass evolves from being very low ( blue black) far form dopant atom clusters to very high (yellow) where the magnetic Cr atoms are observed to be dense.