  We have investigated the magnetic Co atoms self-assembled on the ultraflat
stanene on Cu(111) substrate by utilizing scanning tunneling
microscopy/spectroscopy (STM/STS) in conjunction with density functional theory
(DFT). By means of depositing Co onto the stanene/Cu(111) held at 80 K, Co
atoms have developed into the monomer, dimer, and trimer structures containing
one, two, and three Co atoms respectively. As per atomically resolved
topographic images and bias-dependent apparent heights, the atomic structure
models based on Sn atoms substituted by Co atoms have been deduced, which are
in agreement with both self-consistent DFT calculations and STM simulations.
Apart from that, the projected density of states (PDOS) has revealed a minimum
at around -0.5 eV from the Co-3d3z2-r2 minority band, which contributes
predominately to the peak feature at about -0.3 eV in tunneling conductance
(dI/dU) spectra taken at the Co atomic sites. As a result of the exchange
splitting between the Co-3d majority and minority bands, there are non-zero
magnetic moments, including about 0.60 uB in monomer, 0.56 uB in dimer, and
0.29 uB in trimer of the Co atom assembly on the stanene. Such magnetic Co atom
assembly therefore could provide the vital building blocks in stabilizing the
local magnetism on the two-dimensional (2D) stanene with non-trivial
topological properties.
