Doping-induced spin polarization on the pristine Si surface: a Si(5 5 12)2 × 1 case

While spontaneous spin polarization is a desirable property in semiconductors, it has not been observed in pristine materials. A theoretical study suggested that the Au/Si(553) surface exhibits anti-ferromagnetic properties spontaneously. The Si(5 5 12) surface shares a similar atomic structure with the Au/Si(553) surface, particularly the presence of a stable honeycomb chain. The Si(5 5 12) surface exhibits four distinct surface structures: honeycomb chain, dimer, adatom, and tetramer. We find that while the pristine Si(5 5 12) shows no spin polarization, the doped Si(5 5 12) surface leads to spin splitting, primarily concentrated at the dangling bonds of the adatom and honeycomb chain. This spin splitting induces a transformation of the surface into a ferromagnetic state. Although the behaviors are rather different for the electron and hole doping, the surface magnetization roughly strengthens as the number of doped charges increases. These findings suggest that charge doping can be a viable approach to induce spin polarization in Si(5 5 12) surfaces, offering a potential route towards achieving this desired property in semiconductors.