Spin Properties of Silicon–Germanium Nanotubes

The dependence of the electronic structure on the chirality of single-walled SiGe nanotubes has been studied using a linear augmented cylindrical wave method. It has been shown that all nanotubes have a semiconductor type of band structure with a bandgap E_g of about 0.35 eV. This feature distinguishes them from carbon, silicon, or germanium analogues, which, depending on chirality, have semiconductor, semimetal, or metal properties. This difference is caused by the polarity of the Si–Ge chemical bond and, consequently, the effect of the antisymmetric component of the electronic potential on the band structure of the compounds. The valence band with a width of ~12 eV consists of the inner band with a width of 2 eV made up of predominantly s electrons and the higher-lying band of p electrons with a width of 8 eV. The energies of the spin–orbit gaps of the edges of the valence band and the conduction band differ significantly: for nonchiral nanotubes, they constitute a few tenths of meV, while for chiral nanotubes, these energies are a few meV. Mechanical action on the tube, for example, twisting a nanotube around its axis or uniaxial loading, makes it possible to control the spin–orbit gap energies, which can find application in spintronics for controlling spin transport in nanotubes.