Ab Initio Calculations of Spin Splitting and Transport in the Binary Chiral SiC and BN Nanotubes

In terms of the ab initio cylindrical waves technique with due account of the effects of spin–orbit (SO) splitting of electron states, the band structures of the binary chiral single-walled SiC and BN nanotubes (SWNTs) are investigated. Thanks to the account of the helical symmetry of the tubules, their band structure is presented in a simple form with eight spin-dependent dispersion curves for the occupied states, which are separated from the conduction bands by the gaps with energies of 2.3–3.2 eV in the case of the SiC compounds, the spin–orbit splittings of the boundary bands being equal to 0.05–3.5 meV. A transition to the BN tubes is accompanied by an increase in the band gap by about 1.5 eV and a 10-fold decrease in the SO splitting energies. The band structures of SWNTs do not depend on their helicities, except for the opposite spin orientation in the right- and left-handed tubules. SWNTs suitable for the creation of the high oppositely directed α- and β-spin currents are determined assuming that electrons of the boundary spin states located at the edges of the valence and conduction bands dominate in the spin transport and that the probability of the electron tunneling through the chiral materials depends on a mutual orientation of the electron spin and material helicity vectors.