B与N掺杂对单层石墨纳米带自旋极化输运的影响

Effects of B and N doping on spin polarized transport in graphene nanoribbons

通过第一性原理计算研究了具有锯齿状边沿并且具有反铁磁构型的单层石墨纳米带的自旋极化输运.研究发现,在中心散射区同一位置掺入单个B和N原子,尽管对整个体系磁矩的影响完全相同,但对两个自旋分量电流的影响却完全相反.掺B时,自旋向上的电流显著大于自旋向下的电流;而掺N时,自旋向下的电流显著大于自旋向上的电流.这是由于不管掺B还是掺N都将打破自旋简并,使得导带和价带中自旋向上的能级比自旋向下的能级更高.掺B引入空穴,使完全占据的价带变为部分占据,从而自旋向上的能级正好处于费米能级,使得电子透射能力更强、电流更大,而自旋向下的能级则离费米能级较远使电子透射的能力较弱.掺N则引入电子,使得原来全空的导带变为部分占据,从而费米能级穿过导带中自旋向下的能级,使得自旋向下的电子比自旋向上的电子透射能力更强.

First principles calculations are performed to study the spin polarized transport in zigzag-edged graphene nanoribbons with anti-ferromagnetic ordering. It is found that when a single B or an N atom is doped in the central scattering region, their effects on the different spin components of current are completely different, though they play the same role in reducing the magnetic moments of the edge carbon atoms. In the B doping case, the spin-up component in current is much larger than the spin-down component, while the situation is opposite to the N doping case. This originates from the fact that the spin degeneracy is broken and the spin-up energy levels in the valence band and the conduction band are higher than the spin-down energy levels in both cases. B doping introduces a hole so that the fully filled valence band becomes partially filled and the Fermi level shifts down to the spin-up energy levels in the valence band while the spin-down energy levels in it are a little far from the Fermi level. This strengthens the transmission of electrons in the spin-up channel more than it does for the spin-down electrons. N doping introduces an electron which makes the empty conduction band partially filled so that the Fermi level shifts up to the spin-down energy levels in the conduction band. This strengthens the transmission of electrons in the spin-down channel more than it does for the spin-up electrons.