Question

I read that silicene has a stronger SOC than graphene. As far as I know the SOC ~ Z⁴. Thus, since silicon lies further in the periodic table, it explains why it has a stronger SOC than graphene. But are there other origins or grounds of the stronger SOC in silicene than in graphene?

Answer 1

In addition to silicon's higher atomic number contributing to a stronger Spin-Orbit Coupling (SOC) compared to carbon in graphene, the buckled structure of silicene's lattice allows for orbital mixing that further enhances SOC.

Step-by-step explanation:

The student asked why silicene has a stronger Spin-Orbit Coupling (SOC) than graphene, even though the strength of SOC is generally associated with the atomic number (Z) and increases roughly with Z4.

Aside from silicon (Si) having a higher atomic number than carbon (C), there are additional factors that contribute to silicene's stronger SOC. One of these factors is the structurally induced SOC due to a buckled configuration in silicene as opposed to the planar configuration of graphene.

Graphene's carbon atoms are sp2-hybridized, forming a planar hexagonal lattice that limits SOC. On the other hand, silicene has a somewhat similar hexagonal structure but with a significant difference: the silicon atoms adopt a slightly buckled configuration, which is a result of mixing between the silicon's 3p orbitals and the unoccupied 3d orbitals.

This mixing enhances the SOC in silicene, in addition to the naturally stronger SOC arising from the relativistic effects due to the higher atomic number of silicon compared to carbon.

Therefore, besides the electronic configuration of silicon (3s23p2), the buckling of the silicene structure greatly contributes to its enhanced SOC, differentiating it from the SOC found in graphene.