The carrier doping effects on the magnetic properties of defective graphene with a hydrogen chemisorbed single-atom vacancy(H-GSV)are investigated by performing extensive spin-polarized first-principles calculations.Theoretical results show that the quasi-localized pz-derived states around the Fermi level are responsible for the weakened magnetic moment(MM)and magnetic stabilized energy(MSE)of the H-GSV under carrier doping.The mechanism of reduced MSE in the carrier doped H-GSV can be well understood by the Heisenberg magnetic coupling model due to the response of these p_(z)-derived states to the carrier doping.Within the examined range of carrier doping concentration,the total MM of H-GSV is always larger than 1.0μ_(B) with μ_(B) representing the Bohr magneton,which is mainly contributed by the localized sp^(2) states of the unsaturated C atom around the vacancy.These findings of H-GSV provide fundamental insight into defective graphene and help to understand the related experimental observations.
Topological insulators (TIs) are bulk insulators that possess robust helical conducting states along their interfaces with conventional insulators. A tremendous research effort has recently been devoted to TI-based heterostructures, in which conventional proximity effects give rise to a series of exotic physical phenomena. This paper reviews our recent studies on the potential existence of topological proximity effects at the interface between a topological insulator and a normal insulator or other topologically trivial systems. Using first-principles approaches, we have realized the tunability of the vertical location of the topological helical state via intriguing dual-proximity effects. To further elucidate the control parameters of this effect, we have used the graphene-based heterostructures as prototypical systems to reveal a more complete phase diagram. On the application side of the topological helical states, we have presented a catalysis example, where the topological helical state plays an essential role in facilitating surface reactions by serving as an effective electron bath. These discoveries lay the foundation for accurate manipulation of the real space properties of the topological helical state in TI-based heterostructures and pave the way for realization of the salient functionality of topological insulators in future device applications.
