No abstract

By performing density functional theory calculations, we studied the quantum confinement in charged graphene quantum dots (GQDs), which is found to be clearly edge and shape dependent. It is found that the excess charges have a large distribution at the edges of the GQD. The resulting energy spectrum shift is very nonuniform and hence the Coulomb diamonds in the charge stability diagram vary irregularly, in good agreement with the observed nonperiodic Coulomb blockade oscillation. We also illustrate that the level statistics of the GQDs can be described by a Gaussian distribution, as predicted for chaotic Dirac billiards. The charge stability diagram (left) and the Gaussian distribution of the width of the Coulomb diamonds (right), indicating the nonperiodic Coulomb blockade oscillation in GQD due to quantum confinement. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Silicene is a potential candidate for valleytronics. However, in comparison with the transition metal dichalcogenides, silicene has a tiny energy gap and zero spin splitting at its Dirac valleys, being unfavorable for valleytronic applications. Based on first principles calculations, we find that by proximity with Bi (111) bilayer, the Dirac valleys of silicene acquire a sizable energy gap and giant spin splittings, which are even larger than the splittings of MoS 2 . Our calculations show that the silicene over Bi layer exhibits a strong valley-contrasting circular dichroism, enabling selective optical pumping of valley carriers. Due to the time reversal symmetry and the breaking of inversion symmetry, the Berry curvatures and the spin-splittings are opposite at the K and K′ valleys of silicene, and hence the valley and spin are locked and can be simultaneously polarized. In this way, silicene and likely other similar Dirac materials can be comparable to transition metal dichalcogenides in valleytronics, which not only adds a new dimension to the properties of silicene but also expands the members of valleytronic family.

No abstract

No abstract