Novel Landau-level Structure And Field-modulated Feature In Graphene-like Material

After successful fabrication of graphene in 2004,two-dimensional(2D)graphene have become a research hotspot.Following graphene,other two-dimensional graphene-like materials have been emerging one after another,such as.silicene and monolayer molybdenum disulfide(MoS2).In contrast with the planar hexagonal lattice structure in graphene,silicene is a nonplanar low-buckled lattice structure,with one of the two sublattices of the honeycomb lattice being displaced vertically with respect to the other,and then a measurable bandgap can be opened at the Dirac points due to the spin–orbit interactions in silicene.Monolayer MoS2 is a 2D hexagonal lattice structure which contains two different elements from top view,while from side view,it is consists of a layer of molybdenum atoms between two layers of sulfur atoms forming a sandwich structure.Monolayer MoS2 is an indirect bandgap semiconductor with a considerable bandgap due to the stronger spin-orbit coupling compared to silicene.As well known,the energy spectrum of 2D quantum systems evolves into a series of quantized Landau levels in the presence of a perpendicular magnetic field.The unusual energy band structure in the graphene-like materials should lead to novel Landau energy states.Recently,under the uniform and nonuniform magnetic fields,the Landau level structures inmonolayer and bilayer graphenes were studied.Based on the previous works,in this thesis we further explore the features of the Landau energy states in the silicene and monolayer MoS2 subjected to the uniform or nonuniform magnetic fields.The results indicate that(1)the Landau levels in silicene and monolayer MoS2 are spin-dependent and valley-dependent,with lifting of the Landau-level degeneracy spin degeneracy of;(2)there exist unique Landau levels that is undependent on magnetic fields for certain a particular valley in silicene and monolayer MoS2;(3)especially for monolayer MoS2,the inversion symmetry breaking effect of Landau level spectrum occurs;(4)furthermore,in nonuniform magnetic field,the Landau states of the system are strongly dependent on the inhomogeneity of the magnetic field,and the mixing of the finite Landau levels could occur.We think that the obtained results could be probed by magneto-optical absorption in the graphene-like materials.