UC Riverside

Two-dimensional materials including graphene and transition metal dichalcogenides semiconductors are of tremondous interest for potential electronic applications because of their electronic properties and rich physics. In this work, using tight binding models, first principle calculation and non equilibrium Green’s function(NEGF) simulations, interlayer resistance of misoriented MoS2, electronic properties of tetralayer graphene and edge states of trilayer graphene nanoribbons are successively studied.

In transition metal dichalcogenides like MoS2, interlayer misorientation alters the interlayer distance, the electronic bandstructure, and the vibrational modes, but, its effect on the interlayer resistance is not known. We analyze the coherent interlayer resistance of misoriented 2H-MoS2 for low energy electrons and holes as a function of the misorientation angle. The electronic interlayer resistance monotonically increases with the supercell lattice constant by several orders of magnitude similar to that of misoriented bilayer graphene. The large hole coupling gives low interlayer hole resistance that weakly depends on the misorientation angle. Interlayer rotation between an n-type region and a p-type region will suppress the electron current with little effect on the hole current. We also estimate numerical bounds and explain the results in terms of the orbital composition of the bands at high symmetry points. Density functional theory calculations provide the interlayer coupling used in both a tunneling Hamiltonian and a non-equilibrium Green function calculation of the resistivity.

In multilayer graphene, as the Fermi level and band structure are readily tunable, they constitute an ideal platform for exploring the Lifshitz transition, a change in the topology of a material’s Fermi surface. In tetralayer graphene that hosts two intersecting massive Dirac bands, we provide numerical analysis of multiple Lifshitz transitions and multiband transport, which is manifest as a nonmonotonic dependence of conductivity on the charge density n and out-of-plane electric field D, anomalous quantum Hall sequences and Landau level crossings that evolve with n, D, and B.

Lastly, due to mirror symmetry the bands of ABA stacked trilayer graphene can be identified by their parity with respect to mirror symmetry. The even parity bands exhibit gapped bilayer graphene-like dispersion, while the odd parity bands exhibit a gapped graphene-like dispersion. Using a tight binding model with Slonczewski-Weiss-McClure parameters, we look at the edge states in trilayer graphene nanoribbons in the quantum hall regime. When mirror symmetry is preserved, the system exhibits quantized longitudinal conductance at charge neutrality point, due to counterpropagating even and odd parity edge modes. We study the effects of perpendicular electric field and magnetic field and mirror symmetry breaking disorder on the band structures and longitudinal conductance.