Year

2014

Degree Name

Doctor of Philosophy

Department

School of Physics

Abstract

We study the nonlinear optical response of single layer layer graphene (SLG) and several of its sister-structures, and the transport properties of bilayer graphene (BLG) and two-dimensional electron gas with Rashba spin-orbit interaction (R2DEG) in this Thesis.

We found that SLG exhibits a strong intraband nonlinear optical response, requiring a moderate field strength in the order of 104 V/cm. In the presence of a strong electric field strength, the third-order nonlinear current density increases at elevated temperature. The situation becomes more complicated in the case of gapped graphene. We found that the nonlinear optical response of gapped graphene is sensitively influenced by the temperature and the magnitude of the bandgap.

For the interband nonlinear optical response, the presence of the k-parabolic term in the Hamiltonian of these structures not only preserve their nonlinear interband optical response, but also induces a temperature robustness. These systems exhibit enhanced optical nonlinearity at higher temperature. In gapped graphene, the threephoton interband nonlinear optical absorption generates a sub-gap nonlinear response peak. Together with the linear response peak, gapped graphene exhibits two-color response at terahertz frequency regime. In graphene superlattice, the Dirac cone is elliptically deformed and it is found that this elliptical deformation of the band structure enhances both of the linear and nonlinear optical responses.

In the transport study of bilayer graphene/superconductor (BLG/S) heterojunction we obtained two main results. First, retro reflection of electron can occur at the interface. This retro-type reflection is the most unusual and it represents the last missing pieces of the quantum transport phenomena at a superconductor heterojunction where specular electron reflection, retro and specular Andreev reflections have all been demonstrated. Second, due to the unique spinor structure of the BLG low energy quasiparticle wavefunction, electron transmitting into the superconductor is strictly forbidden and this results in the total absence of the Andreev reflection in a BLG/S heterojunction.

The consequences of band topology on the electron transport properties of R2DEG are studied. Because of the band turning and the band crossing of the two spin-plit branches, the electron transport exhibits hybrid behaviors of massless and massive chiral fermions. Furthermore, we found that the tunneling at the vicinity of the band crossing point produces a spin-polarizing effect.

Finally, we calculate the energy loss rate of a fast charged particle scattering off graphene. We found that the absence of backscattering is not only an intrinsic property between two massless Dirac quasiparticles, but it also occurs between an external charged particle and a massless Dirac quasiparticles. Graphene becomes completely transparent to a charged particle of kinetic energy lower than approximately 3 eV.

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