Light-modulated Electron Retroreflection And Klein Tunneling In A Graphene-based N-p-n Junction

In 2004,Geim et al.successfully prepared and observed single-layer graphene by a simple method of mechanical stripping,and since then,the research upsurge of two-dimensional materials has been set off.How to develop,design and accurately apply it to new quantum devices is a hot topic in the field of condensed matter physics in recent years.In this paper,we focus on typical two-dimensional graphene materials.By combining theoretical derivation and numerical calculation,we study and discuss electron reflection and Klein tunneling phenomena in n-p-n junction irradiated by non-resonant linearly polarized light along the x direction.In Chapter 1,we mainly introduce the basic physical properties and electronic structure of graphene materials and carbon monolayers.In Chapter 2,we mainly introduce Floquet theory,wave function and its connection method.In Chapter 3,we study electron transport in graphene n-p-n junction under optical modulation.In isotropic system,only electron specular reflection occurs at the interface due to the same transverse wave vector and velocity component along the interface direction.In an anisotropic system,the anisotropic band structure causes the transverse wave vector to be opposite to the velocity component along the interface,which makes the electron reflection possible.We use linearly polarized light to induce the anisotropic band structure of graphene and achieve electron reflection in the constructed system by adjusting the direction of the n-p-n junction and the intensity of light.In Chapter 4,we studied the abnormal Klein tunneling based on the light field regulation in graphene n-p-n junction.Floquet theory was used to irradiate linearly polarized light along the x direction,and the phenomenon of abnormal Klein tunneling was found in graphene n-p-n junction.We also deduced the incident wave,reflected wave and transmitted wave functions in different regions of the system.It is demonstrated that light-modulated Klein tunneling can occur at non-zero incident angles.This finding goes beyond the traditional view that Klein tunneling effects occur at specific angles in specific devices,and thus provides a flexible method to modulate electron echo and Klein tunneling.In the last chapter,we summarize this paper and look forward to the future research work.