Theoretical Study Of Electronic Structure In Germanene Modulated By External Field

We investigate the electronic band structure of honeycomb lattice germanene crystal by using the sixteen band tight-binding calculation.We focus on the mod-ulation of its band gap with spin-orbit coupling(SOC),perpendicular electric field and magnetic field.Our calculation show that the SOC opens a tunable band gap in the Dirac-type electronic structures,and plays a crucial rule in the formation of the energy band gap.The influence of SOC on the gap in germanene is much larger than that in graphene,which makes germanene an ideal candidate to exhibit the quantum spin Hall effect at room temperature.We also find that the electron-ic structure and topological property of germanene can be tuned by the external field significantly.Thus the electronic structure of germanene can be controlled to produce metallic,semiconducting,or insulating properties by applying an appro-priate external field.In addition,the key features of the band structure induced by the electrical field and magnetic field are quite different.For the electric field applied,two spin-up states produce a gap at K point,in contrast,two spin-down states do it at K~′points.While for the magnetic field present,the band gaps are formed by the spin-up states from the conduction band and spin-down state from the valance band at both the K and K~′points.This modulation behavior of the band gap by the external field paves a way to the realization of germanene based spintronic devices.The rest of this paper is organized follows:In section 1,we make a brief summary with the 2D materials.In addition,we introduce the lattice structure,band dispersion relation,main physical properties,experimental and theoretical research progress of graphene and silicene in detail.what’s more,the spin-orbit coupling and the quantum spin Hall effect are intro-duced.At last,we concisely explain the background,main content and significance of this thesis.In section 2,We introduced the solid energy band theory which is the theo-retical basis of this work,and the tight-binding which can be used.Then,we uses it to calculate the band structure of germanene and other group-IV material.In section 3,we explores the electronic structure and its band gap are regu-lated by external field,and then,the influence of electric field and magnetic field on the electron structure of germanene in consideration of spin-orbit coupling is analyzed.Finally,the research methods,contents and conclusions of this paper are summarized in detail.We illustrate the main innovation points and the scientific significance of this thesis,and show the prospect of follow-up work.