Study On Quantum Transport In Weyl Semimetal Heterojunction

In 1928,Dirac proposed a wave equation to describe massive spin-1/2 fermions.This Dirac equation is used to describe low energy excitations around certain points in the Brillouin zone.Graphene belongs to this Dirac material system.Due to the low spin-orbit interaction of graphene,physicists who used the method of epitaxial growth were preparation of silicene which performance similars to graphene.The strong spin-orbit in-teraction of silicene makes it appear many attractive features,such as quantum spin Hall effect,giant magnetoresistance effect and so on.In the presence of an applied electric field and an exchange field,silicene can produce various tunable quantum effects.These properties make silicene be an excellent material for the next generation of nanoelec-tronics.In 1929 Weyl discovered that when the mass in the Dirac equation is zero,the equation becomes Weyl equation.The Weyl equation can be used to describe the low-energy excitation behavior of materials in some condensed state systems,which we called Weyl semimetals.The point where the conduction band and the valence band come into contact is called the Weyl point.Weyl points must appear in pairs and are topologically stable.The topological protection of Weyl fermions may be used to achieve high fault tolerance in topological quantum computations.Based on the novel physical properties of silicene and Weyl semimetals,we explored their electronic transport properties.The specific content is arranged as follows:In Chapter 1,we mainly introduces the basic properties of silicene and Weyl semimet-als and experimental findings.In chapter 2,we introduce the theoretical methods used to study the electron trans-port properties of silicene and Weyl semimetals,including the quantum tunneling of the Dirac electron system,transfer matrix,and Landauer-buttiker formula.In Chapter 3,we studied the effect of a velocity barrier on the spin-and valley-dependent transport in ferromagnetic silicene.In the normal/ferromagnetic/normal sil-icene structure,there is a velocity barrier in the middle region.We theoretically calculate the transmission probability of the system.We also numerically calculate the effect of electron transmissivity at different velocity barriers.The transmissions are spin-valley resolved and are very sensitive to the relative Fermi velocity in the region II.When the on-site potential difference between A and B sublattices which we called?_zis same in the three regions,we numerically calculate the conductance and polarization as a function of the length of the second region under different velocity barriers.It was found that when the velocity barrier satisfies the corresponding condition,conductance was suppressed by a small velocity barrier.When?_zin the three regions are different,we also calculate the conductance and polarization as a function of the length of the second region under different velocity barriers,and the results are different from the previous ones.In Chapter 4,we study the magnetic transport in the Weyl semimetal which exists energy tilt.In the Dirac/Weyl/Dirac junction,magnetic field was applied in the middle region,energy tilt was in all three regions.We theoretically calculate the transmission of the system.The numerical calculations show that the electron transmission and conduc-tance will be different under different tilting strength and magnetic field strength.It was found that there is a relationship between the magnitude of the transmission and the tilt strength and the magnetic field strength.In Chapter 5,we briefly summarize the paper and look forward to the future research and development.