Study On Quantum Transport Properties Of ?-T₃ Model And Borophene

In 2004,two British scientists isolated a single-layer graphene experimentally for the first time,and the electronic properties of graphene have become a research hotspot since then.Some special quantum properties have been discovered in graphene,which has achieved great success in both fundamental studies and practical applications.Graphene has found more and more applications in electronic devices.Because of the emergency of graphene,the Dirac two-dimensional materials have attracted considerable attention from the scientific community.As members of graphene-like materials,borephene,silicene and?-T₃lattice,have also been intensively investigated due to the unique quantum transport properties.In this dissertation,we focus on the quantum transport properties of?-T₃lattice and borophene.Firstly,in the first chapter,we introduced the relationship between graphene and?-T₃lattice,described the structure of?-T₃lattice and its research status;then we introduced the structure,preparation and applications in various fields for borophene.Next,we introduce the theories and methods for quantum transport in chapter two.There are many numerical methods to study the quantum transport properties of the two-dimensional materials,such as scattering matrix,transfer matrix and non-equilibrium Green's function,and we mainly focus on the tight-binding model and the non-equilibrium Green's function.At the end of this chapter,we introduce some softwares for theoretical calculations of materials.We detailly introduce the computational software Kwant for 2D materials study,including the advantages and applications of this software.In chapter three,we study the quantum transport in?-T₃lattice in the presence of a perpendicular magnetic field.It is found that valley pseudospin is also a very important degree of freedom for electrons in?-T₃lattice,which can be modulated by the magnetic field.When a perpendicular magnetic field is applied to?-T₃lattice,the electrons in the two valleys have different responses to the magnetic field.We found that the continuous subbands of?-T₃lattice are splitted into discrete Landau levels by the perpendicular magnetic fields,and the Landau levels for the two valleys are different,which leads to high valley polarization.Our results may stimulate further experimental studies of the realization of valleytronic devices.In chapter four,we report a theoretical study of electronic transport properties of?-T₃lattice nanoribbons in the presence of both magnetic and electric fields.A transverse electric field can modify the Landau levels in an interesting way,and Landau levels with an unexcepted fashion are obtained.It is found that the nondispersive flat band of?-T₃lattice is distorted and split to many dispersive energy levels when electric and magnetic fields are applied.A double constriction structure of?-T₃lattice is considered to investigate the quantum transport in the flat band,and the flat bands have great differences from conventional Dirac electron in the quantum transport properties.Our results show that the flat bands of?-T₃lattice can also contribute to the quantum transport properties and play an important role in the development of novel Dirac electron device.In chapter 5,we study the thermoelectric transport properties of borophene,and we mainly focus on the Seebeck effects of borophene.We consider borophene nanoribbons with different types of edges and investigate their band structures.We found that the BB edge type borophene nanoribbons have an energy gap in the absence of an external field,while the other types do not have an energy gap.Based on these results for borophene nanoribbons,we furtherly studied the Seebeck effects of these three different boundary borophene nanoribbons.We found that the Seebeck coefficient of BB edge borophene nanoribbon is much larger than that of AA edge and AB edge borophene nanoribbon.Subsequently,we studied the Seebeck coefficient of BB edge-type borophene with different widths,and we found that the value of Seebeck coefficient is proportional to the energy gap of borophene ribbon.Our results suggest that borophene has potential applications in thermoelectric devices.