The Theoretical Study Of Edelstein Effect In Dirac Pseudospin System

In this thesis,based on the linear response theory and Green's function method,we study the spin polarization induced by an external electric field in a pseudospin Dirac system with low symmetry.We have made an extensive research about Dirac materials.The theoretical background and the concrete research content about the transport properties in these systems are introduced,where the Edelstein effect is included.Besides,we give the main theoretical method and the idea of calculating the transport quantities in this thesis.We focus on the content of the Kubo formula that is very important in the linear response theory.More carefully,we have described the content including the theoretical structure,the rules,and the application of Green's function in many-body physics.Finally,using the Kubo formula based on the Matsubara technique,we give the primary coverage to study the transport theory in equilibrium state,where we get the physical picture of the conventional Edelstein effect.We propose a new mechanism originating from the general spin-orbit coupling about the new type Edelstein effect in pseudospin Dirac system with low symmetry.Through the process of the theoretical calculation,we design an experimental method to observe this type of Edelstein effect in pseudospin Dirac system and predict the other possibility in current-induced spin polarization based on the pseudospin-spin coupling in pseudospin Dirac system with low symmetry.We first pay attention to the conventional Edelstein effect in the model with Rashba spin-orbit coupling in the thesis.These attempts give us the possibility to reveal the new physical picture in the new model.Then,we take the sight into the pseudospin Dirac system.We concentrate on brief contents of the topological invariant and theoretical model in Dirac topological material,which contain some materials with the exotic property like topological insulator,Dirac semimetal and Weyl semimetal,and so on.With the help of Berry theory,we introduce the concept of Chern number and Z₂invariant,which are used to quantify the nontrivial topological phase in topological material.Furthermore,We explore the more sophisticated form in Dirac systems.In the process of studying the transport theory,we exploit linear response theory by adopting the Matsubara technique.The method exhibits the advantage of self-energy extension using the Feynman diagram.To some extent,we simplify the form in calculating current-induced spin polarization in the complex pseudospin Dirac system under the condition of dc and zero temperature.Meanwhile,we give the analytic solution of this model through the tedious derivation.We also introduce the basic content about the orbital Edelstein effect and optical nonlinear Edelstein effect.We give a systematical study on the spin polarization in 1T^?-WTe₂monolayer in the presence of external electric fields.The conventional Edelstein effect can be understood by a spin Zeeman term which straightly comes from an effective magnetic field due to the external electrical field.We propose a mechanism of this new type of Edelstein effect in this thesis.What differs from the conventional Edelstein effect is that the new one is not directly induced by the effective magnetic field.The effective magnetic field first results in a general spin,then the real spin is generated through the coupling between the general spin and the real spin.The values of spin polarization generated by the new type of Edelstein effect,which though involves two processes,could have the same magnitude as the one coming from the conventional Edelstein effect.In addition to the part of the analytical results,we also take the numerical calculations in the monolayer of 1T^?-WTe₂being in accordance with our analytical discussion.We further take the numerical analysis in the crystal multi-valley model to testify our conclusion.The numerical results of the lattice model agree with the result of the continuous model.In conclusion,we study the Edelstein effect in the topological material system.The work will guide the potential applications in the Edelstein effect.It will help the researcher to further understand the spin polarization in the pseudospin Dirac system.