Hydrodynamic Electron Liquid Properties And Exchange Interactions In Two Dimensional Electronic Systems

The discovery of new types of two-dimensional electron gas（2DEG）materials such as graphene and monolayer transitional metal dichalcogenides（TMDs）had greatly enriched the family of 2DEG material systems and further promoted the research and development in the field of 2DEG.In this dissertation,the terahertz（THz）magneto-optical response properties of graphene-based hydrodynamics electron liquid and the quasiparticle char-acteristics induced by the proximity effect and electron-electron interaction in monolayer TMDs are theoretically investigated.We also discuss their potential applications in de-vices for electronics,optics,and optoelectronics.The research work are as follows:The terahertz magneto-optical absorption（magneto-optical conductivity）,Faraday rotation and magnetoplasmonic properties of graphene hydrodynamic electron liquid were investigated by using a momentum balance equation approach derived from Boltzmann equation and the dielectric function under random phase approximation（RPA）.When the magnetic field length（l_B=1/2h/eB）is equivalent to the mean free path of electron-electron interaction (l_B^l_ee),the magneto-optical effects such as cyclotron resonance and Faraday rotation in the terahertz regime can be significantly weaken by the viscous effect in graphene hydrodynamic electron liquid.With a magnetic field,there exists upper hybrid and cyclotron resonance magnetoplasmon modes.With large wave vectors,the magnetoplasmon modes are affected by the viscous effect with resulting in red-shifts of the magnetoplasmon frequencies.The results show that the magneto-optical and magnetoplasmon properties of graphene are strongly affected by the viscous effect.Monolayer molybdenum disulfide（MoS₂）has good electronic properties and strong intrinsic spin-orbit coupling.After considering the many-body effect with electron-electron interaction in monolayer MoS₂,the quasi-particle properties of monolayer MoS2at zero temperature are calculated via the RPA dielectric function and Green’s function theory.The screening effect increases with increasing the electron density.With the screening effect,the contribution of Hartree part on the self-energy only provides a con-stant background and can be ignored.Therefore,the influence from the exchange part on self-energy is mainly considered in this study.The exchange self-energy is mainly affected in small wave-vector.The exchange self-energy decreases gradually with increasing the wave vector.With the diagrammatic technique,the energy spectrum can be obtained by the Green’s function.The exchange self-energy could enhance the spin splitting in the energy spectrum.The spin splitting increases with increasing the total electron con-centration.The effect of self-energy on spin splitting is also mainly occur in small wave vector region.The results in this study indicate that the viscosity effect in graphene and the proxim-ity effect and exchange effect in monolayer MoS₂have strongly influence on the magneto-optical and magnetoplasmon properties of graphene hydrodynamic electron liquid and the spin splitting in the energy spectrum of monolayer MoS₂.