【作者】 魏亚东；

【导师】 姜永远； 李伟奇；

【作者基本信息】 哈尔滨工业大学 ， 物理学， 2021， 博士

【摘要】 随着以电子作为信息传输载体的硅基器件逐渐逼近摩尔定律的极限,光子成为下一代信息传输器件的重要载体。寻找高效率、易集成的非线性光学器件组分材料成为当今构建高效率全光信息处理系统亟待解决的问题。低维材料的量子限域效应赋予了其独特的电学和光学性质。随着石墨烯、二硫化钼和黑磷等二维材料制备技术逐渐成熟并在光电领域应用的迅速拓展,低维材料在非线性光学器件领域的发展逐渐得到重视。量子力学的紧束缚方法和第一性原理是研究材料光和物质的相互作用,尤其是非线性光学性质的有效手段。本论文通过紧束缚模型、态求和方法和现代极化理论态运动方程,研究了几种对称性破缺低维材料的二阶非线性光学性质。利用紧束缚理论,研究了锯齿形石墨烯纳米带在施加横向电场条件下引发的二阶非线性光电流响应。石墨烯纳米带的边缘态受电场作用,简并性和对称性被打破,从而改变了纳米带的能带结构,引发了属于光学二阶非线性的光学电流注入和位移电流。研究结果发现,电场对于光学电流注入响应具有微扰特征,而位移电流对外加电场则有明显的非线性依赖关系。此外,纳米带的宽度和化学势对两种二阶非线性电流响应也有影响。研究纳米带电场诱导的二阶非线性电流响应,对研究纳米带超快电流响应或体光伏效应具有指导性价值。对于具备面内自发极化的二元磷族单层材料,通过密度泛函理论和态求和方法,研究了具有褶皱形结构的黑磷相二维材料的面内极化对其二阶极化率张量元的影响。结果表明,结构对称性破缺引入的面内极化对黑磷相二元磷族单层材料的面内二阶非线性极化张量元有明显增强作用,黑磷相砷化磷单层材料（α-PAs）沿着极化方向具有极高的二阶非线性张量元,比MoS₂单层等材料高出1-2个数量级,该张量元的峰值主要由带边的带内双光子跃迁贡献。研究揭示了具有褶皱形结构的黑磷相二维材料面内极化和二阶非线性极化张量间的定性关系。对于具备面外自发极化的材料,如蓝磷相二元磷族单层和Janus MoSSe的单层和堆叠体块材料,通过现代极化理论态运动方程计算了材料受外加电磁场产生的二阶非线性极化,研究面外极化对非线性光学响应的影响。自发极化首先使得蓝磷的反转对称性被破坏,能带结构组成出现明显差异。此外,面间偶极的增加可以明显增加面内非线性极化率,并引入数量级接近面内极化率的面外极化率。Janus MoSSe的面外对称性破缺增加了非零独立非线性极化率成分的数量,从而提高了各个方向的入射光利用效率。其体块堆叠的面外极化率响应非零,改善了MoS₂材料无面外非线性极化率以及面内非线性极化率的层数依赖的不足。结合多体微扰论,将态运动方程转换为推迟格林函数的运动方程,研究了二元磷族单层材料的线性响应和Janus过渡金属硫族化合物二维材料的二阶非线性响应。研究表明,自发极化、激子和二阶非线性响应三者之间存在密切联系。自发极化对激子的辐射寿命、半径和各向异性产生明显影响。由于自发极化的方向不同,其对不同相的二元磷族单层材料的激子性质产生了相反的影响。对Janus过渡金属硫单层材料的二阶非线性响应研究表明,激子效应可以增强位于带隙以下的面内极化率,并减小带隙以上的面内极化率,对低能区间极化率的面外分量也具有增强作用。更多还原

【Abstract】 Today,with Moore’s Law based on silicon materials and electronic transmission information approaching to the limit,photons become an important carrier of the next generation of information transmission devices.Finding high-efficiency and easy-to-integrate nonlinear optical component materials has become an urgent problem to solve in a high-efficiency all-optical information processing system.The quantum confinement effect of two-dimensional materials endows them with unique electrical and optical properties.With the development of two-dimensional materials,such as graphene,molybdenum disulfide and black phosphorus,becoming mature and rapidly expanding in the field of optoelectronics,the development in the field of nonlinear optical devices has been paid more and more attention.Because of the strong dependence of experimental research on experimental conditions,the tight binding method based on quantum mechanics and first principles are effective means to study the optical properties of materials.In this paper,the tight-binding model,the sum-over-state method based on the first-principles calculation and the state motion equation based on the modern polarization theory are used to study the influence of asymmetry on the second-order nonlinear optical properties of two-dimensional materials.Using tight binding theory,the second-order nonlinear current response induced by applying transverse electric field on zigzag graphene nanoribbons is studied.The edge state of graphene nanoribbons is affected by electric field,and its degeneracy and symmetry are broken,thus changing the band structure and inducing optical current injection and shift current which belong to optical second-order nonlinearity.It is found that electric field has perturbation characteristics for optical current injection response.And the shift current has nonlinear relations to the external electric field.In addition,width and Fermi level also have effects on two kinds of second-order nonlinear current responses.Studying the second-order nonlinear current response induced by nanoribbon electric field has guiding value for developing the ultrafast current response of nanoribbon or bulk photovoltaic effect.For 2D group-VA binary monolayer with in-plane polarization,using sum-over-state method based on density functional theory,we studied the effect of polarization on the second-order susceptibility tensors.The significant enhancement of second-order susceptibility tensor is predicted,due to the in-plane polarization induced by structural asymmetry.We found the giant second harmonic generation component ofα-PAs monolayer along the direction of polarization.It is one or two orders higher than that of MoS₂ monolayer.The peak value originates from the intraband two-photon transition process.This study released the qualitative relations between in-plane polarization and second order nonlinear polarization tensor in 2D materials with puckled structure.For materials with out-of-plane polarization,such as 2D group-VA binary monolayer materials with blue phase and Janus MoSSe monolayer and stacked bulk,the second-order nonlinear polarization of materials caused by external electromagnetic field is studied by modern polarization theory and equation of state motion,and the influence of out-of-plane polarization on nonlinear optical response is also studied.Permanent dipoles first break the inversion symmetry of blue phosphorus,resulting in obvious differences in energy band structure.In addition,the increase of the external dipole can obviously increase the in-plane nonlinear polarizability and the out-of-plane polarizability which is close to the in-plane polarizability.The out-of-plane symmetry breaking of Janus MoSSe increases the number of non-zero independent nonlinear polarizability components,thus improving the utilization efficiency of incident light in all directions.The response of out-of-plane polarizability of bulk stacking is non-zero,which improves the defects of no out-of-plane nonlinear polarizability and layer dependence of in-plane nonlinear polarizability of MoS₂ material.Finally,the influence of exciton effect on second-order nonlinear optical properties is studied.Based on the equation of motion of state and the multi-body perturbation theory,the equation of motion of state is transformed into the equation of motion of retarded Green function,and then the linear response of 2D group-VA binary monolayer and the second-order nonlinear response of Janus TMD two-dimensional material are studied by calculating the polarizability.It is shown that spontaneous polarization,exciton,and second-order nonlinear response are closely related.Spontaneous polarization has obvious influence on the radiation lifetime,radius,and anisotropy of excitons.Due to the different directions of spontaneous polarization,it has opposite effects on exciton properties of 2D group-VA binary monolayer with different phases.The research on the second-order nonlinear response of Janus TMD shows that exciton effect can enhance the in-plane polarizability below the band gap,while reduce the in-plane polarizability above the band gap and enhance the out-of-plane component of the low-energy interval polarizability.更多还原