Rashba自旋-轨道耦合下二维双极化子的基态性质  

Properties of the ground state of two-dimensional bipolaron with Rashba spin-orbit coupling

作　　者：乌云其木格[1] 辛伟[2] 额尔敦朝鲁[2] 

机构地区：[1]内蒙古民族大学物理与电子信息学院,通辽028043 [2]河北科技师范学院物理系,秦皇岛066004

出　　处：《物理学报》2016年第17期332-339,共8页Acta Physica Sinica

基　　金：河北省自然科学基金(批准号:E2013407119);河北省高校科学技术研究项目(批准号:ZD20131008;Z2015149;Z2015219)资助的课题~~

摘　　要：在考虑Rashba自旋-轨道耦合效应下,基于Lee-Low-Pines变换,采用Pekar型变分法研究了量子点中双极化子的基态性质.数值结果表明,在电子-声子强耦合(耦合常数α>6)条件下,量子点中形成稳定双极化子结构的条件(结合能E_b>0)自然满足;双极化子的结合能E_b随量子点受限强度ω_0、介质的介电常数比η和电子-声子耦合强度α的增大而增加,随Rashba自旋-轨道耦合常数αR的增加表现为直线增加和减小两种截然相反的情形;Rashba效应使双极化子的基态能量分裂为E(↑↑),E(↓↓)和E(↑↓)三条能级,分别对应两电子的自旋取向为"向上"、"向下"和"反平行"三种情形;基态能量的绝对值|E|随η和α的增加而增大,随αR的增加表现为直线增加和减小两种截然相反的情形;在双极化子的基态能量E中,电子-声子耦合能所占据的比例明显大于Rashba自旋-轨道耦合能所占比例,但电子-声子耦合与Rashba自旋-轨道耦合间相互渗透、彼此影响显著.In this paper, based on the Lee-Low-Pines transformation, the ground-state properties of the bipolaron with the Rashba spin-orbit coupling effect in the quantum dot are studied by using the Pekar variational method. The expressions for the ground-state interaction energy Eint and binding energy Eb of the bipolaron are derived. The results show that Eint is composed of four parts： the electron-longitudinal optical（LO） phonon coupling energy Ee-ph, confinement potential of the quantum dot Ecouf, Coulomb energy between two electrons Ecouland additional term in the Rashba spin splitting energy ER-phoriginating from the LO phonon, where Ecoufand Ecoulare positive definite. These indicate that Ecoufand Ecoul are the repulsive potential of the bipolaron. Generally, it is unable to form the electron-electron coupling structure in the quantum dot because two electrons repel each other by means of the screened Coulomb potential and confinement potential of the quantum dot. However, the numerical results show that the ground-state binding energy of the bipolaron Eb is greater than zero under the condition of the electron-phonon strong coupling（coupling strengthα 〉6）, so the condition of forming the steady bipolaron structure in quantum dots is naturally met（binding energy Eb〉 0）. In addition, the ground-state energy of the bipolaron E is always less than zero, thus the ground-state biplaron in the quantum dot is in the steady bound state. This can be explained by the physical mechanism. Firstly, the electron-LO phonon coupling energy Ee-phin the ground-state interaction energy of the bipolaron is always negative. Secondly,the electron-LO phonon coupling interaction in the low-dimensional structures of Ⅱ-Ⅵ semiconductors is great enough（generally α〉 6.0） so that the electron-LO phonon coupling energy Ee-phis dominant in the ground-state energy E and,therefore the screened Coulomb potential and confinement potential of the quantum dot can be overcome and a steady electron-electron structure can b

关 键 词：窄禁带Ⅱ-Ⅵ族异质结 双极化子 Rashba自旋-轨道耦合 基态能量 

分 类 号：O471.1[理学—半导体物理]