Effects of magnetic field on the polaron in an asymmetrical Gaussian confinement potential quantum well

The effects of a magnetic field on the vibrational frequency, the ground state energy and the ground state binding energy of a weak-coupling polaron in asymmetrical Gaussian confinement potential quantum well (AGCPQW) are investigated by using linear combination operator and unitary transformation methods.Our calculated results show that the vibrational frequency increases with increasing cyclotron frequency of the magnetic field;meanwhile, the absolute value of the ground state energy and the ground state binding energy decrease.The vibrational frequency, the absolute value of the ground state energy and the ground state binding energy are increasing functions of the barrier height of the AGCPQW.It is shown that the barrier height of the AGCPQW and the magnetic field are important factors that influence the properties of the magnetopolaron in AGCPQW.     

基于Pekar类型变分法的高斯函数型限定势阱量子点中电子的跃迁

分别选取抛物线型限定势阱和高斯函数型限定势阱描写盘状量子点中电子的横向限定势和纵向限定势,采用Pekar类型变分法推导出了电子的基态和激发态能量,并基于费米黄金规则讨论了在磁场作用下电子的跃迁几率。结果表明,高斯函数型限定势阱比抛物线型限定势阱更能精准反映量子点中真实的限定势;量子点的厚度对电子跃迁几率的影响显著;电声耦合强度α、磁场的回旋频率ω_c、抛物线型限定势阱范围R_0、高斯函数型限定势阱的阱深V_0和阱宽L等对电子跃迁几率Q的影响的量度和变化规律方面差异较大。     

The properties of an asymmetric Gaussian potential quantum well qubit in RbCl crystal

With the circumstance of the electron strongly coupled to LO-phonon and using the variational method of Pekar type (VMPT), we study the eigenenergies and the eigenfunctions (EE) of the ground and the first excited states (GFES) in a RbCl crystal asymmetric Gaussian potential quantum well (AGPQW). It concludes: (i) Two-energy-level of the AGPQW may be seen as a qubit. (ii) When the electron located in the superposition state of the two-energy-level system, the time evolution and the coordinate changes of the electron probability density oscillated periodically in the AGPQW with every certain period T₀ =22.475 fs. (iii) Due to the confinement that is a two dimensional x-y plane symmetric structure in the AGPQW and the asymmetrical Gaussian potential (AGP) in the AGPQW growth direction, the electron probability density presents only one peak configuration located in the coordinate of z>0, whereas it is zero in the range of z<0. (iv) The oscillatory period is a decreasing function of the AGPQW height and the polaron radius. (v) The oscillating period is a decreasing one in the confinement potential R<0.24 nm, whereas it is an increasing one in the confinement potential R>0.24 nm and it takes a minimum value in R=0.24 nm.     

温度对于量子线强耦合极化子振动频率的影响

采用线性组合算符和幺正变换法计算了量子线中强耦合极化子的振动频率、基态能量、基态自陷能随温度、电子-声子耦合强度以及受限长度的变化。我们发现振动频率、基态能量、基态自陷能都是温度及耦合强度的函数,且随着温度的增加而增大;受限长度也随温度及耦合强度的增加而增大,但是当温度增大到一定值时,随着温度的增加耦合强度在减小。     

量子阱中弱耦合束缚极化子的温度效应

采用线性组合算符与变分相结合的方法研究了温度对无限深量子阱中弱耦合束缚极化子性质的影响.推导出在弱耦合情况下,无限深量子阱中束缚极化子的基态能量和振动频率与温度的关系.选择GaAs晶体为例,进行数值计算.结果表明:温度升高时,量子阱中弱耦合束缚极化子的振动频率增大；温度升高、阱宽增大时,量子阱中弱耦合束缚极化子的基态能...     

抛物量子阱中强耦合极化子的声子平均数

采用线性组合算符和幺正变换相结合的变分方法,研究电子与体纵光学声子强耦合情况下抛物量子阱中极化子的声子平均数。给出了抛物量子阱中强耦合极化子的声子平均数与量子阱受限强度和电子-体纵光学声子耦合强度的关系。结果表明：强耦合极化子的声子平均数随量子阱受限强度的增大而增大,随电子-体纵光学声子耦合强度的增大而增大。随着量子阱受限强度的减小,声子平均数趋于晶体材料的值。抛物量子阱受限强度和耦合强度的增大加强电声子之间的相互作用。     

量子点中极化子性质:压缩态变分法

利用单模压缩态变分法得到了在电子-体纵光学声子全耦合条件下抛物量子点极化子的基态能量及电子周围平均声子数的表达式。所采用的变分方法是基于逐次正则变换的变分方法,变换处理了包含经常被忽略的声子产生湮灭算符的双线性项。在电子-体纵光学声子全耦合条件下,讨论了受限长度与抛物量子点极化子的基态能量及电子周围平均声子数之间的依赖关系。     

盘型量子点中极化子的温度效应

在考虑电子与体纵光学声子强耦合的条件下,通过求解能量本征方程,得出了盘型量子点中电子的基态能量、第一激发态能量及其相应的本征波函数;采用幺正变换和元激发理论方法研究了圆盘型量子点的声子效应,并讨论了温度对量子盘中极化子性质的影响。数值计算表明：在温度较低时,声子不能被激发,温度对能量无影响,当温度较高时,声子能够被激发,且温度愈高,被激发的声子数愈多,极化子能量愈大;结果还表明基态能量随着电子-声子耦合强度的增大而减小,随量子盘半径的增大而减小. 说明量子盘具有明显的量子尺寸效应。     

Rashba效应下三角量子阱中弱耦合束缚极化子的性质

利用线性组合算符和幺正变换相结合的方法,推导出三角量子阱中弱耦合束缚极化子的基态能量。并讨论了耦合常数,库仑束缚势和电子面密度对极化子基态能量的影响。通过对GaAs材料的数值计算,最后结果显示：由于电-声子耦合作用和Rashba效应的存在,弱耦合束缚极化子的基态能量由四部分组成,而且弱耦合束缚极化子的基态能量随耦合常数,库仑束缚势和电子面密度都发生了分裂。     

极化子速率对量子点中磁极化子性质的影响

采用改进的线性组合算符及么正变换的方法研究了极化子速率对量子点中强耦合磁极化子的性质的影响。在考虑Rashba自旋轨道耦合相互作用影响下,导出了量子点中强耦合磁极化子的振动频率、基态能量、有效质量和相互作用能随极化子速率的变化关系。对RbCl晶体进行数值计算,结果表明：量子点中强耦合磁极化子的振动频率、基态能量、有效质量随极化子速率的增加而增大,相互作用能随极化子速率的增加而减少。     

抛物量子点中弱耦合极化子声子色散效应

利用线性组合算符和幺正变换相结合的方法,研究了声子色散对抛物量子点中弱耦合极化子性质的影响．计及体纵光学（LO）声子抛物色散,导出了量子点中极化子的基态能量和自陷能随量子点有效受限长度、电子-纵光学声子耦合常数和声子色散系数的变化关系．数值计算结果表明基态能量随声子色散系数的增大而减小,而自陷能随声子色散系数的增大而增大．     

Bound polaron in a strained wurtzite GaN/Aix Ga1-xN cylindrical quantum dot

Within the effective-mass approximation, a variational method is adopted to investigate the polaron effect in a strained GaN/AlxGa1-xN cylindrical quantum dot. The electron couples with both branches of longitudinal optical-like (LO-like) and transverse optical-like (TO-like) phonons and the built-in electric field are taken into account. The numerical results show that the binding energy of the bound polaron is reduced obviously by the polaron effect on the impurity states. Furthermore, the contribution of LO-like phonons to the binding energy is dominant, and the anisotropic angle and Al content influence on the binding energy are small.     

量子阱中弱耦合束缚极化子的温度效应

采用线性组合算符与变分相结合的方法研究了温度对无限深量子阱中弱耦合束缚极化子性质的影响。推导出在弱耦合情况下,无限深量子阱中束缚极化子的基态能量和振动频率与温度的关系。选择GaAs晶体为例,进行数值计算。结果表明：温度升高时,量子阱中弱耦合束缚极化子的振动频率增大;温度升高、阱宽增大时,量子阱中弱耦合束缚极化子的基态能量的绝对值增大。     

Property comparison of polarons in zinc-blende and wurtzite GaN/AlN quantum wells

本文详细比较闪锌矿和纤锌矿GaN/AlN量子阱中Fr?hlich电声子相互作用哈密顿量及极化子性质。采用LLP变分方法计算由界面、局域和半空间声子模导致的基态极化子能移。结果表明,若忽略z方向和x-y平面之间异性的影响,闪锌矿和纤锌矿哈密顿量是一致的。各向异性在窄阱情形对界面声子能移的影响较为明显,而在略宽阱时对局域声子能移影响明显。此外,内建电场对各支光学声子引起的能移的影响较大。     

Property comparison of polarons in zinc-blende and wurtzite GaN/AIN quantum wells

The properties ofpolarons in zinc-blende and wurtzite GaN/AlN quantum wells with Fr(o)hlich interaction Hamiltonians are compared in detail.The energy shifts of polarons at ground state due to the interface (IF),confined (CO) and half-space phonon modes are calculated by a finite-difference computation combined with a modified LLP variational method.It is found that the two Fr(o)hlich interaction Hamiltonians are consistent with each other when the anisotropic effect from the z-direction and the x-y plane is neglected.The influence of the anisotropy on the polaron energy shifts due to the IF phonon modes for a smaller well width or due to the CO phonon modes for a moderate well width is obvious.In addition,the built-in electric field has a remarkable effect on the polaron energy shifts contributed by the various phonon modes.     

Property comparison of polarons in zinc-blende and wurtzite GaN/AlN quantum wells

The properties of polarons in zinc-blende and wurtzite GaN/AlN quantum wells with Fr(o|¨)hlich interaction Hamiltonians are compared in detail.The energy shifts of polarons at ground state due to the interface(IF), confined(CO) and half-space phonon modes are calculated by a finite-difference computation combined with a modified LLP variational method.It is found that the two Fr(o|¨)hlich interaction Hamiltonians are consistent with each other when the anisotropic effect from the z-direction and the x-y plane is neglected.The influence of the anisotropy on the polaron energy shifts due to the IF phonon modes for a smaller well width or due to the CO phonon modes for a moderate well width is obvious.In addition,the built-in electric field has a remarkable effect on the polaron energy shifts contributed by the various phonon modes.     

半导体量子点最低导带态的量子限制效应

采用最新计算方法和半导体体材料传统量子计算结果,系统研究了14种半导体(Si,Ge,Sn,AlSb,GaP,GaAs,GaSb,InP,InAs,InSb,ZnS,ZnSe,ZnTe,CdTe)的立方量子点,得到了最低导带态的量子限制效应结果,我们把量子点对尺寸的依赖关系分为三类并详细讨论了它们的差别。     

半导体量子阱中强耦合磁极化子的性质

首次采用线性组合算符结合改进的LLP幺正变换的方法,研究了电子与体纵光学声子强耦合情况下半导体量子阱中磁极化子的性质。导出了无限深量子阱中强耦合磁极化子的振动频率、基态能量和自陷能与阱宽和回旋共振频率的变化关系。对RbCl量子阱进行数值计算,结果表明：强耦合磁极化子的振动频率、基态能量和自陷能随回旋共振频率的增大而增大。振动频率和自陷能随阱宽的增加而增大;基态能量随阱宽的增加而减小,且在阱宽较窄时,表现出奇特的量子尺寸效应。     

声子色散对量子点中弱耦合极化子光学声子平均数的影响

采用幺正变换和线性组合算符相结合的方法,研究声子色散对抛物量子点中弱耦合极化子电子周围光学声子平均数的影响.计及纵光学(LO)声子抛物色散,导出了量子点中极化子的基态能量和电子周围光学声子平均数随声子色散系数的变化关系.数值计算结果表明基态能量随声子色散系数的增大而减小,电子周围光学声子平均数随声子色散系数的增大而增大.