抛物量子点中弱耦合极化子的基态能量

【作者】 刘文；

【导师】 苏希玉；

【作者基本信息】 曲阜师范大学 ， 凝聚态物理， 2006， 硕士

【摘要】 极化子是电子与光频支纵声子相耦合系统的准粒子,是凝聚态物理学中的一个重要课题。极化子的研究对于解释离子晶体和极性半导体的光跃迁过程及输运现象有重要意义。近年来,许多学者用不同的方法研究了量子点内极化子的性质,并得到了一些有意义的结果。 本文首先介绍了极化子、量子点的基本知识以及研究方法。抛物量子点内弱耦合极化子的基态能量是本文的主要内容。在极化子的基态中引入一个代表双声子关联的项,在LLP正则变换的基础上引入电子的线性组合算符,计算系统的基态能量E₀,得到声子关联效应对能量的修正。并与无关联情况下得到的基态能量E′₀作比较,发现考虑声子关联效应时基态能量更低。本文主要包括以下两方面的内容: （1） 讨论了抛物量子点内弱耦合极化子的基态能量E₀随量子点有效受限长度l₀和电子-声子耦合强度α变化的变化关系。计算表明,基态能量随着电子-声子耦合强度和有效受限长度的增加而降低;当有效受限长度l₀>1.0时基态能量的变化趋于平缓。与未考虑关联时得到的基态能量E′₀相比,当α在0～2.5之间变化时,二者差别不大。 （2） 将极性晶体置于磁场中,讨论声子关联效应对束缚在晶体氢化杂质中的抛物量子点内极化子系统的基态能量的影响。得到了基态能量E₀关于库仑束缚势β、有效受限长度l₀、电-声耦合强度α和回旋共振频率ω_c的表达式。结果表明,E₀随l₀、α、β的减小而增大,随磁场强度B的增大而增大。得到声子关联对能量的修正。更多还原

【Abstract】 Polaron is the quasi particle of the electron-longitude optical phonon coupling system, which is an important subject in the condensed matter physics. The study on this subject plays an important role in explaining the phenomena of light transition and transport in the ionic crystal and polar semiconductor. In recent years, there has been a great deal of interest in the investigation of polarons in the quantum dots, and some useful results are obtained.Some basic concepts of polaron and quantum dot and investigation methods are expounded in the first place. The thesis concerns mainly about the ground state energy of weak coupling polaron in a parabolic quantum dot. An item which stands for two-phonon correlation is introduced into the ground-state vector. Under the Lee-Low-Pines canonical transformation and the combination of linearoperators of the electron, the correction of phonon correlation to the ground-state energy of this system is obtained. We find that the energy E_o resulted includingthe phonon correlation is lower than E’_o obtained without correlation. Thispaper focuses on the following aspects:1. We calculate the ground-state energy E_o of a polaron confined in aparabolic quantum dot. The relation between E₀ and effective confinement length l0 and coupling constant α is discussed. The calculation shows that E_o decreases as l₀ and a increase;when l₀ > 1.0 E_o nearly remains steady;when a varies from 0 to 2.5, the difference between E_o and E’_ois negligible.2. In the presence of two-phonon correlation, we consider the effect of anexternal magnetic field B on a weak coupling polaron confined in the hydrogenized impurity. It indicates that E_o increases as B increases, and falls asl₀, α and coulomb bound potential β increase.更多还原