【作者】 张存喜；

【导师】 梁九卿； 聂一行；

【作者基本信息】 山西大学 ， 理论物理， 2008， 博士

【摘要】 本文利用散射矩阵和传输矩阵等方法研究了半导体异质结量子阱和一维光晶格体系中的量子输运特性,为设计和实现具有优良性能的量子过滤器件提供理论依据。主要研究内容有:首先,利用有效质量近似和Floquet理论,研究了空间均匀振荡场作用下,存在自旋轨道耦合的单个半导体异质结量子阱的电子输运特性。数值计算结果表明Dresselhaus自旋轨道耦合不仅可以消除自旋简并,而且可以导致不对称Fano共振电导峰的劈裂。我们可以利用此性质,通过调节振荡场的频率和振幅来控制Fano共振峰的位置及其线性形状,从而实现一个可调的自旋过滤器件。其次,在上述工作基础上,研究了应用在双量子阱上的两个空间均匀振荡场的相位差对其输运特性的影响。与单势阱情况不同,在双量子阱中,由于束缚能级发生劈裂和Dresselhaus自旋轨道耦合作用,电子透射谱分成两组,且每一组都包含两个不对称的共振峰。我们可以通过调节外加振荡场的相位差,有选择性的压制某一个共振峰,因而对于某一个能量范围,可以通过调节其相位差来实现一个可调的自旋过滤器件。另外,当相位差从0到π变化时,共振谷从不对称共振峰的一侧移到另一侧;并且存在一个临界相位差,此时,不对称的Fano共振峰简并成一个对称的Breit-Wigner共振峰。再次,由于在实验装置上,偶极振荡场比空间均匀振荡场更容易实现,因而实验上通常采用偶极振荡场。鉴于上述原因,我们研究了这两种类型的外场对存在Dresselhaus自旋轨道耦合作用的单个半导体异质结量子阱中输运特性的影响。我们发现当外场振幅满足某一特定关系时,偶极振荡场和空间均匀振荡场对电子输运特性的调制是等价的,因而可以利用偶极振荡场及Fano共振峰的劈裂,实现更接近实验条件的可调自旋过滤器件。最后,对于附有缺陷势的一维光晶格系统,我们研究了原子通过该缺陷势中局域BEC的Fano共振输运特性。由于缺陷势和局域BEC的非线性参数可以由激光和磁场来调控,因而,可以通过它们来调节Fano共振峰的大小和阻塞点(投射率为零)的位置,从而实现对透射原子束的控制,为设计可调原子过滤器提供理论依据。更多还原

【Abstract】 In this thesis the quantum transport through semiconductor heterostructures quantum-well structure and one-dimensional optical lattice system are investigated by means of the scattering matrix and transfer-matrix techniques. Our arm is to explore the physical mechanisms of the effects, and to supply physical models and make theoretical validity in designing novel quantum filtering devices with better properties.First, using the effective-mass approximation and Floquet theory, we study the electron transmission over a quantum well in semiconductor heterostructures with Dresselhaus spin-orbit coupling and an applied oscillation field. It is demonstrated by the numerical evaluations that Dresselhaus spin-orbit coupling eliminates the spin degeneracy and leads to the splitting of asymmetric Fano-type resonance peaks in the conductivity. In turn, the splitting of Fano-type resonance induces the spin-polarization-dependent electron current. The location and line shape of Fano-type resonance can be controlled by adjusting the oscillation frequency and the amplitude of the external field as well. These interesting features may be a very useful basis for devising tunable spin filters.Secondly, we have investigated theoretically the field-driven electron transport through a double-quantum-well semiconductor-heterostructure with spin-orbit coupling. The numerical results demonstrate that the transmission spectrums are divided into two sets due to the bound-state level-splitting and each set contains two asymmetric resonance peaks which may be selectively suppressed by altering the phase difference between two driving fields. When the phase difference changes from 0 toπ, the dip of asymmetry resonances shifts from one side of resonance peaks to the other and the asymmetric Fano resonances degenerate into the symmetric Breit-Wigner resonance at a critical value of phase difference. Within a given energy range of incident electron, the spin polarization of transmission current is completely governed by the phase difference which may be used to realize the tunable spin filtering.Then, as is well known to all, the more practical oscillation-type is dipole-oscillation in most of experimental setup, and the dipole-type is easier to exploit experimentally than the spatially uniform field. We study the spin-dependent electron transmission through a quantum well driven by both dipole-type and homogeneous oscillating fields. The numerical evaluations show the dipole modulation and the homogeneous modulation are equivalent. Therefore using the splitting of asymmetric Fano-type resonance peaks in the conductivity, we predict that the dipole-type oscillation, which is more practical in the experimental setup, can be used to realize the tunable spin filters by adjusting the field oscillation-frequency and the amplitude as well.Finally, we study the transport of atoms across a localized Bose-Einstein condensate in an one-dimensional optical lattice with a single defect. The defect potential and the nonlinear parameter of local BEC can be controlled by laser and magnetic fields, thus we can regulate the size of Fano resonance peaks and the location of block point (the position of total reflection) by changing them. Our analytical and numerical results show that the transmission beam of atoms can control by tuning them. These interesting features may be a very useful theoretical basis for devising tunable atom filters.更多还原