Acoustic phonons propagating in semiconductor quantum wires and their mean-free-path

在这项工作中，我们得到了矩形量子线的正常声子模式，采用了超声波声谱学中使用的xyz算法。根据矩形钢丝的空间对称性，将其正常模态分为扩张、剪切/扭转和弯曲模态。剪切/扭转模态对矩形钢丝没有很好的定义，但对方形钢丝有很好的定义。这些模式的色散曲线具有声子子带，这是由于声子在线的横向上的限制造成的。我们通过形变势和声子引起的表面振动研究了这些声子模式下电子的散射。后者被称为光从振动表面散射后的纹波机制。特别注意散射事件之间的相干性，我们发现变形势和纹波机制散射只在扩张声子模式下发生，因此这两种散射相互干扰，提高了散射率。因此，散射率比这些机制对电子散射的单个贡献的总和更强。这种变形势与纹波机制散射之间的相干干涉并不是矩形量子线所特有的，而是其他低空间对称性系统所特有的。由此得出结论，这两个电子-声子相互作用之间的相干干涉对纳米结构中的电子系统至关重要，这表明变形势可以根据经验改变，以纳入表面振动对电子-声子相互作用的影响。

In this work, we obtained normal acoustic phonon modes of rectangular quantum wires, applying an algorithm referred to as the xyz algorithm which is used in the ultrasonic sound spectroscopy. The normal modes are classified, according to the spatial symmetries of the rectangular wires, into the dilatational, shear/torsional, and flexural modes. The shear/torsional mode is not well defined for rectangular wires, but they are well defined for square wires.Dispersion curves of these modes have phonon subbands caused by the phonon confinement in the lateral direction of the wires. We investigated electron scattering by these acoustic phonon modes via the deformation potential and the suface vibrations induced by acoustic phonons. The latter is termed the ripple mechanism after the light scattering from vibrating surface. Paying special attention to coherence among the scattering events, we found the deformation potential and the ripple mechanism scatterings take place only for the dilatational phonon mode and therefore these two kinds of scatterings interfere to enhance scattering rates.Consequently, the scattering rates are more enhanced than the sum of individual contribution of these mechanisms to electron scatterings. This coherent interference between the deformation potential and the ripple mechanism scatterings is not peculiar to the rectangular quantum wires, but bring about for other systems with low spatial symmetries. This leads to the conclusion that the coherent interference between these two electron-phonon interaction is essential to the electron systems confined in the nanostructures, suggesting that the deformation potential can be empirically changed to incorporate the effect of the surface vibrations on the electron-phonon interaction.