Abstract

The role of shear waves and the effect of phonon focusing on the anisotropy of the thermopower of the electron–phonon drag in single-crystal potassium nanowires at low temperatures are analyzed in this work. The deformation potential theory is used for the longitudinal components of elastic modes. For the shear components of vibrational modes, the electron–phonon interaction constant is used, which was determined previously from comparing the results of calculating the thermoelectric power with experimental data for bulk potassium crystals. It is shown that shear waves make a significant contribution to the drag thermopower of nanowires. In the regime of the Knudsen phonon gas flow for nanowires with a cross-section side D = 5 × 10^–6 cm, the contribution of the slow transverse mode t₂ with allowance for only the longitudinal component in the [111] directions turned out to be 32% smaller and, with allowance for the shear component of the t₂ mode, 12% greater than the contribution of longitudinal phonons. Directions corresponding to the maximum and minimum values of the drag thermopower of nanowires are determined. It is shown that, under conditions of competition between the boundary and bulk mechanisms of phonon relaxation with an increase in the cross section of nanowires, the anisotropy of the drag thermopower changes nonmonotonically. It exceeds 30% not only in the Knudsen phonon gas flow regime, but also when the sample thickness is two orders of magnitude greater. This makes the anisotropy of thermopower available for experimental studies.

中文翻译：

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低温下声子聚焦对单晶钾纳米线阻力热功率的影响

摘要

在这项工作中，分析了剪切波的作用和声子对低温下单晶钾纳米线中电子-声子阻力的热功率各向异性的影响。变形势理论被用于弹性模态的纵向分量。对于振动模态的剪切分量，使用了电子-声子相互作用常数，该常数是先前通过将热电功率的计算结果与块状钾晶体的实验数据进行比较而确定的。结果表明，剪切波对纳米线的拖动热功率做出了重要贡献。在横截面为D = 5×10 ^–6 cm的纳米线的克努森声子气流状态下，慢横模的贡献仅在[111]方向上的纵向分量允许的t ₂减小了32％，在t ₂模态的剪切分量允许的情况下，t ₂比纵向声子的贡献大了12％。确定与纳米线的阻力热功率的最大值和最小值相对应的方向。结果表明，在声子弛豫的边界和主体机理之间竞争的条件下，随着纳米线横截面的增加，阻力热力的各向异性非单调变化。它不仅在Knudsen声子气体流动状态下超过30％，而且在样品厚度增加两个数量级时也超过30％。这使得热电各向异性可以用于实验研究。