含半圆弧形腔的量子波导中声学声子输运和热导特性

Characteristics of acoustic phonon transport and thermal conductance in quasi-one-dimensional quantum waveguides with semi-circular-arc cavity

采用散射矩阵方法,研究了在应力自由和硬壁两种典型的边界条件下含半圆弧形腔的量子波导中声学声子输运和热导性质.结果表明在两种边界条件下声子透射谱和热导有着不同的特征.在应力自由边界条件下,能观察到普适的量子化热导现象,当结构为一理想的量子线时,在低温区域有一个量子化平台出现,而当半圆弧形结构存在时,非均匀横向宽度引发的弹性散射使得量子化平台被破坏;在硬壁边界条件下,不可能观察到量子化热导现象,热导随温度的增加单调上升;计算结果表明还可以通过调节半圆弧形结构的半径来调控声子的输运概率和热导.

By using the scattering matrix method, the transmission coefficient and thermal conductance of acoustic phonon through a quantum waveguide with semi-circular-arc cavity under both stress-free and hard-wall boundary conditions at low temperatures are studied. The results show that the transmission spectra and thermal conductance exhibit different characteristics under two different boundary conditions. Under the stress-free boundary condition, the universal quantum thermal conductance can be observed regardless of the geometry details in the limit T→0. The quantized plateau is observed only on assuming that the quantum wire is perfect （uniform）. For quantum structures with semi-circular-arc cavity, the plateau is destroyed due to the additional scattering induced by the nonuniform waveguide widths to the phonon. When the hard-wall boundary condition is applied, the universal quantum thermal conductance disappears. The thermal conductance increases with the increase of temperature. Moreover, it is found that both the transmission coefficient and thermal conductance can be adjusted by changing the radius of the semi-circular-arc cavity.