Promoting coherent transport of phonons at material interfaces is a promising strategy for controlling thermal transport in nanostructures and an alternative to traditional methods based on structural defects. Coherent transport is particularly relevant in short-period heterostructures with smooth interfaces and long-wavelength heat-carrying phonons, such as two-dimensional superlattices of graphene and boron nitride. In this work, we predict phonon properties and thermal conductivities in these superlattices using a normal mode decomposition approach. We study the variation of the frequency dependence of these properties with the periodicity and interface configuration (zigzag and armchair) for superlattices with period lengths within the coherent regime. Our results showed that the thermal conductivity decreases significantly from the first period length (0.44 nm) to the second period length (0.87 nm), 13% across the interfaces and 16% along the interfaces. For greater periods, the conductivity across the interfaces continues decreasing at a smaller rate of 11 W/mK per period length increase (0.43 nm), driven by changes in the phonon group velocities (coherent effects). In contrast, the conductivity along the interfaces slightly recovers at a rate of 2 W/mK per period, driven by changes in the phonon relaxation times (diffusive effects). By changing the interface configuration from armchair to zigzag, the conductivities for all period lengths increase by approximately 7% across the interfaces and 19% along the interfaces.
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机译：促进声子在材料界面处的相干传输是控制纳米结构中热传输的一种有前途的策略，并且是基于结构缺陷的传统方法的替代方法。相干输运在具有光滑界面和长波长载热声子的短周期异质结构中尤其重要，例如石墨烯和氮化硼的二维超晶格。在这项工作中，我们使用正常模式分解方法预测了这些超晶格中的声子性质和热导率。对于相干状态下具有周期长度的超晶格，我们研究了这些特性随周期和界面配置（之字形和扶手椅）的频率依赖性的变化。我们的结果表明，热导率从第一周期长度（0.44 nm）到第二周期长度（0.87 nm）显着降低，在界面处为13％，在界面处为16％。在更长的时间内，由于声子基团速度的变化（相干效应），界面上的电导率以每单位周期长度增加（0.43 nm）的11 W / mK的较小速率持续降低。相反，由于声子弛豫时间的变化（扩散效应），沿界面的电导率每周期以2 W / mK的速率稍微恢复。通过将接口配置从扶手椅更改为锯齿形，所有周期长度的电导率在整个界面上大约增加7％，在整个界面上增加19％。
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