Acoustic Phonon Lifetimes and Thermal Transport in Free-Standing and Strained Graphene
Acoustic Phonon Lifetimes and Thermal Transport in Free-Standing and Strained Graphene
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DOI：
10.1021/nl202694m
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发表时间：
2012-06-01
期刊：
影响因子：
10.8
通讯作者：
Marzari, Nicola
中科院分区：
文献类型：
--
作者：
Bonini, Nicola;Garg, Jivtesh;Marzari, Nicola
我们使用基于密度泛函微扰理论的第一性原理方法来表征声学声子模式的寿命及其对石墨烯热输运性质的影响。我们表明，使用一个标准的微扰方法，横向和纵向的声学声子在独立的石墨烯显示有限的寿命在长波长的限制，使他们不好定义为基本的激发尺寸大于类似于1 μ m的样品。这种行为完全是由于存在的二次色散的平面外声子（ZA）的弯曲模式，出现在独立的低维系统。机械应变解除了这种异常，所有声子在任何波长都保持良好的定义。热输运由ZA模式主导，并且对于任何应变量，热导率被预测为随系统尺寸而发散。这些发现突出了应变和样品大小作为表征或工程化石墨烯热传输的关键参数。
We use first-principles methods based on density functional perturbation theory to characterize the lifetimes of the acoustic phonon modes and their consequences on the thermal transport properties of graphene. We show that using a standard perturbative approach, the transverse and longitudinal acoustic phonons in free-standing graphene display finite lifetimes in the long-wavelength limit, making them ill-defined as elementary excitations in samples of dimensions larger than similar to 1 mu m. This behavior is entirely due to the presence of the quadratic dispersions for the out-of-plane phonon (ZA) flexural modes that appear in free-standing low-dimensional systems. Mechanical strain lifts this anomaly, and all phonons remain well-defined at any wavelength. Thermal transport is dominated by ZA modes, and the thermal conductivity is predicted to diverge with system size for any amount of strain. These findings highlight strain and sample size as key parameters in characterizing or engineering heat transport in graphene.