Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005, Fujian, China.
Phys Rev E. 2017 Dec;96(6-1):062119. doi: 10.1103/PhysRevE.96.062119. Epub 2017 Dec 15.
Through the integration of the power spectral density, we obtain temperature profiles of both multisegment harmonic and anharmonic systems, showing the presence of an anomalous negative temperature gradient inside the interfacial segment. Via investigating patterns of the power spectral density, we found that the counterintuitive phenomenon comes from the presence of interfacial localized phonon modes. Two out-band localized modes of the harmonic model, which make no contributions to local temperature due to the absence of phonon interactions, result in the concave temperature profile and overcooling effect. For the anharmonic model, thanks to the phonon-phonon interactions, the localized modes are excited and make considerable contributions to interfacial temperature, which is clearly shown by examining the temperature accumulation function. When anharmonicity is considerably large, the negative temperature gradient is absent since the localized phonon modes are fully mixed. The presence of localized modes are evidently demonstrated by the inverse participation ratio and normal mode analysis for the isolated harmonic model. The localized modes make contribution to interfacial temperature profiles of the harmonic system when they are excited in initial conditions of simulations.
通过整合功率谱密度，我们获得了多段谐波和非谐波系统的温度分布，显示出界面段内存在异常的负温度梯度。通过研究功率谱密度的模式，我们发现这种违反直觉的现象来自界面局域声子模式的存在。谐波模型的两个带外局域模式由于缺乏声子相互作用而对局部温度没有贡献，导致温度分布呈凹形和过冷效应。对于非谐波模型，由于声子-声子相互作用，局域模式被激发并对界面温度做出了相当大的贡献，这可以通过检查温度积累函数清楚地看出。当非谐性相当大时，由于局域声子模式完全混合，不存在负温度梯度。局域模式的存在通过对孤立谐波模型的逆参与比和正则模式分析得到了明显的证明。在模拟的初始条件下，局域模式被激发时，对谐波系统的界面温度分布有贡献。
