Anomalous interfacial temperature profile induced by phonon localization

TL;DR

This paper investigates how localized phonon modes at interfaces cause anomalous negative temperature gradients, revealing the effects of anharmonicity and phonon interactions on interfacial thermal profiles.

Contribution

It uncovers the role of interfacial localized phonon modes in creating negative temperature gradients and how anharmonicity influences their impact on thermal profiles.

Findings

Localized phonon modes cause negative temperature gradients.

Anharmonicity excites localized modes, altering temperature profiles.

Strong anharmonicity eliminates negative gradients by mode mixing.

Abstract

Through the integration of the power spectral density, we obtain temperature profiles of both multi-segment 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 over-cooling 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.