Observation of strong higher-order lattice anharmonicity in Raman and infrared spectra
Xiaolong Yang, Tianli Feng, Joon Sang Kang, Yongjie Hu, Ju Li, Xiulin Ruan
Abstract
It has been well-known that Raman and infrared linewidths are associated with third-order lattice anharmonicity. Here, the authors go further and establish by means of first-principles calculations and Raman measurements that the previously neglected fourth-order anharmonicity may play a significant, or even dominating, role. The predicted strong fourth-order lattice anharmonicity results from the large four-phonon scattering phase space of zone-center optical phonons. It explains well the significantly broadened Raman or infrared peaks, observed for a wide range of materials at various temperatures. This finding may significantly impact spectroscopy techniques and the understanding of radiative transport.