Joshi Jaydeep, Stone Iris, Beams Ryan, Krylyuk Sergiy, Kalish Irina, Davydov Albert, Vora Patrick
Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA.
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
Appl Phys Lett. 2016;109. doi: https://doi.org/10.1063/1.4959099.
We examine anharmonic contributions to the optical phonon modes in bulk -MoTe through temperature-dependent Raman spectroscopy. At temperatures ranging from 100 K to 200 K, we find that all modes redshift linearly with temperature in agreement with the Grüneisen model. However, below 100 K we observe nonlinear temperature dependent frequency shifts in some modes. We demonstrate that this anharmonic behavior is consistent with the decay of an optical phonon into multiple acoustic phonons. Furthermore, the highest frequency Raman modes show large changes in intensity and linewidth near ≈ 250 K that correlate well with the →1 structural phase transition. These results suggest that phonon-phonon interactions can dominate anharmonic contributions at low temperatures in bulk -MoTe, an experimental regime that is currently receiving attention in efforts to understand Weyl semimetals.
我们通过与温度相关的拉曼光谱研究了块状β-MoTe₂中光学声子模式的非谐贡献。在100 K至200 K的温度范围内，我们发现所有模式的频率都随温度线性红移，这与格林艾森模型一致。然而，在100 K以下，我们观察到某些模式中存在与温度相关的非线性频率偏移。我们证明这种非谐行为与一个光学声子衰变为多个声学声子的过程是一致的。此外，最高频率的拉曼模式在约250 K附近显示出强度和线宽的巨大变化，这与β→1结构相变密切相关。这些结果表明，在块状β-MoTe₂中，声子-声子相互作用在低温下可能主导非谐贡献，这一实验领域目前在理解外尔半金属的研究中受到关注。
