Cheng Bing, Schumann T, Wang Youcheng, Zhang X, Barbalas D, Stemmer S, Armitage N P
Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, United States.
Materials Department, University of California, Santa Barbara, California 93106-5050, United States.
Nano Lett. 2020 Aug 12;20(8):5991-5996. doi: 10.1021/acs.nanolett.0c01983. Epub 2020 Jul 10.
We investigated the magnetoterahertz response of the Dirac semimetal CdAs and observed a particularly low frequency optical phonon as well as a very prominent and field-sensitive cyclotron resonance. As the cyclotron frequency is tuned with the field to pass through the phonon, the phonon becomes circularly polarized, as shown by a notable splitting in its response to right- and left-hand polarized light. This splitting can be expressed as an effective phonon magnetic moment that is approximately 2.7 times the Bohr magneton, which is almost 4 orders of magnitude larger than ab initio calculations predict for phonon magnetic moments in nonmagnetic insulators. This exceedingly large value is due to the coupling of the phonons to the cyclotron motion and is controlled directly by the electron-phonon coupling constant. This field-tunable circular-polarization-selective coupling provides new functionality for nonlinear optics to create light-induced topological phases in Dirac semimetals.
我们研究了狄拉克半金属CdAs的磁太赫兹响应，观测到一个特别低频的光学声子以及一个非常显著且对磁场敏感的回旋共振。当回旋频率随磁场调谐以穿过声子时，该声子变为圆偏振，这通过其对右旋和左旋偏振光响应中的显著分裂得以体现。这种分裂可表示为一个有效声子磁矩，其约为玻尔磁子的2.7倍，这比非磁性绝缘体中声子磁矩的从头算预测值大近4个数量级。这个极大的值源于声子与回旋运动的耦合，并且直接由电子 - 声子耦合常数控制。这种磁场可调谐的圆偏振选择性耦合为非线性光学在狄拉克半金属中创建光诱导拓扑相提供了新功能。
