Coherent Acoustic Phonon and Its Chirping in Dirac Semimetal Cd$_{3}$As$_{2}$
Fei Sun1,2†, M. Yang1,2†, M. W. Yang1,2, Q. Wu1,2, H. Zhao1,2, X. Ye1,2, Youguo Shi1,2, Jimin Zhao1,2**
1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 2School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049
Abstract：Ultrafast optical spectroscopy of a single crystal of a Dirac semimetal Cd$_{3}$As$_{2}$ is carried out. An acoustic phonon (AP) mode with central frequency $f=0.037$ THz (i.e., 1.23 cm$^{-1}$ or 0.153 meV) is unambiguously generated and detected, which we attribute to laser-induced thermal strain. An AP chirping (i.e., variation of the phonon frequency) is clearly detected, which is ascribed to heat capacity variation with time. By comparing our experimental results and the theoretical model, we obtain a chirping time constant, which is 31.2 ps at 6 K and 19.8 ps at 300 K, respectively. Significantly, we identify an asymmetry in the AP frequency domain peak and find that it is caused by the chirping, instead of a Fano resonance. Moreover, we experimentally demonstrate that the central frequency of AP is extremely stable with varying laser fluence, as well as temperature, which endows Cd$_{3}$As$_{2}$ application potentials in thermoelectric devices.
. [J]. 中国物理快报, 2018, 35(11): 116301-.
Fei Sun, M. Yang, M. W. Yang, Q. Wu, H. Zhao, X. Ye, Youguo Shi, Jimin Zhao. Coherent Acoustic Phonon and Its Chirping in Dirac Semimetal Cd$_{3}$As$_{2}$. Chin. Phys. Lett., 2018, 35(11): 116301-.
Zhao J M 2005 Ultrafast Optical Generation of Squeezed Magnon States and Long Lifetime Coherent LO Phonons (The University of Michigan: Phd Dissertation)
2018, Vol. 35 
