Coherent Acoustic Phonon and Its Chirping in Dirac Semimetal Cd3As2

• 来源期刊: 中国物理快报（英文版）
• 年，卷（期）: 2018,（11）
• 页码范围: 56-60
• 页数: 5页
• 语种: 英文
• DOI: 10.1088/0256-307X/35/11/116301

摘要

Ultrafast optical spectroscopy of a single crystal of a Dirac semimetal CdaAs2 is carried out.An acoustic phonon (AP) mode with central frequency f =0.037 THz (i.e.,1.23cm-1 or 0.153meV) 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 31.2ps at 6 K and 19.8ps 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 Cd3As2 application potentials in thermoelectric devices.