We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride (PtTe2) thin films via femtosecond (fs) pump-probe spectroscopy at room temperature. Quantitative analysis revealed that the incoherent electronic relaxation consists of two components: a subpicosecond fast relaxation process and a slow component with a time constant of hundreds of picoseconds (ps). Furthermore, the launch of a coherent acoustic phonon (CAP) in the 20 nm film but absence in the 6.8 nm film uncovers the dominant role of temperature gradient in producing a strain wave. The sound velocity and Young’s modulus in the thick PtTe2 are determined to be 1.736 km/s and 29.5 GPa, respectively. In addition, the coherent optical phonon (COP) with a frequency of 4.7 THz corresponding to Te atoms out-of-plane A1g vibration has been well resolved in all films, which is ascribed to displacive excitation of coherent phonon (DECP). The observation of a strong probe-wavelength dependent COP amplitude reveals the resonant feature of the optical excitation-induced atomic displacement in PtTe2. Our findings provide deep insight into the excitation and dynamics of CAP and COP as well as the photocarriers’ recovery pathway and lifetimes in PtTe2. Our study also demonstrates that the COP spectroscopy is a powerful tool to reveal the modulation of frequency-dependent optical constants induced by atomic vibrations, which may find applications in the fields of optoelectronics and ultrafast photonics.

Peng Suo;Shengnan Yan;Ruihua Pu;Wenjie Zhang;Di Li;Jiaming Chen;Jibo Fu;Xian Lin;Feng Miao;Shi-Jun Liang;Weimin Liu;Guohong Ma

Department of Physics, Shanghai University, Shanghai 200444, China;National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China;e-mail: liuwm@shanghaitech.edu.cn

光子学研究（英文）

[1]Peng Suo;Shengnan Yan;Ruihua Pu;Wenjie Zhang;Di Li;Jiaming Chen;Jibo Fu;Xian Lin;Feng Miao;Shi-Jun Liang;Weimin Liu;Guohong Ma-.Ultrafast photocarrier and coherent phonon dynamics in type-II Dirac semimetal PtTe2 thin films probed by optical spectroscopy)[J].光子学研究（英文）,2022(03):03000653

PtTe2,ditelluride,subpicosecond

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