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," Photonics Res. 10, 653 (2022)

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- Photonics Research
- Vol. 10, Issue 3, 653 (2022)

Fig. 1. Time-resolved transient transmission trace Δ T / T 0 of (a) 6.8 nm and (b) 20 nm PtTe 2 films under various pump fluences with pumping and probing at 780 nm. Blue circles denote experimental data; red solid lines are the fitting curves with convoluted biexponential decay function. The peak Δ T / T 0 versus pump fluence for (c) 6.8 nm and (d) 20 nm PtTe 2 films; red solid lines are the linear fitting.

Fig. 2. Fitting fast lifetime τ f of (a) 6.8 nm and (b) 20 nm PtTe 2 with a convoluted biexponential decay function with respect to pump fluence. (c) The extracted coherent acoustical phonon oscillatory signal by subtracting the fitted incoherent carrier dynamics from total transient trace under pump fluence of 994 μJ / cm 2 . Inset shows the frequency domain after FFT. (d) Schematic diagrams of CAP generation induced by temperature gradient. The left and right drawings respectively express the temperature response of 6.8 and 20 nm PtTe 2 films upon laser irradiation.

Fig. 3. Time- and spectrum-resolved ultrafast TA mapping of (a) 6.8 nm PtTe 2 and (c) 20 nm PtTe 2 photoexcited by 780 nm fs pump pulse with constant 1 mJ / cm 2 pump fluence. The unit OD denotes optical density. The TA spectrum of (b) 6.8 nm and (d) 20 nm PtTe 2 at several selected time delays.

Fig. 4. Probe wavelength-dependent COP dynamics of PtTe 2 film. TA kinetics in the first 5 ps of (a) 20 nm and (c) 6.8 nm PtTe 2 at selective representative probe wavelengths. Extracted typical optical phonon oscillation at 525 nm and the fitting curve of (b) 20 nm and (d) 6.8 nm PtTe 2 , in which the inset denotes the FFT amplitude spectrum. (e) The 532 nm Raman spectrum of 20 nm PtTe 2 ; the red arrows indicate the motion direction of the Te atom. (f) The FFT amplitude of residual oscillations of 6.8 nm PtTe 2 as a function of the probe wavelength.

Fig. 5. The TA plotting of (a) 6.8 nm and (b) 20 nm PtTe 2 film in the initial 5 ps of time delay.

Fig. 6. Residual periodical oscillatory signals of 6.8 nm PtTe 2 film with respect to the probe wavelength in the time domain. The individual signal is obtained by subtracting the incoherent carrier dynamics from the total transient trace.

Fig. 7. Damping time of coherent optical phonon of 6.8 nm PtTe 2 film with respect to probe wavelength.

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