Figure 4 | Scientific Reports

Figure 4

From: Coherent surface-to-bulk vibrational coupling in the 2D topologically trivial insulator Bi2Se3 monitored by ultrafast transient absorption spectroscopy

Figure 4

The pump–probe traces of the topologically trivial insulator phase of the 2D TI Bi2Se3. (a–c) The pump–probe traces for the 2 QL thick Bi2Se3 film, which were measured with the 340 nm (3.65 eV) pumping of 0.5 mW power at the specific probe wavelengths, as indicated by the corresponding colors, and plotted using different timescales. The vertical dotted line in (c) indicates the antiphase character of LO-phonon oscillations for traces measured with Eprobe = 3.54 and 1.77 eV. (d) and (g) Some of the traces shown in parts (a–c) and the corresponding fits, as indicated. The corresponding rise-time and decay-time constants are listed for both panels. (e), (h) and (f), (i) The extracted oscillatory parts of the pump–probe traces shown in parts (d) and (g) and the corresponding fast Fourier transformation (FFT), respectively. The center frequencies are indicated in parts (f) and (i).

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