Figure 3
Chirp correction, pumping regimes, and electron energy loss rates for the topologically trivial insulator phase and the gapped topologically nontrivial insulator phases of the 2D TI Bi2Se3. (a–c) Representative pseudocolor TA spectra plots of the topologically trivial insulator phase convoluted with the temporal chirp of the supercontinuum probing pulse, the temporal chirp itself measured with the pumping pulse at ~ 730 nm (~ 1.7 eV), and the resulting chirp-free TA spectra, respectively. (d) Band structure of the 6 QL thick 3D TI Bi2Se3 film calculated in ref. 4 and the ∼ 340 nm (∼ 3.65 eV photon energy) pumping transitions (blue vertical up arrows) originating from the valence band states and from the surface states below the Fermi energy (EF), respectively. The bulk and surface states are marked as BS and SS, respectively. The predicted in ref. 5 higher energy Dirac SS are marked as "?". (e) and (f) Temporal shift of the low-energy edge of transiently excited electron population (Eedge, as defined in Fig. 1a) for the topologically trivial insulator phase and the gapped topologically nontrivial insulator phases of the 2D TI Bi2Se3, respectively, measured using the ∼ 340 nm pumping of different powers, as indicated by the corresponding colors. The linear fits (red color straight lines) and the corresponding electron energy loss rates in eV ps−1 units are shown. The multicolor bars and the corresponding numbers in ps shown in part (d) present the same data as in part (e) for the 0.5 mW pumping power.
