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(Color online) Normalized transient transmission change as a function of time delay measured with a photon energy of and photocarrier densities of (from to ) , , , , (black lines), and (red line). The inset shows the transient transmission change measured with a photon energy of and a photocarrier density of . The steplike relaxation indicated carrier lifetime under low excitation.
Normalized LO phonon emission rate (solid line) as calculated following the description in the paragraph and the inverse of the carrier cooling time (open circles), which was measured with a photon energy of , with respect to the total electron density . The dash line shows the scattering strength of the phononlike branch of the plasmon-LO phonon coupled modes at long-wavelength limit as given by the theory in Ref. 24. Deviation between two theoretical curves is much less than our experimental uncertainty, suggesting that both models can describe our observed phenomenon well.
Normalized transient transmission change as a function of time delay with a photocarrier density of measured with photon energies of (from top to bottom) 0.925, 0.953, and . The hot carrier cooling time decreases from with increase in photon energy.
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