Nonmonotonous temperature dependence of the initial decoherence in quantum dots

We have analyzed the initial decoherence of strongly confined semiconductor quantum dots by performing four-wave-mixing experiments and comparing with theory. The measurements are in quantitative agreement with analytical results accounting for the pure dephasing induced by acoustic phonons. The experiments confirm the recent prediction of an unusual nonmonotonous temperature dependence of the initial decoherence time.

Figure 1

Nonresonantly excited PL spectra at low excitation intensities at 300 K for the nonannealed (sample 1) and the annealed sample (sample 2).

Figure 2

Time-integrated FWM amplitudes normalized as described in the text plotted vs delay time $\tau$ for both samples $(S1∕S2)$ at temperatures 20 and 100 K. The symbols represent the experiment and lines the theory with $a=12.6\mathrm{nm}$, $b=2.4\mathrm{nm}$ for sample 1 and $a=16\mathrm{nm}$, $b=2.4\mathrm{nm}$ for sample 2. The inset shows the non-normalized FWM amplitude for sample 2 at 20 K and the extracted long-time behavior (dashed).

Figure 3

Fractional signal drop after $\tau =6\mathrm{ps}$ vs temperature: experiment (symbols) and theory (lines) calculated with the same parameters as in Fig. 2. Error bars represent the statistical error of the extraction method (Ref. 23).

Figure 4

Initial decoherence time vs temperature: (a) experiment (symbols) and theory (lines) using the same parameters as in Fig. 2; (b) calculations for different wave-function sizes. Error bars represent the statistical error of the extraction method (Ref. 23).