Intersublevel polaron dephasing in self-assembled quantum dots

Polaron dephasing processes are investigated in $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots using far-infrared transient four wave mixing (FWM) spectroscopy. We observe an oscillatory behavior in the FWM signal shortly $(<5\mathrm{ps})$ after resonant excitation of the lowest energy conduction band transition due to coherent acoustic phonon generation. The subsequent single exponential decay yields long intraband dephasing times of $90\mathrm{ps}$. We find good agreement between our measured and calculated FWM dynamics, and show that both real and virtual acoustic phonon processes are necessary to explain the temperature dependence of the polarization decay.

Figure 1

(Color online) Comparison of time integrated FWM (dashed line) and pump-probe (solid line) signals measured at $10\mathrm{K}$ and transition energy of $\sim 53\mathrm{meV}$ as a function of the delay time between the incoming pulses. The inset exhibits the absorption squared and FWM signal intensity at peak maximum vs the transition energy for the same sample. Also shown is the schematic diagram of the polaron energy structure in InAs QDs.

Figure 2

(Color online) Calculated InAs single-dot polaron absorption at different temperatures. The ZPL transition energy is taken as zero energy. Inset shows the comparison between the acoustic phonon sidebands for intersublevel polaron (solid line) and ground state exciton (dashed line) at $T=80\mathrm{K}$. The ZPL is not considered for clarity.

Figure 3

(Color online) Temperature dependent four wave mixing signals: simulations (a) and experiment (b). Inset: calculated FWM curves at $100\mathrm{K}$ for $\delta$ pulses (dotted line) and $1.5\text{−}\mathrm{ps}$-long pulses compared with experimental data.

Figure 4

(Color online) Temperature dependence of the polaron linewidth: experiment (closed squares) and calculation including real (dashed line), virtual (dash-dotted line), and both virtual and real (solid line) transitions. The dotted line exhibits the temperature dependence of the population relaxation.