Time-resolved measurements of the polarization state of four-wave mixing signals from GaAs multiple quantum wells

Mixed biexcitons in single quantum wells

“…It vanishes in ( ϩ , ϩ ) configuration, since the bound biexciton state XX h cannot be excited. The unbound biexciton state 5,19,20 is neglected for simplicity in the model. It influences in homogeneously broadened systems the signal around the exciton energy, especially for crosslinear polarization, but does not change the signal strength at the bound biexcitonic transitions.…”

(11 IOTA)-Oriented Heterostructures and Devices: The Effects of Strain and Orientation

“…Furthermore, it should be pointed out that this simple phenomenological model produces good qualitative agreement with a large number of features in the TR-FWM and TI-FWM signal that are not discussed in this chapter (see [51,52,58] for a discussion of some of these). Specifically, we note that the density matrix equations for the 5-level system of Figure 9.16 also can be solved to obtain a closed-form solution for the third-order polarization in the 2k2 -ki direction at negative delays (including EID and LFC).…”

“…And finally, we will fix the time delay between the two pump pulses at T21 = +300 fs. We have performed an extensive set of such measurements (at both positive and negative delays) using both the direct time-resolved techniques (TRE) of Section 9.2 [51,52] and the spectral interferometric techniques (POLLIWOG) of Section 9.3 [53,54]. In our presentation here we will feature the POLLIWOG results.…”

“…The splitting between the heavy-hole (hh) and light-hole (lh) excitons is 7.3 meV for one sample and ^ 12 meV for the other. All of the TRE measurements described in [24,51,52] were performed with the 7.3 meV sample, and the POLLIWOG measurements described in this chapter and in [53][54][55][56][57][58] used the % 12 meV sample. This difference in the hh-lh splittings is the only measurable distinction between the two samples that we have observed, and it is most likely the result of differing in-plane strains introduced when the samples are cooled.…”

“…This is appropriate for a dilute medium, such as an atomic gas at low pressures, but is not expected to be accurate for a dense medium, such as semiconductors, where many-body effects are known to be important. In fact, as we have already mentioned in Section 9.1, a complete description of the behavior of the FWM signal has been shown to require the inclusion of various exciton-exciton interaction phenomena [24,[51][52][53][54], such as local field corrections (LFC) [4,7,[15][16][17][18], excitation-induced dephasing (EID) [19][20][21][22][23][24], andbiexciton formation (BIF) [25][26][27][28][29][30][31][32]39]. In particular, each has been shown to produce TI-FWM signals at negative delays and delayed peaks in the TR-FWM signal, as required by experiment.…”