Spin Coherence and Electromagnetically Induced Transparency via Exciton Correlations

We report experimental studies on exciton spin coherence induced via Coulomb correlations between excitons with opposite spins, including correlations associated with unbound as well as bound exciton pairs. Electromagnetically induced transparency resulting from the spin coherence is demonstrated in the transient optical response in GaAs quantum wells.

Figure 1

(a) A $\Lambda$-type three-level system for EIT. (b) Level diagram for the hh exciton transition. (c) Transitions between the one-exciton and two-exciton states.

Figure 2

Absorption of a ${\sigma }^{-}$ probe in the presence of a ${\sigma }^{-}$ (dashed) and a ${\sigma }^{+}$ (solid) pump, and in the absence of the pump (dotted). The pump spectrum is shown at the bottom of each figure. The probe arrives 3 ps before the pump for (a)–(c) and 0, 2, 6 ps after the pump for (d), (e), and (f), respectively. The pump pulse energy flux is $400\mathrm{n}\mathrm{J}/\mathrm{c}{\mathrm{m}}^{\mathrm{2}}$.

Figure 3

Absorption of a ${\sigma }^{-}$ probe in the presence of a ${\sigma }^{-}$ (dashed) and ${\sigma }^{+}$ (solid) pump, and in the absence of the pump (dotted), when the sample is prepared with incoherent spin-up excitons. The pump spectrum is shown at the bottom of (a) and (c) and is the same for (a), (b), and (d). The probe arrives 3 ps before the pump except for (d) where the probe arrives 6 ps after the pump. The pump pulse energy flux is $800\mathrm{n}\mathrm{J}/\mathrm{c}{\mathrm{m}}^{\mathrm{2}}$.

Figure 4

Theoretical results based on the three-level model discussed in the text. (a) The temporal profile of the pump (dashed) and probe (solid) pulses. (b) Evolution of the spin coherence ${\rho }_{+-}$. (c) Absorption of a ${\sigma }^{-}$ probe in the presence of a ${\sigma }^{+}$ pump with the probe pulse spectrally resolved after the sample ($\delta$ is the detuning with respect to the pump). For (b) and (c), dotted, solid, and dashed curves are obtained with the same $\gamma$ and with ${\gamma }_{\mathrm{s}\mathrm{p}\mathrm{i}\mathrm{n}}=5\gamma$, $\gamma$, and $0.5\gamma$, respectively.