Coherent Raman resonance from electron spin coherence in $\mathrm{GaAs}$ quantum wells

We report the experimental demonstration of coherent Raman resonance from electron spin coherence in $\mathrm{GaAs}$ quantum wells. Coherent Raman resonance, which is a precursor for electromagnetically induced transparency, appears in the differential transmission response from localized excitons in an external magnetic field applied in Voigt geometry. The spectral domain spin study reveals that the optical processes involved differ from those in the transient domain, leading to distinct polarization and intensity dependences.

Figure 1

(a) Linear absorption spectrum at $T=10\mathrm{K}$ and $B=0\mathrm{T}$. Coherent Raman measurements for strongly localized and mobile excitons were carried out with the pump $2\mathrm{meV}$ below and at the HH-line center, respectively. Arrows indicate the energy position of the pump beam, as discussed in the text. (b) Zeeman splitting as a function of the applied magnetic field as obtained from the coherent Raman resonance in Fig. 2c.

Figure 2

(a) and (b) Energy level diagram and polarization selection rule for the HH transition in Voigt geometry for circularly and linearly polarized fields. The basis transformation for the valence band states is given in the text. (c) and (d) Field and polarization dependence of the differential transmission response from strongly localized excitons obtained at $T=10\mathrm{K}$.

Figure 3

Calculated differential transmission response for the $V$-type three-level system shown in the inset. Parameters were taken from the experiment: $\gamma ∕2\pi =2.5\mathrm{GHz}$, ${\gamma }_{\mathrm{s}}∕2\pi =200\mathrm{MHz}$, $\mid {\mathrm{g}}_{\mathrm{e}}\mid =0.26$, and exciton radiative recombination rate $\Gamma ∕2\pi =200\mathrm{MHz}$. The two dipole transitions are assumed identical except for the transition energy.

Figure 4

(a) Differential transmission response from mobile excitons obtained at $T=10\mathrm{K}$ and $B=1\mathrm{T}$. Similar results were also obtained at higher magnetic field strengths. (b) Schematic of the energy diagram of ground, one-exciton, and two-exciton states as discussed in the text.