Uniaxial-stress investigation of asymmetrical GaAs-(Ga,Al)As double quantum wells

We present low-temperature-reflectance experiments, performed on GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As asymmetrical double quantum wells, under in-plane uniaxial stress. The results, when compared to what is obtained from single quantum wells, exhibit some peculiar behaviors, which are typical effects of the asymmetry of the structures. A careful examination of these results is proposed in light of theoretical predictions about subband-to-subband transition energies and oscillator strengths. Our conclusion is that asymmetry makes it possible to obtain novel couplings between excitonic states, which cannot be accounted for without an accurate theoretical treatment of the Coulombic interaction, including intersubband mixings of valence wave functions.