Conductivity of coupled quantum wells with nonsymmetric scattering

The Green function of an electron in tunnel-coupled quantum wells with different momentum relaxation times cannot be diagonalized when Δ≃T is comparable to the collisional broadening of states (Δ is the level splitting and T is the tunnel matrix element). In this case, a quasiparticle description of the energy spectrum is invalid and the conductivity σ is determined by the formulas of quantum transport theory [the dependence σ(Δ) is obtained for the short-range scattering case]. The frequency dispersion of conductivity that may be realized in the low-frequency region is also discussed.