Two-electron absorption in a biased quantum well

Linear light absorption of 2D electrons confined within a biased quantum well is studied theoretically. We demonstrate that for light polarization perpendicular to the 2D plane, in addition to conventional absorption peak at frequency ℏω≈Δ, where Δ is the intersubband energy distance, there exists a peak around a double frequency ℏω≈2Δ. This additional peak is entirely due to electron-electron interactions, and corresponds to excitation of two electrons by one photon. The magnitude of two-electron absorption is proportional to U2, where U is the applied bias.