Far-infrared excitations below the Kohn mode: Internal motion in a quantum dot

We have investigated the far-infrared response of quantum dots in modulation doped GaAs heterostructures. We observe modes at frequencies below the center-of-mass Kohn mode. Comparison with Hartree–random-phase-approximation calculations show that these modes arise from the flattened potential in our field-effect confined quantum dots. They reflect pronounced relative motion of the charge density with respect to the center of mass.