Phonon-mediated dark to bright plasmon conversion

The optical response of a matter excitation embedded in nanophotonic devices is commonly described by the Drude-Lorentz model. Here, we demonstrate that this widely used approach fails in the case where quantum-confined plasmons of a two-dimensional electron gas interact strongly with optical phonons. We propose a new quantum model which contains the semiclassical Drude-Lorentz one for simple electronic potentials, but predicts very different results in symmetry-broken potentials. We unveil a new mechanism for the oscillator strength transfer between bright phonon-polariton and dark plasmon modes, enabling thus new quantum degrees of freedom for designing the optical response of nanostructures

Quantum Theory of Multisubband Plasmon-Phonon Coupling

We present a theoretical description of the coupling between longitudinal optical phonons and collective excitations of a two-dimensional electron gas. By diagonalizing the Hamiltonian of the system, including Coulomb electron-electron and Fr\"ohlich interactions, we observe the formation of multisubband polarons, mixed states partially phonon and partially multisubband plasmon, characterized by a coupling energy which is a significant fraction, up to ~40%, of the phonon energy. We demonstrate that multisubband plasmons and longitudinal optical phonons are in the ultra-strong coupling regime in several III-V and II-VI material systems.Comment: 13 pages, 4 figure

Ultra-strong light–matter coupling and superradiance using dense electron gases

AbstractThe physics of the interaction between a dense two-dimensional electron gas and a microcavity photonic mode is reviewed. For high electronic densities, this system enters the ultra-strong coupling regime in which the Rabi energy, which measures the strength of the light–matter coupling, is of the same order of magnitude as the matter excitation. The ultra-strong coupling has been experimentally demonstrated by inserting a highly doped semiconductor layer between two metal plates that produce a microcavity, with extreme sub-wavelength confinement of the electromagnetic field. A record value at room temperature (73%) of the ratio between the Rabi and the matter excitation energies (the relative Rabi energy) has been measured together with a very large photonic gap induced by the polariton splitting. The ultra-strong coupling is a manifestation of a huge cooperative dipole, which is proportional to the number of electrons participating in the interaction. Such a phenomenal interaction with light appears also in the absence of a microcavity and, for a dipole coupled with free space, it gives rise to superradiance