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Colloquium: April 9, 2014

 
 
Carlo Sirtori*
Superradiant Electroluminescence and
Collective Phenomena in a Low Dimensional Electron Gas
Day Time Place
April 09, 2014 Wednesday 15:40 EE01

Host: Atilla Aydınlı

ABSTRACT —  The interaction between light and matter in a quantum structure, can be strongly enhanced by increasing the density of the confined electrons, thus the number of optical available dipoles[1]. In semiconductor quantum structures, this can be readily obtained by rising doping. For very high electronic densities, however, very important collective phenomena appear[2]. The interaction between dipoles becomes so strong that ties all the transitions of the system and gives rise to an important renormalisation of the optical resonances[2]. In this situation the ensemble of free electrons, becomes a superposition of coupled oscillators: the plasmon. The optical properties of the plasmon are no longer related to the energy spectrum imposed by the confining potentials, but depend on the Coulomb interaction between single electrons [2]. This collective excitation couples the electronic ensemble with the light through a huge dipole which is the coherent sum of each individual electronic dipole. The system behaves as a macro-atom (composed of several thousands of billions of electrons), with an exceptionally strong interaction with light[3]. Experimentally we have investigated highly doped semiconductor quantum wells, in which the Fermi energy lays above few of the confined states. By performing absorption experiment we have measured evidences of the Coulomb interaction between dipoles that phases all single electron transitions. By driving a current across the high density electron gas a strong electroluminescent signal have been measured, first evidence of super-coherent emission in a solid at room temperature.

References:
[1] Y. Todorov, et al., Phys. Rev. Lett. 105, 196402 (2010)
[2] Y. Todorov and C. Sirtori, Phys. Rev. B 85, 045304 (2012)
[3] A. Delteil, et al., Phys. Rev. Lett. 109, 246808 (2012).

*Université Paris-Diderot, CNRS, Paris, France

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