Volume 118, Number 4, May 2017
|Number of page(s)||6|
|Section||Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties|
|Published online||27 July 2017|
Scattering amplitudes for dark and bright excitons
1 Department of Physics, National Cheng Kung University - Tainan, 701 Taiwan
2 Institut des NanoSciences de Paris, Université Pierre et Marie Curie, CNRS, Tour 22 - 2 Place Jussieu, 75005 Paris, France
3 Laboratoire de Physique Statistique, Ecole Normale Supérieure - 24 rue Lhomond, 75005 Paris, France
4 Research Center for Applied Sciences, Academia Sinica - Taipei, 115 Taiwan
Received: 24 February 2017
Accepted: 3 July 2017
Using the composite boson many-body formalism that takes single-exciton states rather than free carrier states as a basis, we derive the integral equation fulfilled by the exciton-exciton effective scattering from which the role of fermion exchanges can be unraveled. For excitons made of -spin electrons and -spin holes, as in GaAs heterostructures, one major result is that most spin configurations lead to brightness-conserving scatterings with equal amplitude Δ, despite differences in the carrier exchanges involved. A brightness-changing channel also exists when two opposite-spin excitons scatter: dark excitons can end either in the same dark states with an amplitude , or in opposite-spin bright states , with a different amplitude , the number of carrier exchanges involved in these scatterings being even or odd, respectively. Another major result is that these amplitudes are linked by a striking relation, , which has decisive consequence on exciton Bose-Einstein condensation. By using Born values, we show that the exciton condensate can be optically observed through a bright part when excitons have large dipole only, that is, when the electrons and holes are in two well-separated layers, as in current experiments.
PACS: 71.35.-y – Excitons and related phenomena / 03.75.Kk – Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow / 03.75.Mn – Multicomponent condensates; spinor condensates
© EPLA, 2017
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