Anomalous dephasing of bosonic excitons interacting with phonons in the vicinity of the Bose-Einstein condensation

Abstract

Abstract. The dephasing and relaxation kinetics of bosonic excitons interacting with a thermal bath of acoustic phonons is studied after coherent pulse excitation. The kinetics of the induced excitonic polarization is calculated within Markovian equations both for subcritical and supercritical excitation with respect to a Bose-Einstein condensation (BEC). For excited densities n below the critical density nc, an exponential polarization decay is obtained, which is characterized by a dephasing rate Γ = 1 T 2. This dephasing rate due to phonon scattering shows a pronounced exciton-density dependence in the vicinity of the phase transition. It is well described by the power law Γ ∝ (n − nc) 2 that can be understood by linearization of the equations around the equilibrium solution. Above the critical density we get a non-exponential relaxation to the final condensate value

Kinetics of the Dephasing and the Condensation of Excitons

“…These equations have a variety of highly interesting features that can be also understood analytically [5]. At excitation densities below the critical density n c for a BEC the polarization decays exponentially.…”

“…Due to the fact that in the x system this order parameter equals the polarization unusual dephasing properties can be expected in the vicinity of the phase transition. As a first model x's interacting with a bath of acoustic phonons and an external classical light field Et are considered [5]. The anomalous function F k is completely neglected.…”

“…For definiteness ZnSe parameters are chosen for the numerics. From this Hamiltonian one can derive the Boltzmann equation for the x occupation number n k and similarly for the polarization p [5].…”

“…This clear reduction of the dephasing should be the first sign of the approach to the phase transition and may be observed in experiments sensitive to coherence. For more details we refer to [5].…”

“…In Ref. [5] these correlations have been combined with x±phonon scattering terms. However in the present paper a system of interacting x's will be studied including the coherent x±x correlations and x±x scattering terms for all dynamic variables.…”