Role of the stress trap in the polariton quasiequilibrium condensation in GaAs microcavities

Abstract

Recent experiments have shown several effects indicative of Bose-Einstein condensation in polaritons in GaAs-based microcavity structures when a harmonic potential trap for the two-dimensional polaritons is created by applied stress. These effects include both real-space and momentum-space narrowing, first-order coherence, and onset of linear polarization above a particle density threshold. Similar effects have been seen in systems without traps, raising the question of how important the role of the trap is in these experiments. In this paper we present results for both trapped conditions and resonant nontrapped conditions in the same sample. We find that the results are qualitatively different, with two distinct types of transitions. At low density in the trap, the polaritons remain in the strong-coupling regime while going through the threshold for onset of coherence; at higher density, there is a different threshold behavior which occurs with weak coupling and can be identified with lasing; this transition occurs both with and without a trap.

Determination of operating parameters for a GaAs-based polariton laser

“…This seems to contradict studies in which a redshift of the cavity mode was reported. 17,18 However, in these studies, continuous wave lasers were used which create a rather equilibrium background carrier distribution in contrast to our experimental situation. We note that a blueshift of the cavity mode with increasing carrier density was reported by another group at negative detuning.…”

“…However, for GaAs-based microcavities, there exist only studies for one single detuning 15 or for a limited range of temperatures and detunings. 16 Moreover, there is an ongoing debate about the distinction between polariton condensation (PC) and cavity lasing (CL) 17,18 and the identification of unique criteria for PC is still in the focus of current studies. 19,20 An interpretation of coherent emission in the weak coupling regime in terms of a photon BEC has also been suggested.…”

Experimental Verification of the Very Strong Coupling Regime in a GaAs Quantum Well Microcavity

“…1(b) at zero detuning between cavity mode and heavy holeexciton is estimated to be below 0.05. This value has been determined from modeling the coupling of the cavity mode to both excitons as coupling of three harmonic oscillators, where the coupling term between the two excitons is zero [28]. We therefore neglect the influence of the light hole-exciton in our study.…”

Principles and Methods of Quantum Information Technologies

“…In this respect, further studies are needed for a full understanding of this system. Experimantal studies are also important, in particular, in a high density regime [28][29][30][31][32][33][34]39].…”

“…In experiments [28][29][30][31][32][33][34], the second threshold and the blue shift has been reported since more than 10 years ago, the mechanism of which has been attributed to a shift into the weak coupling regime due to dissociations of Coulomb-bound e-h pairs (excitons); the lasing phase is then achieved as a result. However, there is no convincing discussion why such dissociations lead to nonequilibration essential for lasing.…”