Lasing and polariton condensation: Two distinct transitions in GaAs microcavities with stress traps

Abstract

We have used stress to create a harmonic potential for polaritons in GaAs microcavities and have previously reported that the polaritons undergo spontaneous coherence in the trap. 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. The transition at lower density can therefore be identified as a type of nonequilibrium Bose–Einstein condensation.

Optical bistability in electrically driven polariton condensates

“…2(a). Confirming the observations that we have reported previously [9], we observe a double threshold in the input-output characteristics [35][36][37][38], which strongly suggests a crossover from the linear regime to polariton lasing (at j = 50 A/cm 2 , and a subsequent transition (at j = 110 A/cm 2 ) into the regime of cavity mediated from an electron-hole plasma. It is worth noting that while the second threshold into the weak coupling regime acquires the shape of a smooth S in the double logarithmic plot, the polariton lasing threshold features a sudden increase in intensity.…”

Temperature Dependence of Highly Excited Exciton Polaritons in Semiconductor Microcavities

“…However, a distinct second threshold was not observed, unlike in previous studies. [11][12][13][14][15][16][17] As expected from BEC thermal equilibrium theory, the threshold increased with an increase in the temperature but the second threshold was not observed (e)], the second threshold was not observed, which implies that the system has already reached photon lasing after the first threshold. However, as we will show later, the properties of the second-order correlation function make this slightly ambiguous in the case of 100 K. Looking at the change in the PL energy at k = 0, which gives the maximum PL intensity at each temperature ( another jump in the PL energy at around 40 mW to an energy 7 meV higher than that below the condensation threshold and equal to the cavity photon energy.…”

“…[11][12][13][14][15][16][17][18]32 The PL intensity has a second threshold, 11,15,32 where population inversion is believed to be the reason for the transition to photon lasing. In ref.…”

“…Population inversion then occurs, and photon lasing is observed after the second nonlinear increase, which is often called the second threshold in contrast to the first or condensation threshold. [11][12][13][14][15][16][17][18] However, recent theoretical studies [19][20][21][22][23] have indicated that some e-h pairs can remain in the high-density regime.…”

Preface to Special Topic: Plenary and Invited Papers from the 29th International Conference on the Physics of Semiconductors, Rio de Janeiro, Brazil, 2008

“…Benz et al 4 on the other hand, explore photonic crystals for resonators, to promote the operation of quantum-cascade lasers, the whole also based on such heterostructures now lightly doped in chosen regions. III-V microcavities are used in the work by Nelsen et al 5 to build, with stress-induced trapping, polariton condensation-a type of nonequilibrium Bose-Einstein condensation of the quasiparticles. Again, based on III-V alloys, exploring the enhanced optical characteristics of quantum-dot diatomic molecules is shown by Hermannstädter et al 6 to be a promising approach for quantum information processing.…”