Spin-dependent analysis of homogeneous and inhomogeneous exciton decoherence in magnetic fields

Abstract

This paper discusses the combined effects of optical excitation power, interface roughness, lattice temperature, and applied magnetic fields on the spin coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For low optical powers, at lattice temperatures between 4 and 50 K, the scattering with acoustic phonons and short-range interactions appear as the main decoherence mechanisms. Statistical fluctuations of the band gap, however, become also relevant in this regime and we were able to deconvolute them from the decoherence contributions. The circularly polarized magneto-photoluminescence unveils a nonmonotonic tuning of the coherence for one of the spin components at low magnetic fields. This effect has been ascribed to the competition between short-range interactions and spin-flip scattering, modulated by the momentum relaxation time.

Quantum Dots as an Active Reservoir for Longer Effective Lifetimes in GaAs Bulk

“…This particular range of excitation power is hereby designated as the "carrier redistribution region"; (iii) Subsequently, for high photon densities, where the contribution of peak 3 cannot be distinguish, the QDs PL emissions (peaks 1 and 2) undergo substantial broadening. This broadening is accompanied by a discernible redshift, attributed to the heating of the sample, as supported by the increase in the slope of the high-energy tail of the QD-PL which is an indicative of higher effective temperature 30 (see the Supporting Information file for further details); (iv) The emission linked to the AlGaAs barrier gradually diminishes, eventually disappearing altogether, coinciding with the emergence of peak 4. Our hypothesis is that both the saturation of the barrier and the increased thermal energy of carriers contribute to this phenomenon; (v) The emergence of low-energy emission from peak 4 occurs only under medium to high excitation power conditions, and it is linked to the saturation of more efficient recombination channels.…”

“…Subsequently, for high photon densities, where the contribution of peak 3 cannot be distinguish, the QDs PL emissions (peaks 1 and 2) undergo substantial broadening. This broadening is accompanied by a discernible redshift, attributed to the heating of the sample, as supported by the increase in the slope of the high-energy tail of the QD-PL which is an indicative of higher effective temperature (see the Supporting Information file for further details);…”

“…This is mainly attributed to the lateral coupling effect in a high-density dot structure where carriers more effectively redistribute between dots toward those with lower energy levels. 8,13,17,48 Despite the few experimental points extracted from peak 2 emission, they reveal a blueshift of 4.5 meV until 40 K, ascribed to local band gap fluctuations provoked by interface roughness and composition variation 30,49,50 which could be related to the state-filling mechanisms that lead to the emission blueshift with excitation power. Yet, although the statefilling should, in principle, affect both peaks, it is noteworthy that the indirect peak does not manifest the blueshift behavior with increasing temperature.…”

“…Once the contribution of the band gap is discarded, we are left with the potential tuning of the effective temperature, T → T eff ν , with the excitation configuration (ν = blue, red). This is addressed in Figure g, where the high-energy side of the emission spectra from the bulk GaAs has been approximated by a Boltzmann-like function as I normalP normalL normalb normalu normall normalk ∝ exp ( − ℏ ω k normalB T e f f ν ) …”