Long exciton spin relaxation in coupled quantum wells
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(a) Scheme of GaAs CQW under applied electric field showing formation of direct and indirect excitons. (b) Diagram of resonant polarized excitation in direct excitonic states and emission from two optically active indirect states. (c) Left scale: PL spectra for direct excitons (, solid black line) under nonresonant excitation and for indirect excitons under resonant 1.58 eV excitation, polarization resolved in co (dashed blue) and cross (dotted red) configurations. Right scale: degree of circular polarization for indirect excitons vs excitation laser energy (open circles). The gray arrows indicate the point obtained from the spectra shown in the left part of the figure.
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[(a)–(c)] For three different applied biases under 1.577 eV excitation: left scale—PL decay vs delay time after the excitation pulse (filled circles—experimental data, line—exponential fit), and right scale—circular polarization degree (open circles). Vertical dashed lines mark zero delay and the one corresponding to the PL decay time, respectively. (d) Dependence of transition energy on applied bias (black triangles—experimental data, line—linear fit of the Stark shift), and of PL decay time (opened blue squares).
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