Dark-Bright Mixing of Interband Transitions in Symmetric Semiconductor Quantum Dots

Abstract

In photoluminescence spectra of symmetric [111] grown GaAs/AlGaAs quantum dots in longitudinal magnetic fields applied along the growth axis, we observe in addition to the expected bright states also nominally dark transitions for both charged and neutral excitons. We uncover a strongly nonmonotonic, sign-changing field dependence of the bright neutral exciton splitting resulting from the interplay between exchange and Zeeman effects. Our theory shows quantitatively that these surprising experimental results are due to magnetic-field-induced ±3/2 heavy-hole mixing, an inherent property of systems with C(3v) point-group symmetry.

Magnetic field induced valence band mixing in [111] grown semiconductor quantum dots

“…From the ratio of intensities of identically-polarized lines we can find the ratio g h1 /g h and, therefore, determine values of g e , g h1 and the absolute value of g h2 . 24 2. Neutral exciton X 0…”

“…2c, with the coefficients C 1,2 determined solely by the ratio g h2 /g h1 , see Ref. 24 for details. For non-zero g h2 , all the four radiative transitions are allowed, each transition being circularly polarized, either σ + or σ − .…”

Intertwining of Zeeman and Coulomb interactions on excitons in highly symmetric semiconductor quantum dots

“…This value is also comparable with diamagnetic coefficients measured in other QD systems in the intermediate to strong confinement regime. 45 A comparison of our results with a recent study 46 of the Zeeman effect in symmetric QDs is enlightening as to the origin of the dark-bright mixing of the exciton states that is induced by a longitudinal magnetic field. In this study, the GaAs QDs were grown by droplet epitaxy on a GaAs (111)A substrate.…”

“…This prediction was, however, not validated by recent experimental studies of the Zeeman effect on charged excitons in various QD systems. 23,24,46 The strong sensitivity of the radiative pattern of charged exciton in a transverse magnetic field was attributed to a Coulomb interaction among the three carriers composing a charged exciton, or, in other words, to a charge-dependent extension of the complex wave function. 27 In summary, our theory provides the framework to analyze the experimental radiative pattern of neutral excitons confined in pyramidal quantum dots of C 3v symmetry for different orientations of an applied magnetic field.…”

“…Sallen and co-workers attributed this mixing to a coupling between the heavy-hole states with spin projections +3/2 and −3/2 onto the [111] growth axis, which is induced by a Zeeman interaction term varying linearly with the magnetic field. 27,46 Although this Zeeman interaction term is sufficient to explain the circular polarization and the Zeeman splitting of the emission lines, it alone cannot account for their relative emission intensities. Indeed, the emission intensity of the σ + polarized dark transition is much weaker than the σ − polarized one.…”