Strain-driven spin mixing and dark-exciton recombination in a neutral Ni2+ doped quantum dot

TL;DR

This study reveals how local strain influences spin mixing and dark exciton recombination in Ni2+-doped quantum dots, providing insights into spin interactions and optical properties relevant for quantum information applications.

Contribution

It demonstrates the impact of strain orientation on Ni2+ spin states and exciton spectra, introducing an effective Hamiltonian model that captures these effects.

Findings

Strain-induced mixing of Ni2+ spin states observed in photoluminescence spectra.

Magnetic field restores circular polarization, resolving Ni2+ spin projections.

Dark exciton emission dominated by magnetic ion spin flips at low fields.

Abstract

We investigate the optical properties of neutral excitons in CdTe/ZnTe quantum dots containing a single Ni2+ ion. We show that the photoluminescence spectra provide a direct spectroscopic signature of strain induced mixing of the Ni2+ spin states. A misalignment between the principal axis of the local strain tensor and the quantum dot growth direction reorients the spin quantization axis of the magnetic ion, reducing the hole Ni2+ exchange interaction at low magnetic field and giving rise to photoluminescence replicas around the partially linearly polarized bright-exciton transitions. A longitudinal magnetic field restores the circularly polarized optical selection rules, allowing the three spin projections S_z = 0, +-1 of the Ni2+ ion to be spectrally resolved. Dark exciton emission appears on the low energy side of the spectra and is dominated at low field by transitions involving spin flips of the magnetic ion. An effective spin Hamiltonian including strain orientation and valence band mixing reproduces the magnetic field evolution of both bright and dark exciton spectra. These results highlight the key role of the local strain environment in determining the spin exciton coupling of transition metal dopants in semiconductor quantum dots.