9.2.26

Article: Influence of local strain on the optical probing of a Ni2+ spin in a charged self-assembled epitaxial quantum dot

We investigate the optical and spin properties of semiconductor quantum dots doped with a single Ni²⁺ ion interacting with a charged exciton. The exchange interaction between charge carriers and the localized Ni²⁺ spin—dominated by coupling to holes—provides an efficient optical interface to an individual magnetic atom embedded in a solid-state nanostructure. This makes Ni-doped quantum dots a versatile platform for exploring single-spin physics and carrier–spin interactions at the nanoscale.

Through systematic magneto-optical spectroscopy, we reveal the crucial role played by the local strain environment at the Ni²⁺ site. In positively charged quantum dots dominated by in-plane biaxial strain, the Ni²⁺ ion exhibits three well-defined spin states (𝑆𝑧 = 0, ±1). In this regime, the magneto-optical spectra offer direct access to the local strain anisotropy, enabling the quantum dot itself to function as a sensitive probe of strain on the atomic scale. In contrast, in most dots the presence of lower-symmetry strain leads to strong mixing of all Ni²⁺ spin states, resulting in a much richer optical spectrum with an increased number of allowed transitions.

To interpret the experimental observations, we develop a spin-effective model that explicitly incorporates the orientation and symmetry of the local strain. This model successfully reproduces the key features of the measured spectra and shows that low-symmetry terms in the hole–Ni²⁺ exchange interaction are essential for accurately describing the emission behavior in a magnetic field. Overall, our results establish strain as a powerful control parameter for tailoring the spin structure and optical accessibility of single magnetic ions in quantum dots, opening new perspectives for solotronic and quantum information applications.

Authors: K. E. Połczyńska, S. Karouaz, W. Pacuski and L. Besombes

Physical Review B 112, 245301

Published 1 December, 2025

https://doi.org/10.1103/swfy-f7w8