Magnetic-field-induced abrupt spin state transition in a quantum dot containing magnetic ions

TL;DR

This study reveals an abrupt magnetic-field-induced spin state transition in Mn-doped CdTe quantum dots, characterized by a spectral change from broad to narrow lines, indicating a switch from non-polarized to polarized Mn2+ spins.

Contribution

It demonstrates a novel magnetic-field-driven spin transition in quantum dots containing magnetic ions, highlighting an intrinsic spin reconfiguration mechanism independent of charge carriers.

Findings

Spectral lines split into narrow peaks at a critical magnetic field.

Transition from non-polarized to highly polarized Mn2+ spins.

Effect is intrinsic to Mn2+ spin configuration, not charge carriers.

Abstract

We present the results of a comprehensive magneto-optical characterization of single CdTe quantum dots containing a few Mn2+ ions. We find that some quantum dots exhibit an unexpected evolution of excitonic photoluminescence spectrum with the magnetic field. At a certain value of the magnetic field, specific for every quantum dot, each of the broad spectral lines related to the recombination of various excitonic complexes confined inside the dot transforms into a pair of narrow lines split by several meV. We interpret this abrupt change in the character of excitonic emission spectrum as a consequence of a transition from a non-polarized state of the Mn2+ spins in a low field regime to a highly (almost fully) polarized state above the critical magnetic field. Various optical experiments, including polarization-resolved studies, investigation of different excitation regimes and time-resolved measurements corroborate this scenario. However, these measurements indicate also that the observed effect is not related or influenced by the photo-created charge carriers, but it is rather originating from unusual spin configuration in the cluster of Mn2+ ions.