Optical signatures of spin-dependent coupling in semimagnetic quantum dot molecules

Abstract

We present photoluminescence studies of CdTe and ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ quantum dots grown in two adjacent layers. We show that when the dots are 8 nm apart, their magneto-optical properties---Zeeman shifts and transition linewidths---are analogous to those of individual CdTe or ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ dots. When the dots are grown closer, at a distance of 4 nm, it becomes possible to tune the electron states to resonance and obtain a formation of a molecular state hybridized over the two dots. As a result of the resonant enhancement of the electron--Mn ion exchange interaction, spectroscopic signatures specific to spin-dependent interdot coupling appear. Namely, an anomalous increase of the Zeeman shift and a resonant increase in the transition linewidth are observed. A simple model calculation allows us to quantitatively reproduce the experimental results.