Strain-induced coherent dynamics of coupled carriers and Mn spins in a quantum dot

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Strain-induced coherent dynamics of coupled carriers and Mn spins in a quantum dot

A. Lafuente-Sampietro, H. Boukari, and L. Besombes

Phys. Rev. B 92, 081305(R) – Published 10 August 2015

Abstract

We report on the coherent dynamics of the spin of an individual magnetic atom coupled to carriers in a semiconductor quantum dot which has been investigated by resonant photoluminescence of the positively charged exciton $(X^{+})$ . We demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single Mn atom forms an ensemble of optical $Λ$ systems which can be addressed independently. We show that the spin dynamics of the $X^{+}$ -Mn complex is dominated by the electron-Mn exchange interaction and report on the coherent dynamics of the electron-Mn spin system that is directly observed in the time domain. Quantum beats reflecting the coherent transfer of population between electron-Mn spin states, which are mixed by an anisotropic strain in the plane of the quantum dot, are clearly observed. We finally highlight that this strain-induced coherent coupling is tunable with an external magnetic field.

Received 26 May 2015
Revised 16 July 2015

DOI:https://doi.org/10.1103/PhysRevB.92.081305

Authors & Affiliations

A. Lafuente-Sampietro, H. Boukari, and L. Besombes^*

Université Grenoble Alpes, Institut Néel, F-38000 Grenoble, France and CNRS, Institut Néel, F-38000 Grenoble, France

^*lucien.besombes@grenoble.cnrs.fr

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Issue

Vol. 92, Iss. 8 — 15 August 2015

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Images

Figure 1
(a) PL at $T = 5$ K of a positively charged Mn-doped CdTe QD. Inset: Experimental and calculated intensity maps of the linear polarization dependence of the PL from $X^{+}$ -Mn. (b) Experimental (Exp.) and calculated (Th.) spectra from $X^{+}$ -Mn in linear polarizations. The parameters in the calculation are $I_{h Mn} = 345 μ eV, I_{e Mn} = - 175 μ eV, ρ_{s} / Δ_{l h} = 0.09, θ = 0$ , and $η = 30 μ eV$ . (c) Energy levels of the ground (h-Mn) and excited ( $X^{+}$ -Mn) states as a function of their angular momentum $(M_{z})$ . Optical $Λ$ systems associated with the e-Mn states $| 3, + 1 〉$ and $| 3, - 1 〉$ , coupled by the strain anisotropy $E (S_{y}^{2} - S_{x}^{2})$ , are presented. The levels in dotted lines correspond to the h-Mn states $| - 1 / 2 〉 | ⇑ 〉$ and $| + 1 / 2 〉 | ⇓ 〉$ coupled by the valence band mixing. Optical recombination towards these levels leads to the linearly polarized lines observed in (b).
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Figure 2
(a) Nonresonant (Non Res.) and resonant (Res.) PL of $X^{+}$ -Mn. Co- and cross-circularly polarized PL spectra are collected for three different energies of the cw resonant laser (green). Inset: Intensity map of the cross-circularly polarized PL detected on the low-energy side of $X^{+}$ -Mn as the cw laser is scanned through the high-energy side. (b) Energy levels of $X^{+}$ -Mn and identification of the three resonances observed in (a) corresponding to the optical $Λ$ systems associated with the e-Mn states $| 3, + 1 〉, | 3, + 2 〉$ , and $| 2, + 2 〉$ .
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Figure 3
(a) Configuration of the time-resolved PL experiment for an excitation of $| 3, + 1 〉$ (pulsed laser in green). (b) Top panel: Time-resolved resonant PL of $| 3, + 1 〉$ with a $σ^{+} / σ^{-}$ sequence of laser pulses and a detection in $σ^{+}$ and $σ^{-}$ polarization. Bottom panel: Corresponding time dependence of the circular polarization rate $κ = (σ_{-} - σ_{+}) / (σ_{-} + σ_{+})$ . (c) Time dependence of the circular polarization rate of the resonant PL of the states $| 3, + 1 〉$ (red), $| 3, + 2 〉$ (black), and $| 2, + 2 〉$ (blue). (d) Corresponding polarization rates calculated with $D_{0} = 7 μ eV$ [7], $T_{2}^{e Mn} = 0.6$ ns, $E = 1.8 μ eV$ , a radiative lifetime $T_{r} = 0.3$ ns, and the parameters deduced from PL (Fig. 1).
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Figure 4
(a) Influence of a longitudinal ( $B_{z}$ , red) and a transverse ( $B_{x}$ , blue) magnetic field on the time dependence of the circular polarization rate $κ = (σ_{-} - σ_{+}) / (σ_{-} + σ_{+})$ of the resonant PL of $| 3, + 1 〉, | 3, + 2 〉$ , and $| 2, + 2 〉$ . On the top left panel, curves are shifted by 0.5 for clarity. (b) Corresponding time dependence of the circular polarization rate calculated with $g_{Mn} = 2, g_{e} = - 0.4, g_{h} = 0.6$ [7], and the parameters of Fig. 3. The curves are shifted by 1 for clarity.
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