Direct determination of the zero-field splitting for a singleCo2+ion embedded in a CdTe/ZnTe quantum dot

Abstract

When a Co2+ impurity is embedded in a semiconductor structure, crystal strain strongly influences the zero-field splitting between Co 2+ states with spin projection S z = ±3/2 and S z = ±1/2. Experimental evidence of this effect has been given in previous studies; however, direct measurement of the strain-induced zero-field splitting has been inaccessible so far. Here this splitting is determined thanks to magneto-optical studies of an individual Co 2+ ion in an epitaxial CdTe quantum dot in a ZnTe barrier. Using partially allowed optical transitions, we measure the strain-induced zero-field splitting of the Co 2+ ion directly in the excitonic photoluminescence spectrum. Moreover, by observation of anticrossing of S z = +3/2 and S z = −1/2 Co 2+ spin states in a magnetic field, we determine the axial and in-plane components of the crystal field acting on the Co 2+ . The proposed technique can be applied to optical determination of the zero-field splitting of other transition-metal ions in quantum dots.

Fine structure of an exciton coupled to a single Fe2+ ion in a CdSe/ZnSe quantum dot

“…This idea has been brought to life by the discovery of the fact that a single ion embedded inside the QD does not introduce any non-radiative excitonic recombination channels even for wide energy gap QDs [2,3]. This finding has extended the optical studies of the QDs doped with individual ions from the two classical systems of CdTe/ZnTe [1,[6][7][8][9][10][11][12][13][14][15] and InAs/GaAs [16][17][18] QDs with single Mn 2+ ions to novel systems such as: CdSe/ZnSe QDs with single Mn 2+ [2,3,19] and Fe 2+ [20] or CdTe/ZnTe QDs with single Co 2+ [2,21] and Cr 2+ [22][23][24]. For all of these systems, despite different electronic configurations of the magnetic ions, the ion ground energy level was found to be an orbital singlet exhibiting an effective spin S. The degeneracy of 2S + 1 ion spin states is lifted by the interaction with strained semiconductor lattice as well as the spin-orbit coupling.…”

“…In the leading order, the resulting magnetic anisotropy can be described by the term of DS 2 z , where z corresponds to the QD growth axis. The value of D parameter is relatively small (∼ µeV) for isoelectronic Mn 2+ ion [11][12][13][14] and a few orders of magnitude larger for the ions with a non-zero orbital momentum [2,[20][21][22]25]. As such, in case of the ions like Fe 2+ or Cr 2+ only the subspace of some lowest-energy |S z | ion states is available at low temperatures.…”

Readout of a dopant spin in the anisotropic quantum dot with a single magnetic ion

“…As we show, the simple picture is invalidated by the interplay between optical orientation of the exciton and the non-trivial dependence of the TM ion spin on the selection rules in anisotropic quantum dots. Our considerations will be showcased using a particular system of a CdSe/ZnSe QD with single Fe 2+ ion [14], but the same reasoning should be valid also for all other known systems of that kind [20][21][22].…”

Deterministic Photon Storage and Readout in a Semimagnetic Quantum Dot–Cavity System Doped with a Single Mn Ion

“…[41] Our method facilitates QDs with a single magnetic dopant, which can be deterministically fabricated for several years, [42] with dopand atoms like Manganese (Mn), [43,44] Cromium, [45] Iron, [46] or Cobalt. [47] Interestingly, the spin state of the dopant can be changed via optical control. [48][49][50][51][52] Here, we choose an Mn doped CdTe/ZnTe QD in a microcavity.…”