M. Nawrocki

Optical manipulation of a single Mn spin in a CdTe-based quantum dot.

Two coupled CdTe quantum dots, selected from a self-assembled system, one of them containing a single Mn ion, were studied by continuous wave and modulated photoluminescence, photoluminescence excitation, and photon correlation experiments. Optical writing of information on the spin state of the Mn ion has been demonstrated, using the orientation of the Mn spin by spin-polarized carriers transferred from the neighboring quantum dot. Mn spin orientation time values from 20 to 100 ns were measured, depending on the excitation power. Storage time of the information on the Mn spin was found to be enhanced by application of a static magnetic field of 1 T, reaching hundreds of microseconds in the dark. Simple rate equation models were found to describe correctly the static and dynamical properties of the system.

Designing quantum dots for solotronics

Solotronics, optoelectronics based on solitary dopants, is an emerging field of research and technology reaching the ultimate limit of miniaturization. It aims at exploiting quantum properties of individual ions or defects embedded in a semiconductor matrix. It has already been shown that optical control of a magnetic ion spin is feasible using the carriers confined in a quantum dot. However, a serious obstacle was the quenching of the exciton luminescence by magnetic impurities. Here we show, by photoluminescence studies on thus-far-unexplored individual CdTe dots with a single cobalt ion and CdSe dots with a single manganese ion, that even if energetically allowed, nonradiative exciton recombination through single-magnetic-ion intra-ionic transitions is negligible in such zero-dimensional structures. This opens solotronics for a wide range of as yet unconsidered systems. On the basis of results of our single-spin relaxation experiments and on the material trends, we identify optimal magnetic-ion quantum dot systems for implementation of a single-ion-based spin memory.

Excitation mechanisms of individual Cd Te ∕ Zn Te quantum dots studied by photon correlation spectroscopy

Systematic measurements of auto- and cross-correlations of photons emitted from individual

Picosecond charge variation of quantum dots under pulsed excitation

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Magnetization dynamics down to a zero field in dilute (Cd,Mn)Te quantum wells.

quantum dots under pulsed excitation were used to elucidate nonresonant excitation mechanisms in this self-assembled system. Memory effects extending over a few excitation pulses have been detected in agreement with previous reports and quantitatively described by a rate equation model, fitting a complete set of correlation and PL intensity results. The important role of single carrier trapping in the quantum dot was established. An explanation was suggested for the unusually wide antibunching dip observed previously in

Magnetophotoluminescence study of intershell exchange interaction in CdTe/ZnTe quantum dots

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Nonlinear optical spectroscopy of indirect excitons in coupled quantum wells

autocorrelation experiments on quantum dots under cw excitation.

Tunneling of spin polarized excitons in CdTe based asymmetric double quantum well structure

We present a spectroscopic study of excitation dynamics in self-assembled CdTe/ZnTe quantum dots. Insight into details of kinetics is obtained from the time-resolved microphotoluminescence, single photon correlation, and subpicosecond excitation correlation measurements done on single quantum dots. It is shown that the pulsed excitation at an energy above the energy gap of the barrier material results in separate capture of electrons and holes. We found that the capture of electrons by the quantum dot is delayed with respect to the capture of holes: the electron capture takes place in 20\char21{}40 ps after the excitation pulse, while the capture of holes is much faster.

MBE growth and characterization of a II–VI distributed Bragg reflector and microcavity lattice-matched to MgTe

The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in the absence of a static magnetic field was found to be up to 3 orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.

Single photon emission in the red spectral range from a GaAs-based self-assembled quantum dot

T. Kazimierczuk, ∗ T. Smoleński, M. Goryca, 2 L. K lopotowski, P. Wojnar, K. Fronc, A. Golnik, M. Nawrocki, J.A. Gaj, † and P. Kossacki Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warsaw, Poland Laboratoire National des Champs Magntiques Intenses, Grenoble High Magnetic Field Laboratory, CNRS, 38042 Grenoble, France Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/64, 02-688 Warsaw, Poland (Dated: June 28, 2011)