225 research outputs found
Resonant optical pumping of a Mn spin in a strain free quantum dot
We report on the spin properties of individual Mn atoms in II-VI
semiconductor strain free quantum dots. Strain free Mn-doped CdTe quantum dots
are formed by width fluctuations in thin quantum wells lattice matched on a
CdTe substrate. These quantum dots permit to optically probe and address any
spin state of a Mn atom in a controlled strain environment. The absence of
strain induced magnetic anisotropy prevents an optical pumping of the Mn spin
at zero magnetic field. Thus, a large photoluminescence is obtained under
resonant optical excitation of the exciton-Mn complex. An efficient optical
pumping of the coupled electronic and nuclear spins of the Mn is restored under
a weak magnetic field. The observed reduction of the resonant photoluminescence
intensity under magnetic field is well described by a model including the
hyperfine coupling and a residual crystal field splitting of the Mn atom.
Finally, we show that the second order correlation function of the resonant
photoluminescence presents a large photon bunching at short delay which is a
probe of the dynamics of coupled electronic and nuclear spins of the Mn atom
Spin dynamics of a Mn atom in a semiconductor quantum dot under resonant optical excitation
We analyze the spin dynamics of an individual magnetic atom (Mn) inserted in
a II-VI semiconductor quantum dot under resonant optical excitation. In
addition to standard optical pumping expected for a resonant excitation, we
show that for particular conditions of laser detuning and excitation intensity,
the spin population can be trapped in the state which is resonantly excited.
This effect is modeled considering the coherent spin dynamics of the coupled
electronic and nuclear spin of the Mn atom optically dressed by a resonant
laser field. This spin population trapping mechanism is controlled by the
combined effect of the coupling with the laser field and the coherent
interaction between the different Mn spin states induced by an anisotropy of
the strain in the plane of the quantum dot
Dynamics of a Mn spin coupled to a single hole confined in a quantum dot
Using the emission of the positively charged exciton as a probe, we analyze
the dynamics of the optical pumping and the dynamics of the relaxation of a Mn
spin exchange-coupled with a confined hole spin in a II-VI semiconductor
quantum dot. The hole-Mn spin can be efficiently initialized in a few tens of
under optical injection of spin polarized carriers. We show that this
optical pumping process and its dynamics are controlled by electron-Mn
flip-flops within the positively charged exciton-Mn complex. The pumping
mechanism and its magnetic field dependence are theoretically described by a
model including the dynamics of the electron-Mn complex in the excited state
and the dynamics of the hole-Mn complex in the ground state of the positively
charged quantum dot. We measure at zero magnetic field a spin relaxation time
of the hole-Mn spin in the range or shorter. This hole-Mn spin
relaxation is induced by the presence of valence band mixing in self-assembled
quantum dots
Strain induced coherent dynamics of coupled carriers and Mn spins in a quantum dot
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 Lambda 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
Resonant photoluminescence and dynamics of a hybrid Mn-hole spin in a positively charged magnetic quantum dot
We analyze, through resonant photoluminescence, the spin dynamics of an
individual magnetic atom (Mn) coupled to a hole in a semiconductor quantum dot.
The hybrid Mn-hole spin and the positively charged exciton in a CdTe/ZnTe
quantum dot forms an ensemble of systems which can be addressed
optically. Auto-correlation of the resonant photoluminescence and resonant
optical pumping experiments are used to study the spin relaxation channels in
this multilevel spin system. We identified for the hybrid Mn-hole spin an
efficient relaxation channel driven by the interplay of the Mn-hole exchange
interaction and the coupling to acoustic phonons. We also show that the optical
systems are connected through inefficient spin-flips than can be
enhanced under weak transverse magnetic field. The dynamics of the resonant
photoluminescence in a p-doped magnetic quantum dot is well described by a
complete rate equation model. Our results suggest that long lived hybrid
Mn-hole spin could be obtained in quantum dot systems with large
heavy-hole/light-hole splitting
Optical Stark Effect and Dressed Excitonic States in a Mn-doped Quantum Dot
We report on the observation of spin dependent optically dressed states and
optical Stark effect on an individual Mn spin in a semiconductor quantum dot.
The vacuum-to-exciton or the exciton-to-biexciton transitions in a Mn-doped
quantum dot are optically dressed by a strong laser field and the resulting
spectral signature is measured in photoluminescence. We demonstrate that the
energy of any spin state of a Mn atom can be independently tuned using the
optical Stark effect induced by a control laser. High resolution spectroscopy
reveals a power, polarization and detuning dependent Autler-Townes splitting of
each optical transition of the Mn-doped quantum dot. This experiment
demonstrates a complete optical resonant control of the exciton-Mn system
Optical control of the spin state of two Mn atoms in a quantum dot
We report on the optical spectroscopy of the spin of two magnetic atoms (Mn)
embedded in an individual quantum dot interacting with either a single
electron, a single exciton and single trion. As a result of their interaction
to a common entity, the Mn spins become correlated. The dynamics of this
process is probed by time resolved spectroscopy, that permits to determine the
optical orientation time in the range of a few tens of . In addition, we
show that the energy of the collective spin states of the two Mn atoms can be
tuned through the optical Stark effect induced by a resonant laser field
Coupling of the triplet states of a negatively charged exciton in a quantum dot with the spin of a magnetic atom
Two electrons in a quantum dot (QD) can form triplet states. We analyze the
exchange coupling of the triplet states of the negatively charged exciton in a
QD (X, two electrons and one hole) with the spin of a magnetic atom (Mn).
Two techniques are used to access the spin structure of this magnetic complex:
the resonant excitation of the excited states of X-Mn and the analysis of
the emission of a negatively charged biexciton in a magnetic dot (XX-Mn).
The photo-luminescence (PL) excitation of X-Mn reveals excited states with
a circularly polarized fine structure which strongly depends on the Mn spin
state S and gives rise to negative circular polarization emission. This
fine structure arises from the coupling of the triplet states of an excited
charged exciton with the Mn (X-Mn) and its S dependence can be
described by a spin effective model. The recombination of XX-Mn leaves in
the dot a charged exciton in its excited state and the PL structure is
controlled by the coupling of triplet states of X with the Mn spin. An
analysis of the polarization and magneto-optic properties of this emission
gives access to the electron-hole exchange interaction within the triplets
states. Comparing the fine structure of the singlet X-Mn and of the
triplets of X-Mn we can independently study the different source of
anisotropy in the QD: the valence band mixing and the exchange interaction in
an anisotropic potentia
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