1,021 research outputs found
Engineering of spin-lattice relaxation dynamics by digital growth of diluted magnetic semiconductor CdMnTe
The technological concept of "digital alloying" offered by molecular-beam
epitaxy is demonstrated to be a very effective tool for tailoring static and
dynamic magnetic properties of diluted magnetic semiconductors. Compared to
common "disordered alloys" with the same Mn concentration, the spin-lattice
relaxation dynamics of magnetic Mn ions has been accelerated by an order of
magnitude in (Cd,Mn)Te digital alloys, without any noticeable change in the
giant Zeeman spin splitting of excitonic states, i.e. without effect on the
static magnetization. The strong sensitivity of the magnetization dynamics to
clustering of the Mn ions opens a new degree of freedom for spin engineering.Comment: 9 pages, 3 figure
Signature of the Overhauser field on the coherent spin dynamics of donor-bound electron in a single CdTe quantum well
We have studied the coherent spin dynamics in an oblique magnetic field of
electrons localized on donors and placed in the middle of a single CdTe quantum
well, by using a time-resolved optical technique: the photo-induced Faraday
rotation. We showed that this dynamics is affected by a weak Overhauser field
created via the hyperfine interaction of optically spin-polarized donor-bound
electrons with the surrounding nuclear isotopes carrying non-zero spins. We
have measured this nuclear field, which is on the order of a few mT and can
reach a maximum experimental value of 9.4 mT. This value represents 13 % of the
maximal nuclear polarization, and corresponds also to 13 % of maximal
electronic polarization.Comment: 15 pages, 4 figure
Optical manipulation of a single Mn spin in a CdTe-based quantum dot
A system of two coupled CdTe quantum dots, one of them containing a single Mn
ion, was studied in continuous wave and modulated photoluminescence,
photoluminescence excitation, and photon correlation experiments. Optical
writing of information in the spin state of the Mn ion has been demonstrated,
using orientation of the Mn spin by spin-polarized carriers transferred from
the neighbor quantum dot. Mn spin orientation time values from 20 ns to 100 ns
were measured, depending on the excitation power. Storage time of the
information in 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 static and dynamical
properties of the system.Comment: 4 pages, 3 figure
Ising Quantum Hall Ferromagnet in Magnetically Doped Quantum Wells
We report on the observation of the Ising quantum Hall ferromagnet with Curie
temperature as high as 2 K in a modulation-doped (Cd,Mn)Te
heterostructure. In this system field-induced crossing of Landau levels occurs
due to the giant spin-splitting effect. Magnetoresistance data, collected over
a wide range of temperatures, magnetic fields, tilt angles, and electron
densities, are discussed taking into account both Coulomb electron-electron
interactions and sd coupling to Mn spin fluctuations. The critical behavior
of the resistance ``spikes'' at corroborates theoretical
suggestions that the ferromagnet is destroyed by domain excitations.Comment: revised, 4 pages, 4 figure
Dynamics of Charge Leakage From Self-assembled CdTe Quantum Dots
We study the leakage dynamics of charge stored in an ensemble of CdTe quantum
dots embedded in a field-effect structure. Optically excited electrons are
stored and read out by a proper time sequence of bias pulses. We monitor the
dynamics of electron loss and find that the rate of the leakage is strongly
dependent on time, which we attribute to an optically generated electric field
related to the stored charge. A rate equation model quantitatively reproduces
the results.Comment: 4 pages, submitted to Applied Physics Letter
Optical control of electron spin coherence in CdTe/(Cd,Mg)Te quantum wells
Optical control of the spin coherence of quantum well electrons by short
laser pulses with circular or linear polarization is studied experimentally and
theoretically. For that purpose the coherent electron spin dynamics in a
n-doped CdTe/(Cd,Mg)Te quantum well structure was measured by time-resolved
pump-probe Kerr rotation, using resonant excitation of the negatively charged
exciton (trion) state. The amplitude and phase shifts of the electron spin beat
signal in an external magnetic field, that are induced by laser control pulses,
depend on the pump-control delay and polarization of the control relative to
the pump pulse. Additive and non-additive contributions to pump-induced signal
due to the control are isolated experimentally. These contributions can be well
described in the framework of a two-level model for the optical excitation of
the resident electron to the trion.Comment: 15 pages, 18 figure
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