48 research outputs found
Single spin optical read-out in CdTe/ZnTe quantum dot studied by photon correlation spectroscopy
Spin dynamics of a single electron and an exciton confined in CdTe/ZnTe
quantum dot is investigated by polarization-resolved correlation spectroscopy.
Spin memory effects extending over at least a few tens of nanoseconds have been
directly observed in magnetic field and described quantitatively in terms of a
simple rate equation model. We demonstrate an effective (68%) all-optical
read-out of the single carrier spin state through probing the degree of
circular polarization of exciton emission after capture of an oppositely
charged carrier. The perturbation introduced by the pulsed optical excitation
serving to study the spin dynamics has been found to be the main source of the
polarization loss in the read-out process. In the limit of low laser power the
read-out efficiency extrapolates to a value close to 100%. The measurements
allowed us as well to determine neutral exciton spin relaxation time ranging
from 3.4 +/- 0.1 ns at B = 0 T to 16 +/- 3 ns at B = 5 T.Comment: to appear in Phys. Rev.
Experimental probing of exchange interactions between localized spins in the dilute magnetic insulator (Ga,Mn)N
The sign, magnitude, and range of the exchange couplings between pairs of Mn
ions is determined for (Ga,Mn)N and (Ga,Mn)N:Si with x < 3%. The samples have
been grown by metalorganic vapor phase epitaxy and characterized by
secondary-ion mass spectroscopy; high-resolution transmission electron
microscopy with capabilities allowing for chemical analysis, including the
annular dark-field mode and electron energy loss spectroscopy; high-resolution
and synchrotron x-ray diffraction; synchrotron extended x-ray absorption
fine-structure; synchrotron x-ray absorption near-edge structure; infra-red
optics and electron spin resonance. The results of high resolution magnetic
measurements and their quantitative interpretation have allowed to verify a
series of ab initio predictions on the possibility of ferromagnetism in dilute
magnetic insulators and to demonstrate that the interaction changes from
ferromagnetic to antiferromagnetic when the charge state of the Mn ions is
reduced from 3+ to 2+.Comment: 12 pages, 14 figures; This version contains the detailed
characterization of the crystal structure as well as of the Mn distribution
and charge stat
Wurtzite vs rock-salt MnSe epitaxy: electronic and altermagnetic properties
Newly discovered altermagnets are magnetic materials exhibiting both
compensated magnetic order, similar to antiferromagnets, and simultaneous
non-relativistic spin-splitting of the bands, akin to ferromagnets. This
characteristic arises from the specific symmetry operations that connect the
spin sublattices. In this report, we show with ab initio calculations that the
semiconductive MnSe exhibits altermagnetic spin-splitting in the wurtzite phase
as well as a critical temperature well above room temperature. It is the first
material from such space group identified to possess altermagnetic properties.
Furthermore, we demonstrate experimentally through structural characterization
techniques that it is possible to obtain thin films of both the intriguing
wurtzite phase of MnSe and the more common rock-salt MnSe using molecular beam
epitaxy on GaAs substrates. The choice of buffer layers plays a crucial role in
determining the resulting phase and consequently extends the array of materials
available for the physics of altermagnetism
Possibility of long-range order in clean mesoscopic cylinders
A microscopic Hamiltonian of the magnetostatic interaction is discussed. This
long-range interaction can play an important role in mesoscopic systems leading
to an ordered ground state.
The self-consistent mean field approximation of the magnetostatic interaction
is performed to give an effective Hamiltonian from which the spontaneous,
self-sustaining currents can be obtained.
To go beyond the mean field approximation the mean square fluctuation of the
total momentum is calculated and its influence on self-sustaining currents in
mesoscopic cylinders with quasi-1D and quasi-2D conduction is considered. Then,
by the use of the microscopic Hamiltonian of the magnetostatic interaction for
a set of stacked rings, the problem of long-range order is discussed. The
temperature below which the system is in an ordered state is
determined.Comment: 14 pages, REVTeX, 5 figures, in print in Phys. Rev.
Coexistence of Anomalous Hall Effect and Weak Net Magnetization in Collinear Antiferromagnet MnTe
Anomalous Hall effect (AHE) plays important role in the rapidly developing
field of antiferromagnetic spintronics. It has been recently discussed that it
can be a feature of not only uncompensated magnetic systems but also in
altermagnetic materials. Hexagonal MnTe belongs to this appealing group of
compounds exhibiting AHE and is commonly perceived as magnetically compensated.
Here, we demonstrate that bulk form of MnTe exhibits small but detectable
magnetic moment correlating with hysteretic behaviour of the AHE. We formulate
a phenomenological model which explains how this feature allows to create a
disbalance between states with opposite N\'eel vector and prevent the AHE
signal from averaging out to zero. Moreover, we show how the dependence of AHE
on the N\'eel vector arises on microscopical level and highlight the
differences in Berry curvature between magnetically compensated and
uncompensated systems