Optical Studies of Zero-Field Magnetization of CdMnTe Quantum Dots: Influence of Average Size and Composition of Quantum Dots

We show that through the resonant optical excitation of spin-polarized excitons into CdMnTe magnetic quantum dots, we can induce a macroscopic magnetization of the Mn impurities. We observe very broad (4 meV linewidth) emission lines of single dots, which are consistent with the formation of strongly confined exciton magnetic polarons. Therefore we attribute the optically induced magnetization of the magnetic dots results to the formation of spin-polarized exciton magnetic polarons. We find that the photo-induced magnetization of magnetic polarons is weaker for larger dots which emit at lower energies within the QD distribution. We also show that the photo-induced magnetization is stronger for quantum dots with lower Mn concentration, which we ascribe to weaker Mn-Mn interaction between the nearest neighbors within the dots. Due to particular stability of the exciton magnetic polarons in QDs, where the localization of the electrons and holes is comparable to the magnetic exchange interaction, this optically induced spin alignment persists to temperatures as high as 160 K.Comment: 26 pages, 7 figs - submitted for publicatio

Optical spin pumping of modulation doped electrons probed by a two-color Kerr rotation technique

We report on optical spin pumping of modulation electrons in CdTe-based quantum wells with low intrinsic electron density (by 10^10 cm^{-2}). Under continuous wave excitation, we reach a steady state accumulated spin density of about 10^8 cm^{-2}. Using a two-color Hanle-MOKE technique, we find a spin relaxation time of 34 ns for the localized electrons in the nearly unperturbed electron gas. Independent variation of the pump and probe energies demonstrates the presence of additional non-localized electrons in the quantum well, whose spin relaxation time is substantially shorter

Molecular beam epitaxy of high structural quality Bi2Se3 on lattice matched InP(111) substrates

Epitaxial layers of the topological insulator Bi2Se3 have been grown by molecular beam epitaxy on laterally lattice-matched InP(111)B substrates. High resolution X-ray diffraction shows a significant improvement of Bi2Se3 crystal quality compared to layers deposited on other substrates. The measured full width at half maximum of the rocking curve is Delta omega=13 arcsec, and the (omega-2theta) scans exhibit clear layer thickness fringes. Atomic force microscope images show triangular twin domains with sizes increasing with layer thickness. The structural quality of the domains is confirmed on the microscopic level by transmission electron microscopy.Comment: 4 pages, 4 figure

Spin currents in diluted magnetic semiconductors (extended version)

Spin currents resulting in the zero-bias spin separation have been observed in unbiased diluted magnetic semiconductor structures (Cd,Mn)Te/(Cd,Mg)Te. The pure spin current generated due to the electron gas heating by terahertz radiation is converted into a net electric current by application of an external magnetic field. We demonstrate that polarization of the magnetic ion system enhances drastically the conversion due to the spin-dependent scattering by localized Mn(2+) ions and the giant Zeeman splitting.Comment: 6 pages, 4 figure

Distribution of the DAZ gene transcripts in human testis.

Involvement of variety of genes, especially located on Y chromosome, is critical for the regulation of spermatogenesis. In particular, fertility candidate genes such as deleted in azoospermia (DAZ) are believed to have important function in sperm production, since DAZ is frequently deleted in azoospermic and severy oligozoospermic men. The role of the DAZ gene is supported by its exclusive expression in the testis and by its deletion in about 10% of azoospermic and severely oligozoospermic patients. The distribution of DAZ transcripts in seminiferous epithelium of human testis is reported in the present study. The use of Adobe Photoshop and Scion Image softwares allowed for semi-quantitative analysis of in situ RT-PCR (ISRT-PCR) results. The intensity of ISRT-PCR product's fluorescence was different within individual seminiferous tubules. It was clearly shown by using the pseudocolour scale and transforming the intensity of the fluorescence into levels of greyscale images. The more intense fluorescence characterised single spermatogonia and those organized in small groups inside separate tubules. The most intense accumulation of DAZ mRNA was observed in spermatogonia

The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey

The dust in nearby galaxies absorbs a fraction of the UV-optical-near-infrared radiation produced by stars. This energy is consequently re-emitted in the infrared. We investigate the portion of the stellar radiation absorbed by spiral galaxies from the HRS by modelling their UV-to-submillimetre spectral energy distributions. Our models provide an attenuated and intrinsic SED from which we find that on average 32 % of all starlight is absorbed by dust. We define the UV heating fraction as the percentage of dust luminosity that comes from absorbed UV photons and find that this is 56 %, on average. This percentage varies with morphological type, with later types having significantly higher UV heating fractions. We find a strong correlation between the UV heating fraction and specific star formation rate and provide a power-law fit. Our models allow us to revisit the IRX-AFUV relations, and derive these quantities directly within a self-consistent framework. We calibrate this relation for different bins of NUV-r colour and provide simple relations to relate these parameters. We investigated the robustness of our method and we conclude that the derived parameters are reliable within the uncertainties which are inherent to the adopted SED model. This calls for a deeper investigation on how well extinction and attenuation can be determined through panchromatic SED modelling.Comment: 14 pages, 7 figures. Accepted for publication in Astronomy & Astrophysic

Tuning the properties of magnetic CdMnTe quantum dots

We show that CdMnTe self-assembled quantum dots can be formed by depositing a submonolayer of Mn ions over a ZnTe surface prior to deposition of the CdTe dot layer. Single dot emission lines and strongly polarized quantum dot photoluminescence in an applied magnetic field confirm the presence of Mn in individual quantum dots. The width of PL lines of the single CdMnTe dots is 3 meV due to magnetic moment fluctuations of the Mn ions. After rapid thermal annealing, the emission lines of individual magnetic quantum dots narrow significantly to 0.25 meV showing that effect of magnetic fluctuations is strongly reduced most probably due to an increase in the average quantum dot size. These results suggest a way to tune the spin properties of magnetic quantum dots.Comment: 13 pages, 4 figure