B. R. Namozov

Evidence for Mn2+ fine structure in CdMnSe/ZnSe quantum dots caused by their low dimensionality

The axial fine structure with strong positive zero-field splitting for Mn2+ ions in CdMnSe/ZnSe quantum dots caused by their low dimensionality was revealed. Magnetic resonance was measured as a variation of photoluminescence intensity. In spite of isotropic g factor of Mn2+ ions, the anisotropic behavior of the center of gravity of the resonance has been observed because of the high Boltzmann factor at 35 GHz and 2 K.

Linear polarization of the photoluminescence of quantum wells subject to in-plane magnetic fields

The degree and orientation of the magnetic-field induced linear polarization of the photoluminescence from a wide range of heterostructures containing (Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a function of detection photon energy, applied magnetic field strength and orientation in the quantum well plane. A theoretical description of this effect in terms of an in-plane deformation acting on the valence band states is presented and is verified by comparison with the experimental data. We attempted to identify clues to the microscopic origin of the valence band spin anisotropy and to the mechanisms which actually determine the linear polarization of the PL in the quantum wells subject to the in-plane magnetic field. The conclusions of the present paper apply in full measure to non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain anisotropy.

Nuclear Spin relaxation mediated by Fermi-edge electrons in n -type GaAs

A method based on the optical orientation technique was developed to measure the nuclear-spin lattice relaxation time T1 in semiconductors. It was applied to bulk n-type GaAs, where T1 was measured after switching off the optical excitation in magnetic fields from 400 to 1200 G at low (< 30 K) temperatures. The spin-lattice relaxation of nuclei in the studied sample with nD = 9 × 1016 cm−3 was found to be determined by hyperfine scattering of itinerant electrons (Korringa mechanism) which predicts invariability of T1 with the change in magnetic field and linear dependence of the relaxation rate on temperature. This result extends the experimentally verified applicability of the Korringa relaxation law in degenerate semiconductors, previously studied in strong magnetic fields (several Tesla), to the moderate field range.

Optically detected magnetic resonance of Mn-related excitations in (Cd,Mn)Te quantum wells

Optically detected magnetic resonance (ODMR) was applied to reveal the exchange interaction effects between Mn2+ ions and confined holes in (Cd,Mn)Te quantum wells with 2D hole gas. Two anisotropic ODMR signals with different angular variations were found and ascribed to isolated manganese ions and to exchange-coupled complexes consisting of manganese and holes. It is shown that calculations on the basis of spin Hamiltonian for these systems are in agreement with the experimental data.

Two-step versus one-step model of the interpolarization conversion and statistics of CdSe/ZnSe quantum dot elongations

The magneto-optical interpolarization conversions by a layer of quantum dots have been investigated. Various types of polarization response of the sample were observed as a function of external magnetic field and of the orientation of the sample. The full set of experimental dependences is analyzed in terms of a one-step and a two-step model of spin evolution. The angular distribution of the quantum dots over the directions of elongation in the plane of the sample is taken into account in terms of the two models, and the model predictions are compared with experimental observations.

A series of high-frequency EPR spectrometers with microwave and optical detection channels

We describe a series of high-frequency EPR/optically detected magnetic-resonance (ODMR) spectrometers operating in both continuous-wave and pulsed regimes in 2-, 3-, 4-, and 8-mm. The resonance signal can be monitored in both microwave and optical detection channels. The entire series of EPR/ODMR spectrometers has common design features.

ODMR evidence of the electron cascade in multiple asymmetrical (CdMn)Te quantum wells

Exchange-coupled complexes consisting of Mn ions and holes have been revealed by optically detected magnetic resonance in the narrowest quantum wells of asymmetrical multiple-quantum-well structures (CdMn)Te/(CdMg)Te. Calculations have been performed to estimate the parameters of the complexes (exchange interactions and hole g-factors) and simulate the spectra. The formation of such complexes implies the directional electron tunneling from narrow to larger wells, i.e., an electron cascade, which results in the creation of the excess hole concentration in the narrowest and intermediate-width quantum wells.