Experimental investigations of AlAs/(Al,Ga)As/GaAs vertical-cavity surface-emitting lasers in multimode generation regime are performed. A high degree of circular polarization (>70

Experimental investigations of chiral injection AlAs/(Al, Ga)As/GaAs vertical-cavity surface-emitting lasers in the multimode generation regime are performed. A high circular polarization degree 70% of different generation modes measured with a high spectral resolution, is demonstrated. Detailed maps of spatial and angular distribution of laser radiation intensity were constructed.

Stimulated laser emission with a high degree of circular polarization in chiral semiconductor microcavities has been studied experimentally in a wide temperature range. The kinetics of rearrangement of the emission spectra of injection laser nanostructures during the action of a rectangular electric excitation pulse has been thoroughly investigated.

Raman spectra of magnetic topological crystalline insulators in a wide temperature range including the magnetic ordering region are studied in detail. The anharmonicity parameters and Grüneisen mode parameters of Raman-active phonons in the studied crystals have been determined. It has been shown that the temperature dependence of the frequency of the A_1g^(1) ( 48 cm –1 ) phonon in MnBi 2 Te 4 coincides within ±0.1 cm –1 with the standard anharmonic model disregarding the spin–phonon coupling. The polarization dependences of Raman spectra in the MnSb 2 Te 4 crystals indicate that Sb and Mn atoms are strongly mixed in them unlike the isostructural MnBi 2 Te 4 crystals.

Order–disorder structural transformations in xR2O3·(1 – х)TiO2 (R = Yb, Lu; х = 0.5–0.6) solid solutions with a highly imperfect fluorite-derived structure at 1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two cubic phases identical in composition: a disordered fluorite-like (F) phase (Fm3m) and an ordered pyrochlore-like (P) phase (Fd3m), which is coherent with the disordered phase and consists of nanoscale (<100 Å) and nanocrystalline domains. The lattice parameters of these phases have been determined. The stability range of the solid solutions in the systems studied is 0.5 ≤ x ≤ 0.55. In the samples containing 0.55Yb2O3 and 0.5Lu2O3, the P-phase consists of nanodomains. The Raman spectra of the Yb2TiO5- and Lu2TiO5-based solid solutions contain broad bands at low and high frequencies, with peaks at 101, 175, 290, 346, 384, and 727 (115, 176, 320, and 745) cm–1, which correspond to the P- and F-phases, respectively. The formation of pyrochlore-like phases with different degrees of order in a fluorite matrix is due to the internal stress induced by the high density of structural defects in their unit cells. The materials obtained in this study have a large specific surface area and can be used as catalysts and catalyst supports.

Engineering the chirality of optical microcavities is a central concept of modern photonics to gain full control the polarization of the confined electromagnetic mode. Here, we demonstrate a compact source of coherent radiation based on an electrically driven, chiral semiconductor microcavity. The device is composed of an AlAs/(Al, Ga)As microcavity containing multiple GaAs quantum wells in the active region and a chiral photonic crystal slab etched in the upper distributed Bragg reflector. The structure promotes laser oscillation under electrical current injection in the near-infrared spectral range (h omega similar or equal to 1.565 eV) and degrees of circular polarization exceeding 90%. The sense of circular polarization is controlled by the handedness of the chiral photonic crystal slab and changes to the opposite one in a mirror-symmetrical structure. Our results represent an important step towards the practical implementation of compact sources of circularly polarized light.

A study is performed of the temperature dependence of lasing and the degree of circular polarization of emissions from an electrically pumped semiconductor laser at temperatures of up to ~140 K. The laser is based on an AlAs/AlGaAs microcavity with GaAs quantum wells in the active region and a photonic crystal with chiral symmetry in the top layer of the upper bragg mirror. At maximum values of ~25 mA for the pulsed pump current, developed multimode lasing is observed at temperatures of up to ~90 K. Such lasing is in the form of narrow spectral bands with high degrees of circular polarization of radiation (>70%).

Measurements are made of the spectra and degrees of circular polarization of radiation from single InAs quantum dots embedded in a planar GaAs waveguide of a semiconductor nanostructure, and an electrically pumped semiconductor laser based on an AlAs/AlGaAs microcavity with GaAs quantum wells in the active region. The upper layers of the microcavity are a square lattice of a photonic crystal with chiral symmetry.

Optical harmonic generation on excitons is found in ZnSe/BeTe quantum wells with type-II band alignment. Two experimental approaches with spectrally broad femtosecond laser pulses and spectrally narrow picosecond pulses are used for spectroscopic studies by means of second and third harmonic generation (SHG and THG). The SHG signal is symmetry-forbidden in the electric-dipole approximation for light propagation along the structure's growth axis, which is the [001] crystal axis, but it can be induced by an external magnetic field. The THG signal is detected at zero magnetic field and its intensity is field-independent. A group theory analysis of SHG and THG rotational anisotropy diagrams allows us to identify the involved excitation mechanisms.

— Order–disorder structural transformations in x R 2 O 3 ∙ (1 – х )TiO 2 (R = Tm, Er; х = 0.5−0.6) solid solutions with a highly imperfect fluorite-derived structure at 1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two cubic phases identical in composition: a disordered fluorite-like ( F ) phase ( Fm 3 m ) and an ordered pyrochlore-like ( P ) phase ( Fd 3 m ), which is coherent with the disordered phase and consists of nanoscale (<100 Å) and nanocrystalline domains. The lattice parameters of these phases have been determined. In the stability range of the solid solutions ((0.5 ≤ x ≤ 0.6)), the lattice parameter of the fluorite-like phases follows Vegard’s law. The Raman spectra of the R 2 TiO 5 -based (R = Tm, Er) solid solutions contain broad bands at low and high frequencies, with peaks at 100, 171, 291, 355, 385, and 723 cm –1 for R = Tm and at 100, 169, 292, 355, 390, and 720 cm –1 for R = Er, which correspond to the P - and F -phases, respectively. The formation of pyrochlore-like phases with different degrees of order in a fluorite matrix is due to the internal stress induced by the high density of structural defects in their unit cells. The materials obtained in this study have a large specific surface area and can be used as catalysts and catalyst supports.

The kinetics of variation of the magnetization of Zn0.99Mn0.01Se/Be0.93Mn0.07Te type-II semimagnetic semiconducting superlattices in external magnetic fields has been studied using the optical technique with high time resolution. Picosecond times of transfer of the energy and spin of photoexcited carriers to a magnetic subsystem of manganese ions have been directly measured for the first time.

Order–disorder phenomena in nanocrystalline Gd 2 ZrO 5 and Gd 2 HfO 5 with highly imperfect fluorite- derived structures in the range 1000–1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two coherent phases identical in composition: a nanocrystalline disordered fluorite-like (F) phase ( Fm3m ) and a nanoparticulate ordered fluorite derivative ( C 1 ) ( Ia 3). Their lattice parameters have been determined. In the range 1000–1600°C, the Raman spectra of the Gd 2 ZrO 5 and Gd 2 HfO 5 materials contain broad bands in low- and high-frequency regions, at ~118 (108), 362 (353), and 670 (665) cm –1 , which characterize the C 1 and F phases, respectively.

A detailed study of the degree of circular polarization and the angular dependence of the emission spectra of an array of InAs quantum dots embedded in GaAs photonic nanostructures with chiral symmetry in the absence of an external magnetic field is carried out. A strong angular dependence of the spectra and the degree of circular polarization of radiation from quantum dots, as well as a significant effect of the lattice period of the photonic crystal on the radiation characteristics, is observed. The dispersion of photonic modes near the (±3, 0) and (±2, ±2) Bragg resonances is investigated in detail. The experimentally observed polarization, spectral, and angular characteristics of the quantum-dot emission are explained in the framework of a theory describing radiative processes in chiral photonic nanostructures.

High-precision measurements of the Hall effect and Raman scattering have been performed for single crystals of ZrB 12 superconductor in the wide temperature range of 5–300 K. For ZrB 12 , the boson peak with ω max ~ 100 cm –1 has been observed for the first time within the low-frequency range of the Raman spectrum I (ω). The sizes of vibrational clusters with the correlation length ranging from 25 to 35 Å are estimated. The relation between the renormalization of the low-frequency density of vibrational states accompanying the transition to the cage-glass phase ( T * ~ 90 K) and the enhancement of superconductivity in ZrB 12 is discussed.

The dynamics of spin-lattice relaxation in the magnetic Mn2+ ion system of (Zn,Mn)Se/(Zn,Be) Se quantum-well structures are studied using optical methods. Pronounced cusps are found in the giant Zeeman shift of the quantum-well exciton photoluminescence at specific magnetic fields below 10 T, when the Mn spin system is heated by photogenerated carriers. The spin-lattice relaxation time of the Mn ions is resonantly accelerated at the cusp magnetic fields. Our theoretical analysis demonstrates that a cusp occurs at a spin-level mixing of single Mn2+ ions and a quick-relaxing cluster of nearest-neighbor Mn ions, which can be described as intrinsic cross-relaxation resonance within the Mn spin system.