Alexandra A. Soltamova

Room temperature coherent spin alignment of silicon vacancies in 4H- and 6H-SiC.

We report the realization of the optically induced inverse population of the ground-state spin sublevels of the silicon vacancies (V(Si)) in silicon carbide (SiC) at room temperature. The data show that the probed silicon vacancy spin ensemble can be prepared in a coherent superposition of the spin states. Rabi nutations persist for more than 80 μs. Two opposite schemes of the optical alignment of the populations between the ground-state spin sublevels of the silicon vacancy upon illumination with unpolarized light are realized in 4H- and 6H-SiC at room temperature. These altogether make the silicon vacancy in SiC a very favorable defect for spintronics, quantum information processing, and magnetometry.

Temperature-scanned magnetic resonance and the evidence of two-way transfer of a nitrogen nuclear spin hyperfine interaction in coupled NV-N pairs in diamond

New method for the detection of magnetic resonance signals versus temperature is developed on the basis of the temperature dependence of the spin Hamiltonian parameters of the paramagnetic system under investigation. The implementation of this technique is demonstrated on the nitrogen-vacancy (NV) centers in diamonds. Single NV defects and their ensembles are suggested to be almost inertialess temperature sensors. The hyperfine structure of the 14N nitrogen nuclei of the nitrogen-vacancy center appears to be resolved in the hyperfine structure characteristic of the hyperfine interaction between NV and an Ns center (substitutional nitrogen impurity) in the optically detected magnetic resonance spectra of the molecular NV-Ns complex. Thus, we show that a direct evidence of the two-way transfer of a nitrogen nuclear spin hyperfine interaction in coupled NV-Ns pairs was observed. It is shown that more than 3-fold enhancement of the NV optically detected magnetic resonance signal can be achieved by using water as a collection optics medium.

Electron spin resonance detection and identification of nitrogen centers in nanodiamonds

Individual nitrogen centers N0 and nitrogen pairs N2+ have been detected and identified in natural diamond nanocrystals by means of the high-frequency electron spin resonance method. The N0 nitrogen centers have been observed in synthetic diamond nanocrystallites with a size of less than 10 nm produced by high-temperature high-pressure sintering of detonation nanodiamonds. Thus, the possibility of the stable state of impurity nitrogen atoms in diamond nanoparticles has been demonstrated.

Electron Paramagnetic Resonance Detection of the Giant Concentration of Nitrogen Vacancy Defects in Sintered Detonation Nanodiamonds

A giant concentration of nitrogen vacancy defects has been revealed by the electron paramagnetic resonance (EPR) method in a detonation nanodiamond sintered at high pressure and temperature. A high coherence of the electron spins at room temperature has been observed and the angular dependences of the EPR spectra indicate the complete orientation of the diamond system.

Identification of nitrogen vacancies in an AlN single crystal: EPR and thermoluminescence investigations

The electronic structure of nitrogen vacancies in specially undoped aluminum nitride single crystals has been determined and the depth of the donor level of these vacancies in the band gap has been found to be ∼75 meV by combined electron paramagnetic resonance and thermoluminescence investigations.

Point Defects in SiC as a Promising Basis for Single-Defect, Single-Photon Spectroscopy with Room Temperature Controllable Quantum States

The unique quantum properties of the nitrogen–vacancy (NV) center in diamond have motivated efforts to find defects with similar properties in silicon carbide (SiC), which can extend the functionality of such systems not available to the diamond. As an example, results of experiments on electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) are presented suggests that silicon vacancy (VSi) related point defects in SiC possess properties the similar to those of the NV center in diamond, which in turn make them a promising quantum system for single-defect and single-photon spectroscopy in the infrared region. Depending on the defect type, temperature, SiC polytype, and crystalline position, two opposite schemes have been observed for the optical alignment of the high-spin ground state spin sublevels population of the VSi-related defects upon irradiation with unpolorized light. Spin ensemble of VSi-related defects are shown to be prepared in a coherent superposition of the spin states even at room temperature. Zero-field (ZF) ODMR shows the possibility to manipulate of the ground state spin population by applying radiofrequency field. These altogether make VSi-related defects in SiC very favorable candidate for spintronics, quantum information processing, and magnetometry.

Detection and Identification of Nitrogen Centers in Nanodiamond: EPR Studies

Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band and at high-frequency W-band (95 GHz) have been used to study natural diamond nanocrystals, detonation nanodiamond (ND) with a size of ∼ 4.5 nm and detonation ND after high-temperature, high-pressure sintering with a size of ∼ 8.5 nm. Isolated nitrogen centers N0 and nitrogen pairs N2 + have been detected and identified, and their structure has been unambiguously determined by means of the high frequency EPR and ESE in natural diamond nanocrystals. In detonation ND and detonation ND after sintering, isolated nitrogen centers N0 have been discovered in nanodiamond core. In addition EPR signals of multivacancy centers with spin 3/2 seem to be observed in nanodiamond core of detonation ND.

Point defects in silicon carbide as a promising basis for spectroscopy of single defects with controllable quantum states at room temperature

The spin and optical properties of silicon vacancy defects in silicon carbide of the hexagonal 6H polytype have been investigated using photoluminescence, electron paramagnetic resonance, and X-band optically detected magnetic resonance. It has been shown that different configurations of these defects can be used to create an optical alignment of their spin sublevels as in the case of low temperatures and at temperatures close to room temperature (T = 293 K). The main specific feature of silicon vacancy centers in silicon carbide is that the zero-magnetic-field-splitting parameter of some centers remains constant with variations in the temperature, which indicates prospects for the use of these centers for quantum magnetometry. It has also been shown that a number of centers, on the contrary, are characterized by a strong dependence of the zero-magnetic-field-splitting parameter on the temperature, which indicates prospects for the use of these centers as temperature sensors.

Deep-Level Defects in AlN Single Crystals: EPR Studies

Electron paramagnetic resonance (EPR) at X-band (9.4 GHz) and Q-band (35 GHz) have been used to study defects in two samples of AlN monocrystals, grown by a sublimation sandwich method. These investigations reveal the presence of Fe2+ impurities in the reddish sample. The spectra of substitutional Fe2+ are highly anisotropic and could be observed even up to the room temperature. After illumination the signals showing the DX behavior were detected in the same sample. We assume these signals to arise due to the presence of the shallow donor center namely the isolated substitutional oxygen ON occupying the nitrogen position. In the second slightly amber-coloured sample EPR measurements before and after X-ray showed the presence of a deep-donor center which was assumed to be nitrogen vacancy VN. Based on thermoluminescence measurements the depth of the level was estimated to 0.45-0.5 eV.

Identification of the carbon antisite in SiC: EPR of {sup 13}C enriched crystals

An electron paramagnetic resonance spectrum with axial symmetry along c axis, spin S=1/2 and strong hyperfine interaction with one carbon atom has been observed in neutron-irradiated and annealed 6H-SiC, {sup 13}C isotope enriched. The {sup 13}C concentration was defined from hyperfine structure for the negatively charged silicon vacancy. The spectrum is identified as arising from an isolated carbon atom presumably in Si position C{sub Si}--carbon antisite. The unpaired spin is up to 43% localized in one pure p orbital that is directed along the c axis and 10% localized in three sp{sup 2} hybrid orbitals, and this means that the C atom is relaxed away from Si position.