A method for diagnostics of local stresses/strains in diamond at room temperature based on optically detected magnetic resonance (ODMR) of NV defects in a zero magnetic field using low-frequency microwave power modulation is proposed.

Optically active (bright) and optically inactive (dark) quartet S = 3/2 spin color centers including a negatively charged Si vacancy have been identified in silicon carbide using high-frequency electron nuclear double resonance on the nuclei of the 13 C isotope, enhanced by a tenfold increase in its content. The alignment of populations of spin levels is optically induced in a bright center promising for quantum technologies, whereas the populations of spin levels in a dark center, which is an isolated negatively charged Si vacancy V_Si^ - , correspond to a Boltzmann distribution and do not change under optical excitation.

A method for diagnostics of local stresses/strains in diamond at room temperature based on optically detected magnetic resonance (ODMR) of NV defects in a zero magnetic field using low-frequency microwave power modulation is proposed.

A non-destructive method is proposed for express diagnostics of the local concentration of substituting nitrogen donors (P1 centers) in diamond under environmental conditions by the relative intensity of sideband satellites in the optical detection of magnetic resonance spectrum of the nitrogen vacancy (NV) center. It is shown that the internal satellites which are separated from the central line at a distance of ∼±A/2, where A is the hyperfine (HF) interaction constant for the P1 center, can be explained by the interaction between the NV center and an exchange-coupled P1 pair. The pair of P1 centers strongly interacting with each other leads to the appearance of a state with spin 1 which can be observed in the electron paramagnetic resonance spectra of nitrogen in diamond as additional HF lines. As a result, both interacting spin systems, NV and P1 pair, are characterized by unit spins. The transitions induced by microwave power in two coupled triplet states, which are allowed in spin, lead to the appearance of internal satellites at low microwave powers. These conclusions are confirmed by calculations performed using the EasySpin software package.

The frequencies of electron–nuclear interactions with 13C and 29Si nuclei on remote coordination spheres are determined in triplet spin centers in the form of neutral VSi–VC divacancies in a silicon carbide crystal of the hexagonal polytype 6H–SiC enriched tenfold in the 13C isotope. High-frequency electron–nuclear double resonance and optically detected magnetic resonance under conditions of optical alignment of spins are used. Oscillations of the electron spin density on 29Si and 13C nuclei are found. Nuclear magnetic resonance transitions at Larmor and close-to-Larmor frequencies of 13C and 29Si cause giant changes in the populations of spin sublevels with the transformation of these resonances into electron paramagnetic resonance and optical signals.

High-frequency electron paramagnetic resonance (EPR) is used to study the unique properties of manganese centers in a GaAs : Mn crystal in strong magnetic fields at low temperatures. At frequencies of 94 and 130 GHz, EPR transitions were recorded in the MnGa2+-SH complex, which is a manganese ion with spin S=5/2, which replaces gallium (MnGa2+) and an ionized acceptor (A-) associated via an isotropic antiferromagnetic exchange interaction with a shallow hole (SH) with angular momentum J=3/2. A complex system of energy levels of this complex in a magnetic field and the possibility of accurately determining exchange interactions from EPR spectra are analyzed. Another complex was investigated, in which an ionized acceptor MnGa2+ interacts with a localized hole center in the form of a diamagnetic ion O2- replacing As. This complex, MnGa2+-OAs2-, is characterized by axial symmetry along the <111> axis of the cubic GaAs crystal and an anisotropic EPR spectrum. Due to the high Boltzmann factor, in our studies, the order of the fine structure spin levels of this complex was determined. The effect of the Boltzmann populations of the energy levels on the high-frequency EPR spectra was also demonstrated for the MnGa2+-SH complex. Keywords: high-frequency EPR, GaAs crystal, Mn acceptor, shallow hole, exchange interaction.

Coherent spin manipulations of ensembles of color centers in the form of neutral VSi–VC divacancies with the spin S = 1 in hexagonal silicon carbide 6H–SiC enriched in the 13C isotope (12 T_1 and spin–spin relaxation T_2 times are measured under conditions of optical alignment of spins at the temperature T = 150 K in a magnetic field of about 3 T and are T_1∼ 5 1pt ms and T_2∼ 15 1pt µs, respectively. The optical alignment of populations of spin levels makes it possible to manipulate electron and nuclear spins in the environment using optical, microwave, and radio-frequency radiation.

Optically induced alignment and polarization of electron and nuclear spins in color centers with electron spin $$S = 3{\text{/}}2$$ , which lead to giant changes in photoluminescence in the region of anticrossing of electron and nuclear spin levels, are observed in 13C-enriched 6H-SiC crystals. Electron spin transitions with the flip or preservation of the projection of the nuclear spin of the 13C isotope at the level anticrossing points in an electron–nuclear system with $$S = 3{\text{/}}2$$ and $$I = 1{\text{/}}2$$ coupled by the hyperfine interaction are identified.

High-frequency electron paramagnetic resonance (EPR) is used to study the unique properties of manganese centers in a GaAs:Mn crystal in strong magnetic fields at low temperatures. At frequencies of 94 and 130 GHz, EPR transitions were recorded in the MnGa2+ - SH complex, which is a manganese ion with spin S = 5/2, which replaces gallium (MnGa2+) and is an ionized acceptor (A–) associated via an isotropic antiferromagnetic exchange interaction with a shallow hole (SH) with angular momentum J = 3/2. A complex system of energy levels of this complex in a magnetic field and the possibility of accurately determining exchange interactions from EPR spectra are analyzed. Another complex was investigated, in which an ionized acceptor MnGa2+ interacts with a localized hole center in the form of a diamagnetic ion O2– replacing As. This complex, MnGa2+-OAs2-, is characterized by axial symmetry along the <111> axis of the cubic GaAs crystal and an anisotropic EPR spectrum. Due to the high Boltzmann factor, in our studies, the order of the fine structure spin levels of this complex was determined. The effect of the Boltzmann populations of the energy levels on the high-frequency EPR spectra was also demonstrated for the MnGa2+- SH complex.

Methods of high-frequency electron paramagnetic resonance (EPR), electron spin echo (ESE), and optically detectable magnetic resonance (ODMR) were used to study the unique properties of nitrogen-vacancy defects (nitrogen-vacancy NV center) in diamond in strong magnetic fields. It has been shown that in strong magnetic fields (3 to 5 T), an effective optically-induced alignment of populations of spin levels occurs, with filling of the MS=0 level and emptying of the MS=1 levels, which allowed to observe ODMR via variations of the photoluminescence intensity, reaching 10% at resonance. It has been demonstrated that this efficiency in high magnetic fields is of the same order as that in zero and low magnetic fields. The samples were preliminarily studied by ODMR in zero magnetic fields, which made it possible to accurately determine the main parameters of the fine structure and hyperfine interactions with nitrogen nuclei, as well as dipole-dipole interactions between the NV center and deep nitrogen donors (nitrogen atom replacing carbon, N0). In the spectra of high-frequency ODMR, hyperfine interactions with the nearest carbon atoms (13C isotope) were observed, which opens up possibilities for optical measurements of the processes of dynamic nuclear polarization of carbon in strong magnetic fields. Narrow ODMR lines in high magnetic fields are supposed to be used to measure these fields with submicron spatial resolution. A new method for detecting ODMR of NV centers with modulation of the microwave frequency has been developed, which simplifies the technique of measuring high magnetic fields. A significant increase in the intensity of the ODMR signal at orientation of the magnetic field along the symmetry axis of NV center was demonstrated.

The methods of high-frequency electron paramagnetic resonance (EPR), electron spin echo (ESE) and optically detected magnetic resonance (ODMR) are used to study the unique properties of nitrogen-vacancy (NV) defects in diamond in strong magnetic fields. It is shown that in strong magnetic fields (∼3–5 T) there occurs an effective optically induced alignment of populations of spin levels resulting in filling the level MS = 0 and emptying of the levels MS = ±1, that makes it possible to record ODMR using the change in the intensity of photoluminescence which reaches 10% at resonance. It is demonstrated that the efficiency of the alignment has the same order as in zero and low magnetic fields. The samples were preliminary studied by the ODMR method in zero magnetic fields that allowed accurate determination of the main parameters of the fine structure and hyperfine interactions with nitrogen nuclei, as well as dipole-dipole interactions between the NV center and deep nitrogen donors in the form of a nitrogen atom replacing carbon, N0. Hyperfine interactions with the nearest carbon atoms (isotope 13C) were observed in the high-frequency ODMR spectra, that opens up opportunities for measuring the processes of dynamic polarization of carbon nuclei in strong magnetic fields using optical methods. It is assumed that narrow ODMR lines in strong magnetic fields can be used to measure these fields with submicron spatial resolution. A new method for recording ODMR of NV centers with microwave frequency modulation has been developed, which simplifies the technique of measuring high magnetic fields. A significant increase in the intensity of the ODMR signal was demonstrated when a strong magnetic field was oriented along the symmetry axis of the NV center.

A scanning optical quantum magnetometer with submicron spatial resolution is proposed. It is based on the physical phenomenon of hole burning in an optically detected magnetic resonance (ODMR) signal. This signal has been registered on spin colour centers of atomic size in silicon carbide under conditions of a saturation of spin levels by additional high-frequency resonance pumping. The increase in sensitivity is due to the narrowing of the ODMR line and an increase in the slope of the dependence of the signal frequency on the magnetic field.

A scanning optical quantum magnetometer with submicron spatial resolution is proposed that is based on the phenomenon of hole burning in the signal of optically detected magnetic resonance (ODMR) on atomic-sized color centers in silicon carbide crystals under conditions of spin level saturation by means of additional high-frequency resonance pumping. An increase in the sensitivity is achieved due to narrowing of the ODMR line and increasing slope of the dependence of signal frequency on the magnetic field.

A new diagnostic method for evaluation of the local polytypic composition of silicon carbide at room temperature is proposed using known and tabulated zero-field splitting values for spin color centers with S=3/2 whose frequency parameters are in the megahertz range and depend on the specific polytype. The zero-field splitting values are recorded from the change in the photoluminescence in the near infrared, either under the optically detected magnetic resonance conditions or under the level anticrossing conditions of the spin centers. The proposed method can be used to identify silicon carbide known as carborundum in nature by recording optically induced radio frequency emission of spin color centers, including outer space.

An optical quantum thermometer with a submicron spatial resolution that is based on the physical phenomenon of optical response in the system of spin centers in silicon carbide under conditions of cross-relaxation between the optically active centers in quadruplet spin state and triplet centers, where there is anomalously strong dependence of the splitting of the fine structure on temperature, has been proposed.

AbstractAn optical quantum thermometer with a submicron spatial resolution that is based on the physical phenomenon of optical response in the system of spin centers in silicon carbide under conditions of cross-relaxation between the optically active centers in quadruplet spin state and triplet centers, where there is anomalously strong dependence of the splitting of the fine structure on temperature, has been proposed.

Предложен оптический квантовый термометр с субмикронным разрешением, основанный на физическом явлении оптического отклика в системе спиновых центров в карбиде кремния в условиях антипересечения спиновых подуровней возбужденного квадруплетного состояния (S = 3/2) с зависимым от температуры расщеплением тонкой структуры. DOI: 10.21883/PJTF.2017.07.44471.16539

An optical quantum thermometer with submicrometer resolution is proposed. Its operation is based on the physical phenomenon of the optical response in a system of spin centers in silicon carbide under conditions of anticrossing of spin sublevels of the excited quadruplet state (S = 3/2) with temperature-dependent fine-structure splitting.

Experimental and theoretical studies on the electronic properties of semiconductors have demonstrated that a donor can give rise to two types of electronic states. Either a shallow level with a delocalized effective-mass-like wave function associated with the normal substitutional (interstitional) site configuration, or a deep level with a localized wave function. The latter deep state is usually called a DX center and it arises from a lattice distortion at or near the donor site exhibiting a negative correlation energy U for electrons trapped at this site. A transition of a shallow donor to a DX-like center is an important property that affects the n-type conductivity of semiconductors. The formation of DX centers leads to a self-compensation of a shallow donor (SD) according to the reaction, 2d = d + DX +U. Here d denotes a substitutional SD impurity and DX the displaced deep impurity. In this model a SD can lower its energy by the capture of a second electron followed by a lattice relaxation of the donor impurity away from the substitutional site. The energy gain associated with electron pairing in the dangling bonds of a defect, coupled to a large lattice relaxation, was suggested by Anderson to overcome the Coulombic repulsion of the two electrons. The III-V nitrides could potentially be fabricated into optical devices that are active at wavelengths ranging from the infrared into the ultraviolet. Unfortunately the properties of donors in the nitrides remain contradictory. There were data that the DX state is the stable configuration for Si in AlN, and in contrary it was argued that Si is a shallow effective-mass donor in AlN in contrast to oxygen that forms a DX center. To our knowledge there is no data about the spatial distribution of the electronic wave function of SD's in the III-V nitrides and even more generally in the III-V semiconductors. Moreover the spin state of DX centers in semiconductors has not been demonstrated experimentally. We report the results of high-frequency electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) experiments on as-grown single crystals of AlN that prove the presence of effective-mass-like shallow donors in these crystals with a strongly delocalized electronic wave function. Secondly we demonstrate how the conversion of a shallow donor to an ionized shallow donor and a deep DX-like center and the reversed process take place. The EPR and ENDOR experiments were performed at 1.5-5 K on a home-built spectrometer operating at 94.9 GHz. The spectra were recorded by monitoring the electron-spin echo (ESE) signal. The crystal growth was accomplished by sublimation of the AlN charge placed in the hot zone of a tungsten crucible and subsequent condensation of the vapor species in a cooler region. Two wurtzite polytype small samples labelled I and II were cut from larger boules of AlN grown with similar conditions. Figure 1 shows the EPR spectra measured at 94.9 GHz in the two samples marked I (curve 1) and II (2,3) at 1.8 K after cooling from room temperature (RT) in the dark (1,2) and after 10 min light illumination (3). The EPR signals were detected with the magnetic field perpendicular to the crystal c axis (B⊥c). The observed EPR signal at 3.408 T is characterized by a slightly anisotropic g factor of g//=1.9900 and g⊥=1.9894. This g factor is somewhat smaller than the free electronic g factor as expected for SD's or conduction electrons in a wide-band-gap semiconductor such as AlN [1]. The anisotropy is consistent with the hexagonal symmetry of the AlN crystal. These factors support the assignment of the indicated resonances in Fig. 1 to the shallow donors.