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4H silicon carbide (SiC) polytype is preferred over other SiC polytypes for high-power, high-voltage, and high-frequency applications due to its superior electrical, thermal, and structural characteristics. In this manuscript, we provide a comprehensive study of the spin coupling dynamic between conduction electrons and nitrogen (N) donors in monocrystalline 4H SiC with various concentrations of uncompensated N donors from 10^17 cm^-3 to 5x10^19 cm^-3 by continuous wave, pulsed EPR, and microwave perturbation techniques at T=4.2-300 K. At low temperatures two triplets due to N donors in cubic (Nk) hexagonal (Nh) positions and triplet arisen from spin-interaction between Nh and Nk were observed in 4H SiC having Nd-Na=10^17 cm^-3. A single S-line (S=1/2) dominates the EPR spectra in all investigated 4H SiC monocrystals at high temperatures. It was established that this line occurs due to the exchange coupling of localized electrons (dominate at low temperatures) and non-localized electrons (dominate at high temperatures). The localized electrons were attributed to Nh for Nd-Na=10^17 cm^-3 and Nk donors for Nd-Na>=5x10^18 cm^-3. We have concluded that the conduction electrons in 4H SiC monocrystals are characterized by gpar=2.0053(3) gper=2.0011(3) for Nd-Na<=5x10^18 cm^-3 and gpar=2.0057(3) and gper=2.0019(3) for Nd-Na=5x10^19 cm^-3. Using the theoretical fitting of the temperature variation of S-line EPR linewidth in 4H SiC having Nd-Na<5x10^18 cm-^3, the energy levels of 57-65 meV that correlate with the valley-orbit splitting values for Nk donors in 4H SiC monocrystals were obtained.

We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by Lely method and by sublimation "sandwich method" (SSM) with a donor concentration of about 10^17 cm^-3 at T = 10-40 K. The donor electrons of the N donors substituting quasi-cubic "k1" and "k2" sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1^-1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T^9, respectively. The character of the temperature dependence of the T1^-1 for the donor electrons of N substituting hexagonal ("h") site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm^-1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed.

The exceptional electronic properties of monoatomic thin graphene sheets triggered numerous original transport concepts, pushing quantum physics into the realm of device technology for electronics, optoelectronics and thermoelectrics. At the conceptual pivot point is the particular twodimensional massless Dirac fermion character of graphene charge carriers and its volitional modification by intrinsic or extrinsic means. Here, interfaces between different electronic and structural graphene modifications promise exciting physics and functionality, in particular when fabricated with atomic precision. In this study we show that quasiperiodic modulations of doping levels can be imprinted down to the nanoscale in monolayer graphene sheets. Vicinal copper surfaces allow to alternate graphene carrier densities by several 10^13 carriers per cm^2 along a specific copper high-symmetry direction. The process is triggered by a self-assembled copper faceting process during high-temperature graphene chemical vapor deposition, which defines interfaces between different graphene doping levels at the atomic level.

X- and Q-band electron paramagnetic resonance (EPR) study is reported on the SrTiO3 single crystals doped with 0.5-at.% MnO. EPR spectra originating from the S = 2 ground state of Mn3+ ions are shown to belong to the three distinct types of Jahn-Teller centres. The ordering of the oxygen vacancies due to the reduction treatment of the samples and consequent formation of oxygen vacancy associated Mn3+ centres are explained in terms of the localized charge compensation. The EPR spectra of SrTiO3: Mn crystals show the presence of next nearest neighbor exchange coupled Mn4+ pairs in the <110> directions., Comment: 17 pages, 8 figures