Relaxation processes and high-field coherent spin manipulation in color center ensembles in 6 H-SiC

Coherent spin manipulations of spin-32 color center ensembles in 6H-SiC crystal have been studied in high magnetic fields using methods of pulsed electron paramagnetic resonance, Rabi oscillations, and pulsed electron-electron double resonance under optical alignment conditions of the spin level populations. Rabi oscillation experiments show room temperature coherent control of these spin-32 color center ensembles in strong magnetic fields. A sharp decrease of the spin-lattice relaxation time T1, ∼40 times, was observed in 6H-SiC at magnetic field of ∼3.5 T with increasing temperature from 100 to 300 K, while the spin-spin relaxation time T2 is only shortened by ∼1.3 times. With an increase in the magnetic field, the times T1 and T2 were shown to decrease. The relaxation time T1 in the case of magnetic field directed along the axis of the spin-32 center is ∼2 times longer than T1 in magnetic field perpendicular to this axis. Relaxation times of the spin center in crystal grown with a reduced concentration of an isotope Si29 are significantly longer than crystal, with the natural content of isotopes. With a decrease in the Si29 content in our experiments by a factor of ∼5, the effective nuclear spin bath in SiC is reduced by a factor of ∼2. In a zero magnetic field resonance, transitions are allowed as magnetic dipole transitions with frequency ω0 which correspond to the zero-field splitting. In zero magnetic field and in fixed magnetic fields, the Rabi frequency was shown, using so-called "Feynman-Vernon-Hellwarth transformation,"to be ωR=|γ|B1. In pulsed electron-electron double resonance experiments, a change in the intensity of the electron spin echo signal corresponding to one of the spin-allowed fine structure transitions is recorded depending on the sweep of the second frequency. The experiments show the possibility to coherently detect the optical spin alignment between MS=±32 via optically pumped silent MS=±12 sublevels of the spin-32 color centers, including a detection of Rabi oscillations