Relaxation dynamics of spin- 32 silicon vacancies in 4H -SiC

Room temperature optically detected magnetic resonance experiments on spin 3/2 V2 Silicon vacancies in 4H-SiC are reported. The $m_s=+1/2\leftrightarrow -1/2$ transition is accessed using a two microwave frequency excitation protocol. The ratio of the Rabi frequencies of the $+3/2 \leftrightarrow +1/2$ and $+1/2\leftrightarrow -1/2$ transitions is measured to be $(0.90\pm 0.02)\sqrt{3}/2$. The deviation from $\sqrt{3}/2$ is attributed to small difference in g-factor for different magnetic dipole transitions. Whereas a spin-1/2 system is characterized by a single $T_1$ time, we show that the spin 3/2 system has three distinct relaxation modes that can be preferentially excited and detected. Compared to model where relaxation is caused by fluctuating B-field, a relatively fast relaxation between $m_s=\pm 1/2$ states is observed.