Relaxation dynamics of spin 3/2 silicon vacancies in 4H-Silicon carbide

Room temperature optically detected magnetic resonance experiments on spin 3/2 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 $(0.901\pm 0.013)$. 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 spin lifetime $T_1$, we experimentally demonstrate that the spin 3/2 system has three distinct relaxation modes that can be preferentially excited and detected. The measured relaxation times are $(0.41\pm 0.02) T_{slow}=T_d= (3.3\pm 0.5)T_{fast}$. This differs from the values of $T_p/3 =T_d= 2T_f$ expected for pure dipole ($T_p$), quadrupole ($T_d$), and octupole ($T_f$) relaxation modes, respectively, and implies admixing of the slow dipole and fast octupole relaxation modes.