Dynamic nuclear polarization of ²⁹Si nuclei induced by Li and Li-O centers in silicon

Dynamic nuclear polarization (DNP) of ²⁹Si nuclear spins induced by saturation of electron paramagnetic resonance (EPR) transitions of lithiumrelated centers in float zone (FZ) grown silicon is reported. Both isolated Li and Li-O complex centers showed strong EPR absorption lines in the temperature range 3.4-10 K and led to very efficient orientation of ²⁹Si nuclear spins. The temperature dependence and time constant of ²⁹Si DNP are investigated in detail. The ²⁹Si DNP of 0.72% was achieved at 3.4 K by excitation of the Li-O forbidden EPR transition underillumination, corresponding to a ∼352 fold increase with respect to the thermal equilibrium polarization.