Orders of magnitude improvement in coherence of silicon vacancy ensembles in isotopically purified 4H-SiC*

The interaction of defects spins in semiconductors to their environment offers many sensing opportunities such as magnetic (ac and dc), strain and temperature measurements at ambient conditions. Magnetometers based on the nitrogen vacancy in diamond have already found applications ranging from sensing of biological and condensed matter systems. However, the difficulty of fabrication and price of diamond, as well as the introduction of substitutional nitrogen defects during the NV creation process has motivated exploration of alternative systems. Among these are silicon vacancy defects in silicon carbide, which have been shown to possess long lived spin coherence, spin initialization, and state readout at room temperature. However, the T₂^* of silicon vacancy ensembles (a critical parameter for sensing) has been limited to a few hundred nanoseconds, likely due to nuclear spins in the lattice. Here, we will present work using isotopic purification of the host crystal as well as a novel choice of basis which increases the T₂^* of the silicon vacancy ensemble to more than 20 microseconds. In this basis, the T₂^* has little dependence on defect density, showing promise for the use of the silicon vacancy as a high density, coherent defect ensemble for sensing.