Ligand hyperfine interactions at silicon vacancies in 4H-SiC.

The negative silicon vacancy ([Formula: see text]) in SiC has recently emerged as a promising defect for quantum communication and room-temperature quantum sensing. However, its electronic structure is still not well characterized. While the isolated Si vacancy is expected to give rise to only two paramagnetic centers corresponding to two inequivalent lattice sites in 4H-SiC, there have been five electron paramagnetic resonance (EPR) centers assigned to [Formula: see text] in the past: the so-called isolated no-zero-field splitting (ZFS) [Formula: see text] center and another four axial configurations with small ZFS: T V1a, T V2a, T V1b, and T V2b. Due to overlapping with 29Si hyperfine (hf) structures in EPR spectra of natural 4H-SiC, hf parameters of T V1a have not been determined. Using isotopically enriched 4H-28SiC, we overcome the problems of signal overlapping and observe hf parameters of nearest C neighbors for all three components of the S = 3/2 T V1a and T V2a centers. The obtained EPR data support the conclusion that only T V1a and T V2a are related to [Formula: see text] and the two configurations of the so-called isolated no-ZFS [Formula: see text] center, [Formula: see text] (I) and [Formula: see text] (II), are actually the central lines corresponding to the transition |-1/2〉 ↔ |+1/2〉 of the T V2a and T V1a centers, respectively.