@article{oai:repo.qst.go.jp:00085697,
 author = {Umeda, T. and Watanabe, K. and Hara, H. and Sumiya, H. and Shinobu, Onoda and Uedono, A. and Chuprina, I. and Siyushev, P. and Jelezko, F. and Wrachtrup, J. and Isoya, J. and Shinobu, Onoda},
 issue = {16},
 journal = {Physical Review B},
 month = {Mar},
 note = {Impurity-vacancy complexes in diamond are an attractive family of spin defects since NV−, SiV−, GeV−, and SnV− have emerged as promising platforms for quantum applications. Although boron is most easily incorporated into diamond, a boron-vacancy complex in the negative charge state (BV−) has eluded experimental observation. This center was theoretically predicted as another promising spin qubit. In this work, we experimentally observed an electron paramagnetic resonance (EPR) spectrum identified as BV− in synthetic diamonds via a Fermi-level tuning. Fingerprints of BV− such as the spin multiplicity of S= 1,C3v symmetry, the zero-field splitting (D= 2913 MHz), in addition to 10B and 11 B hyperfine (HF) interactions have been confirmed. Moreover, optically-pumped spin polarization has been observed with 3.0 to 3.6 eV excitation. However, unlike the NV− center, the photoluminescence as well as optically detected magnetic resonance from BV− has not been confirmed even at low temperatures. We speculate that the Jahn-Teller instability in the triplet states of the NV− and BV− centers results in different optical properties.},
 title = {Negatively charged boron vacancy center in diamond},
 volume = {105},
 year = {2022}
}