Designing carbon-based defects in icosahedral alpha boron from first principles*

We propose a new material, alpha boron as a host for quantum defects. Indeed, the insertion of carbon atoms has been shown to facilitate the formation of the alpha phase, hitherto known to be metastable with respect to the beta phase of boron [1].

In the present work, carbon-based defects have been computed with ab initio methods with various concentrations and geometries. The defect formation enthalpy and band have been studied, and possible triplet ground state(s) analogous to the diamond NV center have been searched for.

We demonstrate that the geometry of interstitial carbon atoms plays a significant role in the stability of defects in alpha boron, in link to the interaction with B₁₂ icosahedra, and that engineering the electronic structure and the degeneracy between in-gap levels can be achieved by considering the symmetry, chemical, and charge environments of the defect atomic structure.

[1] A. Chakraborti, Y. Cho, J. Sjakste, B. Baptiste, L. Henry, N. Guignot, Y. Le Godec, N. Vast, Acta Materialia 249, 118820 (2023).