Nitrogen-Related High-Spin Vacancy Defects in Bulk (SiC) and 2D (hBN) Crystals: Comparative Magnetic Resonance (EPR and ENDOR) Study

The distinct spin, optical, and coherence characteristics of solid-state spin defects in semiconductors have positioned them as potential qubits for quantum technologies. Both bulk and two-dimensional materials, with varying structural properties, can serve as crystalline hosts for color centers. In this study, we conduct a comparative analysis of the spin–optical, electron–nuclear, and relaxation properties of nitrogen-bound vacancy defects using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) techniques. We examine key parameters of the spin Hamiltonian for the nitrogen vacancy (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mi>N</mi><mi>V</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></semantics></math></inline-formula>) center in 4H-SiC: <i>D</i> = 1.3 GHz, <i>A_zz</i> = 1.1 MHz, and <i>C</i>_Q = 2.53 MHz, as well as for the boron vacancy (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>V</mi></mrow><mrow><mi>B</mi></mrow><mrow><mo>−</mo></mrow></msubsup></mrow></semantics></math></inline-formula>) in hBN: <i>D</i> = 3.6 GHz, <i>A_zz</i> = 85 MHz, and <i>C</i>_Q = 2.11 MHz, and their dependence on the material matrix. The spin–spin relaxation times <i>T</i>₂ (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mi>N</mi><mi>V</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></semantics></math></inline-formula> center: 50 µs and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>V</mi></mrow><mrow><mi>B</mi></mrow><mrow><mo>−</mo></mrow></msubsup></mrow></semantics></math></inline-formula>: 15 µs) are influenced by the local nuclear environment and spin diffusion while Rabi oscillation damping times depend on crystal size and the spatial distribution of microwave excitation. The ENDOR absorption width varies significantly among color centers due to differences in crystal structures. These findings underscore the importance of selecting an appropriate material platform for developing quantum registers based on high-spin color centers in quantum information systems.