First-Principles Investigation of Surface-Induced Effects on the Properties of Divacancy Qubits in 3C-SiC

TL;DR

This work addresses how proximity to a hydrogen-terminated Si-rich (001) surface alters the spin and electronic properties of neutral V_SiV_C divacancies in 3C-SiC, a promising qubit platform. It employs first-principles spin-polarized DFT on a 628-atom slab to extract atomic structure, defect states, and ZFS components $D$ and $E$ as a function of depth (0.6–1.2 nm) and orientation (axial vs basal), and uses the Lindblad formalism and RF driving to assess spin-state dynamics. The key findings show that the ground state remains a spin triplet, surface passivation suppresses in-gap surface states, and ZFS parameters exhibit clear surface-induced modifications: basal defects have larger $D$, while $E$ shows strong, orientation-dependent sensitivity to depth, implying multiple near-surface spin-resolved features. The results highlight surface proximity as both a perturbation and a tunable tool for engineering SiC-based qubits and nanoscale quantum sensors, enabling depth- and orientation-dependent control of the spin Hamiltonian in solid-state quantum devices.

Abstract

Neutral silicon-carbon divacancy (V$_{Si}$V$_{C}$) in cubic silicon carbide (3C-SiC) is a promising class of point defects for quantum technologies based on active crystalline centers. Within the theoretical framework of spin-polarized Density Functional Theory (DFT), this study examines the structural and electronic characteristics of V$_{Si}$V$_{C}$ centers near a hydrogen-terminated Si-rich (001) surface. A (2x1):H reconstructed slab of 628 atoms represents the near-surface environment, with divacancies located at depths ranging from 0.6 to 1.2 nm in basal and axial orientations. The optimized geometries show localized relaxations, and the electronic structure reveals in-gap defect levels in both spin channels. Furthermore, examination of the zero-field splitting (ZFS) tensor demonstrates sensitivity to the orientation of the spin defects and their distance from the surface. The findings of this investigation suggest that surface proximity exerts a substantial influence on the spin Hamiltonian of divacancies, providing insight for the engineering of SiC-based qubits and nanoscale quantum devices.

Figures (9)

• Figure 1: (a) Atomistic model of a (2$\times$1):H reconstructed 3C-SiC surface showing the various SiC dimer layers. (b) Divacancy (V$_\mathrm{Si}$V$_\mathrm{C}$) defect with an axial configuration. (c) Divacancy (V$_\mathrm{Si}$V$_\mathrm{C}$) defect with a basal configuration.
• Figure 2: Defect electronic states in ($\perp$) and ($\parallel$) orientations of the V$_\mathrm{Si}$V$_\mathrm{C}$ divacancy at different distances from the (2$\times$1):H surface. Blue and green lines indicate spin up and spin down channels, respectively, while arrows define the occupied defect states. Conduction and valence bands are shown in gray.
• Figure 4: Expectation values of the spin operators under a Rabi excitation pulse, tailored on the L6 configuration state energies, and dissipation. Configurations, starting from the upper left and proceeding clockwise, correspond to L6, L5, L4, and L3.
• Figure : (a)
• Figure : ToC Entry