Stability and electronic structure of NV centers at dislocation cores in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-11-28 |
| Journal | Physical review. B./Physical review. B |
| Authors | Reyhaneh Ghassemizadeh, Wolfgang Körner, Daniel F. Urban, Christian ElsÀsser |
| Institutions | Fraunhofer Institute for Mechanics of Materials, University of Freiburg |
| Citations | 16 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study uses Density Functional Theory (DFT) to analyze the stability and quantum properties of negatively charged Nitrogen-Vacancy (NV-) centers when positioned at the cores of common partial glide dislocations in diamond.
- Energetic Advantage: NV- centers exhibit a significant formation energy reduction (up to 3.5 eV) when located at dislocation cores compared to bulk diamond, suggesting dislocation lines act as strong self-assembly traps.
- Optimal Template Identified: The core of the 30° partial glide dislocation is uniquely favorable, providing the lowest formation energy while critically preserving the S=1 spin triplet ground state.
- Qubit State Preservation: The most stable configuration at the 30° core (where the NV axis is parallel to the dislocation line) maintains key quantum properties, with the axial Zero-Field Splitting (D) component deviating by only ~3% from the bulk value.
- Linear Array Potential: This finding proposes a viable mechanism for the self-assembly of linear, aligned arrays of high-quality NV- qubits along the 30° dislocation line.
- 90° Dislocation Failure: NV- centers placed at 90° partial glide dislocation cores (both Single Period and Double Period reconstructions) consistently transition to an energetically stable, but quantum-unusable, singlet ground state.
- Minor Property Shifts: While the axial ZFS (D) and 13C Hyperfine Structure (HFS) constants are largely preserved, the transversal ZFS (E) component is non-zero (120 MHz), indicating minor symmetry breaking, and the 14N HFS constant is significantly reduced.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Max NV- Formation Energy Gain | Up to 3.5 | eV | Relative to bulk NV- triplet state, observed at 30° core. |
| Optimal ZFS Axial Component (D) | 3.08 | GHz | 30° core, position 1 (NV axis parallel to dislocation line). |
| Bulk ZFS Axial Component (D) | 2.99 | GHz | Calculated bulk value (Experimental: 2.872 GHz). |
| Optimal ZFS Transversal Component (E) | 120 | MHz | 30° core, position 1. Non-zero E indicates local symmetry distortion. |
| Optimal HFS 13C (Azz) | 206 | MHz | 30° core, position 1 (C3 atom). Deviation less than 3% from bulk. |
| Optimal HFS 14N (Azz) | 0.7 | MHz | 30° core, position 1. Significant reduction from bulk (-1.7 MHz). |
| Triplet/Singlet Energy Difference (30° core, Pos 1) | Up to 300 | meV | Triplet configuration is the stable ground state. |
| Diamond Band Gap (DFT-1/2) | 5.75 | eV | Calculated value using DFT-1/2 method. |
| Supercell Size (Atoms) | 1176 | Carbon atoms | Used for atomistic supercell models. |
| Supercell Dimensions (Approx.) | 30.5 x 17.6 x 15.1 | Angstrom | Minimum distance of 15 Angstrom maintained to avoid defect self-interaction. |
Key Methodologies
Section titled âKey MethodologiesâThe study relied exclusively on advanced computational modeling using Density Functional Theory (DFT) to simulate the NV- defects within large, distorted diamond supercells.
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Atomistic Supercell Construction:
- Supercells were built using the Atomistic Simulation Environment (ASE) package.
- Models included two oppositely oriented partial glide dislocations (30°, 90° SP, or 90° DP) in a quadrupole arrangement to compensate for long-range elastic strain fields.
- The supercell size was 7ax x 7ay x 6az (1176 C atoms).
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DFT Calculations (VASP):
- Calculations were performed using the Vienna Ab Initio Simulation Package (VASP).
- The generalized gradient approximation (GGA) with the Perdew, Burke, and Ernzerhof (PBE) functional was used for exchange-correlation.
- Bloch waves were expanded using a plane-wave basis with a cutoff energy of 420 eV.
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Structural Relaxation:
- Atomic positions were relaxed until residual forces were less than 0.002 eV/Angstrom.
- The stability of the triplet (S=1) versus singlet (S=0) electronic configuration was determined by constraining the spin difference during relaxation.
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Electronic Structure Refinement (DFT-1/2):
- The DFT-1/2 method was employed to correct the systematic underestimation of the diamond band gap by PBE-GGA, achieving a calculated gap of 5.75 eV.
- This method involved removing half an electron from the valence band maximum and adding half an electron to the conduction band minimum.
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Property Calculation:
- Electronic Density of States (DOS) was analyzed using a fine 2 x 3 x 4 k-point mesh.
- Zero-Field Splitting (ZFS) and Hyperfine Structure (HFS) tensor components were computed using VASP subroutines, including only the Gamma-point due to high computational cost.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to deterministically position and align high-quality NV- centers is crucial for scaling up quantum technologies.
- Quantum Magnetometry and Sensing: Creating linear arrays of aligned NV- centers enhances magnetic sensitivity, scaling the signal with the square root of the number of sensing centers (âX).
- Solid-State Quantum Computing: The 30° dislocation core provides a self-assembly template for building controlled, linear qubit registers, addressing a major challenge in patterning thousands of coupled NV centers needed for practical quantum computers.
- Controlled Qubit Array Fabrication: Utilizing the energetically favorable 30° dislocation core allows for the precise, linear patterning of NV centers, which is superior to current random or large-area decoration methods.
- Spin-Chain Systems: The aligned NV- centers along the dislocation line offer a platform for investigating collective quantum behavior and designing novel spin-chain quantum devices.
- Defect Engineering in Diamond Growth: These findings provide guidance for optimizing diamond growth techniques (HPHT or CVD) to intentionally introduce specific dislocation types (like 30° partial glide) to enhance NV center incorporation and alignment.
View Original Abstract
We present a density functional theory analysis of the negatively charged\nnitrogen-vacancy (NV) defect complex located at or close to the core of\n30$^\circ$ and 90$^\circ$ partial glide dislocations in diamond. Formation\nenergies, electronic densities of states, structural deformations, hyperfine\nstructure and zero-field splitting parameters of NV centers in such\nstructurally distorted environments are analyzed. The formation energies of the\nNV centers are up to 3 eV lower at the dislocation cores compared to the bulk\nvalues of crystalline diamond. We found that the lowest energy configuration of\nthe NV center at the core of a 30$^\circ$ partial glide dislocation is realized\nwhen the axis of the NV center is oriented parallel to the dislocation line.\nThis special configuration has a stable triplet ground state. Its hyperfine\nconstants and zero field splitting parameters deviate by only 3% from values of\nthe bulk NV center. Hence, this is an interesting candidate for a self-assembly\nof a linear array of NV centers along the dislocation line.\n