14N Hyperfine and nuclear interactions of axial and basal NV centers in 4H-SiC - A high frequency (94 GHz) ENDOR study
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-09-28 |
| Journal | Journal of Applied Physics |
| Authors | Fadis F. Murzakhanov, Margarita A. Sadovnikova, G. V. Mamin, S. S. Nagalyuk, H. J. von Bardeleben |
| Institutions | Kazan Federal University, Paderborn University |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research successfully characterized the fundamental electron-nuclear interactions of all four Nitrogen-Vacancy (NV) center configurations in 4H-Silicon Carbide (4H-SiC), providing essential data for advancing solid-state quantum technology.
- Core Achievement: Determined the complete set of 14N Hyperfine Interaction (HFI) and Nuclear Quadrupole Interaction (NQI) parameters for all four inequivalent NV configurations (NVkk, NVhh, NVhk, NVkh) in 4H-SiC.
- Methodology: Utilized high-frequency (94 GHz, W-band) Electron-Nuclear Double Resonance (ENDOR) spectroscopy, which offers kHz resolution, combined with Density Functional Theory (DFT).
- Key Finding (Distinction): The four NV configurations exhibit measurably different electron-nuclear parameters, confirming that each configuration acts as a separate, optically addressable solid-state qubit.
- Axial vs. Basal: Axial centers (NVhh, NVkk) show HFI constants (A||) that are significantly larger than those of the basal centers (NVhk, NVkh).
- Structural Correlation: Observed differences in NQI parameters (e.g., NVhh > NVkk) were rationalized by subtle distinctions in the local atomic structure, specifically the small shift of the 14N atom away from the vacancy site.
- Engineering Impact: The established parameters are crucial for designing and implementing quantum protocols, such as coherent polarization transfer from the electron spin to the 14N nuclear spin, necessary for quantum memory applications.
Technical Specifications
Section titled “Technical Specifications”The following parameters were determined experimentally or used in the synthesis and measurement processes for the NV centers in 4H-SiC.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Crystal Polytype | 4H-SiC | N/A | Bulk crystal, (0001) face |
| Initial N Concentration | 2 x 1017 | cm-3 | Starting material specification |
| Irradiation Energy | 12 | MeV | Proton irradiation for vacancy creation |
| Irradiation Fluence | 1 x 1016 | cm-2 | Proton irradiation dose |
| Annealing Temperature | 900 | °C | Optimal temperature for NV center formation |
| ESR/ENDOR Frequency | 94 | GHz | W-band operating frequency |
| Electron Spin (S) | 1 | N/A | Ground state spin of the NV center |
| Nuclear Spin (I) | 1 | N/A | Central 14N nucleus |
| NVhh NQI (P) | 1.89 (±0.05) | MHz | Nuclear Quadrupole Splitting (Axial center) |
| NVhh HFI (A||) | -1.165 | MHz | Hyperfine Interaction Constant (Axial center) |
| NVkk NQI (P) | 1.81 | MHz | Nuclear Quadrupole Splitting (Axial center) |
| NVkh ZFS (D) | 1275 (±20) | MHz | Zero-Field Splitting (Basal center) |
| NVhk ZFS (E) | 120 (±5) | MHz | Rhombicity parameter (Basal center) |
| NVhk HFI (A||) | -0.617 | MHz | DFT-calculated HFI (Basal center) |
Key Methodologies
Section titled “Key Methodologies”The NV centers were generated and characterized using a combination of high-energy processing and advanced magnetic resonance spectroscopy.
1. Sample Synthesis and Preparation
Section titled “1. Sample Synthesis and Preparation”- Material: n-type, (0001) face 4H-SiC bulk crystal.
- Irradiation: High-energy (12 MeV) proton irradiation was used to create silicon vacancy defects (VSi).
- Fluence: 1 x 1016 cm-2.
- Annealing: Thermal annealing was performed at T = 900 °C.
- Purpose: To mobilize VSi defects, allowing them to complex with substitutional nitrogen atoms (NC) to form the stable NV centers (NCVSi).
2. High-Frequency ENDOR Spectroscopy
Section titled “2. High-Frequency ENDOR Spectroscopy”- Equipment: Bruker Elexsys E680 spectrometer operating at W-band (94 GHz).
- Excitation: Continuous optical excitation (λ = 532 nm) was used to achieve ground state spin polarization (preferential population of the ms= 0 sublevel).
- ESR Detection (Hahn-Echo): Used a standard Hahn-echo microwave (MW) pulse sequence (π/2 - τ - π - ESE) to detect the electron spin resonance signal.
- Pulse lengths: π/2 = 40 ns, π = 80 ns.
- ENDOR Measurement (Mims-Pulse): Used a Mims-pulse sequence (π/2 - τ - π/2 - T - π - τ - π - ESE) to measure the Nuclear Magnetic Resonance (NMR) transitions.
- A Radio Frequency (RF) π-pulse was applied between the second and third MW pulses to induce nuclear spin flips (selection rules Δms = 0, ΔmI = 1).
3. Computational Modeling (DFT)
Section titled “3. Computational Modeling (DFT)”- Method: Density Functional Theory (DFT) utilizing the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional.
- Structure: NV centers were modeled in 432-atom supercells of 4H-SiC, with full relaxation until forces were less than 10-1 Ry/bohr.
- Parameter Calculation: The GIPAW module was used to calculate 14N HFI and NQI parameters, incorporating scalar-relativistic approximations for accurate Fermi-contact term determination.
Commercial Applications
Section titled “Commercial Applications”The precise characterization of the 14N nuclear spin in 4H-SiC NV centers directly supports the development of next-generation quantum technologies.
-
Quantum Computing and Memory:
- Scalable Quantum Memory: The 14N nuclear spin (I=1) serves as a robust, long-lived quantum memory register. The determined HFI parameters are essential for implementing coherent polarization transfer protocols (electron spin to nuclear spin).
- Multi-Qubit Systems: The existence of four distinct, addressable NV configurations (NVkk, NVhh, NVhk, NVkh) within a single crystal allows for the creation of integrated, multi-qubit architectures.
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Quantum Sensing:
- Enhanced Sensitivity: Coupling the electron spin to the nuclear spin improves the coherence time and stability of the sensor, leading to ultra-long spin-relaxation times (previously reported up to 20 ms).
- Near-Infrared (NIR) Sensors: SiC NV centers emit in the NIR (telecommunication O-band), making them ideal for sensing applications that require integration with standard fiber optics.
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Integrated Photonics:
- Spin-Photon Interfaces: 4H-SiC is compatible with mature semiconductor nanostructuring techniques, enabling the formation of optical cavities, nanopillars, and waveguides necessary for scalable quantum device integration.
- Coherent MW Amplifiers: The spin properties of these defects can be leveraged for high-performance microwave signal amplification.
View Original Abstract
The nitrogen-vacancy (NV) centers (NCVSi)− in 4H silicon carbide (SiC) constitute an ensemble of spin S = 1 solid state qubits interacting with the surrounding 14N and 29Si nuclei. As quantum applications based on a polarization transfer from the electron spin to the nuclei require the knowledge of the electron-nuclear interaction parameters, we have used high-frequency (94 GHz) electron-nuclear double resonance spectroscopy combined with first-principles density functional theory to investigate the hyperfine and nuclear quadrupole interactions of the basal and axial NV centers. We observed that the four inequivalent NV configurations (hk, kh, hh, and kk) exhibit different electron-nuclear interaction parameters, suggesting that each NV center may act as a separate optically addressable qubit. Finally, we rationalized the observed differences in terms of distinctions in the local atomic structures of the NV configurations. Thus, our results provide the basic knowledge for an extension of quantum protocols involving the 14N nuclear spin.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
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