Hyperfine Coupling Constants of Photoinduced Axial Symmetry NV Centers in a 6H Silicon Carbide - DFT and High-Field ENDOR Spectroscopy Study

At a Glance

Metadata	Details
Publication Date	2025-10-31
Journal	Applied Nano
Authors	Yuliya Ermakova, Ekaterina Dmitrieva, I. N. Gracheva, D. V. Shurtakova, Margarita A. Sadovnikova
Institutions	Plekhanov Russian University of Economics, Kazan Federal University
Analysis	Full AI Review Included

Hyperfine Coupling Constants of Photoinduced Axial Symmetry NV Centers in 6H Silicon Carbide: DFT and High-Field ENDOR Spectroscopy Study

Executive Summary

Core Achievement: Determined the hyperfine (HFI) and quadrupole (NQI) interaction constants for negatively charged Nitrogen-Vacancy (NV^-) centers in the hexagonal (hh) position of 6H-SiC using high-frequency (94 GHz) Electron Nuclear Double Resonance (ENDOR) and Density Functional Theory (DFT).
Microscopic Model Refinement: Theoretical DFT calculations of spin density distribution showed excellent agreement with experimental HFI and NQI values, confirming the defect structure as a silicon vacancy coordinated with an impurity nitrogen atom in the carbon position.
Temperature Stability: The Zero-Field Splitting (ZFS, D) and NQI (Q) parameters demonstrated high stability, remaining practically unchanged across the 100 K to 280 K range.
HFI Sensitivity: The hyperfine interaction parameter (A) exhibited a weak temperature dependence (δA/δT ≈ 180 Hz/K), which must be accounted for in high-precision quantum control systems.
Room Temperature Operation: The stability of the spin Hamiltonian parameters is a major advantage, supporting the use of 6H-SiC NV centers for quantum applications (sensing, computing) operating at or near room temperature, reducing the need for constant cryogenic cooling.
Quantum Register Potential: Dispersed spin density affects distant ¹³C and ²⁸Si nuclei, providing a mechanism for transferring spin magnetization and implementing multiqubit electron-nuclear registers.

Technical Specifications

Parameter	Value	Unit	Context
Host Crystal Polytype	6H	SiC	Enriched with ²⁸Si (I=0)
Defect Position Studied	hh	-	Hexagonal axial symmetry
Electron Spin (S)	1	-	Ground state of NV^- center
Nuclear Spin (I)	1	-	¹⁴N isotope
EPR/ENDOR Frequency	94	GHz	W-band high-field spectroscopy
Experimental Temperature (T)	150	K	Primary measurement temperature
HFI Constant (A_iso) (Exp, 150 K)	-1.175	MHz	¹⁴N nucleus, hh position
Quadrupole Constant (C_q) (Exp, 150 K)	2.523	MHz	¹⁴N nucleus, hh position
HFI Temperature Sensitivity (δA/δT)	≈ 180	Hz/K	Measured over 100 K to 280 K range
Spin Density Localization (p)	≈ 0.02	%	Spin density fraction on the ¹⁴N nucleus
Electron Irradiation Energy	2	MeV	To form vacancy defects
Electron Irradiation Fluence	4 × 10¹⁸	cm^-2	-
Annealing Temperature	900	°C	2 hours in Argon atmosphere
Optical Excitation Wavelength (λ)	980	nm	IR laser source
RF Pulse Duration (τ_RF)	72	µs	Mims ENDOR sequence

Key Methodologies

Sample Growth and Enrichment: 6H-SiC crystals were grown via high-temperature sublimation (physical vapor transport) using a precursor enriched with the non-magnetic ²⁸Si isotope (up to 99% purity).
Defect Creation: Vacancy defects were formed by high-energy (2 MeV) electron irradiation with a particle flux density (fluence) of 4 × 10¹⁸ cm^-2.
NV Center Stabilization: Irradiated crystals were annealed at T = 900 °C for 2 hours in an argon atmosphere to create stable, negatively charged nitrogen-vacancy complexes (NV^-).
EPR Spectroscopy: Measurements were performed using a Bruker Elexsys E680 spectrometer operating at 94 GHz (W-band) in pulse mode using the Hahn pulse sequence (π_MW/2-τ-π_MW-τ-ESE).
ENDOR Spectroscopy: Electron Nuclear Double Resonance (ENDOR) spectra were detected using the Mims pulse sequence (π_MW/2-τ-π_MW/2-τ_RF-π_MW/2-τ-ESE) with an RF pulse duration (τ_RF) of 72 µs.
Optical Excitation: Photoinduction was achieved using a solid-state diode-pumped laser (λ = 980 nm). High helium flow in the cryostat ensured effective heat rejection, limiting optically induced heating to less than 1.5 K.
Computational Modeling (DFT): Density Functional Theory calculations were performed using the Perdew-Burk-Ernzerhof (PBE) functional in Quantum ESPRESSO (v7.4.1). A supercell consisting of 36 6H-SiC unit cells was structurally optimized (“relax” calculation type).
Parameter Calculation: Electron-nuclear interaction parameters (HFI and NQI) were calculated using the GIPAW module within Quantum ESPRESSO.

Commercial Applications

Quantum Computing and Information Storage: The nuclear spin subsystem (¹⁴N, ¹³C, ²⁸Si) acts as a robust, long-coherence quantum memory cell. The ability to form multiqubit electron-nuclear registers via distributed spin density is key for scalable quantum processors.
Quantum Sensing (RF/Magnetic Fields): The observation of the ¹⁴N NMR signal at room temperature enables the use of NV centers in 6H-SiC for external radio-frequency (RF) sensing and magnetic field detection, particularly in environments where cryogenic cooling is impractical.
High-Temperature Electronics and Devices: SiC’s inherent thermal stability allows NV spin defects to maintain stable spin Hamiltonian values (D and Q) up to 280 K, simplifying device engineering and reducing the energy cost associated with maintaining cryogenic temperatures.
Solid-State Qubits: SiC provides a semiconductor host matrix compatible with existing silicon technology, offering a robust platform for integrating spin defects into scalable quantum integrated circuits.
Single-Photon Emitters: The photoactive nature of the NV centers makes them promising candidates for bright, stable single-photon sources operating in the IR band, essential for quantum communication and networking.

View Original Abstract

Solid-state spin centers are at the forefront of developing advanced quantum technologies, engaging in applications of sensing, communication and computing. A semiconductor host matrix compatible with existing silicon technology provides a robust platform for holding spin defects and an opportunity for external manipulation. In this article, negatively charged nitrogen-vacancy (NV) centers in the hexagonal hh position in a 6H polytype silicon carbide crystal was studied using high-frequency (94 GHz) electron paramagnetic (EPR) and electron nuclear double resonances (ENDOR) spectroscopy. Experimentally determined values of hyperfine and quadrupole interactions of 14N were compared with the values obtained for the centers in NVk2k1 positions. The distribution of spin density of the defect within a supercell of the SiC crystal lattice was calculated using the density functional theory approach. The theoretical estimation of electron-nuclear interaction constants turned out to be in close agreement with the experimental values, which allows us to refine the microscopic model of a point defect. The temperature dependence of the spin Hamiltonian values (δA/δT ≅ 180 Hz/K) was studied with the possibility of observing the 14N NMR signal at room temperature. The fundamental knowledge gained about interactions’ parameters’ behavior lays the foundation for the creation of promising quantum platforms.

Tech Support

Original Source

DOI: https://doi.org/10.3390/applnano6040023

References

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