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6CCVD Research

Exploring High-Spin Color Centers in Wide Band Gap Semiconductors SiC - A Comprehensive Magnetic Resonance Investigation (EPR and ENDOR Analysis)

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-06-26
JournalMolecules
AuthorsЛариса Латыпова, Fadis F. Murzakhanov, G. V. Mamin, Margarita A. Sadovnikova, H. J. von Bardeleben
InstitutionsKazan Federal University, Sorbonne Université
Citations3
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study comprehensively characterizes high-spin Nitrogen-Vacancy (NV) color centers in 4H and 6H Silicon Carbide (SiC) using W-band (94 GHz) photoinduced Electron Paramagnetic Resonance (EPR) and Electron-Nuclear Double Resonance (ENDOR) for quantum technology applications.

  • Quantum Coherence Achieved: Demonstrated long phase coherence times (T2) up to 60 µs in 6H-SiC at 150 K, and 25.3 µs at 275 K in 4H-SiC, confirming suitability for robust electron qubits.
  • Spin Manipulation Verified: Observed clear Rabi oscillations of the electronic magnetization, a critical requirement for implementing quantum gates and spin manipulation protocols.
  • Full Spin Hamiltonian Determined: Precisely quantified key parameters, including Zero-Field Splitting (D ≈ 1.2-1.3 GHz), hyperfine (A ≈ 1.1 MHz), and quadrupole (Cq ≈ 2.45 MHz) interactions for both axial and basal NV centers.
  • Optical Initialization Optimized: Identified optimal laser excitation wavelengths: 532 nm (visible/green) for 4H-SiC and 980 nm (near-IR) for 6H-SiC, aligning with fiber-optic transparency windows.
  • Multi-Qubit Potential: The presence of structurally distinct NV centers (e.g., three groups in 6H-SiC) allows for selective excitation and the potential creation of multiple independent qubits within a single crystal.
  • Room Temperature Viability: EPR signals and coherence properties were successfully measured up to 297 K, paving the way for ambient-condition quantum sensors and registers.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
EPR Operating Frequency94GHzW-band spectroscopy
Zero-Field Splitting (D)1299 ± 10MHzAxial NVkk center (6H-SiC)
Zero-Field Splitting (D)1165 ± 20MHzBasal NVhk center (6H-SiC)
Phase Coherence Time (T2)60µs6H-SiC, T = 150 K, 980 nm laser (125 mW)
Phase Coherence Time (T2)25.3µs4H-SiC (NVkk), T = 275 K
Spin-Lattice Time (T1)1.43ms4H-SiC (NVkh), T = 150 K
Spin-Lattice Time (T1)152µs4H-SiC (NVkk), T = 275 K
Optimal Excitation (4H-SiC)532nmVisible (Green) range
Optimal Excitation (6H-SiC)980nmNear-IR range (Highest polarization)
14N Hyperfine Interaction (Azz)~1.1MHzAxial symmetry
14N Quadrupole Splitting (Cq)2.413MHzBasal NVkk center (4H-SiC)
Isotropic Hyperfine (a)-1.14MHzBasal NVkk center (4H-SiC)
Anisotropic Hyperfine (b)10-20kHzRange for basal centers (4H-SiC)
4H-SiC N Doping2 x 1017cm-3Commercial starting material
6H-SiC 28Si Enrichment~99%Used to minimize nuclear spin influence
4H-SiC Irradiation Dose1 x 1016cm-212 MeV Protons
6H-SiC Irradiation Dose4 x 1018cm-22 MeV Electrons

Key Methodologies

Section titled “Key Methodologies”

The study utilized a combination of material synthesis, defect engineering, and advanced pulsed magnetic resonance techniques:

  1. Sample Preparation (4H-SiC):

    • Starting Material: Commercial N-doped 4H-SiC single crystal (2 x 1017 cm-3).
    • Defect Creation: Irradiated at 295 K with 12 MeV protons to a total fluence of 1 x 1016 cm-2 to create Si-vacancy centers.
    • Complex Formation: Annealed at 900 °C in an argon atmosphere for 2 hours to form stable VSiNC (NV) complexes.

  2. Sample Preparation (6H-SiC):

    • Starting Material: 28Si isotopically enriched crystal (up to ~99% 28Si) grown by Physical Vapor Transport (PVT) to minimize 29Si nuclear spin influence.
    • Defect Creation: Irradiated with 2 MeV electrons at a nominal dose of 4 x 1018 cm-2.
    • Complex Formation: Annealed at 900 °C in an argon atmosphere for 2 hours to form negatively charged NV complexes.

  3. EPR/ENDOR Spectroscopy:

    • Equipment: Multifunctional Elexsys E680 spectrometer operating at 94 GHz (W-band).
    • Optical Pumping: Solid-state lasers (532 nm, 640 nm, 785 nm, 808 nm, 980 nm, 1064 nm) with power up to 500 mW, delivered via an integrated optical fiber.
    • Pulsed EPR Sequences:
      • ESE (Electron Spin Echo): π/2 - τ - π - τ - ESE (used for basic spectra and T2 measurement).
      • Hahn Sequence: Used for initial T2 decay curves.
      • CPMG (Carr-Purcell-Meiboom-Gill): Used to eliminate spin diffusion effects and measure intrinsic T2.
      • Inversion-Recovery: Used to measure spin-lattice relaxation time (T1).
      • Rabi Oscillations: Measured using a three-pulse sequence (Rabi - T - π/2 - τ - π - ESE) to confirm spin manipulation capability.
    • ENDOR Sequence: Mims pulse sequence (πMW/2 - τ - πMW - TRF - πMW/2 - τ - ESE) utilizing a 150 kW RF generator for indirect NMR transition detection.

Commercial Applications

Section titled “Commercial Applications”

The characterized NV centers in SiC are highly promising platforms for next-generation quantum technologies, leveraging their long coherence times and optical addressability in the near-IR spectrum.

  • Quantum Computing and Information Processing:

    • Solid-State Qubits: NV centers serve as robust electron qubits (S=1) with long T2 times, suitable for integration into scalable quantum architectures.
    • Quantum Registers/Memory: The coupling between the electron spin and nearby 14N nuclear spins (characterized by ENDOR) enables the creation of multi-level spin systems for quantum memory.
    • Quantum Gates: Demonstrated Rabi oscillations and precise control over electron-nuclear interactions allow for the implementation of CNOT-type operations and quantum computing algorithms.

  • Spin-Photon Interfaces:

    • Integrated Quantum Systems: The ability to optically initialize the spin state (using 532 nm or 980 nm lasers) and read out the spin state via luminescence facilitates the establishment of efficient spin-photon interfaces.
    • Telecommunications: Luminescence in the 1.1-1.2 µm range aligns with the S- and O-bands of optical fibers, enabling long-distance quantum communication networks.

  • Quantum Sensing:

    • High-Sensitivity Sensors: Optically polarized high-spin defects enable the detection of individual centers at room temperature, leading to highly sensitive temperature and magnetic field sensors with submicron resolution.
    • Biosensing: The near-IR bandwidth of the NV center luminescence is suitable for studying biological objects, opening avenues for sensitive biosensors.
View Original Abstract

High-spin defects (color centers) in wide-gap semiconductors are considered as a basis for the implementation of quantum technologies due to the unique combination of their spin, optical, charge, and coherent properties. A silicon carbide (SiC) crystal can act as a matrix for a wide variety of optically active vacancy-type defects, which manifest themselves as single-photon sources or spin qubits. Among the defects, the nitrogen-vacancy centers (NV) are of particular importance. This paper is devoted to the application of the photoinduced electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) techniques at a high-frequency range (94 GHz) to obtain unique information about the nature and properties of NV defects in SiC crystal of the hexagonal 4H and 6H polytypes. Selective excitation by microwave and radio frequency pulses makes it possible to determine the microscopic structure of the color center, the zero-field splitting constant (D = 1.2-1.3 GHz), the phase coherence time (T2), and the values of hyperfine (≈1.1 MHz) and quadrupole (Cq ≈ 2.45 MHz) interactions and to define the isotropic (a = −1.2 MHz) and anisotropic (b = 10-20 kHz) contributions of the electron-nuclear interaction. The obtained data are essential for the implementation of the NV defects in SiC as quantum registers, enabling the optical initialization of the electron spin to establish spin-photon interfaces. Moreover, the combination of optical, microwave, and radio frequency resonant effects on spin centers within a SiC crystal shows the potential for employing pulse EPR and ENDOR sequences to implement protocols for quantum computing algorithms and gates.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2010 - Quantum Computers [Crossref]
  2. 2020 - Quantum Computers as Universal Quantum Simulators: State-of-the-Art and Perspectives [Crossref]
  3. 2008 - The Quantum Limit to Moore’s Law [Crossref]
  4. 2021 - Materials Challenges and Opportunities for Quantum Computing Hardware [Crossref]
  5. 2018 - Opportunities and Challenges for Quantum-Assisted Machine Learning in near-Term Quantum Computers [Crossref]
  6. 2019 - Quantum Error Correction: An Introductory Guide [Crossref]

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