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6CCVD Research

Superradiance of Spin Defects in Silicon Carbide for Maser Applications

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-05-16
JournalFrontiers in Photonics
AuthorsAndreas Gottscholl, Maximilian Wagenhöfer, Manuel Klimmer, Selina Scherbel, Christian Kasper
InstitutionsHelmholtz-Zentrum Dresden-Rossendorf, University of WĂŒrzburg
Citations9
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research demonstrates the critical steps toward realizing a solid-state maser (Microwave Amplification by Stimulated Emission of Radiation) using silicon vacancy (VSi, or V2) defects in 4H Silicon Carbide (SiC).

  • Maser Gain Material Validation: SiC V2 defects (S = 3/2) are confirmed as a highly promising, technologically mature platform for continuous-wave, solid-state masers, offering advantages over pulsed organic masers and diamond NV centers.
  • Population Inversion Optimization: Population inversion, the prerequisite for stimulated emission, was maximized by optimizing two key parameters:
    1. Wavelength: Resonant optical pumping at the Zero-Phonon Line (ZPL, 916.5 nm) at T = 50 K increased the inversion factor by 5x compared to broad Stokes excitation.
    2. Orientation: Aligning the external magnetic field (B) parallel to the SiC crystal c-axis (B || c-axis) doubled the spin polarization compared to perpendicular alignment.
  • High-Q Resonator Integration: A high-Q sapphire resonator (Q up to 110,000 at 110 K) was successfully coupled to the spin system, significantly enhancing microwave interaction.
  • Superradiance Confirmation: Superradiant stimulated microwave emission was observed at T = 110 K, evidenced by three key indicators:
    1. Superlinear intensity scaling (following the expected N2 law for the number of involved spins N).
    2. A massive population asymmetry between the emissive (B+) and absorptive (B-) transitions (|Δρ+| ≈ 7 · Δρ-).
    3. A collapse of the emissive EPR linewidth by a factor of 0.5 due to monochromatization.
  • Technological Readiness: The results confirm that SiC, with optimized defect density and spin relaxation rates, is on the verge of reaching the maser threshold, enabling wide-ranging applications.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Defect TypeV2 (Silicon Vacancy, VSi)N/ACubic lattice site in 4H SiC
Spin State (Ground)S = 3/2N/ASpin quartet system
Zero-Field Splitting (ZFS)≈70MHzGround state splitting
Microwave Frequency≈9.3GHzEPR and stimulated emission range
Resonator Q-Factor40,000 - 110,000N/AAchieved at T = 110 K using sapphire resonator
Optimal Excitation (Low T)916.5nmResonant pumping at ZPL (T = 50 K)
Standard Excitation (High T)808nmStokes excitation (T > 100 K)
Optimal Magnetic Field Angle0°B
Population Inversion Enhancement5xFactorAchieved via ZPL resonant pumping
Spin Polarization Enhancement2xFactorAchieved via B
Electron Irradiation Energy2MeVUsed to create V2 defects
Electron Irradiation Dose3-10 · 1017cm-2Used for defect creation
High Defect Density Sample2.27 · 1015cm-3Used for superradiance measurements
Linewidth Collapse (Superradiance)0.5FactorReduction of B+ transition linewidth
Superradiance Scaling LawN2.1 ≈ N2N/AObserved intensity scaling with spin number N

Key Methodologies

Section titled “Key Methodologies”

The experiments combined advanced defect engineering, cryogenic control, and high-sensitivity microwave spectroscopy.

  1. Sample Preparation:

    • 4H SiC wafers were used as the host material.
    • V2 spin defects were generated via 2 MeV electron irradiation at doses ranging from 3 · 1017 cm-2 to 10 · 1017 cm-2.

  2. EPR Spectroscopy and Setup:

    • Home-Built Spectrometer: Used for high-Q measurements (Figures 1, 4). Employed a home-made microwave bridge operating at ≈9.3 GHz.
    • Resonator: Cylindrical dielectric sapphire resonator placed inside a copper cavity. Q-factor was tuned (40,000 to 110,000) by adjusting the depth of the coupling loop.
    • Microwave Power: Kept extremely low (Pmw ≈ 10 pW, or -80 dBm) to avoid saturating the transitions.

  3. Optical Pumping and Excitation Control:

    • Stokes Excitation: Standard 808 nm laser used for general optical pumping, especially at temperatures where the ZPL vanishes (T > 100 K).
    • Resonant ZPL Excitation: A tuneable laser (Sacher Lion 920) was used in a modified Bruker spectrometer (E300) to precisely match the 916.5 nm ZPL at T = 50 K.

  4. Temperature and Orientation Control:

    • Cryogenic Operation: Measurements were performed at various temperatures (10 K, 50 K, 110 K) using a MicrostatHe cold finger cryostat to reduce ohmic losses and prolong spin-lattice relaxation time (T1).
    • Angular Dependence: A commercial benchtop spectrometer (Bruker Magnettech ESR5000) with a motorized precision goniometer was used to vary the polar angle (Ξ) between the external magnetic field (B) and the SiC c-axis.

  5. Superradiance Analysis:

    • Superradiance was identified by comparing the intensity ratio of the central EPR peak (spin-less 28Si/30Si neighbors) to the hyperfine (HF) satellite peaks (one 29Si neighbor), confirming the N2 dependence.
    • Linewidth analysis was performed as a function of pump power to observe the expected collapse (monochromatization) of the emissive transition.

Commercial Applications

Section titled “Commercial Applications”

The development of a SiC-based solid-state maser offers robust, scalable, and potentially room-temperature microwave technology for several high-value sectors.

  • Deep-Space Communications:
    • Application as ultra-low-noise amplifiers (LNA) for receiving extremely weak signals from distant probes and satellites.
  • Precision Navigation and Timing (PNT):
    • Use as highly stable, low-noise oscillators and frequency standards (e.g., atomic clocks) for GPS and inertial navigation systems.
  • Quantum Sensing and Metrology:
    • SiC spin defects are excellent quantum sensors. The maser technology can be adapted to create highly sensitive, coherent microwave sources for magnetic field, temperature, and electric field sensing.
  • High-Frequency RF Technology:
    • Development of compact, continuous-wave microwave emitters and amplifiers operating in the X-band (10 GHz range) for radar and telecommunications.
  • Solid-State Quantum Computing:
    • The SiC platform is compatible with existing semiconductor manufacturing, facilitating the integration of coherent microwave sources necessary for controlling and reading out spin qubits.
  • Industrial Scalability:
    • Leveraging the mature SiC manufacturing infrastructure (used in high-power electronics) for large-scale production of maser components, overcoming the material limitations of diamond or specialized organic crystals.
View Original Abstract

Masers as telecommunication amplifiers have been known for decades, yet their application is strongly limited due to extreme operating conditions requiring vacuum techniques and cryogenic temperatures. Recently, a new generation of masers has been invented based on optically pumped spin states in pentacene and diamond. In this study, we pave the way for masers based on spin S = 3/2 silicon vacancy (V Si ) defects in silicon carbide (SiC) to overcome the microwave generation threshold and discuss the advantages of this highly developed spin hosting material. To achieve population inversion, we optically pump the V Si into their m S = ±1/2 spin sub-states and additionally tune the Zeeman energy splitting by applying an external magnetic field. In this way, the prerequisites for stimulated emission by means of resonant microwaves in the 10 GHz range are fulfilled. On the way to realising a maser, we were able to systematically solve a series of subtasks that improved the underlying relevant physical parameters of the SiC samples. Among others, we investigated the pump efficiency as a function of the optical excitation wavelength and the angle between the magnetic field and the defect symmetry axis in order to boost the population inversion factor, a key figure of merit for the targeted microwave oscillator. Furthermore, we developed a high-Q sapphire microwave resonator ( Q ≈ 10 4 -10 5 ) with which we find superradiant stimulated microwave emission. In summary, SiC with optimized spin defect density and thus spin relaxation rates is well on its way of becoming a suitable maser gain material with wide-ranging applications.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2018 - Superradiant Emission from Colour Centres in Diamond [Crossref]
  2. 2021 - Perspective on Room-Temperature Solid-State Masers [Crossref]
  3. 2005 - EPR Identification of the Triplet Ground State and Photoinduced Population Inversion for a Si-C Divacancy in Silicon Carbide [Crossref]
  4. 2001 - Neutral and Negatively Charged Silicon Vacancies in Neutron Irradiated SiC: a High-Field Electron Paramagnetic Resonance Study [Crossref]
  5. 2008 - Measurement of the Fundamental Thermal Noise Limit in a Cryogenic Sapphire Frequency Standard Using Bimodal Maser Oscillations [Crossref]
  6. 2018 - Continuous-wave Room-Temperature Diamond Maser [Crossref]
  7. 2017 - Room-temperature Cavity Quantum Electrodynamics with Strongly Coupled Dicke States [Crossref]
  8. 2015 - Enhanced Magnetic Purcell Effect in Room-Temperature Masers [Crossref]
  9. 2015 - Spin Coherence and Echo Modulation of the Silicon Vacancy in4H−SiCat Room Temperature [Crossref]
  10. 2015 - Influence of Magnetic Field Alignment and Defect Concentration on Nitrogen-Vacancy Polarization in Diamond [Crossref]

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