Coupled charge and spin dynamics in high-density ensembles of nitrogen-vacancy centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-07-02 |
| Journal | Physical review. B./Physical review. B |
| Authors | Rakshyakar Giri, Federico Gorrini, C. Dorigoni, Claudia E. Avalos, M. Cazzanelli |
| Institutions | Center for Neuroscience and Cognitive Systems, Italian Institute of Technology |
| Citations | 46 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Coupled Charge and Spin Dynamics in High-Density NV Ensembles
Section titled âTechnical Documentation & Analysis: Coupled Charge and Spin Dynamics in High-Density NV EnsemblesâThis document analyzes the research paper âCoupled charge and spin dynamics in high-density ensembles of nitrogen-vacancy centers in diamondâ (Giri et al., 2017) to provide technical specifications and demonstrate how 6CCVDâs advanced MPCVD diamond materials and customization capabilities can accelerate and improve similar quantum sensing research.
Executive Summary
Section titled âExecutive Summaryâ- Core Finding: The study reveals a critical interplay between charge dynamics (NV- $\leftrightarrow$ NV$^0$ recharging) and spin dynamics ($T_1$ relaxation) in high-density NV ensembles (10 ppm NV-).
- High-Density Challenge: In high-density samples (X1), charge dynamics dominate the spin depolarization profile, characterized by a sharp luminescence rise with a fast recharging time ($T_r$) of $\approx 100$ ”s, even at very low excitation power (10 ”W).
- Material Limitation: The use of electron-irradiated and annealed HPHT diamond (Sample X1) resulted in high concentrations of unwanted defects (e.g., 100 ppm interstitial nitrogen), complicating the interpretation of charge conversion mechanisms.
- Spin Relaxation: The longitudinal spin relaxation ($T_1$) component, critical for $T_1$-based sensing schemes, was found to be strongly dependent on external magnetic field (B), confirming NV-NV cross-relaxation as the dominant mechanism in the high-density regime.
- 6CCVD Value Proposition: 6CCVD specializes in MPCVD Single Crystal Diamond (SCD) that allows for precise, in-situ control of nitrogen incorporation, enabling the creation of highly uniform NV ensembles with significantly reduced background defects compared to post-processed HPHT substrates.
- Research Impact: Controlling charge dynamics is vital for optimizing NV ensembles for precession magnetometry, sensing applications, and nuclear hyperpolarization schemes.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results and material characterization described in the paper:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Density (High, X1) | $\approx 10$ | ppm | Electron irradiated Type Ib HPHT |
| NV Density (Low, Y1) | $\approx 10$ | ppb | Commercial Type Ib HPHT |
| Substitutional Nitrogen (N$^0$) | > 200 | ppm | Estimated via 1135 cm-1 IR feature |
| Interstitial Nitrogen (N$_{\text{int}}$) | $\approx 100$ | ppm | Present only in high-density sample (X1) |
| Excitation Wavelength | 532 | nm | Green laser source |
| PL Detection Range | 620 - 750 | nm | Filtered luminescence range |
| Excitation Power Range | 10 ”W - 5.0 mW | Power | Used for power dependence studies |
| Initialization Pulse Duration | 500 | ”s | Spin polarization preparation |
| Probe Pulse Duration | 1 | ”s | Spin state readout |
| Reset Time | 100 | ”s | Time to reach charge equilibrium |
| Recharging Time (T$_r$, X1) | $\approx 100$ | ”s | Characteristic time scale for sharp PL rise |
| Spin Relaxation Time (T$_1$, Y1) | Order of | ms | Low NV density regime |
| Zero Field Splitting (D) | 2.87 | GHz | NV ground state (ms=0 to ms=±1) |
| Magnetic Field Range (B) | 0 - 100 | Gauss | External field applied along (100) or (111) |
| Experiment Temperature | Room | °C | All measurements performed at 300 K |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized a combination of material preparation techniques and advanced optical pulse sequences to isolate and measure charge and spin dynamics:
- Material Preparation: Two Type Ib HPHT single crystal diamonds were used. The high-density sample (X1) was created by electron irradiation followed by high-temperature annealing (>800 °C) to generate high concentrations of NV centers.
- Defect Characterization: Standard IR absorption spectroscopy was used to quantify substitutional nitrogen (N$^0$). UV-Vis absorption at 637 nm was used to estimate NV- concentration.
- Optical Setup: A custom confocal microscope was employed, utilizing a 0.65 Numerical Aperture (NA) objective to focus the 532 nm excitation laser to a $\approx 10$ ”m spot.
- PL Detection: Photoluminescence (PL) was collected in the 620-750 nm range and detected using a Single Photon Counting Module (SPCM).
- Pulse Sequence (T$_1$ Measurement): A programmable TTL pulse generator controlled the sequence:
- Initialization: 500 ”s laser pulse (532 nm) to polarize NV centers into the ms=0 state.
- Dark Time ($\tau$): Variable delay time during which relaxation occurs.
- Probe: 1 ”s laser pulse to read out the spin state via PL.
- Reset: 100 ”s pulse to allow the system to reach charge equilibrium.
- Magnetic Control: A 3-axis Helmholtz coil system was used to apply static external magnetic fields (B) up to 100 Gauss, oriented along the (100) and (111) crystallographic directions.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the critical challenge of managing unwanted defects (like interstitial nitrogen and deep level traps) introduced during post-growth processing (irradiation/annealing) of HPHT diamond. 6CCVDâs MPCVD technology offers superior control over defect incorporation, enabling researchers to isolate and study fundamental charge and spin dynamics with unprecedented material purity.
Applicable Materials and Customization Potential
Section titled âApplicable Materials and Customization Potentialâ| Research Requirement | 6CCVD Solution & Capability | Technical Advantage for Quantum Sensing |
|---|---|---|
| High Purity, Controlled NV Density | Optical Grade Single Crystal Diamond (SCD). Nitrogen concentration (N) tailored in-situ during MPCVD growth from ppb to ppm levels. | Eliminates the need for high-fluence electron irradiation and annealing, drastically reducing deep level traps (N$^+$, divacancies) that complicate charge dynamics ($T_r$). |
| Large Area Substrates | SCD plates/wafers up to 125 mm in diameter. Thicknesses from 0.1 ”m to 500 ”m. | Provides scalable platforms for developing large-scale ensemble magnetometers and integrating complex micro-fabrication for sensing arrays. |
| Specific Crystallographic Orientation | Custom SCD growth on (100), (111), or (110) substrates. | Allows precise alignment of the NV symmetry axis relative to the magnetic field, optimizing cross-relaxation studies and maximizing sensing contrast. |
| Integrated Device Fabrication | Internal metalization services: Au, Pt, Pd, Ti, W, Cu. | Enables direct integration of on-chip microwave transmission lines or electrodes for advanced optically detected magnetic resonance (ODMR) and electric field sensing. |
| Surface Quality for Near-Surface NV | Ultra-smooth polishing: Ra < 1 nm (SCD). | Essential for minimizing surface-related charge noise and ensuring stable NV- charge states, particularly for near-surface NV centers used in nanoscale sensing. |
| Boron Doping for Conductivity | Boron-Doped Diamond (BDD) films (SCD or PCD). | If the research requires controlled charge injection or conductivity to manage charge state conversion, 6CCVD offers BDD films with tunable doping levels. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists and engineers can assist researchers in designing custom diamond substrates specifically optimized for NV Ensemble Magnetometry and T$_1$ Sensing projects. We provide consultation on:
- Optimal nitrogen concentration and incorporation methods to achieve desired NV- density while minimizing $T_r$ interference.
- Selection of appropriate crystallographic orientation and surface termination.
- Integration of custom metalization layers for microwave delivery.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We studied the spin depolarization of ensembles of nitrogen-vacancy (NV) centers in nitrogen-rich single crystal diamonds. We found a strong dependence of the evolution of the polarized state in the dark on the concentration of NV centers. At low excitation power, we observed a simple exponential decay profile in the low-density regime and a paradoxical inverted exponential profile in the high-density regime. At higher excitation power, we observed complex behavior, with an initial sharp rise in luminescence signal after the preparation pulse followed by a slower exponential decay. Magnetic field and excitation laser power-dependent measurements suggest that the rapid initial increase of the luminescence signal is related to recharging of the nitrogen-vacancy centers (from neutral to negatively charged) in the dark. The slow relaxing component corresponds to the longitudinal spin relaxation of the NV ensemble. The shape of the decay profile reflects the interplay between two mechanisms: the NV charge state conversion in the dark and the longitudinal spin relaxation. These mechanisms, in turn, are influenced by ionization, recharging and polarization dynamics during excitation. Interestingly, we found that charge dynamics are dominant in NV-dense samples even at very feeble excitation power. These observations may be important for the use of ensembles of NV centers in precession magnetometry and sensing applications.