Achieving 5% 13C nuclear spin hyperpolarization in high-purity diamond at room temperature and low magnetic field
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-29 |
| Journal | Scientific Reports |
| Authors | Vladimir Vladimirovich Kavtanyuk, Changjae Lee, Keunhong Jeong, Jeong Hyun Shim |
| Institutions | Korea University, Korea Military Academy |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a significant advancement in achieving high 13C nuclear spin hyperpolarization in diamond under practical, non-cryogenic conditions.
- Record Polarization: A 13C nuclear spin polarization of 5% was achieved, corresponding to an enhancement ratio exceeding 7 x 106 compared to thermal polarization.
- Practical Conditions: This high polarization was attained at Room Temperature (RT) and a low magnetic field of 9.4 mT, eliminating the need for conventional cryogenic Dynamic Nuclear Polarization (DNP) setups.
- Material Enabler: The use of high-purity, CVD-grown single-crystal diamond with an exceptionally low substitutional nitrogen (NS) concentration (0.2 ppm) was the primary factor enabling the high efficiency.
- Exceptional Storage Time: The low impurity concentration resulted in a long spin storage time (Tdepol) of 102 minutes at 6 T, making the material highly suitable for transfer and application.
- Optimization Strategy: Efficiency was maximized by aligning the external magnetic field along the [100] crystal axis, which effectively quadrupled the number of nitrogen-vacancy (NV) centers contributing to the polarization transfer.
- Mechanism Confirmation: Comprehensive optimization of microwave (MW) sweep parameters suggests that polarization transfer occurs predominantly via the Integrated Solid Effect (ISE), followed by nuclear spin diffusion to the bulk 13C spins.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Achieved 13C Polarization | 5 | % | Maximum achieved at 9.4 mT |
| Enhancement Ratio | >7 x 106 | Ratio | Relative to thermal polarization |
| Polarization Magnetic Field (Bpol) | 9.4 | mT | Optimal low-field condition |
| NMR Readout Field (BNMR) | 6 | T | Superconducting magnet field |
| Polarization Build-up Time (Tpol) | 10.4 | min | Time to saturation |
| Depolarization Time (Tdepol) | 102 | min | Storage time at 6 T (laser off) |
| Diamond Type | CVD Single Crystal | N/A | [100] surface orientation, 15 mg mass |
| Substitutional N (NS) Concentration | 0.2 | ppm | Primary decoherence source |
| NV Center Concentration | 0.3 | ppm | Polarization source |
| Optimal MW Power (PMW) | 40 | W | Used for 5% polarization at 9.4 mT |
| Laser Wavelength | 532 | nm | Continuous irradiation |
| Laser Power Density | 30 | mW/mm2 | Used for 5% polarization |
| Optimal MW Sweep Width (Î) | 6 | MHz | Minimal width covering ODMR linewidth |
| Optimal MW Sweep Rate (Î) | 15 | MHz/ms | High sweep rate peak (ÎH) |
| Polarization Transfer Mechanism | Integrated Solid Effect (ISE) | N/A | Followed by nuclear spin diffusion |
| Sample Shuttling Time | 1.5 | s | Transfer time from low field to 6 T magnet |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure combines optical pumping, repetitive microwave (MW) sweeping, and rapid sample transfer for high-field NMR readout.
- Material Preparation: A high-purity, CVD-grown single-crystal diamond (DNV-B1) with low N concentration (0.2 ppm NS) and [100] surface orientation was selected to minimize decoherence and maximize NV center alignment.
- Field Alignment: The external magnetic field (B) was aligned along the [100] axis. This orientation ensures that the optically detected magnetic resonance (ODMR) peaks for all four NV axes are identical, effectively quadrupling the number of NV spins contributing to hyperpolarization.
- Polarization Setup: The diamond was positioned in a low-field region (up to 9.4 mT) and subjected to continuous 532 nm laser irradiation (30 mW/mm2).
- MW Optimization: A repetitive, frequency-swept MW irradiation sequence was applied to transfer polarization from the NV electron spins to the 13C nuclear spins via the Integrated Solid Effect (ISE).
- The optimal magnetic field was determined to be 9.4 mT.
- Optimal MW power (PMW) was found to exhibit a quadratic relationship with the magnetic field (B).
- The optimal MW sweep width (Î) was set to 6 MHz, matching the ODMR linewidth, and the optimal sweep rate (Î) was 15 MHz/ms.
- Polarization Readout: After 40 minutes of polarization, the diamond sample was rapidly transferred (shuttled) within 1.5 s to the center of a 6 T superconducting magnet.
- NMR Quantification: The 13C polarization level was quantified by recording the 13C NMR signal and comparing its integral against the signal obtained from a thermally polarized reference diamond at 6 T.
- Storage Measurement: Depolarization time (Tdepol) was measured under both low-field (9.4 mT) and high-field (6 T) conditions, confirming the long lifetime enabled by the low N concentration.
Commercial Applications
Section titled âCommercial ApplicationsâThe achievement of high 13C polarization at RT and low field, coupled with exceptionally long spin lifetimes, opens new avenues for diamond-based quantum and medical technologies.
- Medical Imaging (MRI): Hyperpolarized diamond particles show promise as background-free signal agents for Magnetic Resonance Imaging (MRI), particularly due to the long spin lifetime allowing for signal transport.
- Quantum Sensing and Metrology:
- Development of highly sensitive nuclear spin gyroscopes (e.g., for inertial navigation).
- High-field magnetometry utilizing hyperpolarized nuclear spins.
- Radio-Frequency (RF) Devices: The high negative polarization and long spin lifetime are ideal prerequisites for developing solid-state devices based on Radio-frequency Amplification by Stimulated Emission of Radiation (RASER), enabling high-precision NMR or magnetometers.
- External Polarization Source: Hyperpolarized diamond particles can be used as a source to polarize external nuclear spins (e.g., in liquids or biomolecules) via surface contacts, facilitating enhanced NMR spectroscopy of target analytes.
View Original Abstract
Optically polarizable nitrogen-vacancy (NV) centers in diamond enable hyperpolarization of <sup>13</sup>C nuclear spins at a low magnetic field and room temperature. However, it remains a challenge to achieve a high level of polarization, comparable to that of conventional dynamic nuclear polarization. In this paper, we demonstrate that a <sup>13</sup>C polarization of 5%, equivalent to an enhancement ratio of over [Formula: see text], can be attained at less than 10 mT. We used a high-purity diamond with an initial nitrogen concentration below 1 ppm, which resulted in a storage time exceeding 100 min. Aligning the magnetic field along [100] increased the number of NV spins involved in polarization transfer by a factor of four. For this orientation, a comprehensive optimization of the magnetic field intensity and microwave (MW) sweep parameters has been performed. The optimum MW sweep width suggests that polarization transfer occurs primarily to the bulk <sup>13</sup>C spins through the integrated solid effect, followed by nuclear spin diffusion.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 1970 - Spin Temperature and Nuclear Magnetic Resonance in Solids