Nanoscale Detection of Magnon Excitations with Variable Wavevectors Through a Quantum Spin Sensor
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-04-16 |
| Journal | Nano Letters |
| Authors | Eric Lee-Wong, Ruolan Xue, Feiyang Ye, Andreas Kreisel, Toeno van der Sar |
| Institutions | Leipzig University, Harvard University |
| Citations | 80 |
| Analysis | Full AI Review Included |
Nanoscale Detection of Magnon Excitations via Quantum Spin Sensor
Section titled âNanoscale Detection of Magnon Excitations via Quantum Spin SensorâExecutive Summary
Section titled âExecutive SummaryâThis research details the development and application of a quantum sensing platform utilizing Nitrogen-Vacancy (NV) single-spin centers to probe nanoscale spin dynamics in magnetic insulator thin films.
- Core Achievement: Demonstrated optical detection of magnons (spin waves) in Yttrium Iron Garnet (YIG) thin films across a broad range of wavevectors.
- Wavevector Range: The platform successfully accessed magnons with wavevectors up to ~5.1 x 107 m-1, exceeding the limits of conventional Ferromagnetic Resonance (FMR) and approaching the limits of Brillouin Light Scattering (BLS).
- Sensing Mechanism: Magnon excitations are detected indirectly via multi-magnon scattering processes, which redistribute magnon density to the NV Electron Spin Resonance (ESR) frequencies, accelerating NV spin relaxation (T1) and causing a measurable decrease in photoluminescence (PL).
- Nanoscale Sensitivity: The NV-to-sample distance, typically maintained around 100 nm, ensures nanoscale spatial resolution, enabling the study of exchange magnons.
- Versatility Demonstrated: The technique was applied to YIG films of varying thicknesses (100 nm to 3 ”m) and geometries (microdisks), allowing detailed extraction of the magnon band structure and discrete spin wave modes.
- Technological Impact: The results highlight significant opportunities for NV single-spin sensors in spintronics and pave the way for developing NV-magnon-based hybrid quantum architectures.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Detected Wavevector (kmax) | 5.1 x 107 | m-1 | Achieved in 3 ”m YIG film via parametric excitation. |
| NV-to-Sample Distance (d) | ~100 | nm | Typical distance determining nanoscale spatial sensitivity. |
| YIG Thin Film Thickness Range | 100 nm to 3 | ”m | Range used to modify magnon band structure. |
| Au Stripline Thickness | 600 | nm | Used for microwave control and excitation. |
| Local Microwave Field (Bmw) | 1.8 | Oe | Estimated field applied at the NV site. |
| NV Coherence Time (T2) | 1.3 | ”s | Used for calculating ultimate frequency resolution. |
| Calculated Frequency Resolution (Îf) | 0.06 | MHz | Ultimate resolution based on Heisenberg uncertainty principle. |
| Calculated Wavevector Resolution (Îk) | 2000 | m-1 | Resolution corresponding to Îf at k = 107 m-1. |
| YIG Microdisk Radius (R) | 5 | ”m | Used for studying discrete magnetostatic spin wave modes. |
| NV ESR Frequency (f+) | 2.87 + ÎłBext | GHz | Ground state transition frequency. |
Key Methodologies
Section titled âKey MethodologiesâThe experimental platform integrates quantum sensing with spintronic materials using a hybrid device structure and optical detection techniques:
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Device Assembly:
- A patterned diamond nanobeam containing individually addressable NV centers was fabricated.
- The nanobeam was transferred onto YIG (Y3Fe5O12) thin films grown on a Gd3Ga5O12 (GGG) substrate.
- An Au stripline (600 nm thick, 6 ”m wide) was fabricated on the YIG film for microwave delivery.
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Magnetic Field Configuration:
- An external magnetic field (Bext) was applied along the NV axis, oriented 61° relative to the normal of the YIG film plane.
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Magnon Excitation:
- Magnons were generated primarily through nonlinear parametric excitation (parallel pumping).
- A microwave field (Bmw) with frequency fmw was applied parallel to the out-of-plane magnetization component. This process generates high-wavevector exchange magnons at the half-frequency, fmw/2.
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Detection via ODMR (Optically Detected Magnetic Resonance):
- The NV center was continuously excited using a green laser.
- The resulting spin-dependent photoluminescence (PL) intensity was monitored as a function of the microwave frequency (fmw) and external magnetic field (Bext).
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Coupling Mechanism (Four-Magnon Scattering):
- Excited magnons (magnon #1) scatter with thermal magnons (magnon #2) via exchange interaction.
- This scattering generates two new incoherent magnons (magnons #3 and #4), redistributing the magnon population.
- The continuous circulation of these multi-magnon processes enhances the magnon density specifically at the NV ESR frequencies (f±).
- This enhanced magnetic fluctuation accelerates the NV spin relaxation (T1), leading to a measurable decrease (dip) in the normalized PL intensity.
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Wavevector Access and Tuning:
- To access different wavevector regimes, the YIG film thickness was varied (100 nm for thin film modes, 3 ”m for thickness modes).
- YIG films were also patterned into microdisks (5 ”m radius) to study discrete magnetostatic spin wave modes (where k = NÏ/R).
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated NV-magnon coupling and high-resolution wavevector detection capability are critical enablers for next-generation technologies in spintronics and quantum computing.
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Quantum Information Technologies:
- Hybrid Quantum Architectures: Building blocks for NV-magnon hybrid systems, enabling long-range spin-entanglement and spin-wave-mediated control of quantum states.
- Quantum Memory/Transduction: Magnons in YIG act as excellent mediators for transferring quantum information over distances due to their long coherence length.
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Advanced Spintronics and Magnonics:
- Energy-Efficient Devices: Characterization and optimization of magnetic insulators (like YIG) for designing devices that rely on spin currents, such as spin-torque oscillators and spin-superfluidity components.
- Nanoscale Device Prototyping: High-resolution mapping of spin wave dynamics in patterned magnetic microstructures (e.g., microdisks, waveguides) essential for magnonic circuits.
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High-Resolution Materials Characterization:
- Fundamental Physics Research: Revealing microscopic magnon-magnon interactions, thermalization processes, and Bose-Einstein condensation phenomena in magnetic systems.
- Quality Control: Non-destructive, local probing of magnetic excitations in thin films, providing feedback for material synthesis and growth processes.
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Quantum Sensing and Metrology:
- Broadband Magnetometry: Utilizing NV centers to detect magnetic fluctuations across a broad frequency and wavevector spectrum, surpassing the limitations of traditional optical and electrical detection methods.
View Original Abstract
We report the optical detection of magnons with a broad range of wavevectors in magnetic insulator Y<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> thin films by proximate nitrogen-vacancy (NV) single-spin sensors. Through multimagnon scattering processes, the excited magnons generate fluctuating magnetic fields at the NV electron spin resonance frequencies, which accelerate the relaxation of NV spins. By measuring the variation of the emitted spin-dependent photoluminescence of the NV centers, magnons with variable wavevectors up to âŒ5 Ă 10<sup>7</sup> m<sup>-1</sup> can be optically accessed, providing an alternative perspective to reveal the underlying spin behaviors in magnetic systems. Our results highlight the significant opportunities offered by NV single-spin quantum sensors in exploring nanoscale spin dynamics of emergent spintronic materials.