All-optical and microwave-free detection of Meissner screening using nitrogen-vacancy centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-13 |
| Journal | Journal of Applied Physics |
| Authors | D. Paone, D. Pinto, G. KIM, Feng L, M. J. Kim |
| Institutions | University of Stuttgart, Ăcole Polytechnique FĂ©dĂ©rale de Lausanne |
| Citations | 15 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Novel Sensing Technique: Developed an all-optical, microwave-free method utilizing Nitrogen-Vacancy (NV) centers in diamond for non-invasive, nanoscale magnetic field sensing.
- Thermal Artifact Mitigation: By relying solely on the magnetic field dependence of the NV photoluminescence (PL) yield, the technique avoids the local heating effects typically associated with resonant microwave excitations (ODMR).
- Meissner Screening Detection: Successfully detected and spatially mapped the Meissner screening effect in a 20 nm thick La2-xSrxCuO4 (LSCO) superconducting thin film at 4.2 K.
- Quantitative Analysis: The measured spatial variation of the PL drop was converted to a magnetic field profile and fitted using Brandtâs analytical model for thin film superconductors.
- Critical Current Density: The analysis yielded a critical current density (jc) of 1.4 · 108 A/cm2, which aligns well with values obtained from complementary SQUID measurements and literature for LSCO nanowires.
- High Resolution Potential: The NV center acts as a nanoscale magnetic field sensor, opening avenues for future extension using optical pump-probe spectroscopy to study fast dynamical phenomena.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Superconductor Material | La2-xSrxCuO4 (LSCO) | N/A | Epitaxially grown thin film |
| LSCO Thickness (d) | 20 | nm | Sample geometry |
| LSCO Critical Temperature (Tc) | 34 | K | Measured via mutual inductance |
| Operating Temperature | 4.2 | K | UHV-He bath cryostat base temperature |
| Applied Magnetic Field (Bz) | 4.2 | mT | External field for Meissner detection |
| Extracted Critical Current Density (jc) | 1.4 · 108 | A/cm2 | Derived from Brandtâs model fit |
| NV-SC Separation Distance | â 1 | ”m | Estimated distance (Section 6 of SI) |
| NV Excitation Wavelength | 512 | nm | Green pulsed laser |
| NV Emission Wavelength | 637 | nm | Red photon emission peak (range 637-750 nm) |
| Laser Power (Confocal Scan) | 0.688 | ”W | Low power used to avoid changing SC properties |
| Unscreened PL Drop (Outside SC) | â 5.1 | % | Corresponds to â 4 mT field strength |
| Screened PL Drop (Inside SC) | â 2.5 | % | Corresponds to 1.8 mT to 2.1 mT field strength |
| NV Gyromagnetic Ratio (Îł) | 28 | MHz/mT | Used for ODMR calibration |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Integration: An NV-implanted diamond membrane was physically positioned and attached (glued) across the edge of the 20 nm thick LSCO superconducting thin film.
- Cryogenic Setup: Measurements were conducted using a confocal microscope integrated into an Ultra-High Vacuum (UHV) Helium bath cryostat operating at 4.2 K and equipped with a 3D vector magnet.
- Optical Excitation: NV centers were excited using a 512 nm pulsed green laser, and the resulting red photoluminescence (PL) was collected confocally.
- Calibration (ODMR): Optically Detected Magnetic Resonance (ODMR) spectroscopy was performed separately using microwave excitation to establish the quantitative relationship between the applied magnetic field (Bz) and the resulting NV PL yield drop (calibration curve).
- Microwave-Free Sensing: The primary sensing was performed by raster scanning the laser focal spot along the y-direction across the diamond membrane while recording the PL count rate drop under an applied external field (4.2 mT).
- Data Normalization: All PL measurements were normalized against corresponding zero-field (B = 0) confocal scans to isolate the relative magnetic field changes caused by the Meissner screening.
- Modeling and Extraction: The measured spatial magnetic field profile was fitted using Brandtâs analytical model (Equation 1) for a superconducting thin film to accurately extract the critical sheet current (Jc) and subsequently the critical current density (jc).
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Sensing and Metrology: Utilizing the NV centerâs high sensitivity (1 ”T/âHz for single NV, 1 pT/âHz for ensembles) for non-invasive magnetic field mapping in environments where microwave heating is detrimental (e.g., cryogenic quantum circuits).
- Superconducting Device Characterization: Nanoscale quality control and failure analysis for high-Tc superconducting thin films, nanowires, and SQUIDs, allowing precise mapping of current pathways and flux penetration.
- Fundamental Condensed Matter Physics: Enabling the study of non-equilibrium collective phenomena, such as vortex formation and motion in Type II superconductors, by providing high spatial resolution (nanoscale) and potential for fast temporal resolution (via pump-probe extension).
- Nanomagnetism and Spintronics: Characterization of magnetic properties (e.g., spin waves, ferromagnetism) in 2D materials and complex magnetic heterostructures without thermal interference.
- Cryogenic Electronics R&D: Providing a sensitive, non-contact tool for profiling magnetic fields generated by novel cryogenic electronic components and quantum bits (qubits).
View Original Abstract
Microscopic studies on thin film superconductors play an important role for probing non-equilibrium phase transitions and revealing dynamics at the nanoscale. However, magnetic sensors with nanometer scale spatial and picosecond temporal resolution are essential for exploring these. Here, we present an all-optical, microwave-free method that utilizes the negatively charged nitrogen-vacancy (NV) center in diamond as a non-invasive quantum sensor and enables the spatial detection of the Meissner state in a superconducting thin film. We place an NV implanted diamond membrane on a 20nm thick superconducting La2âxSrxCuO4 (LSCO) thin film with Tc of 34K. The strong B-field dependence of the NV photoluminescence allows us to investigate the Meissner screening in LSCO under an externally applied magnetic field of 4.2mT in a non-resonant manner. The magnetic field profile along the LSCO thin film can be reproduced using Brandtâs analytical model, revealing a critical current density jc of 1.4Ă108A/cm2. Our work can be potentially extended further with a combination of optical pump probe spectroscopy for the local detection of time-resolved dynamical phenomena in nanomagnetic materials.