Strong Correlation Between Superconductivity and Ferromagnetism in an Fe-Chalcogenide Superconductor
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-08-20 |
| Journal | Nano Letters |
| Authors | Nathan J. McLaughlin, Hailong Wang, Mengqi Huang, Eric Lee-Wong, LunâHui Hu |
| Institutions | University of California, San Diego, Westlake University |
| Citations | 45 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Superconductivity Induced Ferromagnetism via NV Centers
Section titled âTechnical Documentation & Analysis: Superconductivity Induced Ferromagnetism via NV CentersâThis document analyzes the research paper âObservation of Superconductivity Induced Ferromagnetism in an Fe-Chalcogenide Superconductorâ to highlight the critical role of high-quality diamond substrates and to position 6CCVDâs MPCVD diamond capabilities as the ideal solution for replicating and advancing this quantum sensing research.
Executive Summary
Section titled âExecutive Summaryâ- Core Achievement: Direct nanoscale quantum sensing and imaging of magnetic flux generated by an Fe-chalcogenide superconductor (FeTe${x}$Se${1-x}$) flake, providing clear evidence of superconductivity-induced ferromagnetism (BFM).
- Methodology: Exploitation of Nitrogen Vacancy (NV) centers implanted in a single crystal diamond (SCD) substrate, utilizing NV Rabi oscillation and Optical Detection of Magnetic Resonance (ODMR) techniques.
- Material Requirements: The experiment relies critically on high-purity, low-strain SCD substrates with precisely controlled, shallow NV center implantation (~5 nm depth, ~1500/”mÂČ density).
- Key Findings: Confirmed coexistence of superconductivity (T$_{c}$ = 14.5 K) and ferromagnetism, demonstrating time-reversal symmetry breaking and unconventional pairing mechanisms in the topological superconductor.
- Application Potential: The demonstrated coupling between NV centers and superconducting materials opens new avenues for developing hybrid quantum architectures and solid-state quantum information technologies.
- 6CCVD Value Proposition: 6CCVD provides the necessary Optical Grade SCD substrates, custom metalization (Au striplines), and ultra-smooth polishing (Ra < 1 nm) required for high-fidelity NV quantum sensing experiments.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table extracts key quantifiable parameters and material specifications relevant to the experimental platform and results.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| FTS Flake Thickness | 140 | nm | Exfoliated FeTe${0.7}$Se${0.3}$ sample |
| Superconducting Transition Temperature (T$_{c}$) | 14.5 | K | Characteristic phase transition of FTS flake |
| NV Center Implantation Depth | ~5 | nm | Below the surface of the diamond substrate |
| NV Center Density | ~1500 | /”mÂČ | Used for wide-field ensemble imaging |
| Maximum Supercurrent Density (J$_{su}$) | ~1 | mA/”mÂČ | Reconstructed spatial distribution at T < T$_{c}$ |
| External Magnetic Field (B$_{ext}$) | ~60 | G | Applied for ODMR measurements |
| Reconstructed Magnetization (4$\pi$M) | ~4 | G | Average value for T < T$_{c}$ |
| Maximum Theoretical Magnetization (4$\pi$M$_{max}$) | 15 | Oe | Estimated upper limit based on Fe polarization |
| Initialization Laser Pulse Duration | 1 | ”s | Green laser pulse for NV initialization |
| Microwave Pulse Delay | 700 | ns | Delay after initialization to minimize laser heating |
Key Methodologies
Section titled âKey MethodologiesâThe experiment successfully combined advanced material preparation with nanoscale quantum sensing techniques:
- Substrate Preparation: A single crystal diamond (SCD) substrate was prepared with a shallow layer of Nitrogen Vacancy (NV) centers implanted approximately 5 nm below the surface, achieving a density suitable for wide-field imaging (~1500/”mÂČ).
- Device Fabrication: An on-chip Au stripline was fabricated directly onto the diamond surface to generate the necessary microwave magnetic fields (B$_{MW}$) for controlling the NV quantum spin state.
- Sample Transfer: A thin, exfoliated FeTe${0.7}$Se${0.3}$ (FTS) flake (140 nm thick) was transferred onto the diamond membrane, positioned ~4 ”m from the Au stripline.
- Supercurrent Imaging (Rabi Oscillation): NV wide-field microscopy was used to measure the Rabi oscillation frequency (f${Rabi}$). Changes in f${Rabi}$ across the FTS flake, caused by the Meissner screening effect (B${su}$), allowed for the spatial reconstruction of circular AC supercurrents (J${su}$).
- Ferromagnetism Detection (Pulsed ODMR): Pulsed NV ODMR measurements were performed under an external, tilted DC magnetic field (B${ext}$ ~ 60 G). This technique allowed for the separation and extraction of the stray field components generated by supercurrents (B${su}$) and the superconductivity-induced ferromagnetism (B$_{FM}$).
- Quantitative Analysis: Machine learning analysis was applied to the spatial distribution data to reconstruct 2D maps of the London penetration depth ($\lambda$) and the spatially dependent magnetization (4$\pi$M).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research demonstrates the critical need for ultra-high-quality diamond materials for hybrid quantum architectures. 6CCVD is uniquely positioned to supply the necessary materials and customization services to replicate and scale this work.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, the following 6CCVD materials are required:
- Optical Grade Single Crystal Diamond (SCD): Essential for NV quantum sensing. Our SCD features ultra-low nitrogen concentration (N < 1 ppb) and minimal strain, maximizing the NV center coherence time (T$_{2}$) required for high-fidelity magnetic field detection.
- Custom Substrates for Implantation: We provide SCD substrates optimized for subsequent ion implantation, ensuring precise control over the depth and density of the resulting shallow NV layer (~5 nm depth used in this study).
Customization Potential
Section titled âCustomization PotentialâThe complexity of the experimental platformâinvolving material transfer, on-chip microwave control, and high-resolution sensingâdirectly aligns with 6CCVDâs advanced customization capabilities:
| Research Requirement | 6CCVD Customization Service | Technical Benefit to Client |
|---|---|---|
| On-Chip Microwave Control | In-House Metalization (Au, Ti, Pt, Pd, Cu) | We offer custom deposition of the Au striplines directly onto the diamond surface, ensuring optimal microwave field delivery (B$_{MW}$) and electrical contact for NV spin control. |
| Large-Area Hybrid Architectures | Custom Dimensions (Plates/Wafers up to 125 mm) | While the FTS flake was small (~11 ”m), 6CCVD can provide large-format SCD substrates, enabling the integration of multiple FTS devices or complex quantum circuits on a single platform. |
| Intimate Material Coupling | Ultra-Smooth Polishing (Ra < 1 nm for SCD) | Our superior polishing ensures an atomically flat surface, critical for the reliable transfer and intimate coupling of 2D materials (like FTS) to the NV layer, maximizing the magnetic coupling efficiency. |
| Specific Thickness Needs | SCD Thickness Control (0.1 ”m to 500 ”m) | We supply diamond membranes and substrates tailored to specific experimental needs, whether for thin membranes used in wide-field imaging or thicker substrates (up to 10 mm) for robust thermal management. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in MPCVD growth and material science for quantum applications. We can assist researchers in optimizing material selection for similar hybrid quantum architecture projects, including:
- Selecting the optimal diamond orientation ([100] vs. [111]) for specific NV spin alignment requirements.
- Consulting on post-processing techniques (e.g., surface termination, annealing) to enhance NV center stability and performance.
- Providing custom PCD or BDD materials for applications requiring high thermal conductivity or electrochemical sensing beyond quantum magnetometry.
Call to Action: For custom specifications or material consultation regarding NV-based quantum sensing platforms or hybrid quantum architectures, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The interplay among topology, superconductivity, and magnetism promises to bring a plethora of exotic and unintuitive behaviors in emergent quantum materials. The family of Fe-chalcogenide superconductors FeTe<sub><i>x</i></sub>Se<sub>1-<i>x</i></sub> are directly relevant in this context due to their intrinsic topological band structure, high-temperature superconductivity, and unconventional pairing symmetry. Despite enormous promise and expectation, the local magnetic properties of FeTe<sub><i>x</i></sub>Se<sub>1-<i>x</i></sub> remain largely unexplored, which prevents a comprehensive understanding of their underlying material properties. Exploiting nitrogen vacancy (NV) centers in diamond, here we report nanoscale quantum sensing and imaging of magnetic flux generated by exfoliated FeTe<sub><i>x</i></sub>Se<sub>1-<i>x</i></sub> flakes, demonstrating strong correlation between superconductivity and ferromagnetism in FeTe<sub><i>x</i></sub>Se<sub>1-<i>x</i></sub>. The coexistence of superconductivity and ferromagnetism in an established topological superconductor opens up new opportunities for exploring exotic spin and charge transport phenomena in quantum materials. The demonstrated coupling between NV centers and FeTe<sub><i>x</i></sub>Se<sub>1-<i>x</i></sub> may also find applications in developing hybrid architectures for next-generation, solid-state-based quantum information technologies.