Magnetic flux trapping in hydrogen-rich high-temperature superconductors
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-06-15 |
| Journal | Nature Physics |
| Authors | Vasily S. Minkov, Vadim Ksenofontov, Sergey L. Budâko, E. F. Talantsev, M. I. Eremets |
| Institutions | Ames National Laboratory, Iowa State University |
| Citations | 72 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Novel Measurement Protocol: A non-conventional trapped magnetic flux protocol was successfully implemented in a SQUID magnetometer coupled with a Diamond Anvil Cell (DAC) to characterize high-temperature superconductors (HTS) under extreme pressure.
- Background Signal Elimination: This trapped flux method operates at zero external magnetic field, effectively eliminating the large, confounding background signal generated by the DAC body (gasket, diamonds) that plagues traditional magnetic susceptibility (Meissner) measurements.
- Material Characterization: The technique confirmed bulk superconductivity in hydrogen-rich hydrides: H3S (Tc â 195 K at 155 GPa) and LaH10 (Tc â 200 K at 120 GPa).
- Strong Vortex Pinning: The materials exhibited a suppressed Meissner effect, which was directly correlated with extremely strong pinning of magnetic vortices inside the samples.
- High Critical Current Density (Jc): Analysis of the trapped flux in H3S revealed an exceptionally high critical current density, Jc(0 K) â 7.3 x 1010 A m-2, which is two orders of magnitude greater than that found in iron-based superconductors.
- Versatile Tool: The trapped flux method is highly beneficial for studying multiphase samples or materials with a low superconducting fraction, where electrical transport or standard magnetic measurements are often inconclusive.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Critical Temperature (H3S) | 195 | K | Im-3m phase, at 155 ± 5 GPa |
| Critical Temperature (LaH10) | 200 | K | C2/m phase, at 120 ± 5 GPa |
| Critical Current Density (Jc(0 K), H3S) | 7.3 x 1010 | A m-2 | Extrapolated value, Im-3m phase |
| Depairing Current Density (Jd, H3S) | 4 x 1013 | A m-2 | Theoretical limit |
| Jc(0 K) / Jd Ratio (H3S) | 10-3 to 10-2 | Dimensionless | Indicates strong pinning |
| Coherence Length (Ο, H3S) | 1.85 | nm | At 10 K |
| London Penetration Depth (λL, H3S) | 37 | nm | At 10 K |
| Ginzburg-Landau Parameter (Îș, H3S) | 20 | Dimensionless | At 10 K |
| H3S Sample Pressure | 155 ± 5 | GPa | Measurement pressure |
| LaH10 Sample Pressure | 120 ± 5 | GPa | Measurement pressure (C2/m phase) |
| Magnetic Moment Decay (H3S) | 2.8 | % | Within 53.6 hours at 165 K (Vortex creep rate) |
| Magnetization Field Range (”0HM) | 0.5 to 6 | T | Applied field for flux trapping |
| Laser Wavelength (Synthesis) | 1.064 | ”m | Nd:YAG pulse laser |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Preparation and Pressurization: Superconducting Im-3m-H3S and Fm-3m-LaH10 phases were synthesized from sandwiched reactants (S + NH3BH3 or LaH3 + NH3BH3) loaded into a miniature Diamond Anvil Cell (DAC) designed for SQUID magnetometers.
- High-Pressure Synthesis: Samples were pressurized to approximately 167 GPa (H3S) and then heated using a pulsed Nd:YAG laser (1.064 ”m wavelength) by traversing the laser spot across the diamond culets.
- SQUID Measurement Setup: Magnetization measurements (m(T)) were performed using a commercial S700X SQUID magnetometer. The miniature DAC was mounted on a specialized 140-mm Kapton polyimide straw to minimize magnetic end effects.
- Trapped Flux Protocol (ZFC/FC): The magnetic moment (mtrap) was measured at zero external magnetic field (H = 0) after a magnetization step.
- ZFC (Zero-Field-Cooled) Protocol: Sample cooled below Tc at H = 0, then HM applied, held, and removed.
- FC (Field-Cooled) Protocol: Sample cooled below Tc at HM, then HM removed.
- Background Subtraction: The trapped flux signal (mtrap) was determined by subtracting the residual magnetic moment (arising from the DAC body) from the measured moment. This residual background was measured separately after the sample was decomposed (non-superconducting state) or extrapolated from the normal state (T > Tc).
- Critical Current Density Calculation: The critical current density (Jc) was derived from the trapped magnetic moment (mtrap) using the critical-state Bean model, assuming a thin disc geometry.
- Vortex Pinning Analysis: The temperature dependence of Jc was analyzed using models for ÎŽT-type and ÎŽl-type pinning to determine the dominant pinning mechanism (found to be ÎŽT-type pinning in H3S).
Commercial Applications
Section titled âCommercial Applicationsâ- Fundamental HTS Research: The trapped flux protocol offers a superior method for characterizing the magnetic properties (Hc1, λL, Jc, pinning strength) of novel high-pressure superconductors, overcoming the limitations of DAC background noise.
- Superconducting Wire Development: The demonstration of extremely high critical current density (Jc â 7.3 x 1010 A m-2) in H3S provides crucial data for theoretical modeling and material selection for future high-power superconducting cables and magnets.
- High-Field Magnet Engineering: The observed strong vortex pinning and slow magnetic creep rate in H3S inform strategies for engineering robust flux pinning centers in conventional Type-II superconductors (e.g., Nb3Sn, MgB2) to improve performance stability in high-field environments (e.g., MRI, fusion energy).
- Quality Assurance for SC Materials: The methodology can be adapted for non-destructive quality control and screening of new superconducting films or bulk materials, especially those that are multiphase or contain impurities, where standard electrical testing is impractical.
- Cryogenic Device Design: The precise determination of fundamental parameters like the Ginzburg-Landau parameter (Îș â 20) and coherence length (Ο â 1.85 nm) is essential for designing microscale superconducting devices and quantum circuits.
View Original Abstract
Abstract Recent discoveries of superconductivity in various hydrides at high pressures have shown that a critical temperature of superconductivity can reach near-room-temperature values. However, experimental studies are limited by high-pressure conditions, and electrical transport measurements have been the primary technique for detecting superconductivity in hydrides. Here we implement a non-conventional protocol for the magnetic measurements of superconductors in a SQUID magnetometer and probe the trapped magnetic flux in two near-room-temperature superconductors H 3 S and LaH 10 at high pressures. Contrary to traditional magnetic susceptibility measurements, the magnetic response from the trapped flux is almost unaffected by the background signal of the diamond anvil cell due to the absence of external magnetic fields. The behaviour of the trapped flux generated under zero-field-cooled and field-cooled conditions proves the existence of superconductivity in these materials. We reveal that the absence of a pronounced Meissner effect is associated with the very strong pinning of vortices inside the samples. This approach can also be a tool for studying multiphase samples or samples that have a low superconducting fraction at ambient pressure.