Solving mystery with the Meissner state in La3Ni2O7-δ
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2024-11-05 |
| Journal | Superconductivity Fundamental and Applied Research |
| Authors | E. F. Talantsev |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This analysis resolves the long-standing puzzle regarding the absence of the Meissner state observation in the highly compressed nickelate superconductor, La3Ni2O7-δ, despite confirmed zero resistance.
- Meissner State Puzzle Solved: The failure to detect diamagnetism is attributed to an extremely low ground state lower critical field, Bc1(0) = 34 µT, which is comparable in magnitude to the Earth’s magnetic field. Any ambient magnetic field easily drives the material into the mixed state.
- Superconducting Symmetry: Analysis of the self-field critical current density (Jc(sf,T)) confirms that La3Ni2O7-δ exhibits d-wave superconductivity.
- Extreme Type-II Material: The material is characterized by an extremely high Ginzburg-Landau parameter, κ(0) = 1500, classifying it as a high-κ Type-II superconductor.
- Large Penetration Depth: The ground state London penetration depth is very large, λ(0) = 6.0 µm, implying a low bulk density of Cooper pairs.
- Recommended Measurement: To observe the unique magnetic response, the author strongly recommends performing magnetic flux trap effect measurements, a technique recently adapted for high-pressure studies in diamond anvil cells (DACs).
Technical Specifications
Section titled “Technical Specifications”The following fundamental superconducting parameters were deduced for La3Ni2O7-δ single crystals compressed at P = 16.6 GPa, based on the analysis of E(J) and Bc2(T) datasets.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Superconducting Symmetry | d-wave | N/A | Confirmed by Jc(sf,T) fit quality |
| Transition Temperature (Tc) | 25 | K | Fixed for Jc(sf,T) fit |
| Ground State London Penetration Depth (λ(0)) | 6.0 ± 0.05 | µm | Very large; indicates low Cooper pair density |
| Ground State Coherence Length (ξ(0)) | 4.0 | nm | Fixed average value used in fitting |
| Ginzburg-Landau Parameter (κ(0)) | 1500 | N/A | Extremely high-κ Type-II superconductor |
| Ground State Lower Critical Field (Bc1(0)) | 34 | µT | Comparable to Earth’s magnetic field |
| Ground State Energy Gap (Δm(0)) | 4.3 ± 0.3 | meV | Maximum amplitude of the d-wave gap |
| Gap-to-Tc Ratio (2Δm(0)/kBTc) | 4.0 ± 0.3 | N/A | Characteristic of strong coupling |
| Relative Jump in Electronic Specific Heat (ΔC/(γTc)) | 0.8 ± 0.2 | N/A | Deduced from d-wave fit |
| Sample Cross-Sectional Width (2a) | 70 | µm | Assumed from source data [39] |
| Sample Thickness (2b) | 5 | µm | Assumed from source data [39] |
| Upper Critical Field (Bc2(0)) | ~20 | T | Estimated from literature |
Key Methodologies
Section titled “Key Methodologies”The fundamental superconducting parameters were extracted through a rigorous analytical approach applied to existing experimental data (V-I and Bc2(T) curves) from highly compressed La3Ni2O7-δ.
- Data Conversion and Standardization:
- Raw Voltage-Current (V-I) datasets were converted into Electric Field-Current Density (E-J) datasets using assumed sample dimensions (2a = 70 µm, 2b = 5 µm) and potential tab distance (l = 100 µm).
- Critical Current Criterion:
- Due to large current step sizes in the source data, a high electric field criterion of Ec = 3 mV/cm was adopted to define the self-field critical current density, Jc(sf,T). This criterion is 3000 times higher than the conventional 1 µV/cm standard but provided the best balance for fitting the noisy E-J data.
- Coherence Length Determination (ξ(0)):
- Upper critical field (Bc2(T)) data (measured at P = 20.5 GPa and P = 26.6 GPa) was fitted using the approximated Werthamer-Helfand-Hohenberg (WHH) theory (Eq. 4 and 5).
- This fitting yielded ground state coherence lengths, ξ(0), ranging from 3.8 nm to 4.3 nm. An average value of ξ(0) = 4 nm was fixed for subsequent Jc(sf,T) analysis.
- Fundamental Parameter Extraction:
- The Jc(sf,T) dataset (at P = 16.6 GPa) was fitted using the universal equation (Eq. 1), which links Jc to fundamental parameters (λ(T), ξ(0), Δ(T)).
- Fits were performed assuming both s-wave (Eq. 6) and d-wave (Eq. 8, 9) gap symmetries. The d-wave fit provided parameters consistent with an extremely high-κ superconductor.
- Lower Critical Field Calculation:
- The ground state lower critical field, Bc1(0), was calculated using the extracted London penetration depth λ(0) and the Ginzburg-Landau parameter κ(0) via the standard formula (Eq. 10).
Commercial Applications
Section titled “Commercial Applications”The findings regarding the fundamental parameters of La3Ni2O7-δ and the proposed measurement techniques are relevant to several advanced materials science and engineering fields.
- High-Pressure Materials Research:
- The study provides crucial validation for the use of the magnetic flux trap effect methodology to measure magnetic properties in superconductors confined within Diamond Anvil Cells (DACs), especially those with extremely low Bc1 values (like La3Ni2O7-δ and high-pressure hydrides).
- Advanced Superconducting Electronics:
- As an extremely high-κ Type-II superconductor (κ(0) = 1500), La3Ni2O7-δ belongs to the class of materials (like HTS cuprates) potentially suitable for high-field applications, provided the challenge of the low Bc1 can be managed in device design.
- Fundamental Physics of Superconductivity:
- The large London penetration depth (λ(0) = 6.0 µm) places this material alongside organic superconductors, offering a new platform to study the physics of low Cooper pair density systems and their relationship to high-Tc behavior.
- Cryogenic Technology Development:
- The high Tc (up to 80 K reported in related nickelates) makes this class of materials attractive for developing next-generation superconducting wires and tapes operating at liquid nitrogen temperatures, although the current material requires extreme pressure.
View Original Abstract
Recently, zero resistance state in highly compressed La3Ni2O7-δ has been observed. However, all attempts of many research groups to detect the Meissner state in the La3Ni2O7-δ have been failed. To explain this puzzle, an exotic superconducting state (for instance, filamentary superconductivity) in the La3Ni2O7-δ has been supposed. Here, I extracted temperature dependent self-field critical current, Ic(sf,T), dataset from current-voltage curves and performed the Ic(sf,T) analysis. As a result, I found that highly compressed La3Ni2O7-δ to exhibits d-wave superconductivity with the gap-to-transition temperature ratio 2Δ(0)/(kBTc) = =4.0 ± 0.3, a very large ground state London penetration depth, λ(0, P = 16.6 GPa) = 6.0 μm, and a very high Ginzburg-Landau parameter k(0, P = 16.6 GPa) = 1500. This implies that the ground state lower critical field Bc1(0, P = 16.6 GPa) = 34 μT is of the same order as the Earth’s magnetic field. Based on this, to detect the Meissner state in the La3Ni2O7-δ becomes a very challenging task. I can hypothesize that the magnetic flux trap effect recently proposed to eliminate the diamond anvil cell (DAC) background in experiments on magnetic properties of the superconducting hydrides can also apply in studies of magnetic properties in the La3Ni2O7-δ superconductor.