| Metadata | Details |
|---|
| Publication Date | 2023-02-02 |
| Journal | NPG Asia Materials |
| Authors | Zi-Yu Cao, Harim Jang, Seokmin Choi, Jihyun Kim, SuâYoung Kim |
| Institutions | Sungkyunkwan University, Center for High Pressure Science and Technology Advanced Research |
| Citations | 10 |
| Analysis | Full AI Review Included |
- Methodological Breakthrough: Successfully implemented Point-Contact Spectroscopy (PCS) within a Diamond Anvil Cell (DAC) up to 48.6 GPa, providing the first energy-resolved spectroscopic evidence of superconductivity (SC) in elemental Yttrium (Y) under extreme pressure.
- Strong Coupling Confirmed: Yttrium is identified as a strongly coupled BCS superconductor, evidenced by a large SC gap-to-Tc ratio (2ÎL/kBTc) of 8.2, significantly exceeding the weak-coupling BCS limit of 3.53.
- Two-Gap Superconductivity: Analysis using the modified Blonder-Tinkham-Klapwijk (BTK) model reveals two distinct SC gaps at 48.6 GPa: a large gap (ÎL = 3.63 meV) and a small gap (ÎS = 0.46 meV).
- High Critical Fields: Pressurized Y exhibits an extremely high upper critical field (Ό0Hc2(0)) estimated at 13.6 T at 48.6 GPa, classifying it as a Type-II superconductor with a short coherence length (4.8 nm).
- High Tc Potential: The Tc of elemental Y reaches 20 K near 100 GPa, one of the highest among elemental superconductors, supporting its role as a component in ultra-high-Tc superhydrides (e.g., YHn).
- Future Research Tool: The established DAC-PCS technique is essential for probing the SC properties of other pressure-induced high-Tc materials, including metal hydrides, under megabar conditions.
| Parameter | Value | Unit | Context |
|---|
| Maximum Tc Observed | 20 | K | Achieved near 100 GPa (resistivity measurements). |
| Tc for PCS Analysis | 10.3 | K | Superconducting transition temperature at 48.6 GPa. |
| Maximum Pressure (PCS) | 48.6 | GPa | Pressure limit for successful Point-Contact Spectroscopy. |
| Large SC Gap (ÎL(0)) | 3.63 | meV | Zero-temperature gap derived from BTK fit at 48.6 GPa. |
| Small SC Gap (ÎS(0)) | 0.46 | meV | Zero-temperature gap derived from BTK fit at 48.6 GPa. |
| Large Gap Ratio (2ÎL/kBTc) | 8.2 | Dimensionless | Indicates strong electron-boson coupling. |
| Initial Slope of Hc2 | -1.9 | T/K | Measured near Tc at 48.6 GPa. |
| Estimated Upper Critical Field (Ό0Hc2(0)) | 13.6 | T | Calculated using Werthamer-Helfand-Hohenberg (WHH) theory (dirty limit) at 48.6 GPa. |
| SC Coherence Length (Ο(0)) | 4.8 | nm | Derived from Hc2(0) at 48.6 GPa. |
| Yttrium Sample Thickness | 2-3 | ”m | Polycrystalline Yttrium used in the DAC. |
| DAC Culet Size (PCS) | 300 | ”m | Used in the miniature Be-Cu DAC for spectroscopy. |
- Pressure Cell Setup: Experiments utilized two types of DACs: a symmetric DAC (100 ”m culet) for high-pressure resistance measurements (up to 109.4 GPa) and a miniature Be-Cu DAC (300 ”m culet) for Point-Contact Spectroscopy (PCS) and upper critical field (Hc2) measurements (up to 48.6 GPa).
- Sample Loading and Medium: Polycrystalline Yttrium (99.9%) slices were loaded in an argon-filled glove box. Salt was used as the pressure-transmitting medium to ensure quasihydrostatic conditions (verified by sharp resistance drop at Tc).
- Pressure Calibration: Pressure was determined using the high-frequency diamond Raman signal (symmetric DAC) or the spectral shift of the R1 fluorescence peak of ruby (Be-Cu DAC).
- Point-Contact Junction Formation: A Pt/Y junction was formed inside the DAC. A sharp Pt cut, pre-flattened to less than 1 ”m, was mechanically pressed against the Y sample surface.
- Spectroscopy Measurement: Differential conductance (dI/dV) was measured using the 3-point moving average technique. The voltage response to DC current was measured at three small current steps (ÎI), ensuring ÎI was less than 0.5% of the total curve to approximate dI/dV accurately.
- Data Modeling: PCS spectra were analyzed using the modified Blonder-Tinkham-Klapwijk (BTK) model, which included contributions from two s-wave SC bands (Large and Small gaps) and an Intergrain Josephson Effect (IGJE) term to account for anomalous dip features.
- High-Pressure Superconductor Development: The DAC-PCS technique is essential for characterizing the SC mechanism in extreme high-Tc materials, particularly metal hydrides (like YH6, LaH10) that require pressures exceeding 100 GPa for synthesis and stabilization.
- Strongly Coupled SC Materials Engineering: The discovery of strong coupling in elemental Y provides fundamental data for designing new SC alloys or compounds that utilize d-orbital electron transfer under compression to achieve high Tc and high Hc2.
- High-Field Magnet Technology: Materials exhibiting high upper critical fields (Ό0Hc2(0) > 10 T) and strong coupling, like pressurized Y, inform the development of next-generation superconducting wires and coils for high-energy physics and medical imaging (MRI).
- Quantum Device Fabrication: The short coherence length (4.8 nm) and two-gap structure are relevant for designing nanoscale superconducting junctions and devices (e.g., Josephson junctions, SQUIDs) where interface physics and multiband effects are critical.
- Fundamental Physics Validation: Providing experimental SC gap data under pressure is crucial for validating advanced theoretical models (e.g., ab initio calculations, Eilenberger formalism) used to predict electron-phonon coupling and Tc in novel materials.
View Original Abstract
Abstract Very high applied pressure induces superconductivity with the transition temperature ( T c ) exceeding 19 K in elemental yttrium, but relatively little is known about the nature of that superconductivity. From point-contact spectroscopy (PCS) measurements in a diamond anvil cell (DAC), a strong enhancement in the differential conductance is revealed near the zero-biased voltage owing to Andreev reflection, a hallmark of the superconducting (SC) phase. Analysis of the PCS spectra based on the extended Blonder-Tinkham-Klapwijk (BTK) model indicates two SC gaps at 48.6 GPa, where the large gap Î L is 3.63 meV and the small gap Î S is 0.46 meV. When scaled against a reduced temperature, both small and large SC gaps collapse on a single curve that follows the prediction from BCS theory. The SC gap-to- T c ratio is 8.2 for the larger gap, and the initial slope of the upper critical field is â1.9 T/K, indicating that Y belongs to a family of strongly coupled BCS superconductors. The successful application of PCS to Y in DAC environments demonstrates its utility for future research on other pressure-induced high- T c superconductors.