Spectroscopic evidence for the superconductivity of elemental metal Y under pressure

At a Glance

Metadata	Details
Publication Date	2023-02-02
Journal	NPG Asia Materials
Authors	Zi-Yu Cao, Harim Jang, Seokmin Choi, Jihyun Kim, Su‐Young Kim
Institutions	Center for High Pressure Science & Technology Advanced Research, Sungkyunkwan University
Citations	10
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Pressure Superconductivity in Yttrium using Diamond Anvil Cells

This document analyzes the research paper “Spectroscopic evidence for the superconductivity of elemental metal Y under pressure” to highlight the critical role of high-quality diamond materials in extreme environment research and to position 6CCVD’s MPCVD diamond solutions for future high-pressure physics applications.

Executive Summary

Breakthrough Methodology: Successful implementation of Point-Contact Spectroscopy (PCS) within a Diamond Anvil Cell (DAC) environment, pushing the pressure limit for this technique to 48.6 GPa.
Material Discovery: Confirmed pressure-induced superconductivity in elemental Yttrium (Y) with a high transition temperature ($T_c$) exceeding 19 K.
Two-Gap Superconductivity: Spectroscopic evidence reveals two distinct superconducting (SC) energy gaps at 48.6 GPa: a large gap ($\Delta_L$) of 3.63 meV and a small gap ($\Delta_S$) of 0.46 meV.
Strong Coupling: The large SC gap-to-$T_c$ ratio (8.2) significantly exceeds the standard BCS weak-coupling limit (3.53), classifying pressurized Y as a strongly coupled BCS superconductor.
Type-II Characteristics: A large initial slope of the upper critical field ($-1.9$ T/K at 48.6 GPa) suggests that pressurized Y metal is a robust Type-II superconductor.
Diamond Requirement: The success of this high-pressure, high-sensitivity measurement relies fundamentally on the mechanical integrity and optical purity of the diamond anvils used in the DAC.

Technical Specifications

The following hard data points were extracted from the experimental results, primarily focusing on the 48.6 GPa measurement condition where spectroscopic data was obtained.

Parameter	Value	Unit	Context
Maximum $T_c$ Observed	19.1	K	At 90.2 GPa
Primary PCS Pressure	48.6	GPa	Pressure for two-gap analysis
Large SC Energy Gap ($\Delta_L(0)$)	3.63	meV	Measured at 48.6 GPa
Small SC Energy Gap ($\Delta_S(0)$)	0.46	meV	Measured at 48.6 GPa
Large Gap-to-$T_c$ Ratio ($2\Delta_L(0)/k_B T_c$)	8.2	N/A	Indicator of strong coupling
Initial Slope of Upper Critical Field ($d(\mu_0 H_{c2})/dT$)	-1.9	T/K	Measured at 48.6 GPa
SC Coherence Length ($\xi(0)$)	4.8	nm	Calculated at 48.6 GPa
DAC Culet Size (PCS)	300	µm	Miniature Be-Cu DAC configuration
Point-Contact Radius	< 5	µm	Pt/Y interface contact size

Key Methodologies

The experiment successfully combined high-pressure generation with sensitive spectroscopic measurement techniques.

Pressure Cell Configuration: Experiments utilized both a symmetric DAC (100 µm culet) for high-pressure resistance and a miniature Be-Cu DAC (300 µm culet) for upper critical field and PCS measurements.
Sample and Gasket: Polycrystalline Yttrium (99.9%, 2-3 µm thickness) was loaded in a c-BN gasket (20 µm thickness). Salt was used as the pressure-transmitting medium to maintain quasi-hydrostatic conditions.
Pressure Calibration: Pressure was monitored in situ using the high-frequency diamond Raman signal (in the symmetric DAC) and the spectral shift of the R1 peak of ruby fluorescence (in the Be-Cu DAC).
Point-Contact Junction Fabrication: Four Platinum (Pt) slices were adhered to the Y sample. The Pt tip was flattened to < 1 µm prior to loading. Careful mechanical pressure was applied to reduce the final Pt/Y contact radius to below 5 µm.
Spectroscopy: Differential conductance ($dI/dV$) was measured using the van der Pauw configuration and a 9 T commercial cryostat. Measurements were conducted with small current steps ($\Delta I < 0.5%$) to approximate $dI/dV$.
Data Modeling: Spectroscopic data was analyzed using the modified Blonder-Tinkham-Klapwijk (BTK) model, incorporating contributions from two s-wave SC gaps and an Intergrain Josephson Effect (IGJE) term.

6CCVD Solutions & Capabilities

The successful execution of high-pressure PCS relies on ultra-high-quality diamond components. 6CCVD is uniquely positioned to supply the specialized MPCVD diamond materials and customization services required to replicate and advance this research into other high-$T_c$ systems.

Research Requirement/Challenge	6CCVD Solution & Capability	Technical Advantage
High-Pressure Anvils (DAC)	Optical Grade Single Crystal Diamond (SCD) Substrates.	SCD offers the highest mechanical strength and purity, essential for achieving and sustaining pressures exceeding 100 GPa without catastrophic failure.
Optical Access for Calibration	High Purity, Low Birefringence SCD (Type IIa).	Required for accurate in situ pressure measurement via the diamond Raman signal or ruby fluorescence, ensuring minimal optical distortion and high signal clarity.
Integrated Electrical Contacts (PCS)	Custom Metalization Services (Au, Pt, Ti, Pd, W, Cu).	We offer precise, cleanroom-quality deposition of contact metals (e.g., the Pt used in this study) directly onto the diamond surface, enabling integrated electrodes and complex micro-patterning for advanced transport and spectroscopic measurements.
Custom Anvil Geometries	Custom Dimensions and Thicknesses.	6CCVD supplies SCD plates (0.1 µm to 500 µm thick) and substrates up to 10 mm thick. We provide custom laser cutting and polishing services to achieve the precise culet sizes (e.g., 100 µm or 300 µm) and geometries required for specialized DAC designs.
Junction Quality and Ballistic Transport	Ultra-Low Roughness Polishing (Ra < 1 nm for SCD).	A superior surface finish is critical for minimizing energy dissipation and ensuring the high-quality, nonballistic junction required for accurate Andreev reflection spectroscopy (PCS).
Future High-$T_c$ Research	Boron-Doped Diamond (BDD) Electrodes.	For future experiments requiring integrated, conductive electrodes within the pressure cell, 6CCVD offers highly conductive BDD films and substrates, providing a robust, chemically inert, and pressure-resistant alternative to metal wires.

6CCVD’s in-house PhD engineering team specializes in material selection and customization for extreme environment physics, including high-pressure, high-temperature, and quantum applications. We can assist researchers in designing optimal diamond substrates and metalization schemes to extend the successful PCS technique to other pressure-induced high-$T_c$ superconductors, such as metal hydrides.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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 Δ L is 3.63 meV and the small gap Δ 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 −1.9 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.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41427-022-00457-6