Experimental Observation of Pressure-Induced Superconductivity in Layered Transition-Metal Chalcogenides (Zr,Hf)GeTe4 Explored by a Data-Driven Approach
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-05-05 |
| Journal | Chemistry of Materials |
| Authors | Ryo Matsumoto, Zhufeng Hou, Shintaro Adachi, Sayaka Yamamoto, Hiromi Tanaka |
| Institutions | Chinese Academy of Sciences, National Institute of Advanced Industrial Science and Technology |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study reports the first experimental observation of pressure-induced superconductivity in the layered transition-metal chalcogenides (Zr,Hf)GeTe4, identified through a data-driven materials screening approach.
- Core Discovery: Superconductivity was successfully induced in both ZrGeTe4 and HfGeTe4 single crystals under high pressure using a custom diamond anvil cell (DAC).
- Maximum Tc: ZrGeTe4 achieved a maximum superconducting transition temperature (Tc) of 6.5 K at 57 GPa, while HfGeTe4 reached 6.6 K at 60 GPa.
- Data-Driven Validation: The materials were selected from the Atomwork database based on theoretical predictions of a narrow band gap and high density of states (DOS) near the Fermi level, validating the high-throughput screening methodology.
- Structural Transition: DFT calculations show the materials transition rapidly from a narrow-gap semiconductor (0.40 eV for ZrGeTe4) to a metallic state under compression (<10 GPa).
- Deficiency Effect: HfGeTe4 exhibited Hf deficiency (Hf0.83GeTe4), resulting in a lower critical pressure (Pc) for superconductivity onset (8.1 GPa vs. 17.4 GPa for ZrGeTe4), suggesting carrier doping enhances the superconducting phase.
- Measurement Technology: The high-pressure measurements relied on an originally designed DAC equipped with boron-doped diamond (BDD) electrodes and an undoped diamond (UDD) insulating layer.
- Phase Coexistence: Both compounds exhibited multi-step superconducting transitions, indicating the likely coexistence of two distinct superconducting phases under high compression.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Max Tc (ZrGeTe4) | 6.5 | K | Achieved under 57 GPa |
| Max Tc (HfGeTe4) | 6.6 | K | Achieved under 60 GPa |
| Tc Zero Resistance (ZrGeTe4) | 2.4 | K | Observed under 30.3 GPa |
| Tc Zero Resistance (HfGeTe4) | 2.0 | K | Observed under 13.9 GPa |
| Onset Pressure Pc (ZrGeTe4) | 17.4 | GPa | Pressure where Tonset first appeared |
| Onset Pressure Pc (HfGeTe4) | 8.1 | GPa | Pressure where Tonset first appeared |
| Band Gap (ZrGeTe4) | 0.40 | eV | Ambient pressure (DFT calculation) |
| Crystal Structure | Orthorhombic (Cmc21) | N/A | Determined by single crystal XRD |
| Lattice Constant a (ZrGeTe4) | 3.986(6) | A | Refinement result |
| Lattice Constant b (ZrGeTe4) | 15.95(3) | A | Refinement result |
| Hf Composition (Refined) | Hf0.83GeTe4 | N/A | Indicates Hf site deficiency |
| Zr 3d Spin-Orbit Splitting | 2.4 | eV | Between Zr4+ peaks (XPS analysis) |
| Hf 4f Spin-Orbit Splitting | 1.6 | eV | Between Hf4+ peaks (XPS analysis) |
| Resistance Exponent n (ZrGeTe4) | 1.96 | N/A | At 57 GPa (suggests electronic correlation scattering) |
| Resistance Exponent n (HfGeTe4) | 2.75 | N/A | At 86 GPa (suggests interband electron-phonon scattering) |
Key Methodologies
Section titled âKey MethodologiesâThe investigation involved computational screening, single crystal synthesis, comprehensive structural characterization, and specialized high-pressure electrical transport measurements.
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Computational Screening and DFT:
- Materials were screened from the Atomwork database, focusing on compounds exhibiting a narrow band gap and high DOS near the Fermi level, criteria favorable for pressure-induced superconductivity.
- First-principles calculations (DFT using generalized gradient approximation) were used to model band structures and DOS under ambient pressure and 10 GPa, confirming the semiconductor-to-metal transition.
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Single Crystal Synthesis:
- Stoichiometric starting materials (Zr/Hf grains, Ge powders, Te chips) were sealed in evacuated quartz ampoules.
- The ampoules were subjected to a multi-step heating process: 650 °C (20 hours) â 900 °C (50 hours) â slow cooling to 500 °C (50 hours) â furnace cooling.
- The resulting samples were hair-like fiber single crystals.
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Structural and Chemical Characterization:
- Crystal Structure: Determined by single crystal X-ray diffraction (XRD) using Mo-Kα radiation and refined using SHELXT/ShelXle software.
- Composition: Analyzed via Energy Dispersive X-ray Spectrometry (EDX).
- Valence State: Estimated by X-ray Photoelectron Spectroscopy (XPS) on a surface milled by an Ar gas cluster ion beam (GCIB) to ensure intrinsic chemical state analysis.
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High-Pressure Electrical Transport Measurement:
- Device: An originally designed Diamond Anvil Cell (DAC) was employed.
- Electrodes: Boron-doped diamond (BDD) served as the electrode material.
- Insulation: An undoped diamond (UDD) layer was used to insulate the BDD electrodes from the metal gasket.
- Pressure Medium: Cubic boron nitride (cBN) powder mixed with ruby manometer powder.
- Pressure Calibration: Pressure was monitored using both ruby fluorescence peak shift and the Raman mode of the diamond anvil.
- Measurement: Electrical resistance was measured using a four-terminal method (PPMS).
Commercial Applications
Section titled âCommercial ApplicationsâThe research findings and methodologies have implications for several high-technology sectors, particularly those involving extreme conditions and advanced materials.
- High-Pressure Research Equipment: The successful implementation of the custom DAC utilizing BDD electrodes and UDD insulation provides a proven, robust design for electrical transport measurements in high-pressure environments (up to 100 GPa).
- Superconducting Electronics: The layered structure and observed Tc values position (Zr,Hf)GeTe4 as new candidates for fundamental research into low-temperature superconducting quantum interference devices (SQUIDs) or specialized interconnects.
- Materials Informatics Software: The validation of the narrow band gap/high DOS screening criteria strengthens the commercial viability of materials informatics platforms designed for high-throughput discovery of novel functional materials, including superconductors and topological insulators.
- 2D and Nano-Electronics: The layered, anisotropic, two-dimensional nature of these chalcogenides suggests potential use in next-generation nano-electronic devices, such as highly efficient field-effect transistors (FETs) or sensors, leveraging the improved surface adhesion properties of their zigzag structure compared to flat TMDs.
- Diamond Material Technology: The use of BDD as a high-performance electrode in extreme pressure environments demonstrates a key application for advanced diamond materials in specialized scientific instrumentation and high-reliability sensors.
View Original Abstract
Layered transition-metal chalcogenides (Zr,Hf)GeTe${4}$ were screened out from database of Atomwork as a candidate for pressure-induced superconductivity due to their narrow band gap and high density of state near the Fermi level. The (Zr,Hf)GeTe${4}$ samples were synthesized in single crystal and then the compositional ratio, crystal structures, and valence states were investigated via energy dispersive spectrometry, single crystal X-ray diffraction, and X-ray photoelectron spectroscopy, respectively. The pressure-induced superconductivity in both crystals were first time reported by using a diamond anvil cell with a boron-doped diamond electrode and an undoped diamond insulating layer. The maximum superconducting transition temperatures of ZrGeTe${4}$ and HfGeTe${4}$ were 6.5 K under 57 GPa and 6.6 K under 60 GPa, respectively.