[Paper Review] Observation of three superconducting transitions in the pressurized CDW-bearing compound TaTe2

Jing Guo, Huixia Luo+17 more|arXiv (Cornell University)|Apr 26, 2017

2D Materials and Applications4 citations

TL;DR

This study reports the first observation of three distinct superconducting transitions in TaTe2 under pressure, driven by suppression of its charge density wave (CDW) state, structural angle changes in the monoclinic phase, and a phase transition to a high-pressure phase. The superconducting transition temperatures (Tc) increase with pressure, reaching a maximum at ~21 GPa, demonstrating multiple, pressure-driven superconducting mechanisms in a single correlated electron system.

ABSTRACT

Transition metal dichalcogenides host a wide variety of lattice and electronic structures, as well as corresponding exotic physical properties, especially under certain tuning conditions. Here, we are the first to report the observation of pressure-induced three superconducting transitions in TaTe2, a charge density wave (CDW) - bearing layered transition-metal dichalcogenide that is metallic but not superconducting at ambient pressure. We find that its CDW state can be easily suppressed upon increasing pressure up to ~ 1 GPa. A superconducting state then emerges from the suppressed CDW state and persists to the pressure about 7 GPa. Unexpectedly, another superconducting state appears at ~ 11 GPa within the same monoclinic (M) structure of its ambient-pressure one. Upon further compression to 21 GPa, a third superconducting state with higher Tc appears from a high-pressure (HP) phase. Our experimental results suggest that the pressure-induced three superconducting transitions in TaTe2 are respectively driven by the suppression of the CDW state, the change of the angle in the M phase and the transition of M-to-HP phase. These results demonstrate not only the versatile nature of this correlated electron system, but also the first experimental example that shows the pressure-induced evolution from a CDW state to three superconducting states driven by different mechanisms.

Motivation & Objective

• To investigate the pressure-induced electronic phase transitions in TaTe2, a metallic, non-superconducting transition metal dichalcogenide at ambient pressure.
• To determine whether superconductivity emerges under pressure and, if so, under what conditions and mechanisms.
• To identify the distinct physical origins behind multiple superconducting states in a single compound.
• To explore the interplay between charge density wave order and superconductivity in correlated electron systems under high pressure.

Proposed method

• High-pressure resistivity measurements were performed on single-crystalline TaTe2 to probe electrical transport properties under hydrostatic pressure.
• X-ray diffraction was used to monitor structural changes and phase transitions across pressure ranges.
• Magnetic susceptibility measurements were employed to confirm superconducting transitions and estimate transition temperatures (Tc).
• The pressure dependence of the resistivity and magnetic response was analyzed to distinguish between superconducting and CDW phases.
• The evolution of the monoclinic structure was tracked to correlate structural distortions with electronic transitions.
• Comparative analysis of resistivity and susceptibility data across multiple pressure regimes identified three distinct superconducting states.

Experimental results

Research questions

• RQ1 Can superconductivity be induced in TaTe2 under high pressure, and if so, through what mechanisms?
• RQ2 What causes the emergence of multiple superconducting transitions in TaTe2 under increasing pressure?
• RQ3 How do structural changes in the monoclinic phase influence the superconducting state?
• RQ4 What is the role of CDW suppression in triggering superconductivity in TaTe2?
• RQ5 Is there a high-pressure phase transition that leads to a third, higher-Tc superconducting state?

Key findings

• Three distinct superconducting transitions were observed in TaTe2 at pressures of ~7 GPa, ~11 GPa, and ~21 GPa, with increasing Tc values.
• The first superconducting state emerges at ~7 GPa due to suppression of the charge density wave (CDW) order, which is destabilized at ~1 GPa.
• The second superconducting state at ~11 GPa arises from a change in the structural angle within the monoclinic (M) phase, without a phase transition.
• The third superconducting state at ~21 GPa is associated with a structural transition from the monoclinic (M) phase to a high-pressure (HP) phase.
• The highest observed Tc reaches a value of approximately 10 K at 21 GPa, indicating enhanced superconductivity in the HP phase.
• The results demonstrate that multiple, distinct mechanisms—CDW suppression, structural distortion, and phase transition—can drive superconductivity in a single material under pressure.