Progress in Pressure-induced Superconductivity in Tungsten Diode Tungide of Giant Magnetoresistive Compounds

Tungsten ditungstate (WTe2) is a transitional metal chalcogenide with a layered structure. In its orthorhombic cell, the tungsten chain is distributed along the a-axis of the ruthenium layer in a one-dimensional direction, and is a non-magnetic semi-metal. material. WTe2 has long been known for its good thermoelectric properties. The Cava research group of Princeton University unexpectedly discovered in 2014 that WTe2 has unsaturated large magnetoresistance (LMR) properties under normal pressure [Nature, 514 (2014) 205 ], That is, this material exhibits an unusually large positive resistance effect in a magnetic field and is not saturated in a very high magnetic field. This characteristic not only provides potential for its application in electronic devices, but also opens up new directions for the research of giant magnetoresistive materials. In semimetals, the very high reluctance is due to the "resonance" of the hole-electrons, and the WTe2 is the first material discovered to have this perfect resonance.

Recently, Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter State (SSC) National Key Laboratory of Superconductivity SC4 Group Research Associate Sun Liling and PhD students Kang Defen, Zhou Asia, etc. and Institute of Physics Associate Professor Shi Youguo, Tsinghua University Professor Zhang Guangming Collaboration, a systematic and in-depth study of the high pressure behavior of WTe2, found that the LMR phenomenon was continuously suppressed under pressure, and finally disappeared under a pressure of about 10.5 GPa, and at the same time exhibited superconductivity. The highest superconducting transition temperature (Tc=6.5K) occurs at a pressure of 13 GPa, and the Tc continuously decreases at a higher pressure. At 24 GPa, Tc=2.6 K. High-voltage in-situ Hall measurements show that the Hall coefficient changes from positive to negative under the critical pressure of LMR suppression and superconductivity, revealing that a quantum with Fermi surface reconstruction occurs under this critical pressure. Phase transitions. Such phase transitions can often be described by the Lifshitz phase transition. XRD results of high-voltage synchrotron radiation confirmed that WTe2 did not exhibit structural phase transition below 20.1 GPa pressure, but c-axis was compressed by 6.5% under critical pressure, and the compression ratio was 10 times that of a-axis compression, which was the b-axis compression ratio. Doubled, indicating that the reconstruction of the Fermi surface at this critical pressure point is accompanied by a sharply anisotropic lattice reduction.

Superconductivity is often closely related to the electronically ordered state, and its relevance has always been one of the key research topics in the field of superconductivity. For the first time, this study found the phenomenon of pressure-induced superconductivity in the neighboring LMR state, enriching people's research on the correlation between superconducting states and other quantum states. The results of this research are published in Nature Communications, 6 (2015) 7804.

The study was supported by the National Natural Science Foundation of China, the "973" and the Chinese Academy of Sciences Class B pilot project.