Superconductivity emerging from a suppressed large magnetoresistant state in WTe2
Date：24-09-2015 Print
Tungsten ditelluride (WTe2) is a well known non-magnetically thermoelectric semimetal. Recently, its unexpected property of large magnetoresistance (LMR) has been discovered by Prof. Cava's group [Nature, 514 (2014) 205], yielding a research hotspot in condensed matter physics and material science.
The LMR effect found in WTe2 and some other nonmagnetic compounds is a peculiar transport property. Theoretical and experimental investigations indicate that the LMR effect is resulted from the perfect balance between electron and hole Fermi pockets along the Γ-Χ direction in the Brillouin zone, different from that of giant and colossal magnetoresistance previously found in magnetic materials. Pressure as an important control parameter can effectively tune lattice structures and the corresponding electronic states in a more systematic fashion, avoiding the complexity brought by chemical doping. Recently, Prof. Liling Sun and Ph.D students Defen Kang and Yazhou Zhou etc. from National Lab for Superconductivity in Institute of Physics, Chinese Academy of Science, systematically investigated the WTe2 compound using a house-build system integrated with high pressure, low temperature and magnetic field, in collaboration with Prof. Youguo Shi of IOP and Prof. Guangming Zhang from Tsinghua University. They find that, upon increasing pressure, the LMR effect is gradually suppressed and turned off at a critical pressure of 10.5 GPa where superconductivity accordingly emerges. The superconducting transition temperature (Tc) reaches 6.5 K at ~13.0 GPa and then decreases monotonically with increasing pressure down to 2.6 Kat ~24.0 GPa. In-situ high-pressure synchrotron XRD measurements results indicate no first-order structure phase transition under pressure up to 20.1 GPa. Significantly, high-pressure Hall measurements reveal a sign change in the Hall coefficient at the critical pressure, indicating a quantum phase transition of the Fermi surface reconstruction.
Superconductivity usually arises in the proximity of an electron order state (antiferromagnetic state, ferromagnetic state, charge density wave state etc.), however, the superconductivity found in the pressurized WTe2 emerges near a LMR state. These results may bring new physics on understanding the superconducting mechanism.
This work has been published in nature Communications, 6, 7804 (2015). This research was supported by National Natural Science Foundation of China, 973 projects and Chinese Academy of Sciences.
http://www.nature.com/ncomms/2015/150723/ncomms8804/pdf/ncomms8804.pdf
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| Pressure dependences of the characteristic temperatures and Hall coefficient of WTe2.(a) The plot of T*ZF and Tc versus pressure. The red, pink and blue solid circles represent Tc extracted from different runs of electrical resistance measurements, and the green triangles represent the Tc determined from the ac susceptibility measurements. The acronyms LMR and SC stand for large magnetoresistance and superconductivity, respectively. (b) Hall coefficient (RH) as a function of pressure measured at 10 K and 1 Tesla, displaying a sign change from the positive to the negative at the critical pressure. Solid purple circles and pink squares represent the RH obtained from different runs. The inset shows the second derivative of the Hall coefficient and the maximum corresponds to the sign change of Hall coefficient. |
Contact:
Institute of Physics
SUNLiling
Email：llsun@iphy.ac.cn
Institute of Physics
ZHAOZhongxian
Email：zhxzhao@iphy.ac.cn
Key word:
Superconductivity; LMR state;WTe2;
Abstract:
The recent discovery of large magnetoresistance in tungsten ditelluride provides a unique playground to find new phenomena and significant perspective for potential applications. The large magnetoresistance effect originates from a perfect balance of hole and electron carriers, which is sensitive to external pressure. Here we report the suppression of the large magnetoresistance and emergence of superconductivity in pressurized tungsten ditelluride via high-pressure synchrotron X-ray diffraction, electrical resistance, magnetoresistance and alternating current magnetic susceptibility measurements. Upon increasing pressure, the positive large magnetoresistance effect is gradually suppressed and turned off at a critical pressure of 10.5 GPa, where superconductivity accordingly emerges. No structural phase transition is observed under the pressure investigated. In situ high-pressure Hall coefficientmeasurements at low temperatures demonstrate that elevating pressure decreases thepopulation of hole carriers but increases that of the electron ones. Significantly, at the criticalpressure, a sign change of the Hall coefficient is observed.
