Researchers Makes Progress on Fe-based High Temperature Superconductor

  • [2020-10-07]


    A sample of a high-temperature superconductor hovers in a magnetic field. (Image by D. PARKER/IMI/UNIV. BIRMINGHAM HIGH TC CONSORTIUM/SPL)

    The superconducting research team lead by CHEN Xianhui and WU Tao found pseudogap behavior existing at the temperature below T60K in two kinds of layered FeSe-based superconductors, and the 2D structure was confirmed to have a strong relationship with the superconducting fluctuations. This study was published on Physical Review Letters.

    Known superconducting materials at ordinary pressure currently work far below ambient temperatures and therefore require cooling. Specially, high-temperature superconductors (HTS) are usually defined as materials that behave as superconductors at temperature above 77K (-196.2).

    Superconductivity of the Fe-based HTS discovered in 2008 has been studied for years.In other words, answering whether pseudogap phenomenon in Fe-based HTS is existed and where it comes from has significant impact on establishing a unified high-temperature superconducting mechanism. 

    Phase fluctuation is an important parameter for HTS and determines the condensation of cooper pairs in traditional HTS materials. However, former researchers have not given a certain evidence on the relationships between the superconduct fluctuation and pseudo-energy gap. 

    Prof. CHEN’s team has worked on the exploration of the new HTS materials based on iron, and has achieved the transition of two-dimensional (2D) HTS via organic ion intercalation.

    In this work, the researchers first confirmed that there is indeed a significant "pseudogap" feature above the superconducting transition temperature (Tc ~ 43K) in the organic intercalated two-dimensional FeSe-based HTS, (TBA)xFeSe (TBA: tetrabutylammonium), through nuclear magnetic resonance technology. The starting temperature of the "pseudogap" is about 60K.

    Then, through anisotropic diamagnetism and Nernst effect methods, they concluded that the two-dimensional superconducting fluctuation in the Fe-Se based HTS leads to the above-mentioned important experimental findings.

    Crystal structure and superconducting properties of (TBA)xFeSe (Image by CHEN et al.)

    This work not only revealed the "pseudogap" phenomenon in the two-dimensional layered FeSe based high-temperature superconductor, but also provided a new understanding and explanation for the high-temperature superconductivity in single-layer FeSe film samples.

    In addition, the team also made a breakthrough in the experimental study on the electron nematic mechanism of FeSe superconductors. They found nontrivial spin-orbit coupling (SOC) effect in the nematic state and dug deeper on the mechanism of nematic transitionin FeSe HTS. This study was published in Physical Review X

    A proposed physical scenario for the spin-orbital intertwined nematic state in FeSe (Image by CHEN et al.)

    Paper links:

    https://link.aps.org/doi/10.1103/PhysRevLett.125.097003

    https://link.aps.org/doi/10.1103/PhysRevX.10.011034

    (Written by ZHANG Liying, edited by JIANG Pengcen, USTC News Center)

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