中国物理B ›› 2024, Vol. 33 ›› Issue (6): 66802-066802.doi: 10.1088/1674-1056/ad334a

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Superconducting state in Ba(1-x)SrxNi2As2 near the quantum critical point

Chengfeng Yu(余承峰)1,2, Zongyuan Zhang(张宗源)1,2,†, Linxing Song(宋林兴)3,4, Yanwei Wu(吴彦玮)1,2, Xiaoqiu Yuan(袁小秋)1,2, Jie Hou(侯杰)1,2, Yubing Tu(涂玉兵)1,2, Xingyuan Hou(侯兴元)1,2, Shiliang Li(李世亮)3,4,5,‡, and Lei Shan(单磊)1,2,§   

  1. 1 Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China;
    2 Key Laboratory of Structure and Functional Regulation of Hybrid Materials (Anhui University), Ministry of Education, Hefei 230601, China;
    3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
    4 School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China;
    5 Songshan Lake Materials Laboratory, Dongguan 523808, China
  • 收稿日期:2024-01-10 修回日期:2024-02-18 接受日期:2024-03-13 出版日期:2024-06-18 发布日期:2024-06-18
  • 通讯作者: Zongyuan Zhang, Shiliang Li, Lei Shan E-mail:zongyuanzhang@ahu.edu.cn;slli@iphy.ac.cn;lshan@ahu.edu.cn
  • 基金资助:
    Project supported by the National Key R&D Program of China (Grant Nos. 2022YFA1403203, 2022YFA1403400, and 2021YFA1400400), the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302802), the National Natural Science Foundation of China (Grant Nos. 12074002, 12104004, 12204008, and 12374133), the Chinese Academy of Sciences (Grant Nos. XDB33000000 and GJTD-2020-01), and the Major Basic Program of Natural Science Foundation of Shandong Province (Grant No. ZR2021ZD01).

Superconducting state in Ba(1-x)SrxNi2As2 near the quantum critical point

Chengfeng Yu(余承峰)1,2, Zongyuan Zhang(张宗源)1,2,†, Linxing Song(宋林兴)3,4, Yanwei Wu(吴彦玮)1,2, Xiaoqiu Yuan(袁小秋)1,2, Jie Hou(侯杰)1,2, Yubing Tu(涂玉兵)1,2, Xingyuan Hou(侯兴元)1,2, Shiliang Li(李世亮)3,4,5,‡, and Lei Shan(单磊)1,2,§   

  1. 1 Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China;
    2 Key Laboratory of Structure and Functional Regulation of Hybrid Materials (Anhui University), Ministry of Education, Hefei 230601, China;
    3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
    4 School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China;
    5 Songshan Lake Materials Laboratory, Dongguan 523808, China
  • Received:2024-01-10 Revised:2024-02-18 Accepted:2024-03-13 Online:2024-06-18 Published:2024-06-18
  • Contact: Zongyuan Zhang, Shiliang Li, Lei Shan E-mail:zongyuanzhang@ahu.edu.cn;slli@iphy.ac.cn;lshan@ahu.edu.cn
  • Supported by:
    Project supported by the National Key R&D Program of China (Grant Nos. 2022YFA1403203, 2022YFA1403400, and 2021YFA1400400), the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302802), the National Natural Science Foundation of China (Grant Nos. 12074002, 12104004, 12204008, and 12374133), the Chinese Academy of Sciences (Grant Nos. XDB33000000 and GJTD-2020-01), and the Major Basic Program of Natural Science Foundation of Shandong Province (Grant No. ZR2021ZD01).

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摘要： In the phase diagram of the nickel-based superconductor Ba$_{1-x}$Sr$_{x}$Ni$_{2}$As$_{2}$, $T_{\rm c}$ has been found to be enhanced sixfold near the quantum critical point (QCP) $x = 0.71$ compared with the parent compound. However, the mechanism is still under debate. Here, we report a detailed investigation of the superconducting properties near the QCP ($x \approx 0.7$) by utilizing scanning tunneling microscopy and spectroscopy. The temperature-dependent superconducting gap and magnetic vortex state were obtained and analyzed in the framework of the Bardeen-Cooper-Schrieffer model. The ideal isotropic s-wave superconducting gap excludes the long-speculated nematic fluctuations while preferring strong electron-phonon coupling as the mechanism for $T_{\rm c}$ enhancement near the QCP. The lower than expected gap ratio of $\varDelta /(k_{\rm B}T_{\rm c})$ is rooted in the fact that Ba$_{1-x}$Sr$_{x}$Ni$_{2}$As$_{2 }$ falls into the dirty limit with a serious pair breaking effect similar to the parent compound.

关键词: nickel-based superconductor, electron-phonon coupling, dirty limit, scanning tunneling microscopy/spectroscopy

Abstract: In the phase diagram of the nickel-based superconductor Ba$_{1-x}$Sr$_{x}$Ni$_{2}$As$_{2}$, $T_{\rm c}$ has been found to be enhanced sixfold near the quantum critical point (QCP) $x = 0.71$ compared with the parent compound. However, the mechanism is still under debate. Here, we report a detailed investigation of the superconducting properties near the QCP ($x \approx 0.7$) by utilizing scanning tunneling microscopy and spectroscopy. The temperature-dependent superconducting gap and magnetic vortex state were obtained and analyzed in the framework of the Bardeen-Cooper-Schrieffer model. The ideal isotropic s-wave superconducting gap excludes the long-speculated nematic fluctuations while preferring strong electron-phonon coupling as the mechanism for $T_{\rm c}$ enhancement near the QCP. The lower than expected gap ratio of $\varDelta /(k_{\rm B}T_{\rm c})$ is rooted in the fact that Ba$_{1-x}$Sr$_{x}$Ni$_{2}$As$_{2 }$ falls into the dirty limit with a serious pair breaking effect similar to the parent compound.

Key words: nickel-based superconductor, electron-phonon coupling, dirty limit, scanning tunneling microscopy/spectroscopy

中图分类号:  (Properties of superconductors)

  • 74.25.-q
07.79.Fc (Near-field scanning optical microscopes) 74.55.+v (Tunneling phenomena: single particle tunneling and STM) 74.25.Uv (Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses))