中国物理B ›› 2023, Vol. 32 ›› Issue (4): 47201-047201.doi: 10.1088/1674-1056/ac8343

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Anisotropy of 2H-NbSe2 in the superconducting and charge density wave states

Chi Zhang(张驰)1,2,4,5, Shan Qiao(乔山)1,4,5, Hong Xiao(肖宏)3, and Tao Hu(胡涛)2,†   

  1. 1 State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China;
    2 Beijing Academy of Quantum Information Sciences, Beijing 100193, China;
    3 Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China;
    4 CAS Center for Excellence in Superconducting Electronics(CENSE), Shanghai 200050, China;
    5 University of Chinese Academy of Sciences, Beijing 100049, China
  • 收稿日期:2022-04-21 修回日期:2022-06-10 接受日期:2022-07-22 出版日期:2023-03-10 发布日期:2023-04-10
  • 通讯作者: Tao Hu E-mail:hutao@baqis.ac.cn
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11574338 and 12074038) and NSAF (Grant No. U1530402).

Anisotropy of 2H-NbSe2 in the superconducting and charge density wave states

Chi Zhang(张驰)1,2,4,5, Shan Qiao(乔山)1,4,5, Hong Xiao(肖宏)3, and Tao Hu(胡涛)2,†   

  1. 1 State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China;
    2 Beijing Academy of Quantum Information Sciences, Beijing 100193, China;
    3 Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China;
    4 CAS Center for Excellence in Superconducting Electronics(CENSE), Shanghai 200050, China;
    5 University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2022-04-21 Revised:2022-06-10 Accepted:2022-07-22 Online:2023-03-10 Published:2023-04-10
  • Contact: Tao Hu E-mail:hutao@baqis.ac.cn
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 11574338 and 12074038) and NSAF (Grant No. U1530402).

摘要: Anisotropy is an important feature of layered materials, and a large anisotropy is usually related to the two-dimensional characteristics. We investigated the anisotropy of the layered transition metal dicalcogenide 2H-NbSe$_2$ in the superconducting and charge density wave (CDW) states using magnetotransport measurements. In the superconducting state, the normalized $H_{\rm c2}^{||c}/H_{\rm p}$ is independent of the thickness of 2H-NbSe$_2$, while $H_{\rm c2}^{||ab}/H_{\rm p}$ increases significantly with decreasing thickness, where $H_{\rm p}$ is the Pauli limiting magnetic field and $H_{\rm c2}^{||c}$ and $H_{\rm c2}^{||ab}$ are the upper critical fields in the $c$ and $ab$ directions, respectively. It is found that the superconducting anisotropy parameter $\gamma_{H_{\rm c2}}=H_{\rm c2}^{||ab}/H_{\rm c2}^{||c}$ increases with reduction in the thickness of 2H-NbSe$_2$. In the CDW state, the angular ($\theta$) dependence of magnetoresistance, $R(H,\theta)$ scales with $H(\cos^2\theta+\gamma_{\rm CDW}^{-2}\sin^2\theta)^{1/2}$, which decreases with increasing temperature and disappears at about 40 K. It is found that the CDW anisotropy parameter $\gamma_{\rm CDW}$ is much larger than the effective mass anisotropy but does not change a lot for ultrathin and bulk samples. Our results suggest the existence of three-dimensional superconductivity and quasi-two dimensional CDWs in bulk 2H-NbSe$_2$.

关键词: anisotropy, superconductivity, charge density wave, transition metal dicalcogenides

Abstract: Anisotropy is an important feature of layered materials, and a large anisotropy is usually related to the two-dimensional characteristics. We investigated the anisotropy of the layered transition metal dicalcogenide 2H-NbSe$_2$ in the superconducting and charge density wave (CDW) states using magnetotransport measurements. In the superconducting state, the normalized $H_{\rm c2}^{||c}/H_{\rm p}$ is independent of the thickness of 2H-NbSe$_2$, while $H_{\rm c2}^{||ab}/H_{\rm p}$ increases significantly with decreasing thickness, where $H_{\rm p}$ is the Pauli limiting magnetic field and $H_{\rm c2}^{||c}$ and $H_{\rm c2}^{||ab}$ are the upper critical fields in the $c$ and $ab$ directions, respectively. It is found that the superconducting anisotropy parameter $\gamma_{H_{\rm c2}}=H_{\rm c2}^{||ab}/H_{\rm c2}^{||c}$ increases with reduction in the thickness of 2H-NbSe$_2$. In the CDW state, the angular ($\theta$) dependence of magnetoresistance, $R(H,\theta)$ scales with $H(\cos^2\theta+\gamma_{\rm CDW}^{-2}\sin^2\theta)^{1/2}$, which decreases with increasing temperature and disappears at about 40 K. It is found that the CDW anisotropy parameter $\gamma_{\rm CDW}$ is much larger than the effective mass anisotropy but does not change a lot for ultrathin and bulk samples. Our results suggest the existence of three-dimensional superconductivity and quasi-two dimensional CDWs in bulk 2H-NbSe$_2$.

Key words: anisotropy, superconductivity, charge density wave, transition metal dicalcogenides

中图分类号:  (Superconducting materials other than cuprates)

  • 74.70.-b
74.78.-w (Superconducting films and low-dimensional structures) 74.25.F- (Transport properties)