Abstract Body

BiS₂-based superconductor La(O, F)BiS₂ has a layered structure composed of an insulating rare-earth oxide layer and two conducting BiS₂ layers stacked alternately. This material exhibits superconductivity at about 3 K[1]. The application of physical pressure increases the superconducting transition temperature (T_c) to about 10 K, and the application of chemical pressure through elemental substitution also increases T_c to about 5 K [2,3]. Recently, it was reported that the T_c increased by partially substituting Sn for Bi to about 6 K [4]. In this study, in order to further improve the T_c of Sn-substituted LaO_0.5F_0.5BiS₂, we investigated the effect of chemical pressure application on the superconducting properties in LaO_0.5F_0.5(Bi, Sn)S₂ using  the partial substitution of Nd ion for La ion.

Single crystals of La_1-xNd_xO_0.5F_0.5Bi_1-ySn_yS₂ were prepared using the molten flux method. The physical properties of these samples were evaluated by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and electrical resistivity measurements. Figure 1 shows the temperature dependence of electrical resistivity. It was found that T_c^zero reaches a maximum of about 6 K at y = 0.12 and x = 0.05, which is the highest value at ambient pressure among the BiS₂-based compounds. This Nd dependence indicates that the superconducting properties in the Sn-substituted sample do not increase with increasing chemical pressure, suggesting that other factors to control the superconducting properties exist. In this presentation, the effects of Nd and Sn substitutions will be discussed in more detail.

References

[1] Y. Mizuguchi et al, J. Phys. Soc. Jpn., 81, 114725(2012).

[2] Y. Mizuguchi, J. Phys. Soc. Jpn, 88, 041001(2019).

[3] S. Demura, J. Phys. Soc. Jpn, 88, 041002(2019).

[4] S. Kobayashi et al, J. Phys. Soc. Jpn. 93, 024707 (2024).

Figure 1. Temperature dependence of the electrical resistivity for La_1-xNd_xO_0.5F_0.5Bi_1-ySn_yS₂, y = 0.12, x = 0 - 0.30. (The inset shows an enlarged view near the transition temperature.)

Keywords: Superconductivity, Single crystal, Element-substitution, Structural instability