In-plane chemical pressure essential for superconductivity in BiCh2-based (Ch: S, Se) layered structure.

Yoshikazu Mizuguchi,Osuke Miura,Kiyoharu Tadanaga,Yoshihiro Kuroiwa,Eisuke Magome,Joe Kajitani,Chikako Moriyoshi,Takafumi Hiroi,Nobuhiro Kumada,Akira Miura

doi:10.1038/srep14968

Abstract

BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated. In this study, we investigate the relationship between crystal structure and superconducting properties of the BiCh2-based superconductor family, specifically, optimally doped Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)2. We use powder synchrotron X-ray diffraction to determine the crystal structures. We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle. Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure.

Highlights

BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated
In 2012, we reported layered superconductors composed of alternate stacks of BiS2 superconducting layers and various spacer layers[12,13]
The crystal structure parameters are plotted as a function of x in Fig. 2; the crystal structure data are listed in the supplementary information (Table S1)

Summary

Introduction

BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated. We investigate the relationship between crystal structure and superconducting properties of the BiCh2-based superconductor family, optimally doped Ce1−xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1−ySey)[2]. Many Fe-based superconductors containing various types of spacer layers have been discovered, several of which attained high Tc2–8 With this wide selection of related layered superconductors having various structures and properties, one can determine which crystal structure parameters are essential for the emergence of superconductivity in a given family of layered superconductors. Tc enhancement under HP has been observed in other REO0.5F0.5BiS2 superconductors[32] These facts strongly suggest that superconducting properties of BiCh2-based superconductors are correlated with changes in crystal structure, which is analogous to findings for the Fe-based family[9,10]

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Conclusion