Extremely high upper critical field in BiCh(2)-based (Ch: S and Se) layered superconductor LaO(0.5)F(0.5)BiS(2−x)Se(x) (x = 0.22 and 0.69)

Centrosymmetric compounds with local inversion symmetry breaking have tremendously interesting and intriguing physical properties. In this study, we focus on a BiCh(2)-based (Ch: S, Se) layered superconductor, as a system with local inversion asymmetry, because spin polarisation based on the Rashba–Dresselhaus-type spin–orbit coupling has been observed in centrosymmetric BiCh(2)-based LaOBiS(2) systems, while the BiCh(2) layer lacks local inversion symmetry. Herein, we report the existence of extremely high in-plane upper critical fields in the BiCh(2)-based system LaO(0.5)F(0.5)BiS(2−x)Se(x) (x = 0.22 and 0.69). The superconducting states are not completely suppressed by the applied magnetic fields with strengths up to 55 T. Thus, we consider that the in-plane upper critical field is enhanced by the local inversion symmetry breaking and its layered structure. Our study will open a new pathway for the discovery of superconductors that exhibit a high upper critical field by focusing on the local inversion symmetry breaking.