  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.
