  Recently, two-fold symmetric in-plane anisotropy of the superconducting
properties have been observed in a single crystal of BiCh2-based (Ch: S, Se)
layered superconductor LaO0.5F0.5BiSSe having a tetragonal
(four-fold-symmetric) in-plane structure; the phenomena are very similar to
those observed in nematic superconductors. To explore the origin of the
two-fold symmetric anisotropy in the BiCh2-based system, we have investigated
the electron-doping dependence on the anisotropy by examining the in-plane
anisotropy of the magnetoresistance in the superconducting states for a single
crystal of LaO0.9F0.1BiSSe under high magnetic fields up to 15 T. We observed a
two-fold symmetry of in-plane anisotropy of magnetoresistance for
LaO0.9F0.1BiSSe. The results obtained for LaO0.9F0.1BiSSe are quite similar to
those observed for LaO0.5F0.5BiSSe, which has a higher electron doping
concentration than LaO0.9F0.1BiSSe. Our present finding suggests that the
emergence of the in-plane symmetry breaking in the superconducting state is
robust to the carrier concentration in the series of LaO1-xFxBiSSe.
