Proximity to Fermi-surface topological change in superconducting LaO0.54F0.46BiS2

The electronic structure of nearly optimally-doped novel superconductor LaO${}_{1-x}$F${}_x$BiS${}_2$ ($x$ = 0.46) was investigated using angle-resolved photoemission spectroscopy (ARPES). We clearly observed band dispersions from 2 to 6 eV binding energy and near the Fermi level (${\it E}_{\rm F}$), which are well reproduced by first principles calculations when the spin-orbit coupling is taken into account. The ARPES intensity map near $E_{\mathrm{F}}$ shows a square-like distribution around the $\mathrm{\Gamma }$(Z) point in addition to electronlike Fermi surface (FS) sheets around the X® point, indicating that FS of LaO${}_{0.54}$F${}_{0.46}$BiS${}_2$ is in close proximity to the theoretically-predicted topological change.