  We have performed high-resolution angle-resolved photoemission spectroscopy
of the quasi-one-dimensional (1D) topological superconductor candidate
Tl2Mo6Se6 consisting of weakly-coupled Mo3Se3 chains. We found a quasi-1D Fermi
surface arising from a Dirac-like energy band, which is associated with the
nonsymmorphic screw symmetry of the chains and predicted to trigger topological
superconductivity. We observed a significant spectral-weight reduction over a
wide energy range, together with a tiny Fermi-edge structure which exhibits a
signature of a superconducting-gap opening below the superconducting-transition
temperature. The observed quasi-1D Dirac-like band and its very small density
of states point to an unconventional nature of superconductivity in Tl2Mo6Se6.
