  Searching for new quantum spin Hall insulators with large fully opened energy
gap to overcome the thermal disturbance at room temperature has attracted
tremendous attention due to the one-dimensional (1D) spin-momentum locked
topological edge states serving as dissipationless channels for the practical
applications in low consumption electronics and high performance spintronics.
Here, we report the investigation of topological nature of monolayer Bi4Br4 by
the techniques of scanning tunneling microscopy and angle-resolved
photoemission spectroscopy (ARPES). The topological non-triviality of 1D edge
state integrals within the large bulk energy gap (~ 0.2 eV) is revealed by the
first-principle calculations. The ARPES measurements at different temperature
show a temperature-induced Lifshitz transition, corresponding to the
resistivity anomaly caused by the shift of chemical potential. The connection
between the emergency of superconductivity and the Lifshitz transition is
discussed.
