  We have performed systematic angle-resolved photoemission spectroscopy of the
topological crystalline insulator (TCI) Pb1-xSnxTe to elucidate the evolution
of its electronic states across the topological phase transition. As previously
reported, the band structure of SnTe (x = 1.0) measured on the (001) surface
possesses a pair of Dirac-cone surface states located symmetrically across the
Xbar point in the (110) mirror plane. Upon approaching the topological phase
transition into the trivial phase at x_c ~ 0.25, we discovered that Dirac cones
gradually move toward the Xbar point with its spectral weight gradually reduced
with decreasing x. In samples with x <= 0.2, the Dirac-cone surface state is
completely gone, confirming the occurrence of the topological phase transition.
Also, the evolution of the valence band feature is found to be consistent with
the bulk band inversion taking place at x_c. The tunability of the location of
the Dirac cones in the Brillouin zone would be useful for applications
requiring Fermi-surface matching with other materials, such as spin injection.
