  The topology of Weyl semimetals requires the existence of unique surface
states. Surface states have been visualized in spectroscopy measurements, but
their connection to the topological character of the material remains largely
unexplored. 1T'-MoTe2, presents a unique opportunity to study this connection.
This material undergoes a phase transition at 240K that changes the structure
from orthorhombic (putative Weyl semimetal) to monoclinic (trivial metal),
while largely maintaining its bulk electronic structure. Here we show from
temperature-dependent quasiparticle interference measurements that this
structural transition also acts as a topological switch for surface states in
1T'-MoTe2. At low temperature, we observe strong quasiparticle scattering,
consistent with theoretical predictions and photoemission measurements for the
surface states in this material. In contrast, measurements performed at room
temperature show the complete absence of the scattering wavevectors associated
with the trivial surface states. These distinct quasiparticle scattering
behaviors show that 1T'-MoTe2 is ideal for separating topological and trivial
electronic phenomena via temperature dependent measurements.
