  We present experimental evidence of an intriguing phase transition between
distinct topological states in the type-II Weyl semimetal MoTe2. We observe
anomalies in the Raman phonon frequencies and linewidths as well as electronic
quasielastic peaks around 70 K, which, together with structural, thermodynamic
measurements, and electron-phonon coupling calculations, demonstrate a
temperature-induced transition between two topological phases previously
identified by contrasting spectroscopic measurements. An analysis of
experimental data suggests electron-phonon coupling as the main driving
mechanism for the change of key topological characters in the electronic
structure of MoTe2.We also find the phase transition to be sensitive to sample
conditions distinguished by synthesis methods. These discoveries of temperature
and material condition-dependent topological phase evolutions and transitions
in MoTe2 advance the fundamental understanding of the underlying physics and
enable an effective approach to tuning Weyl semimetal states for technological
applications.
