  Transition metal dichalcogenides host a wide variety of lattice and
electronic structures, as well as corresponding exotic physical properties,
especially under certain tuning conditions. Here, we are the first to report
the observation of pressure-induced three superconducting transitions in TaTe2,
a charge density wave (CDW) - bearing layered transition-metal dichalcogenide
that is metallic but not superconducting at ambient pressure. We find that its
CDW state can be easily suppressed upon increasing pressure up to ~ 1 GPa. A
superconducting state then emerges from the suppressed CDW state and persists
to the pressure about 7 GPa. Unexpectedly, another superconducting state
appears at ~ 11 GPa within the same monoclinic (M) structure of its
ambient-pressure one. Upon further compression to 21 GPa, a third
superconducting state with higher Tc appears from a high-pressure (HP) phase.
Our experimental results suggest that the pressure-induced three
superconducting transitions in TaTe2 are respectively driven by the suppression
of the CDW state, the change of the angle in the M phase and the transition of
M-to-HP phase. These results demonstrate not only the versatile nature of this
correlated electron system, but also the first experimental example that shows
the pressure-induced evolution from a CDW state to three superconducting states
driven by different mechanisms.
