Separation of the charge density wave and superconducting states by an intermediate semimetal phase in pressurized TaTe2
  In layered transition metal dichalcogenides (LTMDCs) that display both charge
density waves (CDWs) and superconductivity, the superconducting state generally
emerges directly on suppression of the CDW state. Here, however, we report a
different observation for pressurized TaTe2, a non-superconducting CDW-bearing
LTMDC at ambient pressure. We find that a superconducting state does not occur
in TaTe2 after the full suppression of its CDW state, which we observe at about
3 GPa, but, rather, a non-superconducting semimetal state is observed. At a
higher pressure, ~21 GPa, where both the semimetal state and the corresponding
positive magnetoresistance effect are destroyed, superconductivity finally
emerges and remains present up to ~50 GPa, the high pressure limit of our
measurements. Our pressure-temperature phase diagram for TaTe2 demonstrates
that the CDW and the superconducting phases in TaTe2 do not directly transform
one to the other, but rather are separated by a semimetal state, - the first
experimental case where the CDW and superconducting states are separated by an
intermediate phase in LTMDC systems.
