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.

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