Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS2 and 2H-TaSe2

We present measurements of the superconducting and charge-density-wave (CDW) critical temperatures (T-c and T-CDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that T-c increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of T-CDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases, coexisting with superconductivity within our full pressure range.