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 (Tc and TCDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that Tc 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 TCDW 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 ; D.C.F. gratefully acknowledges support from the Brazilian agencies CAPES and CNPq. This work was partially supported by the French National Research Agency through the project Subrissyme ANR-12-JS04-0003- 01 and by the Spanish MINECO (FIS2014-54498-R, MAT- 2014-56143-R, MDM-2014-0377, and MDM-2015-0538), by the Comunidad de Madrid through program Nanofrontmag, and by the European Union (Graphene Flagship Contract No. CNECT-ICT-604391 and COST MP1201 action). The susceptibility versus temperature data at high pressures, where the strong increase in Tc was first noticed, were taken by the late V. G. Tissen of the Institute of Solid State Physics, Chernogolovka, Russia, during his sabbatical stay in Madrid, which was financed by MINECO