The pressure dependence of the critical temperature T c and upper critical field H c2 (T ) has been measured up to 19 GPa in the layered superconducting material 2H-NbSe 2 . T c (P ) has a maximum at 10.5 GPa, well above the pressure for the suppression of the CDW order. Using an effective two band model to fit H c2 (T ), we obtain the pressure dependence of the anisotropy in the electron phonon coupling and Fermi velocities, which reveals the peculiar interplay between CDW order, Fermi surface complexity and superconductivity in this system.

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 -TaSe 2 and 2H -TaS 2 . 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 -TaS 2 and 8.2 K at 23 GPa in 2H -TaSe 2 . 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 T CDW slowly decreases, coexisting with superconductivity within our full pressure range.

In an experiment in a diamond anvil cell utilizing helium pressure medium, yttrium metal displays a superconducting transition temperature which increases monotonically from T c ≃ 3.5 K at 30 GPa to 17 K at 89.3 GPa, one of the highest transition temperatures for any elemental superconductor. The pressure dependence of T c differs substantially from that observed in previous studies under quasihydrostatic pressure to 30 GPa. Remarkably, the dependence of T c on relative volume V /V o is linear over the entire pressure range above 33 GPa, implying that higher values of T c are likely at higher pressures. For the trivalent metals Sc, Y, La, Lu there appears to be some correlation between T c and the ratio r a /r c of the Wigner-Seitz radius to the ion core radius.