Effect of hydrostatic pressure on the superconductivity in Na_xCoO_2⋅yH₂O

The effect of hydrostatic pressure on the superconducting transition temperature of Na_xCoO_2⋅yH₂O was investigated by ac susceptibility measurements up to 1.6 GPa. The pressurecoefficient of T_c is negative and the dependence T_c(p) is nonlinear over the pressure range investigated. The magnitude of the average d ln T_c/dp≈−0.07 GPa⁻¹ is comparable to the pressure coefficient of electron-doped high-T_c copper oxide superconductors witha similar value of T_c. Our results provide support to the assumption of two-dimensional superconductivity in Na_xCoO_2⋅yH₂O, which is similar to the cuprate systems, and suggest that intercalation of larger molecules may lead to an enhancement of T_c.