Effect of pressure on the superconductivity of MgB2

The superconducting transition temperature T-c of polycrystalline samples of MgB2 was studied under hydrostatic and quasi-hydrostatic pressures up to 1 and 12 GPa, respectively. The rate of T-c change with hydrostatic pressure, (dT(c)/dP), was found to be -1.18 K(GPa)(-1). Quasi-hydrostatic measurements yield a slightly higher value: (dT(c)/dP) = -1.2 K(GPa)(-1). Analysis of the electron-phonon coupling parameter lambda and its logarithmic volume derivative using the McMillan expression for T-c yields results that fall within the range of a conventional s-wave BCS superconductor with intermediate coupling, in agreement with several experimental and theoretical studies that have already been reported. Based on electronic structure calculations performed by us as well as those reported in the literature, it is concluded that the change in the coupling parameter lambda is dominated by the change of the average phonon frequency with pressure. (C) 2002 Elsevier Science B.V. All rights reserved.