Near constancy of the pressure dependence of ${\mathit{T}}_{\mathit{c}}$ across families of organic and fullerene superconductors

Pressure strongly depresses the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ of both the doped fullerenes and the β-ET[(BEDT-TTF${)}_{\mathit{nX}\mathit{m}}$, (BEDT-TTF)=bis(ethylenedithio)tetrathiofulvalene)] organic superconductors. An outstanding puzzle in these materials is the weak variation ${\mathit{dT}}_{\mathit{c}}$/dP across families of compounds with large variations in ${\mathit{T}}_{\mathit{c}}$. This property has been used to argue against phonon-induced pairing. However, closer examination of the volume dependence of ${\mathit{T}}_{\mathit{c}}$ reveals that the weak variation of ${\mathit{dT}}_{\mathit{c}}$/dP is consistent with moderate (but not weak) electron-phonon coupling. © 1996 The American Physical Society.