Anomalous high pressure effect in superconducting fullerides

Here we report pressure dependence of Tc and lattice parameter of two types of fullerene superconductors with expanded unit cells. In trivalent complex fullerides (NH3)xNaAAʹC60 (A,A′=K,Rb and Cs), chemical and physical pressure effects on Tc are considerably diferent. Similar deviations are observed in ternary superconductors A3Ba3C60. These finding contrast in a striking way with the empirical rule, implying that, in the large interfullerene distance regime, Tc is not controlled simply by lattice parameters.