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 comple x fullerides (NH3)(x)NaAA'C-60 (A,A'=K,Rb and Cs), chemical and physical pr essure effects on Tc are considerably different. Similar deviations are obs erved in ternary superconductors A(3)Ba(3)C(60). These finding contrast in a striking way with the empirical rule, implying that, in the large interfu llerene distance regime, Tc is not controlled simply by lattice parameters.