Anomalous high pressure effect in superconducting fullerides

Abstract

Here we report pressure dependence of Tc and lattice parameter of two types of fullerene superconductors with expanded unit cells. In trivalent complex fullerides (NH 3) xNaAA'C 60 (A,A′=K,Rb and Cs), chemical and physical pressure effects on Tc are considerably diferent. Similar deviations are observed in ternary superconductors A 3Ba 3C 60. 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.