On the Thermodynamic Critical Field for the K3C60 and Rb3C60 Fullerides

In the paper the temperature dependence of the thermodynamic critical field (H-c) for the alkali-metal-doped fullerides K3C60 and Rb3C60 has been considered. The numerical calculations have been conducted in the framework of the Migdal-Eliashberg formalism. It has been shown that the obtained numerical values of H-c agree with the experimental data. Finally, the dimensionless ratio: R-H TcCN (T-c)/H-c(2) (0) has been calculated, where T-c is the critical temperature and C-N denotes the specific heat in the normal state. The theoretical analysis has proved that for the considered fullerides the parameter R-H is beyond the RCS prediction. In particular: R-H = 0.143 for K3C60, and R-H = 0.145 for Rb3C60.