The pressure dependence of the superconducting transition temperature Tc of simple-cubic Na2CsC60 is studied by an ac susceptibility method with a Swenson-type piston-cylinder apparatus. The observed value of dTc/dP is -12.5±0.2 K/GPa, significantly larger than the values of -7.8 and -9.7 K/GPa reported earlier for K3C60 and Rb3C60, respectively. Using the compressibility available (that of K3C60), we find that the evolution of Tc with interfullerene spacing in Na2CsC60 is significantly different from that established for merohedrally disordered face-centered-cubic superconductors M3C60 (M=alkali metal), but in excellent agreement with the ambient pressure data for the simple cubic superconductors Na2RbC60 and Na2CsC60. The present results provide an additional dimension to the existing features of fulleride superconductors, establishing the importance of the relative orientation of C603- ions in affecting the electronic and conducting properties of these materials.
ASJC Scopus subject areas
- Condensed Matter Physics