The isotope effect in (6Li-7Li)Ti2O4

The authors have measured the superconducting transition temperature from ac susceptibility measurements in isotopically pure samples of 6LiTi2O4 and 7LiTi2O4. The transition temperature and transition widths are found to be identical for the two samples. Past measurements on this compound show it to be a d band coupling BCS superconductor involving the Ti-O network in the spinel structure. However, it is surprising that the high energy phonons due to the Li vibrations have absolutely no effect on the superconducting transition temperature in that the normal state conductivity is dominated by the Li concentration with a metal insulator transition occurring as a function of Li doping