A plausible explanation of non-zero isotope shifts in superconductors

We propose to consider a charge Bose liquid model as a phenomenological explanation of three puzzling features of non-zero isotope shifts (α) in superconductors. These features are (i) large value of α (∼ 0.5) in normal superconductors; (ii) an overall trend of lower values of α with increasing Tc and (iii) a very striking feature of negative value of α (= - 0.013 in Bi 2:2:2:3 with Tc = 108 K) in high Tc superconductors. This phenomenon of non-zero isotope shifts observed in high Tc oxides are explained on the basis of (bi) polaronic theory. (author)