On the Isotope-Like Effect for High-T_c Superconductors in the Scenario of 2-Phonon Exchange Mechanism for Pairing

Abstract

By generalizing the isotope effect for elemental superconductors (SCs) to the case of pairing in the 2-phonon exchange mechanism for composite SCs, we give here an explanation of the well-known increase in the critical temperature (T c ) of Bi 2 Sr 2 CaCu 2 O 8 from 95 K to 110 K and of Bi 2 Sr 2 Ca 2 Cu 3 O 10 from 105 to 115 - 125 K when Bi and Sr in these are replaced by Tl and Ba, respectively. On this basis, we also give the estimated T c s of some hypothetical SCs, assuming that they may be fabricated by substitutions similar to Bi → Tl and Sr → Ba.