Tuning High- T c Superconductors via Multistage Intercalation

Abstract

Multistage intercalation has been used to tune the interaction between adjacent blocks of CuO₂ sheets in the bigh-T_c (high superconducting transition temperature) superconductor Bi₂Sr₂CaCu₂O_x. As revealed by atomic-resolution transmission electron microscopy images, foreign iodine atoms are intercalated into every nth BiO bilayer of the host crystal, resulting in structures of stoichiometry IBi_2nSr_2nCa_nCu_2nO_x with stage index n up to 4. An expansion of 3.6 angstroms for each intercalated BiO bilayer decouples the CuO₂ sheets in adjacent blocks. A comparison of the superconducting transition temperatures of the pristine host material and intercalated compounds of different stages suggests that the coupling between each pair of adjacent blocks contributes ∼5 K to T_c in Bi₂Sr₂CaCu₂O_x.