Two effects of iodine intercalation on T_c in Bi₂Sr₂Ca_1-xY_xCu₂O₈. Two-dimensionality and charge transfer

The effects of stage-1 iodine intercalation on T_c have been investigated in Bi₂Sr₂Ca_1-xY_xCu₂O₈. The iodine intercalation causes two large effects: one is a change of the two-dimensionality due to an expansion of the crystal along the c-axis, the other is an increase of conducting hole carriers due to charge transfer between intercalated iodine atoms and CuO₂ sheets in the host material. For the stage-1 iodine-intercalation compounds, it has been found that the former effect decreases T_c by about 10 K and that the latter effect shifts the x dependence of T_c to larger x values by about 0.05 because of the increase of conducting hole carriers by about 0.025 per CuO₂ unit. It has been concluded that the decrease in T_c through iodine intercalation in Bi₂Sr₂CaCu₂O₈ is due to both effects.