Pressure dependence of the superconducting transition temperature and the Hall coefficient inIBi2.2Sr1.8CaCu2O8+ysingle crystals

The superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ and the Hall coefficient have been measured on ${\mathrm{IBi}}_{2.2}$ ${\mathrm{Sr}}_{1.8}$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathit{y}}$ single crystals under hydrostatic pressure. The ${\mathit{T}}_{\mathit{c}}$ linearly decreases at the rate ${\mathit{dT}}_{\mathit{c}}$/dP∼-3.5 K/GPa, indicating the facts that the charge transfer occurs between intercalated iodine atoms and ${\mathrm{CuO}}_2$ layers, and the hole concentration situates in the overdoped region. The facts have been further identified by our Hall-coefficient measurements at ambient pressure, showing an increase of the hole concentration after intercalation. The number of holes transferred from intercalated iodine atoms was calculated to be 0.3 per iodine atom. The pressure derivative of the Hall coefficient is -0.39×${10}^{\mathrm{-}3}$ ${\mathrm{cm}}^3$ ${\mathrm{C}}^{\mathrm{-}1}$ ${\mathrm{GPa}}^{\mathrm{-}1}$, which is approximately twice as large as the value on the pristine crystal, indicating the valence change of the intercalated iodine under pressure.