Approaching the Mott-Hubbard insulator in the 85-K superconductor Bi2(Sr,Ca)3Cu2O8+d by doping with Tm.

Abstract

As x increases in ${\mathrm{Bi}}_{4}$${\mathrm{Sr}}_{3}$${\mathrm{Ca}}_{3\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Tm}}_{\mathit{x}}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{16+\mathit{y}}$ the Hall carrier density ${n}_{H}$ decreases linearly. The variation is consistent with Mott-Hubbard behavior, but in conflict with band-structure results which ignore correlations. We find that the variation of ${T}_{c}$ vs ${n}_{H}$ is nonmonotonic. The source of the large carrier population (0.4/Cu) in the undoped (x=0) compound is discussed.