Superconductor-to-metal transition caused by oxygen nonstoichiometry in ${\mathrm{TlSr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ having a Cu-O pyramidal layer

A transition from a 68-K superconductor to an overdoped nonsuperconducting metal has been observed in ${\mathrm{TlSr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ having a Cu-O pyramidal layer. This reversible transition is caused by a small change (∼0.08) in oxygen deficiency δ, without showing a significant change in the crystal structure. The Hall measurements demonstrate that the superconductivity is suppressed by overdoping of hole carriers. No significant changes of the Hall coefficient or the magnetic susceptibility are observed at the superconductor-metal phase boundary, suggesting a similarity and continuity between both the electronic structures. These features are quite similar to those for another overdoped system: ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{CuO}}_{6+\mathrm{\delta }}$ with a Cu-O octahedral layer.