  A systematic muon-spin-relaxation study in Bi-2201 high-Tc cuprates has
revealed for the first time that the Cu-spin correlation (CSC) is developed at
low temperatures below 2 K in a wide range of hole concentration where
superconductivity appears. The CSC tends to become weak gradually with
increasing hole-concentration. Moreover, CSC has been enhanced through the 3%
substitution of Zn for Cu. These results are quite similar to those observed in
La-214 high-Tc cuprates. Accordingly, it has been suggested that the intimate
relation between the so-called spin-charge stripe correlations and
superconductivity is a universal feature in hole-doped high-Tc cuprates.
Furthermore, apparent development of CSC, which is suppressed through the Zn
substitution oppositely, has been observed in non-superconducting heavily
overdoped samples, being argued in the context of a recently proposed
ferromagnetic state in heavily overdoped cuprates.
