Investigations of the pseudogap phase in overdoped Bi_2+xSr_2−xCaCu₂O_8+δ with μSR

A recent μSR study of Bi_2+xSr_2−xCaCu₂O_8+δ (Bi2212) single crystals revealed the presence of weak quasi-static magnetism in the pseudogap (PG) phase [A. Pal et al., Phys. Rev. B 97, 060502(R) (2018)]. However, it is unclear whether the magnetism is associated with the PG, as muon diffusion above T ~ 160 K prevented determination of an onset temperature. In an attempt to circumvent this limitation, we have carried out sensitive muon Knight-shift and new zero-field muon spin relaxation (ZF-μSR) measurements of overdoped Bi2212. The temperature dependence of the muon-Knight shift in the normal state exhibits a saturation below a temperature that scales with T_c, whereas the ZF-μSR relaxation rate appears to track the hole-doping dependence of the PG temperature T*. In addition, our measurements of highly overdoped Bi2212 provide evidence for phase separation. The results suggest the presence of two distinct phases above T_c.