No pseudogap magnetism detected in optimally to heavily overdoped Bi_2+<i>x</i>Sr_2-<i>x</i>CaCu₂O₈₊_d single crystals by μSR

Weak, temperature-dependent, quasi-static magnetism has been detected within the pseudogap (PG) phase of optimally-doped (T_c = 91 K) and overdoped (T_c = 80 K) Bi_2+xSr_2-xCaCu₂O_8+d (Bi2212) single crystals by zero-field (ZF) muon spin relaxation (mSR) [A. Pal et al., Phys. Rev. B 97, 060502(R) (2018)]. However, in this study it was not possible to determine whether the magnetism onsets at the PG temperature (T*) due to the occurrence of muon diffusion above T ~ 150 K. To address this issue, we performed a similar ZF-mSR investigation of overdoped single crystals (T_c = 70 K and 55 K) in which T* lies below the muon diffusion temperature. The results are similar to that obtained for the lower doped samples, indicating that the anomalous magnetism is independent of hole-doping concentration and thus apparently not associated with the PG. We have carried out additional ZF-mSR measurements on these samples using an ultra-low background spectrometer. The new measurements verify the source of the magnetism comes from the Bi2212 samples. Potential origins of the anomalous magnetism will be discussed.