Title: Quasi-Static Internal Magnetic Field Detected in the Pseudogap Phase of Bi$_{2+x}$Sr$_{2-x}$CaCu$_2$O$_{8+δ}$ by $μ$SR,
Abstract: We report muon spin relaxation ($\mu$SR) measurements of optimally-doped and
overdoped Bi$_{2+x}$Sr$_{2-x}$CaCu$_2$O$_{8+\delta}$ (Bi2212) single crystals
that reveal the presence of a weak temperature-dependent quasi-static internal
magnetic field of electronic origin in the superconducting (SC) and pseudogap
(PG) phases. In both samples the internal magnetic field persists up to 160~K,
but muon diffusion prevents following the evolution of the field to higher
temperatures. We consider the evidence from our measurments in support of PG
order parameter candidates, namely, electronic loop currents and
magnetoelectric quadrupoles.