Quasistatic internal magnetic field detected in the pseudogap phase of Bi2+xSr2-xCaCu2 O8+δ by muon spin relaxation

We report muon spin relaxation (μSR) measurements of optimally doped and overdoped Bi2+xSr2-xCaCu2O8+δ single crystals that reveal the presence of a weak temperature-dependent quasistatic internal magnetic field of electronic origin in the superconducting 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 measurements in support of PG order parameter candidates, namely, electronic loop currents and magnetoelectric quadrupoles.