Quasi-Static Internal Magnetic Field Detected in the Pseudogap Phase of Bi$_{2+x}$Sr$_{2-x}$CaCu$_2$O$_{8+\delta}$ by $\mu$SR

TL;DR

This study uses muon spin relaxation to detect a weak, temperature-dependent internal magnetic field in Bi2212 superconductors, providing evidence relevant to pseudogap order parameters such as loop currents and quadrupoles.

Contribution

First muon spin relaxation measurements revealing a quasi-static internal magnetic field in the pseudogap phase of Bi2212, supporting specific order parameter hypotheses.

Findings

Internal magnetic field persists up to 160 K in both doping levels.

Muon diffusion limits the temperature range of field observation.

Evidence supports loop currents and magnetoelectric quadrupoles as pseudogap order parameters.

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.