Charge order, superconducting correlations, and positive muons

• Superconducting fluctuations in high-T cuprates probed by positive muons are discussed.
• Superconducting fluctuations are detected at higher temperatures than by other methods.
• The muon experiments indicate that the superconducting fluctuations are inhomogeneous.
• The compatibility with short-range charge order in the normal state is considered.

The recent discoveries of short-range charge-density wave order in the normal state of several hole-doped cuprate superconductors constitute a significant addition to the known intrinsic properties of these materials. Besides likely being associated with the normal-state pseudogap, the charge-density wave order presumably influences the build-up of known superconducting correlations as the temperature is lowered toward the superconducting state. As a pure magnetic probe, muon spin rotation (μ SR) is not directly sensitive to charge order, but may sense its presence via the effect it has on the magnetic dipolar coupling of the muon with the host nuclei at zero or low magnetic field. At higher field where μ SR is completely blind to the effects of charge order, experiments have revealed a universal inhomogeneous normal-state response extending to temperatures well above Tc. The measured inhomogeneous line broadening has been attributed to regions of superconducting correlations that exhibit varying degrees of fluctuation diamagnetism. Here, the compatibility of these results with other measurements showing charge order correlations or superconducting fluctuations above Tc is discussed.