High-field μSR studies of superconducting and magnetic correlations in cuprates above Tc

The advent of high transverse field muon spin rotation (TF-mu SR) has led to recent mu SR investigations of the magnetic field response of cuprates above the superconducting transition temperature T-c. Here the results of such experiments on hole-doped cuprates are reviewed. Although these investigations are currently ongoing, it is clear that the effects of high field on the internal magnetic field distribution of these materials is dependent upon competition between superconductivity and magnetism. In La2-xSrxCuO4 the response to the external field above T-c is dominated by heterogeneous spin magnetism. However, the magnetism that dominates the observed inhomogeneous line broadening below x similar to 0.19 is overwhelmed by the emergence of a completely different kind of magnetism in the heavily overdoped regime. The origin of the magnetism above x similar to 0.19 is probably related to intrinsic disorder, but the systematic evolution of the magnetism with doping changes in the doping range beyond the superconducting 'dome'. In contrast, the width of the internal field distribution of underdoped YBa(2)Cu(3)Oy above T-c is observed to track T-c and the density of superconducting carriers. This observation suggests that the magnetic response above T-c is not dominated by electronic moments, but rather inhomogeneous fluctuating superconductivity. The spatially inhomogeneous response of YBa(2)Cu(3)Oy to the applied field may be a means of minimizing energy, rather than being caused by intrinsic disorder.