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

TL;DR

High-field muSR studies reveal complex magnetic and superconducting correlations in cuprates above Tc, indicating a competition between magnetism and superconductivity that varies with doping level.

Contribution

This review summarizes recent high-field muSR experiments on hole-doped cuprates, highlighting the different magnetic responses above Tc across doping regimes.

Findings

Magnetic response above Tc varies with doping and is influenced by competing phases.

In La_{2-x}Sr_xCuO_4, heterogenous spin magnetism dominates above Tc.

In underdoped YBa_2Cu_3O_y, magnetic response correlates with Tc and superconducting carrier density.

Abstract

The advent of high transverse-field muon spin rotation (TF-muSR) has led to recent muSR 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 a competition between superconductivity and magnetism. In La_{2-x}Sr_xCuO_4 the response to the external field above Tc is dominated by heterogeneous spin magnetism. However, the magnetism that dominates the observed inhomogeneous line broadening below x ~ 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 ~ 0.19 is currently unknown, but its presence hints at a competition between superconductivity and magnetism that is reminiscent of the underdoped regime. In contrast, the width of the internal field distribution of underdoped YBa_2Cu_3O_y above Tc is observed to track Tc and the density of superconducting carriers. This observation suggests that the magnetic response above Tc is not dominated by electronic moments, but rather inhomogeneous fluctuating superconductivity.