A magnetic origin of cuprate superconductivity? A MaxEnt-μSR view

Abstract

The fundamental physics of cuprate superconductivity is still much deliberated after three decades of research. In contrast to phononic or polaronic roots, some major theories promote a magnetic origin. In this perspective, we review cuprate magnetism, as probed by muon-spin-rotation [Formula: see text] in [Formula: see text] (RBCO), [Formula: see text] (Bi2212) and [Formula: see text] (Tl2223). Site-search RBCO studies show that muons localize and probe in locations away from the superconducting CuO2 planes. Maximum entropy (MaxEnt, ME) analysis of transverse field [Formula: see text] data of [Formula: see text] (GdBCO) indicates that the muon probes in an undisturbed insulating environment, allowing [Formula: see text] to detect (weak) magnetic features in these cuprates. Concerning Varma’s predicted loop currents, MaxEnt has shown weak [Formula: see text] signals for GdBCO in zero field above and below the critical temperature, [Formula: see text]; these are near the predicted [Formula: see text] Oe. Concerning Zhang’s predicted antiferromagnetism (AF) connected to the vortex cores, we have observed Lorentzian relaxation of cuprate vortex signals below half [Formula: see text], consistent with AF-broadening effects. For both Bi2212 and Tl2223, Lorentzians describe the [Formula: see text] vortex signals much better below [Formula: see text] than Gaussians, indicating that extra AF fields occur near and in the vortex cores. In sum, both our MaxEnt-[Formula: see text] (ME-[Formula: see text]) studies point toward magnetic roots of cuprate superconductivity.