Pseudogap and cuprate superconductivity: MaxEnt-μSR studies

• A magnetic origin of cuprate superconductivity is plausible.
• Cuprate loop currents are observed, close to predictions.
• Pseudogap effects are seen above and below Tc.

The basic physics of cuprate superconductivity is still much deliberated after 27 years of research. In contrast to phononic or polaronic roots, Varma’s theory promotes a magnetic origin. To probe cuprate magnetism, we examine zero field (ZF) muon-spin-rotation (μSR) data of RBa2Cu3O7−δ (RBCO; R = Gd, Eu) especially near Tc. Possible weak effects are analyzed using Maximum Entropy (MaxEnt, ME) to transform our μSR time series. Concerning predicted pseudogap loop currents, we have observed μSR signals in zero field for GdBCO above and now also below Tc. These are near predicted fields of about 100 Oe. Using MaxEnt, we analyze transverse field (TF) μSR data of optimal doped EuBCO. Our focus is also on a temperature interval above Tc to comprehend precursor effects.Our results point toward magnetic roots of cuprate superconductivity.