Magnetism and superconductivity of an electron-doped superconductor (Sr_1-xLa_x)₂

We investigated the infinite-layer electron-doped cuprate superconductor (Sr1-xLax)CuO2 with the muon spin relaxation (μSR) technique. Zero-field measurements detect a slowing down of magnetic moments at a characteristic temperature (TN1), below which the volume fraction of the magnetic region increases as the sample is cooled. Below the doping concentration x<0.10, an onset of the (quasi) static order occurs at another characteristic temperature (TN2). The magnetic volume fraction increases under application of a magnetic field, suggesting that magnetism may be enhanced by an external field. As a function of the doping concentration, the superconducting transition temperature (Tc≈42K) remains constant, but the Meissner fraction reaches a maximum at x=0.1. The transverse-field μSR exhibits an increase of the relaxation rate below Tc, which reaches to σ(T→0)≈4.5μs-1 for x=0.1 doping. This relaxation rate is about 4 times larger than the one expected from the Uemura relation, and there may be a contribution from the field-induced magnetism to the relaxation rate.