Strong correlation between field-induced magnetism and superconductivity in Pr _0.89LaCe _0.11CuO ₄

We report the local magnetic response of an electron-doped cuprate superconductor, Pr _0.89LaCe _0.11-CuO _4-y (T _c ≃ 26K), studied by muon spin rotation (μSR) over a field range from 200 Oe to 50 kOe. In the paramagnetic state, the muon Knight shift along the crystal c-axis (K _μ ^z) is proportional to the in-plane susceptibility χ _ab. More surprisingly, K _μ ^z is strongly enhanced by the occurrence of superconductivity (below ∼40 kOe), changing its sign from positive to negative around ∼1 kOe with increasing field. This finding can be understood by considering the weak polarization of Pr ions due to the superexchange interaction with the antiferromagnetic Cu sublattice, which coexists with superconductivity.