High-temperature (high-T c) superconductivity in the copper oxides arises from electron or hole doping of their antiferromagnetic (AF) insulating parent compounds. The evolution of the AF phase with doping and its spatial coexistence with superconductivity are governed by the nature of charge and spin correlations, which provides clues to the mechanism of high-T c superconductivity. Here we use neutron scattering and scanning tunnelling spectroscopy (STS) to study the evolution of the bosonic excitations in electron-doped superconductor Pr 0.88 LaCe 0.12 CuO 4? with different transition temperatures (T c) obtained through the oxygen annealing process. We find that spin excitations detected by neutron scattering have two distinct modes that evolve with T c in a remarkably similar fashion to the low-energy electron tunnelling modes detected by STS. These results demonstrate that antiferromagnetism and superconductivity compete locally and coexist spatially on nanometre length scales, and the dominant electron-boson coupling at low energies originates from the electron-spin excitations.
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