Resonance in the electron-doped high-transition-temperature superconductor Pr0.88LaCe0.12CuO4-δ

In conventional superconductors, the interaction that pairs the electrons to form the superconducting state is mediated by lattice vibrations(1) (phonons). In high-transition-temperature (high-T-c) copper oxides, it is generally believed that magnetic excitations might play a fundamental role in the superconducting mechanism because superconductivity occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds(2). Indeed, a sharp magnetic excitation termed 'resonance' has been observed by neutron scattering in a number of hole-doped materials(3-11). The resonance is intimately related to superconductivity(12), and its interaction with charged quasi-particles observed by photoemission(13,14), optical conductivity(15), and tunnelling(16) suggests that it might play a part similar to that of phonons in conventional superconductors. The relevance of the resonance to high-T-c superconductivity, however, has been in doubt because so far it has been found only in hole-doped materials(17). Here we report the discovery of the resonance in electron-doped superconducting Pr0.88LaCe0.12CuO4-delta (T-c = 24 K). We find that the resonance energy (E-r) is proportional to T-c via E-r approximate to 5.8k(B)T(c) for all high-T-c superconductors irrespective of electron- or hole-doping. Our results demonstrate that the resonance is a fundamental property of the superconducting copper oxides and therefore must be essential in the mechanism of superconductivity.